Structural transformations and solid-state reactivity involving nano lead(II) coordination polymers via thermal, mechanochemical and photochemical approaches

Single-Crystal-to-Single-Crystal Transformation of Two Copper(II) Metal-Organic Frameworks Modulated by Auxiliary Ligands

The single-crystal-to-single-crystal (SCSC) transformations of metal-organic frameworks (MOFs) are fascinating because we can directly observe the change of the crystal structure during the transformation process. It also greatly helps to understand the delicate interaction between the guest molecules and the skeleton framework and therefore fosters a deep understanding of gas storage and separation within the frameworks. Herein, we report two novel MOFs, [Cu₈(BCB)₄(μ₃-OH)₂(μ₃-O)(H₂O)₈(Py)₅]·16DMF·52H₂O (1) and [Cu₃(BCB)₂(Py)₆]·DMF·11H₂O (2) (Py = pyridine; DMF = N,N'-dimethylformamide), which were constructed through the self-assembly of Cu²⁺ and 4,4',4″-benzenetricarbonyltribenzoic acid (H₃BCB) by a solvothermal reaction. Although the structure and coordination patterns of compound 1 are pretty different from those of 2, the two Cu-MOFs were prepared from identical ligands and similar reaction conditions. Interestingly, compound 1 will change to 2 wholly and gradually after the addition of a certain amount of Py with a small amount of dilute hydrochloric acid. This conversion represents a scarce example of SCSC transformation involving transition-metal-based MOFs. Moreover, with its microporous nature, compound 2 shows large carbon dioxide (CO₂) uptake capability and good selectivity for CO₂/N₂ separation. Furthermore, both compounds 1 and 2 could be used as excellent heterogeneous catalysts toward the cyanosilylation reaction under solvent-free conditions.

Supramolecular assembly and structural transformation of d10-metal complexes containing (aza-15-crown-5)dithiocarbamate

[Au(O4NCS2)]2 underwent structural transformation by heating to give [Au(O4NCS2)]6. Moreover, [Ag(O4NCS2)]n and [Cu(O4NCS2)]4 can be isolated, and notably [Cu(O4NCS2)]4 structurally transformed to [Cu(O4NCS2)]8 by heating can be also observed.

Synthesis, crystal structures and reversible solid-state crystal-to-crystal transformation of three isostructural lead(ii) halide coordination polymers with different luminescence properties in bulk and nanoscale

Novel isostructural lead(ii) halide CPs have been synthesized in bulk and nanoscale. The compounds exhibited reversible solid-state CTC transformations under mechanochemical reactions. The CPs displayed different thermal and fluorescence properties.

Synthesis, X-ray structure, physicochemical properties and anticancer activity of mer and fac Ru(iii) triphenylphosphine complexes with a benzothiazole derivative as a co-ligand

Two mononuclear ruthenium(iii) mer- and fac-isomers of the formula [RuCl3(PPh3)(dmpbt)] (where PPh3 = triphenylphosphine, dmpbt = 2-(3,5-dimethylpyrazoll-yl)benzothiazole) have been synthesised from the reaction of [RuCl3(PPh3)3] with a bidentate ligand - dmpbt. Appropriate reaction conditions allowed obtaining the two isomers separately without separation techniques. X-ray crystallography has determined the crystal and molecular structures of the new complexes. mer-Ru(iii) (1) crystallised in the monoclinic P2(1)/n group, and fac-Ru(iii) (2, 2') in the triclinic P1[combining macron] space group. The composition of the ruthenium coordination sphere was confirmed and characterised using spectroscopic techniques (FT-IR, UV-vis and EPR), elemental analysis and mass spectrometry (MS-FAB). The structures of the complexes obtained were analysed using X-ray and other spectroscopic methods (IR and UV-vis). The electrochemical properties of the ligand and the complex compound were identified using cyclic voltammetry, determining the potential and charge of faradaic processes. Both isomers are redox active and display quasi-reversible metal centered redox processes for the Ru(iii)/Ru(ii) pair. Moreover, preliminary tests of their biological activity were performed. The cytotoxicity of these compounds has been tested for human lung carcinoma (A549), chronic myelogenous leukemia (K562), human cervix carcinoma (HeLa) cells, acute lymphoblastic leukemia (MOLT-4), human breast adenocarcinoma cell line (MCF-7) and normal human umbilical vein endothelial cells (HUVEC). The ability to induce apoptosis has been demonstrated in caspase 3/7 activity assay. In addition, the lipophilicity of both isomers was described by a partition coefficient, log P, values of which were estimated by the shake-flask method. The interesting and promising preliminary results of the biological and chemical activities of the new octahedral mer/fac Ru(iii) complexes motivate further in vitro and in vivo studies.

