Consecutive Single-Crystal-to-Single-Crystal Isomerization of Novel Octamolybdate Anions within a Microporous Hybrid Framework with Robust Water Sorption Properties

The 3D hybrid framework [{Cu(cyclam)}3 (κ-Mo8 O27 )] ⋅ 14H2 O (1) (cyclam=1,4,8,11-tetraazacyclotetradecane) undergoes sequential single-crystal-to-single-crystal transformations upon heating to afford two different anhydrous phases (2 a and 3 a). These transitions modify the framework dimensionality and enable the isomerization of κ-octamolybdate (κ-Mo8 ) anions into λ (2 a) and μ (3 a) forms through metal migration. Hydration of 3 a involves condensation of one water molecule to the cluster to afford the γ-Mo8 isomer in 4, which dehydrates back into 3 a through the 6 a intermediate. In contrast, 2 a reversibly hydrates to form 5, exhibiting the same Mo8 cluster as that of 1. It is remarkable that three of the Mo8 clusters (κ, λ and μ) are new and that up to three different microporous phases can be isolated from 1 (2 a, 3 a, and 6 a). Water vapor sorption analyses show high recyclability and the highest uptake values for POM-based systems. The isotherms display an abrupt step at low humidity level desirable for humidity control devices or water harvesting in drylands.

Systematic Approach to the Synthesis of Cobalt-Containing Polyoxometalates for Their Application as Energy Storage Materials

New energy storage materials are an object of study within the framework of the global energy transition. The development of renewable sources is being boosted thanks to stationary energy storage systems such as redox flow batteries (RFBs). This work reports the synthesis of the cobalt-containing Keggin-type polyoxometalates [CoW₁₂O₄₀]^6- (CoW₁₂) and [Co(H₂O)SiW₁₁O₃₉]^6- (CoSiW₁₁), which have previously been shown to have applicability in RFBs. These procedures were reassessed to meet the strict requirements associated with the further implementation of RFBs, including fast and affordable synthetic procedures with high reaction yields. In contrast to the lengthy and complicated synthetic approaches published to date, the optimized synthesis reported in this work enables the isolation of the pure crystalline salt of the CoW₁₂ anion with a 75% reduction of the time of the whole reaction procedure, eliminating tedious steps such as the recrystallization and including a 20% increased yield. The control of the stoichiometry, fine-tuning of reaction conditions, and the identification of intermediate species, as well as the acidic equilibria taking place during the process, were monitored via thermal, spectroscopic, and structural analyses. In the case of the CoSiW₁₁ anion, its preparation was based on a simple and highly efficient procedure. Moreover, promising electrochemical properties were observed with the use of the one-pot synthetic approach, in which the stoichiometric amounts of the starting reagents are dissolved in the supporting electrolyte to be directly implemented as the electrolyte for a RFB.

Reversible First-Order Single Crystal to Single Crystal Thermal Phase Transition in [(CH3)3CNH3]4[V4O12]

The well-known compound tetrakis(tert-butylammonium)-cyclo-tetrametavanadate (V), [(CH₃)₃CNH₃]₄[V₄O₁₂] (1h_RT), which crystallizes in the tetragonal I4/m space group, undergoes an irreversible solid state transformation upon heating, constituting one of the few examples in which the initial and the final stages are structurally characterized by sc-XRD. Now, we observed the ability of the same compound to undergo an additional single-crystal-to-single-crystal (SCSC) transformation upon thermal stimuli, but this time at low temperatures (153 K). Compound 1h_RT contains a discrete unprotonated [V₄O₁₂]^4- tetrahedral anion in which V and O bridging atoms are coplanar. In both phases, these tetrameric anions are linked through tert-butylammonium cations in an extensive network of hydrogen bonds, but at low temperatures, this phase loses its characteristic O-V-O coplanarity, with the resulting rearrangement of the crystal packing and hydrogen-bond network which provide its reversibility at low temperatures. Again, the initial and final stages have been characterized structurally by sc-XRD.

Slow Magnetic Relaxation and Luminescent Properties of Mononuclear Lanthanide-Substituted Keggin-Type Polyoxotungstates with Compartmental Organic Ligands

The reaction of mid to late lanthanide ions with the N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylene-diamine organic ligand and monolacunary Keggin type [α-SiW₁₁O₃₉]^8– anion affords a series of isostructural compounds, namely, K₅[Ln^III(α-SiW₁₁O₃₉)(C₂₀H₂₂Br₂N₂O₄)]·14H₂O (1-Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the Ln^III ion in a biaugmented trigonal prismatic geometry, which occupies the external O₄ site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N₂O₂ coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and π–π interactions established between adjacent molecular units govern the crystal packing, which results in the formation of assemblies containing six hybrid species assembled in a chairlike conformation. 1-Gd and 1-Yb display slow relaxation of the magnetization after the application of an external magnetic field with maxima in the out-of-phase magnetic susceptibility plots below ∼5–6 K, which is ascribed to the presence of various relaxation mechanisms. Moreover, photoluminescent emission is sensitized for 1-Sm and 1-Eu in the visible region and 1-Er and 1-Yb in the NIR. In contrast, the quenching of metal-centered luminescence in the 1-Tb derivative has been attributed to the out-of-pocket coordination mode of the lanthanide center within the POM fragment. It is demonstrated that the 1-Yb dual magneto-luminescent material represents the first lanthanide-containing POM reported to date with simultaneous slow magnetic relaxation and NIR emission. Solution stability of the hybrid molecular species in water is also confirmed by ESI-mass spectrometry experiments carried out for 1-Tb and 1-Tm.

