Synthesis and physical properties of M4M′3Mo26O48 (M = Sr, Eu; M′ = Al, Ga) containing Mo7 clusters and infinite Mo7–Mo10–Mo7 chains

We present the synthesis and physical properties of the M4M′3Mo26O48 (M = Sr, Eu; M′ = Al, Ga) compounds. The latter crystallize in the monoclinic P21/c space group. Their crystal structure is characterized by monocapped octahedral Mo7 clusters and infinite chains based on the tricluster Mo7–Mo10–Mo7 unit with oxygen atoms above all free apices and edges. Both cluster units are arranged in layers parallel to the ac plane. These compounds show semiconducting behavior with activation energies of about 0.12 eV at high-temperature and room-temperature resistivities in the range 0.16–0.47 Ω·cm. The magnetic susceptibility data indicated paramagnetic behavior due to the Eu2+ moment at high temperature and did not reveal the existence of localized moments on the Mo sublattice.