EPR STUDIES OF THE MIXED-METAL CUBANE-TYPE COMPLEX HAVING A [MO3CUS4(H2O)(10)](4+) CORE

The mixed-metal single-cubane-type complex [Mo3CuS4(H2O)(10)](4+), whi ch was generated by disintegration of the double-cubane-type complex [ (H2O)(9)Mo3S4CuCuS4Mo3(H2O)(9)](8+), was studied by EPR spectroscopy a nd EHMO calculations. The hyperfine coupling constants of the molybden um and copper nuclei were determined from frozen solution EPR spectra for the Mo-95-enriched and -unenriched complexes. EPR analyses show th at the single-cubane-type complex [Mo3CuS4(H2O)(10)](4+) is a paramagn etic of S = 1/2 and the paramagnetic center is mainly situated on one of the three molybdenum ions; the three molybdenum ions are not equiva lent to each other, but they are formally close to Mo(III), Mo(IV), an d Mo(IV), respectively. It is also shown that there is little spin den sity on copper, which may be close to Cu(I) rather than Cu(II), and th at the paramagnetic site, Mo(III), is jumping among the three molybden um ions at such a rate as to cause a line width broadening effect on t he molybdenum hyperfine components of the EPR spectrum.