Alkali cation-π interactions in aqueous systems, modulating supramolecular stereoisomerism of nanoscopic metal-organic capsules

Contrary to common chemical intuition, cation-π interactions can persist in polar, aqueous reaction solutions, rather than in dry non-coordinative solvent systems. This account highlights how alkali ion-π interactions impart distinctive structure-influencing supramolecular forces that can be exploited in the preparation of nanoscopic metal-organic capsules. The incorporation of alkali ions from polar solutions into molecular pockets promotes the assembly of otherwise inaccessible capsular entities whose structures are distinctive to those of common polyoxovanadate clusters in which {V=O} moieties usually point radially to the outside, shielding the molecular entities. The applied concept is exemplified by homologous {V20} and {V30} cages, composed of inverted, hemispherical {V5O9} units. The number and geometrical organization of these {V5O9} sub-units in these cages are associated with prevailing cation- π interactions and competing steric effects. The stereoisomers of these resulting nano-sized objects are comparable to Alfred Werner-type structural isomers of simple mononuclear complexes in-line with fundamental coordination chemistry principles.

Three organic-inorganic polyoxoniobate-based compounds modified with Cu(II) amine complexes: synthesis, characterization, and catalytic studies for oxidation of styrene

Three novel organic-inorganic polyoxoniobate-based compounds modified with Cu(II) amine complexes were synthesized under hydrothermal conditions with the chemical formulas as follows: K0.5[Cu(enMe)2]4[K0.5SiNb12O40(VO)4.25](OH)1.5·9H2O (1), K0.5[Cu(enMe)2]4[K0.5H2PNb12O40(VO)2]·12.5H2O (2), and K0.5[Cu(enMe)2]4[K0.5H2VNb12O40(VO)2]·12.5H2O (3) (enMe = 1,2-diaminopropane). These compounds were characterized by single crystal X-ray diffraction, infrared spectroscopy (IR), UV-Vis spectroscopy, elemental analysis and powder X-ray diffraction (PXRD) analysis. Notably, while these three compounds exhibit identical cell parameters, they possess distinct stoichiometric compositions and differing polyoxometalate building block structures. Typically, compounds with the same cell parameters are classified as isostructural, sharing identical structures with only minor elemental variations in their compositions. To the best of our knowledge, compounds 1-3 represent the first instances of compounds that share the same cell parameters yet are not isostructural. In this study, we not only synthesized these three compounds and thoroughly examined the differences in their structures and properties, but also investigated their catalytic performances as catalysts for the oxidation of styrene.

Two binuclear Ni-inserted polyoxotantalates based on {NiTa10O32} units with catalytic activity

Two Ni-inserted polyoxotantalates, K5.5Na2H0.5[Ni(H2O)2{NiTa10O30(OH)2}]·21H2O (1) and K6Na4[Ni(en){NiTa10O32}]·22H2O (2, en = ethanediamine), were synthesized in this work. Crystallographic data analyses reveal that 1 and 2 have similar configurations. A minor difference between these two structures is that the {Ni(H2O)2} unit in 1 is replaced by {Ni(en)} unit in 2. Notably, the other Ni in 1 and 2 is located as a heteroatom at the center of the {Ta10} unit, which is reported in POTas for the first time. Moreover, 2 exhibits excellent catalytic performance in transesterification reactions in a preliminary exploration of the catalytic ability of the synthesized POTas.

Decoration of the [Nb6O19]8– cluster shell with six Cu2+-centred complexes generates the [(Cu(cyclen))6Nb6O19]4+ moiety: room temperature synthesis, crystal structure and selected properties

Mixing an aqueous solution of K8[Nb6O19]⋅16H2O with a DMSO/H2O solution of Cu(ClO4)2 · 6 H2O and cyclen at room temperature afforded crystallization of blue crystals of [(Cu(cyclen))6Nb6O19]⋅[ClO4]4·≈4H2O after slow evaporation of the solvents. The crystal structure contains the Lindqvist anion [Nb6O19]8– which is covalently expanded by six symmetry-related [Cu(cyclen)]2+ complexes via Nb-μ 2-O-Cu bridges yielding the positively charged [(Cu(cyclen))6Nb6O19]4+ cluster shell. The ClO4 − anions and crystal water molecules reside in the empty spaces of the packed clusters. The compound shows two electronic d-d transitions at energetic positions explaining the blue color.

