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The polycrystalline EPR spectra of three cubane-type tetranuclear molybdenum cluster compounds Mo4S4(μ-OAc)2(dtp)4(1), Mo4S4(μ-OAc)2(dtp)4-·H (2), Mo4OS3(μ-dtp)3(dtp)3(3) are reported. By comparison of the EPR parameters at room temperature and at 77K, it is found that the EPR spectra of (1) and (2) should be attributed to the whole molecule of the cluster compounds while that of (3) to the molybdenum atoms under two different local environments. According to the results of quantum chemistry calculations by means of SCC-EHMO method and the data of X-ray crystal structure analysis, it is shown that the frontier orbital (HOMO), which is composed mainly of the multiple centre d-pπ bonds botween the metal atoms and the bridge (or terminal) groups and occupied by the unpaired electrons of the clusters, is similar to that of the π-conjugated system of free radicals. In many circumstances, the local environment around the Mo atom in cluster distors from ideal Td symmetry to a lower symmetry as to make th
The polycrystalline EPR spectra of three cubane-type tetranuclear molybdenum cluster compounds Mo4S4 (μ-OAc) 2 (dtp) 4 (1), Mo4S4 (3) are reported. By comparison of the EPR parameters at room temperature and at 77K, it is found that the EPR spectra of (1) and (2) should be attributed to the whole molecule of the cluster compounds while that of (3) to the molybdenum atoms under two different local environments. According to the results of quantum chemistry calculations by means of SCC-EHMO method and the data of X-ray crystal structure analysis, it is shown that the frontier orbital (HOMO), which is composed mainly of the multiple center d-pπ bonds botween the metal atoms and the bridge (or terminal) groups and occupied by the unpaired electrons of the clusters, is similar to that of the π-conjugated system of free radicals. In many cases, the local environment around the Mo atom in cluster distors from ideal Td symmetry to a lower symm etry as to make th