A series of solution stable, molecular polyoxometalate hybrids, namely, [α-SiW₁₁O₃₉Ln^III(C₂₀H₂₂N₂Br₂O₄)]⁵⁻ (Ln^III = Sm to Lu) have been synthesized from the combination of mid-to-late lanthanides, lacunary Keggin-type anions, and a compartmental organic ligand. Metal-centered luminescence in both the visible and NIR region as well as slow relaxation of magnetization was found for different members of this family, including the Yb derivative, which represents the first POM-based system with slow magnetic relaxation and sensitized emission in the NIR region.

Single-Crystal-to-Single-Crystal Cluster Transformation in a Microporous Molybdoarsenate(V)-Metalorganic Framework

The hybrid compound [Cu(cyclam)(H₂O)₂]_0.5[{Cu(cyclam)}_1.5{B-H₂As₂Mo₆O₂₆(H₂O)}]·9H₂O (1) (cyclam = 1,4,8,11-tetraazacyclotetradecane) was synthesized in aqueous solution by reacting the {Cu(cyclam)}²⁺ complex with a mixture of heptamolybdate and an arsenate(V) source. Crystal packing of 1 exhibits a supramolecular open-framework built of discrete covalent molybdoarsenate/metalorganic units and additional [Cu(cyclam)(H₂O)₂]²⁺ cations, the stacking of which generates squarelike channels parallel to the z axis with an approximate cross section of 10 × 11 Ų where all the hydration water molecules are hosted. Thermal evacuation of solvent molecules yields a new anhydrous crystalline phase, but compound 1 does not preserve its single-crystalline nature upon heating. However, when crystals are dehydrated under vacuum, they undergo a structural transformation that proceeds via a single-crystal-to-single-crystal pathway, leading to the anhydrous phase [{Cu(cyclam)}₂(A-H₂As₂Mo₆O₂₆)] (2). Total dehydration results in important modifications within the inorganic cluster skeleton which reveals an unprecedented solid-state B to A isomerization of the polyoxoanion. This transition also involves changes in the Cu^II bonding scheme that lead to covalent cluster/metalorganic layers by retaining the open-framework nature of 1. Compound 2 adsorbs ambient moisture upon air exposure, but it does not revert back to 1, and the hydrated phase [{Cu(cyclam)}₂(A-H₂As₂Mo₆O₂₆)]·6H₂O (2h) is obtained instead. Structural variations between 1 and 2 are reflected in electron paramagnetic resonance spectroscopy measurements, and the permanent microporosity of 2 provides interesting functionalities to the system such as the selective adsorption of gaseous CO₂ over N₂.

A supramolecular open framework built of copper(II)-complexes of a macrocyclic tetraaza ligand and arsenomolybdate anions undergoes a single-crystal-to-single-crystal transformation upon dehydration that implies an unprecedented solid state cluster isomerization. The permanent porosity of the system allows the selective adsorption of CO₂ over N₂.

Isolation of the Elusive Heptavanadate Anion with Trisalkoxide Ligands

The unprecedented heptavanadate cluster has been isolated from reactions between trisalkoxide ligands and vanadate in water at pH = 2 as a series of alkylammonium [H_xV₇O₁₈(H₂O)((OCH₂)₃CR)]^(4–x)- salts (1–3, R = CH₂OH; 4, R = CH₃). Their structures have been determined and the partial stability of 4 in water assessed by a combination of multinuclear NMR spectroscopy and ESI-MS. The heptavanadate unit reported herein could represent an intermediate species in the formation of decavanadate that is blocked by attachment of tripodal ligands.

The elusive heptavanadate anion has been isolated from the reaction between trisalkoxide ligands and a vanadate source in acidic aqueous solution. A series of alkylammonium salts of the monofunctionalized [H_xV₇O₁₈(H₂O)((OCH₂)₃CR)]^(4−x)− anion (1−3, R = CH₂OH; 4, R = CH₃) has been structurally characterized. The partial stability of the hybrid anion in water has been addressed by a combination of multinuclear NMR spectroscopy and ESI-MS, which reveals that the nude heptavanadate core rapidly rearranges into the well-known decavanadate anion.

Structural Characterization of Mono and Dihydroxylated Umbelliferone Derivatives

Coumarin derivatives are a class of compounds with a pronounced wide range of applications, especially in biological activities, in the medicine, pharmacology, cosmetics, coatings and food industry. Their potential applications are highly dependent on the nature of the substituents attached to their nucleus. These substituents modulate their photochemical and photophysical properties, as well as their interactions in their crystalline form, which largely determines the final field of application. Therefore, in this work a series of mono and dihydroxylated coumarin derivatives with different chemical substituents were synthesized and characterized by UV-Visible spectroscopy, thermal analysis (differential scanning calorimetry (DSC) and TGA), ¹H NMR and X-Ray Diffraction to identify limitations and possibilities as a function of the molecular structure for expanding their applications in polymer science.

Structural Transformations in the Thermal Dehydration of [Cu2(bpa)(btec)(H2O)4]n Coordination Polymer

Reactions between pyridinic ligands such as 1,2-bis(4-pyridyl)ethane (bpa) and transition metal cations are a very widespread technique to produce extended coordination polymers such as Metal-Organic Frameworks. In combination with a second ligand these systems could present different topologies and behaviors. In this context, the use of 1,2,4,5-benzenetetracarboxylic acid (H₄btec) gave us a novel 2D compound, [Cu₂(bpa)(btec)(H₂O)₄]_n (1), which was prepared by microwave-assisted synthesis and structurally characterized by means of single crystal X-ray diffraction. Its thermal behavior was analyzed through thermogravimetric analysis and variable temperature powder X-ray diffraction, concluding that thermal stability is influenced by the coordination water molecules, allowing two sequential thermochromic phase transformations to take place. These transformations were monitored by electronic paramagnetic resonance spectroscopy and magnetic susceptibility measurements. In addition, the crystal structure of the anhydrous compound [Cu₂(bpa)(btec)]_n (1.ah) was determined. Finally, a topological study was carried out for the bpa ligand considering all the structures deposited in the Cambridge Structural Databased. More than 1000 structures were analyzed and classified into 17 different topologies, according to the role of the ligand.