Structural Variety of Niobium(V) Polyoxo Clusters Obtained from the Reaction with Aromatic Monocarboxylic Acids: Isolation of {Nb2 O}, {Nb4 O4 } and {Nb8 O12 } Cores

The reactivity of aryl monocarboxylic acids (benzoic, 1- or 2-naphtoic, 4'-methylbiphenyl-4-carboxylic, and anthracene-9-carboxylic acids) as complexing agents for the ethoxide niobium(V) (Nb(OEt)5 precursor has been investigated. A total of eight coordination complexes were isolated with distinct niobium(V) nuclearities as well as carboxylate complexation states. The use of benzoic acid gives a tetranuclear core Nb4 (μ2 -O)4 (L)4 (OEt)8 ] (L=benzoate (1)) with four Nb-(μ2 -O)-Nb linkages in a square plane configuration. A similar tetramer, 7, was obtained with 2-naphtoic acid by using a 55 % humid atmosphere synthetic route. Two types of dinuclear brick were identified with one central Nb-(μ2 -O)-Nb linkage; they differ in their complexation state, with one bridging carboxylate ([Nb2 (μ2 -O)(μ2 -OEt)(L)(OEt)6 ], with L=1-naphtoate (3) or anthracene-9-carboxylate (5)) or two bridging carboxylate groups ([Nb2 (μ2 -O)(L)2 (OEt)6 ], with L=4'-methylbiphenyl-4-carboxylic (4) or anthracene-9-carboxylate (6)). An octanuclear moiety [Nb8 (μ2 -O)12 (L)8 (η1 -L)4-x (OEt)4+x ] (with L=2-naphtoate, x=0 or 2; 8) was obtained by using a solvothermal route in acetonitrile; it has a cubic configuration with niobium centers at each node, linked by 12 μ2 -O groups. The formation of the niobium oxo clusters was characterized by infrared and liquid 1 H NMR spectroscopy in order to analyze the esterification reaction, which induces the release of water molecules that further react through oxolation with niobium atoms, in different {Nb2 O}, {Nb4 O4 } and {Nb8 O12 } nuclearities.

Vanadium O-Centered Selenoiodide Complex: Synthesis and Structure of V4O(Se2)4I6·I2

The first vanadium selenoiodide V₄O(Se₂)₄I₆·I₂ was synthesized at a moderate temperature of 220 °C from V, Se, I₂, and water. Its crystal structure (tetragonal space group P4₂/nbc, a = 11.838(1) Å, c = 18.689(1) Å) contains O-centered vanadium(IV) tetranuclear fragment [V₄(μ₄-O)(μ₂-Se₂)₄(μ₂-I)₂I₄], where the edges of the distorted tetrahedron V₄ are bridged by four diselenide (Se₂)^2- and two iodide ligands; four terminal iodides coordinate V atoms additionally. This type of complex is known for Ti, Nb, and Ta but is new for vanadium. Magnetic susceptibility measurements of V₄O(Se₂)₄I₆·I₂ showed four unpaired electrons on vanadium atoms at room temperature and drop of the effective magnetic moment at cool down, presumably due to partial electron pairing. Probability of this transition to the diamagnetic state is in accord with the calculated electronic structure.

Synthesis and crystal structure of bis-[μ-N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-bis-[N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-μ4-oxido-hexa-μ3-oxido-octa-μ2-oxido-tetra-oxido-tetra-nickel(II)hexa-tantalum(V) nona-deca-hydrate

Reaction of K8{Ta6O19}·16H2O with [Ni(tren)(H2O)Cl]Cl·H2O in different solvents led to the formation of single crystals of the title compound, [Ni4Ta6O19(C6H18N4)4]·19H2O or {[Ni2(κ4-tren)(μ-κ3-tren)]2Ta6O19}·19H2O (tren is N,N-bis-(2-amino-eth-yl)-1,2-ethanediamine, C6H18N4). In its crystal structure, one Lindqvist-type anion {Ta6O19}8- (point group symmetry ) is connected to two NiII cations, with both of them coordinated by one tren ligand into discrete units. Both NiII cations are sixfold coordinated by O atoms of the anion and N atoms of the organic ligand, resulting in slightly distorted [NiON5] octa-hedra for one and [NiO3N3] octa-hedra for the other cation. These clusters are linked by inter-molecular O-H⋯O and N-H⋯O hydrogen bonding involving water mol-ecules into layers parallel to the bc plane. Some of these water mol-ecules are positionally disordered and were refined using a split model. Powder X-ray diffraction revealed that a pure crystalline phase was obtained but that on storage at room-temperature this compound decomposed because of the loss of crystal water mol-ecules.