The mechanochemical conversion of potassium coordination polymer nanostructures to interpenetrated sodium coordination polymers with halogen bond, metal–carbon and metal–metal interactions

Two new Na and K coordination polymers with halogen bond, metallophilic and hydrogen bonding interactions were synthesized. These two compounds were synthesized sonochemically and solid-state conversions of them to each other were investigated.

The effect of coordinated solvent molecules on metal coordination environments in single-crystal-to-single-crystal transformations

We summarized the effect of coordinated solvent molecules on the metal coordination environments in single-crystal to single-crystal transformations.

Structural conversion of three copper(ii) complexes with snapshot observations based on the different crystal colours and morphology

Three novel Cu(ii) complexes [Cu₂(L)₂(MeOH)₂] (1), [Cu₂(L)₂(H₂O)₂] (2) and [CuL(H₂O)] (3) (L = (E)-2-((2-hydroxy-4-methoxybenzylidene)amino)acetic acid) have been obtained in different time scales of reaction processing. Complexes 1 and 2 are kinetically controlled products and 3 is a thermodynamically stable product. Single crystal X-ray diffraction analyses revealed that 1 and 2 are binuclear complexes except for different coordination solvents. 3 is a mononuclear complex. Complex 1 is mainly obtained in methanol solution, while 2 and 3 are stable in aqueous solvents. Based on the understanding of crystal structures of the three complexes, reversibly transforming crystal 2 to crystal 1 at room temperature has been realised, which has been confirmed by the change of colours and morphology measured by SEM. The research work is very important for controllable synthesis of coordination complexes.

Structural conversion of three novel Cu(ii) complexes [Cu₂(L)₂(MeOH)₂] (1), [Cu₂(L)₂(H₂O)₂] (2) and [CuL(H₂O)] (3) (L = (E)-2-((2-hydroxy-4-methoxybenzylidene)amino)acetic acid) in different time scales of reaction processing.

Solvent-assisted structural conversion involving bimetallic complexes based on the tris(oxalato)ferrate(iii) unit with the green → blue → red crystal color sequence

Three new complexes forming a dynamic system and given by the following formulae: [Cu₂(bpy)₄Fe(ox)₃]NO₃·H₂O 1, [Fe(bpy)₃]₂[Fe(ox)₃]NO₃·10H₂O 2 and [Cu(bpy)₃]₂[Fe(ox)₃]NO₃·10H₂O 3 (bpy - 2,2'-bipyridine, ox - oxalate), were synthesized from a methanol-water mixture or water, and characterized structurally, spectroscopically and magnetically. Compound 1 contains trinuclear [(bpy)₂Cu(μ-ox)Fe(ox)(μ-ox)Cu(bpy)₂]⁺ cations, while 2 and 3 can be classified as isomorphous ionic compounds, with alternately arranged hydrophobic and hydrophilic layers of mononuclear complex ions. The green crystals of 1 are perfectly stable in air, whereas in selected solvents they undergo irreversible solvent-assisted recrystallization towards red crystals of 2, which is also accompanied by the appearance of mononuclear blue copper complexes with oxalate, 2,2'-bipyridine and aqua ligands, already described in the literature. The above crystallization/recrystallization processes indicate variable solution contents. The whole effect is accelerated by both the increased temperature and day light irradiation, however, different products from the pool prevail under various conditions. The observed transformation can be understood in terms of thermodynamic and kinetic control, involving the known photo-activity of [Fe(ox)₃]^3- moieties and the effect of quadruple aryl embrace (QAE) on the stability of the crystal network. Considering the presence of Fe^III-ox-Cu^II connectivity in 1 we performed detailed magnetic studies and theoretical calculations for this compound. Due to the strong asymmetry of Cu-O bonds the antiferromagnetic coupling is rather weak, with J_Cu-Fe being ca. -3.4 cm^-1 (using Hamiltonian of the type H = -J_Cu-Fe(S_Cu1S_Fe + S_FeS_Cu2) -J_Cu-Cu(S_Cu1S_Cu2)). We found that these values are very close to those predicted by B3LYP/6-311G* calculations.

