This Perspective summarises the chemistry of the pyrazole ring, and reviews the metal coordination modes adopted by 1H-pyrazoles and their anions. Pyrazolide anions are probably the most versatile ligands in coordination chemistry, with 20 different terminal or bridging coordination modes having been identified so far. Metal cluster compounds supported by pyrazolido ligation are surveyed, concentrating on those reported during the past ten years. Highlights include the wide structural diversity in apparently simple main group pyrazolides; luminescence and charge-transfer complexes in coinage metal pyrazolide clusters; the use of robust metal pyrazolide clusters to construct liquid crystals, supramolecular materials and metal–organic frameworks; and supramolecular complexes formed by pyrazolide-supported metallacrowns.

Pyrazoles and pyrazolides—flexible synthons in self-assembly

Eight members of the Ag/1,2,4-triazole/polyoxometalates (POMs) hybrid supramolecular family, namely, [Ag4(dmtrz)4][Mo8O26] (dmtrz = 3,5-dimethyl-1,2,4-triazole, 1), [Ag6(3atrz)6][PMo12O40]2·H2O (3atrz = 3-amino-1,2,4-triazole, 2), [Ag2(3atrz)2]2[HPMoVI10MoV2O40] (3), [Ag2(dmtrz)2]2[HPMoVI10MoV2O40] (4), [Ag2(trz)2]2[Mo8O26] (trz = 1,2,4-triazole, 5), [Ag2(3atrz)2][Ag2(3atrz)2(Mo8O26)] (6), [Ag4(4atrz)2Cl][Ag(Mo8O26)] (4atrz = 4-amino-1,2,4-triazole, 7), and [Ag5(trz)4]2[Ag2(Mo8O26)]·4H2O (8), were synthesized through hydrothermal reactions of 1,2,4-triazole or its derivatives with appropriate silver salts and molybdates. Crystal structure analysis reveals that the POM-dependent Ag−1,2,4-triazolate units in these hybrid compounds form a novel tetranuclear cluster (1), a unique double calix[3]arene-shaped hexamer (2), zigzag chains (5 and 6), helix chains (3, 4, and 8), and an interesting looped chain (7). A series of hydrogen bonding-based supramolecular assemblies varying among the 0-D + 0-D (1 and 2), 0-...

Construction of Ag/1,2,4-triazole/polyoxometalates hybrid family varying from diverse supramolecular assemblies to 3-D rod-packing framework

The Anderson–Evans polyoxometalate: From inorganic building blocks via hybrid organic–inorganic structures to tomorrows “Bio-POM”

Six polyoxometalate (POM)-based hybrid materials have been designed and synthesized based on octamolybdate building blocks and copper-organic units at different pH values under hydrothermal conditions, namely, [H2bbi][CuII(bbi)2(β-Mo8O26)] (1), [CuII(bbi)2(H2O)(β-Mo8O26)0.5] (2), [CuII(bbi)2(α-Mo8O26)][CuI(bbi)]2 (3), [CuIICuI(bbi)3(α-Mo8O26)][CuI(bbi)] (4), [CuI(bbi)]2[CuI2(bbi)2(δ-Mo8O26)0.5][α-Mo8O26]0.5 (5), and [CuI(bbi)][CuI(bbi)(θ-Mo8O26)0.5] (6), where bbi is 1,1′-(1,4-butanediyl)bis(imidazole). Their crystal structures have been determined by X-ray diffraction. In compound 1, the bbi ligands with bis-monodentate coordination modes link CuII cations to generate a 2D copper-organic unit with (4, 4) net, which is pillared by the (β-Mo8O26)4− anions to form a 3D framework with α-Po topology. The similar copper-organic units are connected alternately by (β-Mo8O26)4− anions to generate a 3D 2-fold interpenetrating (4,6)-connected framework with (44·62)(44·610·8) topology in compound 2. Compounds 3 and ...

Self-Assembly of Polyoxometalate-Based Metal Organic Frameworks Based on Octamolybdates and Copper-Organic Units: from CuII, CuI,II to CuI via Changing Organic Amine

Four inorganic−organic hybrid compounds, [CuI4(bte)4(SiW12O40)] (1), [CuII2(bte)4(SiW12O40)]·4H2O (2) [bte = 1,2-bis(1,2,4-triazol-1-yl)ethane], [CuI4(btb)2(SiW12O40)]·2H2O (3), and [CuII2(btb)4(SiW12O40)]·2H2O (4) [btb = 1,4-bis(1,2,4-triazol-1-yl)butane], were hydrothermally synthesized through use of the same Keggin polyoxometalate as the template and tuning the molar ratio of the bis(triazole) ligand to the CuII ion. The ratio of the bis(triazole) ligand to CuII has a crucial influence on the structures of this series. Single-crystal X-ray diffraction analyses indicate that compound 1 is constructed by tetranuclear ring-connecting chains and polymerized [Cu(bte)]+ chains, between which SiW12 anions are inserted to form a three-dimensional (3D) structure. Compound 2 shows a (44·62) two-dimensional grid sheet. The discrete SiW12 anions are sandwiched by the sheets, just like “hamburgers”. Compound 3 presents channel-like [Cu2(btb)]2+ polymerized chains, which are further connected by SiW12 anions to con...

