Chain and layer networks of germanato-polyoxovanadates

Abstract

Two new members of the {V15E6} (E = As, Sb, Ge, and Si) polyoxovanadate family, [{Mn(tren)(trenH2)}{Mn(tren)}4V15Ge6O48(H2O)0.5]·tren·2H2O (1, tren = tris(2-aminoethyl)amine) and [{Ni(tren)}4(trenH2)2V15Ge6O48(H2O)]·2H2O (2), have been prepared under solvothermal conditions. In 1, the {V15Ge6} cluster is expanded by five in situ formed crystallographically independent Mn2+ complexes via Mn–O(–V/Ge) bonds. Two independent Mn2+ complexes create a rare dinuclear [Mn2O2(tren)2]4+ moiety by bond formation with two terminal O atoms of the Ge2O7 groups of the adjacent {V15Ge6O48(H2O)0.5} clusters, thus connecting the {V15Ge6} cluster shells into a unique charge-neutral helical chain. In the structure of 2, the unusual and hitherto never observed {Ni(tren)(trenH2)Ni(tren)}6+ complex is formed in situ consisting of two tren molecules acting as tetradentate ligands to Ni2+ cations and one additional tren molecule connecting two Ni2+ cations bonded to neighboring cluster anions. The complexes act as linkers joining the {V15Ge6} moieties via Ni–OV bridges, forming a 2D structure. In the coordination polymers of 1 and 2, the spin structure of the {V15Ge6} cluster remains virtually unaffected by the coordinated MnII or NiII spin centers. For both compounds, the magnetic susceptibility can be decomposed into a sum of the contributions of both the {V15Ge6} cluster and the MnII or NiII cations, and a molecular field correction suffices to represent the weak antiferromagnetic coupling between them. Compound 1 is stable up to 350 °C as evidenced by in situ temperature-resolved X-ray powder diffraction studies.