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[摘要]：The solid solution GaV4-xCrxSe8 (x = 0-4) was synthesized; their crystal structures and magnetic properties were determined and compared with results of ab initio density functional theory (DFT) calculations. The compounds crystallize in the GaMo4S8-type structure (F (4) over bar 3m), consisting of GaS4 tetrahedra and heterocubane-like (V4-xCrx)Se-4 units. Significant metal-metal bonding within tetrahedral metal clusters exists up to GaV2Cr2Se8 (x = 2), while the bonds gradually disperse when x > 2. The dissolving of the metal-metal bonds is associated with large increases in the magnetic moments. This can be explained by metal-metal bonded tetrahedral V4-xCrx clusters with (small) magnetic moments localized in cluster molecular orbitals for x <= 2, whereas the magnetism of Cr-rich compounds is better described by a mixture of V2Cr2 clusters and nonbonded Cr atoms with stronger magnetism. GaV4Se8 and hypothetical GaCr4Se8 were investigated as model systems by ab initio DFT calculations. Thus, the ground state of GaV4Se8 contains V-4 cluster units with small magnetic moments, while GaCr4Se8 has no tendency to form strong Cr-Cr bonds, but a much higher magnetic moment, both in good agreement with the experimental data. |
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