Thermostructural Behavior in a Series of Lanthanide-Containing Polyoxotungstate Hybrids with Copper(II) Complexes of the Tetraazamacrocycle Cyclam: A Single-Crystal-to-Single-Crystal Transformation Study

A series of 14 isostructural [Cu(cyclam)]₂[{Cu(cyclam)}₄{(α-GeW₁₁O₃₉)Ln(H₂O)(OAc)}₂]·18H₂O (1-Ln, where Ln = La-Lu; cyclam = 1,4,8,11-tetraazacyclotetradecane) polyoxometalate-based hybrids reported herein represent (i) the first example of a two-dimensional covalent hybrid lattice involving the [{(α-XW₁₁O₃₉)Ln(H₂O)(OAc)}₂] ^n- archetype and (ii) the first structural characterization of such a dimeric polyoxotungste for Ln = La and Pr as well as for the combination of X = Ge and Ln = Ce, Nd, Sm, or Lu. Compounds 1-Ln have been characterized by elemental analyses, infrared spectroscopy, and thermogravimetric analysis, and their thermostructural behavior has been monitored by powder and single-crystal X-ray diffraction. The title compounds undergo two single-crystal-to-single-crystal transformations triggered by thermal dehydration leading to the [{Cu(cyclam)}₆{(α-GeW₁₁O₃₉)Ln(H₂O)(OAc)}₂]·4H₂O intermediate (2-Ln, where Ln = Eu or Er) and [Cu(cyclam)]_0.5[{Cu(cyclam)}_5.5{(α-GeW₁₁O₃₉)Ln(OAc)}₂] (3-Ln, where Ln = Ce or Eu) final anhydrous phases, the latter evidencing a coordinatively unsaturated derivative of the dimeric archetype for the first time. These transitions involve formation and disruption of Cu-O_POM bonds that result in different {Cu(cyclam)}²⁺ moieties grafting onto and being released from Keggin surfaces, which reduces the dimensionality of 1-Ln to one-dimensional covalent assemblies for 2-Ln and 3-Ln. While all 3-Ln phases rehydrate fully upon exposure to air for 24 h, the kinetics governing the crystal transitions back toward 1-Ln through 2-Ln depend on the nature of Ln. Under ambient moisture, the anhydrous structures fully revert back to the parent framework for Ln = La-Sm, while the samples containing Eu to Lu afford mixtures of 1-Ln and 2-Ln and require immersion in water for the structural reversion to reach completion. Single-crystal X-ray diffraction analyses of the rehydrated 1R-Ln samples (Ln = Ce, Eu, and Er) support these observations.

Six tris-(bipyrid-yl)iron(II) complexes with 2-substituted 1,1,3,3-tetra-cyano-propenide, perchlorate and tetra-fluorido-borate anions; order versus disorder, hydrogen bonding and C-N⋯π inter-actions

Structures are reported for six closely related salts of tris-(bipyrid-yl)iron(II) cations, namely tris-(2,2'-bi-pyridine)-iron(II) bis-(1,1,3,3-tetra-cyano-2-meth-oxy-propenide) 0.776-hydrate, [Fe(C10H8N2)3](C8H3N4O)2.0.776H2O, (I), tris-(2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-(propyl-sulfan-yl)propenide perchlor-ate, [Fe(C10H8N2)3](C10H7N4S)(ClO4), (II), tris-(5,5'-dimethyl-2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-meth-oxy-propenide tetra-fluorido-borate ethanol 0.926-solvate, [Fe(C12H12N2)3](C8H3N4O)(BF4).0.926C2H2O, (III), tris-(5,5'-dimethyl-2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-eth-oxy-propenide tetra-fluorido-borate, [Fe(C12H12N2)3](C9H5N4O)(BF4), (IV), tris-(5,5'-dimethyl-2,2'-bi-pyridine)-iron(II) 1,1,3,3-tetra-cyano-2-(ethyl-sufanyl)propenide tetra-fluorido-borate, [Fe(C12H12N2)3](C9H5N4S)(BF4), (V), and tris-(5,5'-dimethyl-2,2'-bi-pyri-dine)-iron(II) 1,1,3,3-tetra-cyano-2-prop-oxypropenide tetra-fluorido-borate, [Fe(C12H12N2)3](C10H7N4O)(BF4), (VI). In compound (I), one of the anions is disordered over two sets of atomic sites with equal occupancies while, in the second anion, just one of the C(CN)2 units is disordered, again over two sets of atomic sites with equal occupancies: the anionic components are linked by multiple C-H⋯N hydrogen bonds to form a three-dimensional framework. In compound (II), the polynitrile anion is disordered over two sets of atomic sites with occupancies in the approximate ratio 3:1, while the perchlorate anion is disordered over three sets of atomic sites: there are C-N⋯π inter-actions between the cations and the polynitrile anion. The polynitrile anion in compound (III) is fully ordered, but the tetra-fluorido-borate anion is disordered over two sets of atomic sites with occupancies 0.671 (4) and 0.329 (4): the cations and the tetra-fluorido-borate anions are linked by C-H⋯F inter-actions to form an inter-rupted chain. Compounds (IV) and (V) are isostructural and all of the ionic components are fully ordered in both of them: the cations and tetra-fluorido-borate anions are linked into C 2 2(12) chains. The polynitrile anion in compound (VI) is disordered over two sets of atomic sites with approximately equal occupancies, and here the chains formed by the cations and the tetra-fluorido-borate anions are of the C 2 2(13) type.

