Vibrational spectra and potential constants of the (.eta.6-benzene)chromium(0) chalcocarbonyl complexes, (.eta.6-C6H6)Cr(CO)2(CX) (X = oxygen, sulfur, selenium) (original) (raw)

1982, Inorganic Chemistry

Infrared and laser Raman spectra have been recorded at rcom temperature for the ten chromium(0) chalcocarbonyl complexes BzCr('2C0)2('2CX), (B z-~,) C~(" C~)~(' * C X) , BzCr(I3CO),, B z C~('~C O)~(' * C S) , B Z C~('~C O) , ('~C S~) , and BzCr-('2co)2('3cs) (Bz = T6-C6H6; x = 0, s, Se), as solids and in various organic solvents. Vibrational assignments are proposed for most of the fundamental modes on the basis of general quadratic compliance and force field calculations in which the u(CO), v(CS), and v(CSe) vibrations were corrected for anharmonicity. The variations observed on comparing the primary CX and CrC(X) potential constants of the BzCr(CO),(CX) complexes with those of the related Cr(CO),(CX) derivatives are in line with the so-called "charge buffering ability" of CS (and presumably CSe as well) originally proposed by Andrews. Also, in agreement with earlier studies on transition-metal chalcocarbonyls, the net r-acceptor/o-donor capacity of the C X ligands increases in the order C O < CS < CSe. There is no appreciable mixing between the u(C0) and v(CS) or u(CSe) modes, but there is extensive mixing between v(CX) and the corresponding v[CrC(X)] mode, particularly in the case of the selenocarbonyl complex. In fact, comparisons of the general quadratic and energy-factored force fields for the CX modes shows that energy factoring for the thio-and selenocarbonyl is an extremely poor approximation, and any conclusions based on such calculations will be grossly in error.