An inorganic−organic hybrid material, [HMTAH]₂[{Zn(H₂O)₅}{Zn(H₂O)₄}{Mo₇O₂₄}].2H₂O (1) (where HMTAH = protonated hxamethylenetetramine) has been synthesized and structurally characterized. The compound 1 crystallizes in a monoclinic space group $C2/c$. The crystal data of 1: 𝑎 = 43.12(3), 𝑏 = 12.399(10), 𝑐 = 16.285(13), 𝛽 = 111.131(11), 𝑍 = 8. Its crystal structure shows that two different Zn(II)-aqua complexes, [Zn(H₂O)₅]²⁺ and [Zn(H₂O)₄]²⁺ are covalently coordinated to a heptamolybdateanion [Mo₇O₂₄]^6- resulting in an anionic species of polyoxometalate supported zinc-aqua complexes, [{Zn(H₂O)}{Zn(H₂O)₄}{Mo₇O₂₄}]^2-, that is stabilized with two protonated hexamethylenetetramine cations in the title compound 1. In the crystal structure, both lattice water molecules are found to interact with the heptamolybdate cluster anion and the protonated hexamethylenetetramine cation resulting in an intricate three-dimensional hydrogen bonding network. Interestingly, compound 1 exhibits catalytic activity towards oxidation of some primary alcohols.

An inorganic-organic hybrid material, [2-AmpH]₄[Mo₈O₂₆] (1) has been isolated by the reaction of Na₂MoO$_4·2$H₂O with 2-aminopyrimidine (2-Amp) from an acidic aqueous medium. In this low pH synthesis, the organic molecule (2-Amp) gets mono-protonated (2-AmpH⁺) and acts as the cation in stabilizing the octamolybdate anion in 1. Compound 1 crystallizes in the triclinic space group 𝑃-1 with 𝑎 = 9.925(3), 𝑏 = 10.020(3), 𝑐 = 10.414(3) Å, 𝛼 = 88.811(4), 𝛽 = 64.907(4), 𝛾 = 89.506(4)°, 𝑍 = 1. An interesting three-dimensional supramolecular structure, having well-defined channels, is formed through N-H$\cdots$O and C-H$\cdots$O hydrogen bonds, in which the protonated organic cation plays a significant role. The crystal structure also reveals an unusual cluster-cluster (non-covalent O$\cdots$O) interaction using cis-(MoO₂} moieties of the isopolyanion. N-H$\cdots$O hydrogen bonds, originated from pyridimidinium cation and isopolyanion, are found to influence to attain such non-covalent O$\cdots$O interactions among polyoxometalate anions. An interesting helical arrangement, formed from isopolyanion and organic cation, is observed.

This article describes an account of some of our polyoxometalate (POM)-based research, we have been doing in our laboratory last several years. There are several well-defined POM cluster anions, that are structurally characterized. We have chosen Anderson-type of heteropolyanion [Al(OH)₆Mo₆O₁₈]$^{3−}$ and explored its linking propensity in different dimensions using `s', `d' and `f' block elements as linkers.We have demonstrated how a lanthanide linker provides a new pathway in forming a two-dimensional linked {As₈V₁₄} system [{Ln(H₂O)₆}₂As₈V₁₄O₄₂(SO₃)]$_n$.8nH₂O, that is derived from discrete {As₈V₁₄} cluster containing compound (NH₄)₆[As₈V₁₄O₄₂(SO₃)]. A polyoxometalate compound has been described in which a reduced tungstovanadate-heteropolyanion clusters get linked via capped V = O groups into one-dimensional chains. All these systems have already been reported elsewhere. The last portion of this article will be described by a new system [3-ampH]₆[V₁₀O₂₈]$\cdot$2H₂O having discrete molecular structure and extended supramolecular structure.