Single-crystal-to-single-crystal transformations triggered by dehydration in polyoxometalate-based compounds

Single-crystal-to-single-crystal transformations are solid-state phase transitions between different crystalline states in which the crystal integrity and the long-range structural order are retained through the whole transformation process. Such a phenomenon constitutes the structural response that some compounds afford when being exposed to a given external stimulus (temperature, pressure, light, etc.) and, therefore, its study has become a relevant focus of interest within crystal engineering because it allows for monitoring how certain properties (colour, magnetism, luminescence, porosity) of the stimuli-responsive material are modified as the structure evolves into the activated form. A range of organic, inorganic and hybrid systems have been found to undergo such phase transitions, but these examples only include a small number of compounds that incorporate polyoxometalate anions, among which the removal of guest solvent molecules (dehydration) stands out as the most common external stimulus able to induce the occurrence of a single-crystal-to-single-crystal transformation. This feature article compiles the examples of dehydration-triggered single-crystal-to-single-crystal transformation studies that have been reported to date for polyoxometalate-based compounds and reviews some of their most relevant structural aspects.

Immobilization of Polyoxometalates on Tailored Polymeric Surfaces

Herein we describe the preparation of hybrid polymer-inorganic interfaces by the immobilization of polyoxometalate nanoclusters on functionalized polymer surfaces. The polymeric surfaces were made of polystyrene-b-poly(acrylic acid)/polystyrene (PS-b-PAA/PS) blends by spin coating on a silicon wafer. The functionalization of the polymer film was obtained by interfacial migration of the amphiphilic block copolymer toward the interface upon water vapor annealing. The carboxylic acid functional groups contained in the PAA block were then employed to anchor the [LnIII(α-SiW11O39)]5- polyoxometalates (Ln: Ce, Er). This purpose was achieved by immersing the films in aqueous solutions of the in situ-formed inorganic nanoclusters. X-ray photoelectron and confocal Raman spectroscopies, together with atomic force microscopy, confirmed the immobilization of the inorganic species at the interface.

A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes

The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O (1, cyclam = 1,4,8,11-tetraazacyclotetradecane) was prepared by reaction of (VO3)(-) anions and {Cu(cyclam)}(2+) complexes in NaCl (aq) at pH 4.6-4.7 and characterized by elemental analyses, thermogravimetry, and X-ray diffraction (powder, single-crystal) techniques. Compound 1 exhibits a POMOF-like supramolecular open-framework built of covalent decavanadate/metalorganic layers with square-like voids, the stacking of which is aided by interlamellar cementing complexes and generates water-filled channels with approximate cross sections of 10.4 × 8.8 Å(2). The framework is robust enough to remain virtually unaltered upon thermal evacuation of all water molecules of hydration, as demonstrated through single-crystal X-ray diffraction studies on the anhydrous phase 1a. This permanent microporosity renders interesting functionality to 1, such as selective adsorption of CO2 over N2 and remarkable activity as heterogeneous catalyst toward the H2O2-based oxidation of the highly-stable, tricyclic alkane adamantane.

Crystal structure of trans-di-aqua-bis-(1H-pyrazole-3-carboxyl-ato-κ(2) N,O)copper(II) dihydrate

In the title compound, [Cu(C4H3N2O2)2(H2O)2]·2H2O, the Cu(II) ion is located on an inversion centre and exhibits an axially elongated octa-hedral coordination geometry. The equatorial plane is formed by two N,O-bidentate 1H-pyrazole-3-carboxyl-ate ligands in a trans configuration. The axial positions are occupied by two water mol-ecules. The mononuclear complex mol-ecules are arranged in layers parallel to the ab plane. Each complex mol-ecule is linked to four adjacent species through inter-molecular O-H⋯O and N-H⋯O hydrogen bonds that are established between the coordinating water mol-ecules and carboxyl-ate O atoms or protonated N atoms of the organic ligands. These layers are further connected into a three-dimensional network by additional hydrogen bonds involving solvent water mol-ecules and non-coordinating carboxyl-ate O atoms.

Sequential single-crystal-to-single-crystal transformations promoted by gradual thermal dehydration in a porous metavanadate hybrid

The porous hybrid metavanadate [{Cu(cyclam)}(VO₃)₂]·5H₂O undergoes a series of sequential and reversible transformations upon thermally-triggered gradual dehydration that have been monitored by single-crystal X-ray diffraction.

Functionalization of Krebs-type polyoxometalates with N,O-chelating ligands: a systematic study

The first organic derivatives of 3d-metal-disubstituted Krebs-type polyoxometalates have been synthesized under mild bench conditions via straightforward replacement of labile aqua ligands with N,O-chelating planar anions on either preformed or in situ-generated precursors. Nine hybrid clusters containing carboxylate derivatives of five- or six-membered aromatic N-heterocycles as antenna ligands have been obtained as pure crystalline phases and characterized by elemental and thermal analyses, infrared spectroscopy, and single-crystal X-ray diffraction. They all show the general formula [{M(II)L(H2O)}2(WO2)2(B-β-XW9O33)2](n-) and can be classified as follows: 1-SbM, where L = 1H-imidazole-4-carboxylate (imc), X = Sb(III), n = 12, and M(II) = Mn, Co, Ni, Zn; 1-TeM, where L = imc, X = Te(IV), n = 10, and M(II) = Mn, Co; 2-SbNi, where L = 1H-pyrazole-3-carboxylate (pzc), X = Sb(III), n = 12, and M(II) = Ni; and 3-SbM, where L = pyrazine-2-carboxylate (pyzc), X =Sb(III), n = 12, and M(II) = Co, Zn. The 3d-metal-disubstituted tungstotellurate(IV) skeleton of compounds 1-TeM is unprecedented in polyoxometalate chemistry. The stability of these hybrid Krebs-type species in aqueous solution has been confirmed by (1)H NMR spectroscopy performed on the diamagnetic 1-SbZn and 3-SbZn derivatives. Our systematic study of the reactivity of disubtituted Krebs-type polyoxotungstates toward diazole-, pyridine-, and diazinecarboxylates demonstrates that organic derivatization is strongly dependent on the nature of the ligand, as follows: imc displays a "universal ligand" character, as functionalization takes place regardless of the external 3d metal and heteroatom; pzc and pyzc show selectivity toward specific 3d metals; pyridazine-3-carboxylate and pyrimidine-4-carboxylate promote partial decomposition of specific precursors, leading to [M(II)L2(H2O)2] complexes; and picolinate is inert under all conditions tested.