Assemblies of Copper Bis(triazole) Coordination Polymers Using the Same Keggin Polyoxometalate Template

The hydrothermal reaction of an aqueous ammonium heptamolybdate solution with cobalt or copper metal salts in the presence of imidazole (imi) or pyrazole (pz) in the temperature range 120–180 °C and at autogenous pressure yields four fully oxidized metal-complex-templated octamolybdates, namely [{CuI(imi)2}4(imi)2Mo8O26]·4H2O (1), (Himi)2[{CuII(imi)2}2Mo8O27] (2), [{CoII(pz)4}2(pz)2Mo8O26] (3), and [{CuII(pz)4}2Mo8O26]·2H2O (4). The single-phase nature of the solids was established by single-crystal and powder X-ray diffraction, thermal analysis, and spectroscopic techniques. Compounds 1, 3, and 4 are neutral composite solids – 1 is a discrete molecular unit while 3 and 4 are 2D sheets. Compound 2 consists of anionic chains with imidazolium counter cations. The influence of the metal complex and temperature of the hydrothermal reaction on the formation of the different hybrid solids built of octamolybdate clusters is discussed. We also provide plausible mechanisms for the self-assembly of the crystals in terms of supramolecular organization between metal complexes and soluble molybdenum precursors in the initial stages of the reaction. The magnetic properties of 2, 3, and 4 confirm the presence of Cu and Co in the divalent state with no appreciable long-range order down to 5 K, whereas 1 is diamagnetic.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The Hydrothermal Synthesis of Transition Metal Complex Templated Octamolybdates

The hydrothermal reaction of an aqueous ammonium heptamolybdate solution with first-row transition metal salts in the presence of 2-aminopyridine at around 180 °C and under autogenous pressure yields several molybdates, such as the 1D chains in (C5N2H7)4Mo8O26 (1), zero-dimensional (C5N2H7)6Mo7O24·3H2O (2), and the first synthesis of Lindgrenite [Cu3Mo2O8(OH)2 (3)] The structures of these materials were established by single-crystal and powder X-ray diffraction techniques. The crystal structures of wolframite-based MnMoO4 (4) and ZnMoO4 (5) were established by powder X-ray diffraction. The role of 2-aminopyridine (2-ampy) in the formation of the different solids under hydrothermal conditions is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Influence of 2-Aminopyridine on the Formation of Molybdates under Hydrothermal Conditions

The synthesis of four new Anderson-Evans type cluster based solids was carried out from an aqueous solution containing sodium molybdate, chromium chloride, cupric chloride and pyrazole at room temperature: [{Cr3O(CH3COO)6(H2O)3}2{H7CrMo6O24}]·24H2O, 1; [{Cu2(ox)(pz)4}{H7CrMo6O24}]·11H2O, 3; [{Cu(pz)2(H2O)2}{Cu2(ox)(pz)4}{H5CrMo6O24}]·8H2O, 4; and [{Cu(pz)3Cl}{Cu2(ox)(pz)4}{H6CrMo6O24}]·8H2O, 5. In 1, the discrete Anderson-Evans cluster aggregates with trimeric chromium acetate cationic complex through supramolecular interactions. In 3–5, the Anderson-Evans cluster is covalently linked into a 1D chain through oxalate bridged copper pyrazole units. In 3, the chains are further stabilized by water oligomers. In 4 and 5, the chains are covalently linked into 2D sheets by different copper pyrazole complexes. The oxalate molecules in 3–5 are probably generated in situ in the reaction medium, through a reductive coupling of dissolved carbon dioxide assisted by copper pyrazole units.

Oxalate Bridged Copper Pyrazole Complex Templated Anderson-Evans Cluster Based Solids

Hydrothermal synthesis of copper coordination polymers based on molybdates: Chemistry issues

Two new fully oxidized polyoxovanadate cluster-based solids (C4N2S2H14)2[H2V10O28]·4H2O,1 and (C4N2S2H14)5[H4V15O42]2·l0H2O,2 are crystallized under self-assembly process in the presence of cysteamine. In both1 and2, cysteamines are oxidized forming disulphide linkages and occur as counter cations. The organic cations assemble around V10O28 cluster anions in1 whereas they aggregate around V15O42 clusters in 2· pH appears to be the structure determinant in the occurrence of decavanadate cluster in1 and pentadecavanadate in2, with the same counter cation.

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K. Pavani

Papers

The Hydrothermal Synthesis of Transition Metal Complex Templated Octamolybdates

Influence of 2-Aminopyridine on the Formation of Molybdates under Hydrothermal Conditions

Oxalate Bridged Copper Pyrazole Complex Templated Anderson-Evans Cluster Based Solids

Hydrothermal synthesis of copper coordination polymers based on molybdates: Chemistry issues

Two new polyoxovanadate clusters templated through cysteamine