Solvent-mediated structural transformations of copper(II) coordination polymers induced by different short-chain alcohols

A three-dimensional copper(II) coordination polymer (CP), {Cu(L-F)(N₃)}_n (1), was synthesized by reacting Cu(NO₃)₂ with 5-fluoronicotinic acid (HL-F) and NaN₃ in a water medium. Complex (1) shows a 3D network, in which the 1D [Cu₂(COO)N₃]_n chains are interconnected via L-F ligands. By immersing (1) into different short-chain alcohols (CH₃OH, C₂H₅OH and HOC₂H₄OH), three different CPs were isolated, including {Cu₃(L-F)₄(N₃)₂(CH₃OH)₂}_n (2), {Cu₃(L-F)₄(N₃)₂(C₂H₅OH)₂}_n (3) and {Cu_2.5(L-F)₃(N₃)₂(HOC₂H₄OH)_0.5}_n (4). CPs (2) and (3) display a similar structure, in which trinuclear subunit [Cu₃(COO)₂(N₃)₂(solvent)₂] is generated. Furthermore, such entities are interconnected via L-F ligands to give rise to a 3D network. As for (4), there are trinuclear [Cu₃(COO)₂(N₃)₂] and binuclear [Cu₂(COO)N₃] units, which are interconnected by L-F ligands to generate a 3D network. Notably, in (2) and (3), the coordination modes of CH₃OH and C₂H₅OH solvents are monodentate; whereas for (4), the HOC₂H₄OH solvent adopts a bridging mode to link two Cu atoms. Of further interest, these processes are solvent-mediated structural transformations, with obvious colour changes in the crystals. Structural changes and mechanisms of transformation are discussed in detail.

Crystal-to-crystal transformation and linker exchange in Cd(ii) coordination polymers based on flexible bis-pyridyl-bis-amide and 1,4-naphthalenedicarboxylate

Solvothermal reactions of Cd(ii) salts and naphthalene-1,4-dicarboxylic acid with bis(N-pyrid-3-ylmethyl)adipoamide and bis(N-pyrid-3-ylmethyl)suberoamide yield three Cd(ii) coordination polymers that undergo reversible crystal-to-crystal transformation and linker exchange.

Sonochemical synthesis and characterization of microrod to nanoparticle of new mixed-ligand zinc(II) fumarate metal-organic polymer

Micro and nano-structures of a new mixed-ligand Zn(II) fumarate metal-organic polymer, {[Zn(tptz)(fum)].DMF}_n (1), (tptz=2,4,6-tris(2-pyridyl)-s-triazine, fum=fumarate, DMF=N,N-dimethylforamide), were synthesized by sonochemical method. These new micro and nano-structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), IR spectroscopy and elemental analyses. Compound 1 was structurally characterized by single-crystal X-ray diffraction and consists of the primary unit of [Zn(tptz)(fum)]. Self assembly between the units of [Zn(tptz)(fum)] from Zn-O bonds results in the formation of a one-dimensional zinc(II) coordination polymer. The Zn^II-ion in compound 1 has ZnO₂N₃ coordination sphere with a trigonal bipyramidal molecular geometry. Compound 1 was synthesized by ultrasound irradiation under different concentrations and times. The microrods structure of compound 1 with increasing of concentration and ultrasound radiation time were synthesized as nanoparticles structure successfully. So ultrasound radiation change morphology from microrods to nanoparticles.