trans-Diaquabis(pyridazine-3-carboxylato-κ2N2,O)copper(II)

In the title compound, [Cu(C5H3N2O2)2(H2O)2], the CuIIion, located on an inversion center, exhibits an octahedral coordination geometry. The equatorial plane is defined by twotrans-relatedN,O-bidentate pyridazine-3-carboxylate ligands and the axial positions are occupied by two water molecules. In the crystal, molecules are connected by O—H...O hydrogen bonds between the water molecules and the noncoordinating carboxylate O atoms, forming layers parallel to thebcplane. The layers are stacked along theaaxis by further O—H...O hydrogen bonds between the water molecules and the coordinating carboxylate O atoms. Weak C—H...O hydrogen bonds are also observed between the pyridazine rings and the water molecules and between the pyridazine rings and the non-coordinating carboxylate O atoms.

trans-Di-aqua-bis-(pyridazine-3-carboxyl-ato-κ(2) N (2),O)cobalt(II) dihydrate

The title compound, [Co(C5H3N2O2)2(H2O)2]·2H2O, contains a Co(II) ion on an inversion center, exhibiting an octa-hedral coordination geometry. The equatorial plane is formed by two trans-related N,O-bidentate pyridazine-3-carboxyl-ate ligands and the axial positions are occupied by two water mol-ecules. The Co(II) complex mol-ecules are stacked in a column along the a-axis direction by an O-H⋯N hydrogen bond between the non-coordinating pyridazine N atom and the coordinating water mol-ecule. These columns are further connected into a layer parallel to the ac plane by additional hydrogen bonds involving the coordinating and non-coordinating water mol-ecules, and the non-coordinating carboxyl-ate O atom. The crystal packing is completed by inter-layer weak C-H⋯O inter-actions.

Diaqua-bis-(1H-imidazole-4-carboxyl-ato-κ(2)N(3),O)cobalt(II)

The title compound, [Co(C₄H₃N₂O₂)₂(H₂O)₂], contains a Co^II cation on a twofold rotation axis, exhibiting a distorted octa­hedral coordination geometry. The equatorial plane is formed by two N,O-bidentate 1H-imidazole-4-carboxyl­ate ligands and the axial positions are occupied by water mol­ecules. The crystal packing consists of a three-dimensional network stabilized by O—H⋯O and N—H⋯O hydrogen bonds, together with weak π–π inter­actions [centroid–centroid distance = 3.577 (2) Å] between the imidazole rings.

Tetra-kis(μ(2)-ferrocene-carboxyl-ato-κO:O')bis-[(methanol-κO)copper(II)] methanol disolvate

The complex mol­ecule of the title compound, [Cu₂Fe₄(C₅H₅)₄(C₆H₄O₂)₄(CH₃OH)₂]·2CH₃OH, lies about an inversion centre and contains two centrosymetrically related Cu^II atoms bridged by four O:O′-bidentante ferrocene­carboxyl­ate anions, leading to a dimeric tetra­bridged unit with a paddle-wheel geometry. The Cu^II atom has a distorted square-pyramidal coordination environment with four O atoms from four ferrocene­carboxyl­ate ligands in basal positions and an O atom from a methanol mol­ecule in an apical position. One of the two crystallographically independent ferrocenyl groups has a staggered conformation, while the other is eclipsed. The mol­ecules are connected into a chain along the b axis by O—H⋯O hydrogen bonds involving coordinated and uncoordinated methanol mol­ecules and the O atom from a ferrocene­carboxyl­ate unit.

Coexistence of Five Different Copper(II)−Phenanthroline Species in the Crystal Packing of Inorganic−Metalorganic Hybrids Based on Keggin Polyoxometalates and Copper(II)−Phenanthroline−Oxalate Complexes

Reaction of in situ generated copper(II)-monosubstituted Keggin polyoxometalates and copper(II)-phenanthroline-oxalato complexes in ammonium or rubidium acetate buffers led to the formation of the hybrid inorganic-metalorganic compounds E4[Cu(phen)(H2O)4]2[Cu4(phen)4(H2O)4(ox)3]0.6[Cu2(phen)2(H2O)4(ox)]0.4[Cu(phen)(ox)]0.8[{SiW11O39Cu(H2O)}2{Cu2(phen)2(ox)}].20H2O [E: Rb (1), NH4 (2)]. The two compounds have been characterized by means of elemental analysis, thermogravimetry, infrared and electron paramagnetic resonance spectroscopies, and magnetic susceptibility measurements, and their structures have been established by single-crystal X-ray diffraction. Both compounds are isostructural, and they contain a discrete bimolecular hybrid polyanion and several types of copper-phenanthroline complexes of variable nuclearity. The main structural features of these compounds are the presence of the new hybrid POM [{SiW11O39Cu(H2O)}2{Cu2(phen)2(mu-ox)}]10-, where the dinuclear copper-oxalato complex is sandwiched by two copper-monosubstituted POMs, and the coexistence of five different copper-phenanthroline species with nuclearities ranging from one to four.

