Chain and layer networks of germanato-polyoxovanadates

Two new members of the {V15E6} (E = As, Sb, Ge, and Si) polyoxovanadate family, [{Mn(tren)(trenH(2))} {Mn(tren)}(4)V15Ge6O48(H2O)(0.5)]center dot tren center dot 2H(2)O (1, tren = tris(2-aminoethyl)amine) and [{Ni(tren)}(4)(trenH(2))(2)V15Ge6O48(H2O)]center dot 2H(2)O (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)(trenH(2))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-O=V 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 Mn-II or Ni-II spin centers. For both compounds, the magnetic susceptibility can be decomposed into a sum of the contributions of both the {V15Ge6} cluster and the Mn-II or Ni-II cations, and a molecular field correction suffices to represent the weak antiferromagnetic coupling between them. Compound 1 is stable up to 350 degrees C as evidenced by in situ temperature-resolved X-ray powder diffraction studies.