Phosphomolybdate cluster based solids mediated by transition metal complexes

Reaction of molybdate and phosphate precursors in the presence of 3d transition metal ions and pyrazole (pz) under hydrothermal condition resulted in the crystallization of four new phosphomolybdate cluster based solids: (pz)2[{Co(pz)4}5{P2Mo5O23}2]·6H2O (1), (pz){Ni(pz)4(H2O)2}[{Ni(pz)4}5{P2Mo5O23}2]·2H2O (2), {Cu(pz)4(H2O)2}[{Cu(pz)4}{Cu(pz)4(H2O)}{P2Mo5O23}]·2H2O (3) and (pz)[{Zn(pz)3}3{P2Mo5O23}]·2H2O (4). In all the solids, a metal complex {M(pz)n} covalently links{P2Mo5O23} clusters to form a chain. The dimensionality of the structures differs in the way the chains link or self assemble with counter ions and water molecules. To the best of our knowledge, 4 is the first example of a zinc complex incorporated with {P2Mo5O23} cluster. The paper discusses the self assembly occurring between in situ metal pyrazole complex and phosphomolybdate clusters through coordinate/covalent and noncovalent interactions during crystallization of a particular solid.

Four metal pyrazole complex based phosphomolybdates are self assembled from an aqueous solution containing sodium molybdate, metal chlorides and pyrazole acidified with phosphoric acid. The results suggest that the complexing ability of metal ions towards pz, pH and temperature seem to influence the growth of solids 1–5.Figure optionsDownload as PowerPoint slideHighlights
► Formation of four new metal pyrazole complex based phosphomolybdates.
► Influence of complexing ability of metal ions towards pz, pH and temperature on the growth of solids.
► The formation of double sheets (metal complex linking {P2Mo5O23} clusters to form double sheets) as observed in 1 and 2 has not been reported earlier.
► Compound 4, is first example of zinc complex incorporated with {P2Mo5O23} cluster.