Tetrahydroxy-p-benzoquinone as a Source of Polydentate O-Donor Ligands. Synthesis, Crystal Structure, and Magnetic Properties of the [Cu(bpy)(dhmal)]2 Dimer and the Two-Dimensional [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2]·16H2O Inorganic−Metalorganic Hybrid

The use of tetrahydroxy-p-benzoquinone as a slow source of dihydroxymalonato and oxalato ligands led to the isolation under open-air mild reaction conditions of five different compounds, two of them prepared for the first time: [Cu(bpy)(dhmal)]2 (1) and [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2].16H2O (5) (bpy, 2,2'-bipyridine; dhmal, dihydroxymalonate; ox, oxalate). A possible mechanism for the oxidation of the benzoquinone to give the croconate dianion, which undergoes further ring-opening oxidation to decompose into dihydroxymalonate and oxalate, is proposed. All compounds have been characterized by elemental analysis, thermogravimetry, infrared spectroscopy, and powder X-ray diffraction. Single-crystal X-ray diffraction, electron paramagnetic resonance, and magnetic susceptibility measurements have been performed for compounds 1 and 5. A complete band assignment of the experimental FT-IR spectra is given through comparison with the ones calculated using density functional theory (DFT). The neutral dimer 1 constitutes the first structurally characterized example of a transition metal-dhmal complex, and it contains two copper atoms bridged by two dihydroxymalonato ligands acting in a mu2-kappa3O,O',O":kappa1O coordination fashion, so that an equatorial-axial Cu2(mu2-O)2 rhomboid core is formed. On the other hand, the inorganic-metalorganic hybrid compound 5 shows a two-dimensional arrangement of Keggin polyanions linked by one of the Cu atoms of the oxalate cationic dimers to give layers parallel to the (10) plane, the remaining ox-Cu-bpy fragments acting as interlamellar separators. In both cases, magnetic and EPR results are discussed with respect to the crystal structure of the compounds and, for compound 1, also with respect to DFT calculations of the exchange coupling constant.

Synthesis, X-ray structures and luminescence properties of three multidimensional metal–organic frameworks incorporating the versatile 5-(pyrimidyl)tetrazolato bridging ligand

The hydrated sodium salt of the novel and versatile 5-(pyrimidyl)tetrazolato ligand (pmtz(-)), Na(pmtz).H(2)O (1), has been prepared in very mild conditions from 2-cyanopyrimidine and NaN(3). Two coordination polymers [Cd(pmtz)(2)]n (2)and [Cd(pmtz)(micro-Cl)(0.5)(micro-N(3))(0.5)(H(2)O)](n)(3), , have been synthesized from (1)under conventional or hydrothermal conditions, respectively, and fully characterized by single-crystal or powder X-ray diffraction methods. Compounds and consist of mono-dimensional polymeric chains, further stabilized by interchain pi-pi stacking and hydrogen bond interactions. Compound , containing octacoordinated Cd ions of crystallographic D(2) symmetry, exhibits neutral (4, 4) layers formed by square units of the metallacalix[4]arene type in 1,3-alternate conformation. Species , and display intense, room temperature, photoluminescence in the solid state.

Hybrid Inorganic−Metalorganic Compounds Containing Copper(II)-Monosubstituted Keggin Polyanions and Polymeric Copper(I) Complexes

Four hybrid inorganic-metalorganic compounds containing copper(II)-monosubstituted Keggin polyoxotungstates, K3[Cu(I)(4,4'-bpy)]3[SiW11Cu(II)O39].11H2O (1), (paraquat)3[SiW11Cu(II)O39].6H2O (2; paraquat = N,N'-dimethyl-4,4'-bipyridinium), K3[Cu(I)(4,4'-bpy)]3[GeW11Cu(II)O39].11H2O (3), and Na2[Cu(I)(4,4'-bpy)]3[PW11Cu(II)O39(H2O)].4H2O (4), have been synthesized under autogenous pressure hydrothermal conditions and characterized by elemental analysis and infrared spectroscopy (FT-IR). The crystal structures of 1, 2, and 4 have been established by single-crystal X-ray diffraction. The crystal packings are characterized by the presence of monodimensional extended entities: either the polymeric polyanion [SiW11CuO39]n(6n-) (2), the cationic [Cu(4,4'-bpy)]n(n+) chain (4), or both simultaneously as in compound 1, where the inorganic and metalorganic sublattices are mutually perpendicular. To asses the influence of packing in the copper(I) complex structural diversity found in compounds 1 and 4, a search in the CSD database has been performed and the resulting geometrical features have been analyzed and compared with experimental crystallographic data and DFT calculations.

Inorganic−Metalorganic Hybrids Based on Copper(II)-Monosubstituted Keggin Polyanions and Dinuclear Copper(II)−Oxalate Complexes. Synthesis, X-ray Structural Characterization, and Magnetic Properties

Reaction of in situ generated copper(II)-monosubstituted Keggin polyoxometalates and copper(II)-bipyridine-oxalate complexes in the corresponding alkaline acetate buffer led to the formation of hybrid metal organic-inorganic compounds K(2)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(H(2)O)(2)(mu-ox)}(2)].14H(2)O (1), K(14)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}](2)[SiW(11)O(39)Cu(H(2)O)].55H(2)O (2), (NH(4))(4)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}].10H(2)O (3), and Rb(4)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}].10H(2)O (4). Their structures have been established by single-crystal X-ray diffraction. The main structural feature of these compounds is the presence of copper(II)-monosubstituted alpha-Keggin polyoxoanions as inorganic building blocks, on which the mu-oxalatodicopper metalorganic blocks are supported. Compound 1contains the discrete hybrid polyanion [{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(H(2)O)(2)(mu-ox)}(2)](2)(-), whereas the polymeric hybrid polyanion [{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}(2)](n)(4)(n)(-) gives a monodimensional character to compounds 2-4. Magnetic and EPR results are discussed with respect to the crystal structure of the compounds. DFT calculations on both the [Cu(2)(bpy)(2)(H(2)O)(4)(mu-ox)](2+) cationic complex and the metalorganic blocks have been performed in order to determine the optimized geometry and the magnetic coupling constants, respectively.

