α-Keggin tungstogermanate-supported transition metal complexes: hydrothermal synthesis, characterization, and magnetism of Cu2(phen)4(GeW12O40) and [Ni2(bpy)4(H2O)2(GeW12O40)]•2H2O

Two new alpha-Keggin polyoxometalates, [Cu-2(phen)(4)(GeW12O40)] (1) and [Ni-2(bpy)(4)(H2O)(2)(GeW12O40)]center dot 2H(2)O (2) (phen = 1,10-phenanthroline, bpy = 2,2 '-bipyridine), have been hydrothermally synthesized and characterized by elemental analysis, IR, TG, single-crystal X-ray diffraction, and magnetic properties. Compound 1 crystallizes in the monoclinic system, space group P2(1)/c, and 1 is assembled into two-dimensional (2-D) layers parallel to (1 0 1) based on the adjacent phen pi center dot center dot center dot pi stacking interactions (3.788(8) angstrom). Variable temperature magnetic measurements show ferromagnetic behavior from 300 to 2 K. Compound 2 crystallizes in the triclinic system, space group P-1, and 2 is assembled into 2-D layers parallel to (1 0 1) based on the adjacent bpy pi center dot center dot center dot pi stacking interactions (3.07 angstrom). Variable temperature magnetic measurements show a weak ferromagnetic behavior from 300 to 26 K followed by antiferromagnetic behavior below 26 K.