Binuclear and trinuclear chromium carbonyls with linear bridging carbonyl groups: isocarbonyl versus carbonyl bonding of carbon monoxide ligands.
Isocarbonyl groups bonded to chromium through their oxygen atoms as well as the usual carbonyl groups bonded to carbon atoms have been considered as possible structural features for Cr(CO)(6), Cr(2)(CO)(n) (n = 11, 10, 9), and Cr(3)(CO)(16). In this connection, Cr(CO)(6) structures with one of the six CO groups bonded to the chromium either solely through its oxygen atom or side-on through both its carbon and oxygen atoms are predicted by density functional theory to lie >30 kcal/mol above the well-known Cr(CO)(6) structure, in which all six carbonyl groups are bonded to the chromium atom in the normal manner through their carbon atoms. The binuclear Cr(2)(CO)(11) structure of the type (OC)(5)Cr-C-O-Cr(CO)(5) with a linear bridging carbonyl group bonded to one chromium atom through its carbon atom and to the other chromium atom through its oxygen atom is of lower energy than previously studied Cr(2)(CO)(11) structures and indeed is viable with respect to dissociation into Cr(CO)(5) + Cr(CO)(6). Similar binuclear structures are found for Cr(2)(CO)(10) and Cr(2)(CO)(9) with linear bridging carbonyl groups. However, the Cr(2)(CO)(9) structure with a linear bridging carbonyl group, no Cr-Cr bond, and 16-electron chromium configurations is found to lie higher by 22 +/- 5 kcal/mol than the previously found Cr(2)(CO)(6)(mu-CO)(3) structure with three bridging carbonyl groups, a formal Cr[triple bond]Cr triple bond, and the favorable 18-electron chromium configuration. For the trinuclear Cr(3)(CO)(16), nearly degenerate trans- and cis-Cr(CO)(4)[OCCr(CO)(5)](2) structures are found that are viable with respect to dissociation into 2Cr(CO)(5) + Cr(CO)(6).
Zhang
Zhong
Z
Center for Computational Quantum Chemistry, South China Normal University, Guangzhou 510631, People's Republic of China.
Li
Qian-shu
QS
Xie
Yaoming
Y
King
R Bruce
RB
Schaefer
Henry F
HF