Analysis of Weak Interactions in the Crystal Packing of Inorganic Metalorganic Hybrids Based on Keggin Polyoxometalates and Dinuclear Copper(II)−Acetate Complexes

Reaction of in situ generated copper-monosubstituted Keggin polyoxometalate (POM) and copper-phenanthroline complexes in potassium or sodium acetate buffers led to the formation of the potassium salt of [[SiW(11)O(39)Cu(H(2)O)][Cu(2)(phen)(2)(H(2)O)(ac)(2)]](4-) (1) and [[Si(2)W(22)Cu(2)O(78)(H(2)O)][u(2)(phen)(2)(H(2)O)(ac)(2)](2)](8-) (2, where phen = phenanthroline and ac = acetate) hybrid polyanions, respectively. Both compounds are the first discrete mono- and bimolecular transition-metal-substituted Keggin POMs that support a binuclear copper-acetate complex. Despite the different nature of the POMs, the crystal packing of the two compounds is closely related, being formed of hybrid parallel layers that give rise to an alternate sequence of inorganic and metalorganic regions. This packing type seems to be determined by the extensive network of weak intermolecular interactions established by the dicopper complexes, as a Hirshfeld surface analysis shows. Electron paramagnetic resonance studies indicate that both the supported [Cu(2)(ac)(2)(phen)(2)(H(2)O)](2+) complexes and the copper(II)-monosubstituted POMs are magnetically isolated.

Organic-Inorganic Hybrids Based on Novel Bimolecular [Si2W22Cu2O78(H2O)]12−Polyoxometalates and the Polynuclear Complex Cations [Cu(ac)(phen)(H2O)]nn+(n=2, 3)

The reaction of a monosubstituted Keggin polyoxometalate (POM) generated in situ with copper-phenanthroline complexes in excess ammonium or rubidium acetate led to the formation of the hybrid metal organic-inorganic compounds A7[Cu2(ac)2(phen)2(H2O)2][Cu3(ac)3(phen)3(H2O)3][Si2W22Cu2O78(H2O)].approximately 18 H2O (A=NH4+ (1), Rb+ (2); ac=acetate; phen=1,10-phenanthroline). These compounds are constructed from inorganic and metalorganic interpenetrated sublattices containing the novel bimolecular Keggin POM, [Si2W22Cu2O78(H2O)]12-, and Cu-ac-phen complexes, [Cu(ac)(phen)(H2O)]n n+ (n=2, 3). The packing of compound 1 can be viewed as a stacking of open-framework layers parallel to the xy plane built of hydrogen-bonded POMs, and zigzag columns of pi-stacked Cu-ac-phen complex cations running along the [111] direction. Magnetic and EPR results are discussed with respect to the crystal structure of the compounds. DFT calculations on [Cu(ac)(phen)(H2O)]n n+ cationic complexes have been performed, to check the influence of packing in the complex geometry and determine the magnetic exchange pathways.

A Novel Hybrid Inorganic–Metalorganic Compound Based on a Polymeric Polyoxometalate and a Copper Complex: Synthesis, Crystal Structure and Topological Studies

Reaction of monosubstituted Keggin polyoxometalates (POMs) and [Cu(ac)(pmdien)]+ generated in situ led to the formation of the hybrid metal organic-inorganic compound K5[Cu(ac)(pmdien)][SiW11CuO39].12H2O; its crystal structure and magnetic properties have also been determined. The packing of this compound can be viewed as a stacking of hydrogen-bonded chiral double chains, with the cationic complexes located between the two-dimensional arrangement of POM double chains. DFT calculations performed on [Cu(ac)(pmdien)]+ suggest that the distortion presented in this cationic copper complex is due to electronic effects. An AIM stability study of the cationic copper complex, in order to determine the relationship between the bond angle Cu-O-C and the denticity of the acetate ligand, has been carried out. Topological analyses over the polyhedral distortion, both of the monosubstituted polyanion and copper complexes, have been performed by means of continuous shape measures (CSM).

A novel organic-inorganic hybrid based on a dinuclear copper complex supported on a keggin polyoxometalate

The autoassembly process of copper-oxalate dimers and Keggin type polyoxometalates leads to the first example of a new family of organic-inorganic hybrids, K(14)[(Cu(2)(bpy)(2)(mu-ox))(SiW(11)O(39)Cu(H(2)O))](2)[SiW(11)O(39)Cu(H(2)O)]. approximately 55H(2)O. This compound crystallizes in the monoclinic space group C2/m, a = 37.932(6) A, b = 21.303(3) A, c = 12.546(2) A, beta = 106.16(1) degrees, Z = 2. The crystal structure reveals the presence of a polymeric hybrid built up of alternating dimer and polyoxometalate entities.

Water displacement by cyanogold complexes in binuclear nickel(II) compounds based on bridging oxalate. Synthesis, structural diversity, magnetic properties, and DFT calculations

Several cyanogold complexes react with the binuclear nickel complex [(Ni(dien)(H(2)O))(2)(mu-ox)](PF(6))(2).2H(2)O to give the compounds [(Ni(dien)(H(2)O))(2)(mu-ox)]Br(2) (1), [(Ni(dien)(Au(CN)(2)))(2)(mu-ox)] (2), and [(Ni(dien))(2)(mu-ox)(mu-Au(CN)(4))](PF(6)) (3) (dien, diethilenetriamine; ox, oxalate). In the case of compounds 2 and 3, water displacement by the corresponding cyanogold complex takes place, whereas compound 1 is formed by a substitution of the anion. The crystal structures of compounds 1 and 2 present a 2D arrangement where the layers are connected by van der Waals forces (1) or N-H.Ntbd1;C hydrogen bonds (2), where each binuclear complex is hydrogen bonded to its neighbors, whereas compound 3 presents a novel structure where the tetracyanoaurate acts as a bridging ligand to give a polymeric compound. Magnetic studies of these compounds reveal an antiferromagnetic behavior. Finally, density functional theory (DFT) calculations have been performed on isolated models of compounds 2 and 3 in order to gain some insight about the different behavior of the [Au(CN)(2)](-) and [Au(CN)(4)](-) groups as ligands and proton acceptors in hydrogen bonds.

