Structure and magnetism of [n-BuNH3]12[Cu4(GeW9O34)2].14H2O sandwiching a rhomblike Cu4(8+) tetragon through alpha-Keggin linkage.

A sandwich-type polyoxometalate, [Cu4(GeW9O34)2]12− (1a), in which two B-α-[GeW9O34]12− ligands sandwich a rhomblike Cu48+ tetragon through α-Κeggin linkage, is first isolated as a [n-BuNH3]+ salt, [n-BuNH3]12[Cu4(GeW9O34)2]·14H2O (1). A Cu4O14 cluster for the rhomblike Cu48+ tetragon in 1a with C2h local symmetry consists of two Jahn−Teller (JT) distorted CuO6 octahedra (at internal sites) with a short diagonal Cuint···Cuint distance of 3.10−3.11 A and two CuO5 square pyramids (at external site) with a long diagonal Cuext···Cuext distance of 5.34−5.35 A, the feature of which is different from [Cu4(H2O)2(GeW9O34)2]12− (2a), comprising the four JT-distorted CuO6 octahedral Cu48+ tetragons through β-Keggin linkage: the axial Cuext−O bond distance (2.27−2.29 A) for 1a is shorter than the corresponding JT-axial distance (2.36 A) for 2a. Measurements of magnetic susceptibility, magnetization, and electron spin resonance spectroscopy for 1 are carried out for better understanding of the molecular magnetism of t...