Synthesis, crystal structure and selected properties of K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O

The new compound K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O crystallized at room temperature applying a diffusion based reaction in a H2O/DMSO mixture using K8{Ta6O19}·16 H2O, Ni(NO3)2·6H2O and dien (diethylenetriamine). In the crystal structure, the Lindqvist-type anion [Ta6O19]8– is structurally expanded by two octahedrally Ni2+-centered complexes via three Ni–µ 2-O–Ta bonds thus generating the new {[Ni(dien)]2Ta6O19}4– anion. Two KO8 polyhedra share a common edge to form a K2O14 moiety, which connects the {[Ni(dien)]2Ta6O19}4– cluster shells into chains. The isolated [Ni(dien)2]2+ complexes are located in voids generated by the structural arrangement of the chains. An extended hydrogen bonding network between the different constituents generates a 3D network. The crystal water molecules can be thermally removed to form a highly crystalline dehydrated compound. Partial water uptake leads to the formation of a crystalline intermediate with a reduced unit cell volume compared to the fully hydrated sample. Water sorption experiments demonstrate that the fully dehydrated sample can be fully reconverted to the hydrated compound. The crystal field splitting parameters for the octahedrally coordinated Ni2+-centered complexes have been evaluated from an UV/Vis spectrum yielding D q = 1056 cm−1 and B = 887 cm−1.

The crystal structure of tetrakis(1-isopropyl-1H-imidazolium) octamolybdate, C24H44Mo8N8O26

C24H44Mo8N8O26, monoclinic, P21/n (no. 14), a = 10.3214(11) Å, b = 21.810(2) Å, c = 10.9371(11) Å, V = 2340.4(4) Å3, Z = 2, R gt (F) = 0.0423, wR ref (F 2) = 0.0893, T = 298(2) K.

Lacunary {Se4V10} Heteropolyoxovanadate Precursor with Monometal, Metal-Richer-Sandwiched Derivatives {Se8V20M} and {Se8V20M3}: Correlations between the Synthesis, Structure, and Catalytic Property

A new family of trinuclear transition-metal (TM)-sandwiched heteropolyoxovanadates (hetero-POVs) [(SeV₁₀O₂₈(SeO₃)₃M(H₂O)₃)₂(M(H₂O)₄)]^10- (Se₈V₂₀M₃, where M = Mn²⁺, Co²⁺, and Zn²⁺) were prepared using two feasible approaches: a stepwise assembly strategy atop the POV precursor Se₄V₁₀ and a one-pot reaction approach of KVO₃, SeO₂, TM²⁺, and a proline ligand. The crystallographic studies reveal that Se₈V₂₀M₃ consist of two asymmetric [SeV₁₀O₂₈(SeO₃)₃M(H₂O)₃)]^6- units, linked by another TM²⁺ ion, thus forming an interesting staggered sandwich-type arrangement. Additionally, Se₈V₂₀M₃ and Se₈V₂₀M present strong correlations between their structures and catalytic properties. In particular, Se₈V₂₀M₃ demonstrate an analogical heterogeneous catalytic performance as Se₈V₂₀M in the sulfoxidation reaction of thioethers owing to their structural similarities.

An inorganic Co-containing heteropolyoxoniobate: reversible chemochromism and H2O-dependent proton conductivity properties

A novel pure inorganic cobalt-containing heteropolyoxoniobate is constructed from crescent-shaped [SiNb18O54]14− units. It exhibits reversible chemochromism, H2O-dependent proton conductivity, water vapor adsorption and magnetic properties.

Vanadoborates: cluster-based architectures, preparation and properties

The different connections of [VO_x] (x = 4, 5, 6) and [AO_x] (A = B, x = 3, 4; A = P, x = 4) polyhedral units ultimately result in a fascinating variety of vanadoborate anionic clusters.