Advances in Solid-State Transformations of Coordination Bonds: From the Ball Mill to the Aging Chamber

Controlling the formation of coordination bonds is pivotal to the development of a plethora of functional metal-organic materials, ranging from coordination polymers, metal-organic frameworks (MOFs) to metallodrugs. The interest in and commercialization of such materials has created a need for more efficient, environmentally-friendly routes for making coordination bonds. Solid-state coordination chemistry is a versatile greener alternative to conventional synthesis, offering quantitative yields, enhanced stoichiometric and topological selectivity, access to a wider range of precursors, as well as to molecules and materials not readily accessible in solution or solvothermally. With a focus on mechanochemical, thermochemical and “accelerated aging” approaches to coordination polymers, including pharmaceutically-relevant materials and microporous MOFs, this review highlights the recent advances in solid-state coordination chemistry and techniques for understanding the underlying reaction mechanisms.

Solvent-mediated single-crystal-to-single-crystal transformation from a dimeric to tetrameric copper(i) complex based on a substituted pyridine derived from a Diels–Alder adduct

A solution of [Cu₂I₂L₂(MeCN)₂] (1) in dichloromethane (DCM) assisted the removal of MeCN and N-(4-pyridinyl)-9,10-dihydroethanoanthracene-11,12-dicarboximide (L) from the crystal of 1, leading to an unprecedented SCSC transformation.

Temperature-induced reversible single-crystal-to-single-crystal isomerisation of uranyl polyrotaxanes: an exquisite case of coordination variability of the uranyl center

A reversible solid-state isomerisation mediated by the change of uranyl-ligand coordination modes has been achieved in uranyl polyrotaxanes by a temperature-induced strategy.

Supramolecular Assemblies, Luminescence and Anion Exchange of Helical Pb(II) Complexes Based on Enantiomeric N-(2-pyridylmethyl) Alanine Ligands

Two pairs of PbII coordination polymers have been synthesised using pyridine-functionalised amino acid derivatives N-(2-pyridylmethyl)-L(D)-alanine hydrochlorides [(L-Hpala)Cl or (D-Hpala)Cl] and PbII salts. Their X-ray structures confirm their formulations as [Pb(L-pala) (NO3)]n, [Pb(D-pala)(NO3)]n, [Pb(L-pala)(Cl)]n and [Pb(D-pala)(Cl)]n. They show similar coordination environments of PbII cations with two kinds of five-membered chelating rings, which are further assembled into 1D helical chains through the bridging carboxylates from amino acids. Thermal and fluorescent properties of these complexes have also been investigated.

Sonochemical synthesis of two new nano lead(II) coordination polymers: Evaluation of structural transformation via mechanochemical approach

Two new lead(II) mixed-ligand coordination polymers, [Pb(PNO)(SCN)]n (1) and [Pb(PNO)(N3)]n (2), (HPNO=picolinic acid N-oxide) were synthesized by a sonochemical method and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analysis. Compounds 1 and 2 were structurally characterized by single crystal X-ray diffraction. The thermal behavior of 1 and 2 were studied by thermal gravimetric analysis. Structural transformations of compounds 1 and 2 were evaluated through anion-replacement processes by mechanochemical method. Moreover, the effect of sonication conditions including time, concentrations of initial reagents and power of irradiation were evaluated on size and morphology of compounds 1 and 2.

Metal-center exchange of tetrahedral cages: single crystal to single crystal and spin-crossover properties

Effective SCSC metal-center exchange was observed in a tetrahedral metal–organic cage, in which the metal centers can be induced to display spin crossover behaviors.

A new fluorescent probe based on quinoline for detection of Al3+ and Fe3+ with “off–on–off” response in aqueous solution

A new quinoline-based fluorescent probe has been designed and synthesized. It showed highly selective relay recognition of Al³⁺ and Fe³⁺via a fluorescence “off–on–off” mechanism by central metal displacement.