Tetracyanometalates of Ni, Pd, and Pt with cyclic diquaternary cations of 2,2'-bipyridine and 1,10-phenanthroline. A vibrational, crystallographic, and theoretical study of intermolecular weak interactions

The compounds (bpy-dq)[Ni(CN)(4)].2H(2)O (1), (bpy-dq)[Pd(CN)(4)].2H(2)O (2), and ((bpy-dq)[Pt(CN)(4)].2H(2)O (3) (bpy-dq = (C(12)H(12)N(2))(2+), 6,7-dihydrodipyrido[1,2-a:2',1'-c]pyrazinediium) and (phen-dq)[Ni(CN)(4)] (4), (phen-dq)[Pd(CN)(4)].H(2)O (5), and (phen-dq)[Pt(CN)(4)].H(2)O (6) (phen-dq = (C(14)H(12)N(2))(2+), 5,6-dihydropyrazino[1,2,3,4-lmn]-1,10-phenanthrolinediium) have been synthesized and characterized by X-ray diffraction. The three bipyridinium diquaternary salt derivatives are isostructural. The crystal structures of these dihydrated compounds consist of columns formed by alternating anion complexes and diquaternary cations, pi-pi interacting through cyanide ligands and the aromatic rings, and stabilized by an extended hydrogen-bond network. On the other hand, the packing in the phenanthrolinium diquaternary salt derivatives is strongly dependent on the hydration degree. Thus, the anhydrous [Ni(CN)(4)](2-) compound presents a laminar arrangement and the hydrated salts show a columnar packing, similar but not the same as compounds 1-3. The anhydrous form of compound 5 is isostructural with compound 4. Vibrational (IR, Raman) and thermogravimetric studies of these compounds have been carried out. Finally, DFT calculations have been performed on the isolated tetracyanometalate anions and diquaternary cations to assign the fundamental modes in the vibrational spectra. The intermolecular weak interactions were studied through the analysis of the charge density by using the theory of atoms in molecules (AIM).

(Mu-oxalato-O1,O2:O1',O2')bis[aqua(diethylenetriamine)nickel(II)] bis(hexafluorophosphate) dihydrate

The title compound, [Ni(2)(C(2)O(4))(C(4)H(13)N(3))(2)(H(2)O)(2)](PF(6))(2).2H(2)O, contains a dinuclear oxalato-bridged nickel(II) complex cation. The structure determination reveals the presence of a centrosymmetric binuclear complex where the oxalate ligand is coordinated in a bis-bidentate mode to the Ni atoms. The distorted octahedral environment of each Ni atom is completed by the three N atoms of the diethylenetriamine ligand in a fac arrangement and by one O atom from a water molecule. PF(6)(-) acts as counter-anion. A two-dimensional network of hydrogen bonds links the cations and anions and stabilizes the structure.

Ion-Pair Charge-Transfer Complexes Based on (o-Phenylenebis(oxamato))cuprate(II) and Cyclic Diquaternary Cations of 1,10-Phenanthroline and 2,2'-Bipyridine: Synthesis, Crystal Structure, and Physical Properties

The ion pair charge-transfer (IPCT) complexes (C(14)H(12)N(2))[Cu(opba)].3H(2)O (1) and Na(2)(C(12)H(12)N(2))[Cu(opba)](2).4H(2)O (2), opba = o-phenylenebis(oxamate), have been isolated. Both compounds crystallize in the triclinic space group P&onemacr;. Crystal data for the compounds 1, a = 7.3216(13) Å, b = 10.1756(9) Å, c = 16.4890(16) Å, alpha = 107.786(8) degrees, beta = 94.79(1) degrees, gamma = 104.16(1) degrees, V = 1117.4(3) Å(3), Z = 2, R = 0.033 for 5332 observed reflections with I > 3sigma(I); 2, a = 6.732(3) Å, b = 11.169(3) Å, c = 12.126(2) Å, alpha = 111.01(2) degrees, beta = 102.71(3) degrees, gamma = 93.57(3) degrees, V = 820.1(5) Å(3), Z = 2, R = 0.065 for 3354 observed reflections with I > 3sigma(I). The crystal structures consist of alternated anion complex and diquaternary cation layers pi-pi interacting through the corresponding aromatic rings. The metallic layers contain the [Cu(opba)](2)(4)(-) dimeric group where the copper(II) ions are in square-pyramidal environment. For both compounds an ion-pair charge-transfer (IPCT) band is observed at 517 nm. Their thermal behavior has also been explained on the basis of the different crystal arrangements. The dimeric nature of compound 1 is clearly confirmed by the observation of temperature-dependent ESR transitions between its singlet and triplet states. The |J| value, determined from the positions of these transitions, is 0.085 cm(-)(1) at room temperature and increases notably with decreasing temperature being 0.14 cm(-)(1) at 4.2 K. Comparison of these exchange constants with those observed for other carboxylate-bridged copper compounds allow us to deduce that the temperature dependence of J is due to lattice shrinkage leading to appreciable change of the Cu-O(ap) distance. The ESR spectrum of compound 2 is characteristic of an axial g-tensor with g( parallel) = 2.178 and g( perpendicular) = 2.049, showing a weak half-field DeltaM(s) = 2 transition in agreement with the dimeric nature of the complex. The thermal evolution of the magnetic susceptibility corresponds to a compound with weak antiferromagnetic interactions. The best fit of the magnetic data to a dimer S = (1)/(2) model gives J = -0.8 cm(-)(1), in good agreement with the topology of the bridging unit with the magnetic orbitals in parallel planes and a Cu-O-Cu angle of 95.4 degrees.