Photochemistry of transition metal carbonyls.

The purpose of this Tutorial Review is to outline the fundamental photochemistry of metal carbonyls, and to show how the advances in technology have increased our understanding of the detailed mechanisms, particularly how relatively simple experiments can provide deep understanding of complex problems. We recall some important early experiments that demonstrate the key principles underlying current research, concentrating on the binary carbonyls and selected substituted metal carbonyls. At each stage, we illustrate with examples from recent applications.

The "silent CO": a new technique for calculating transition metal carbonyl force fields.

The notion of a "silent CO group" (effectively an infinitely heavy CO group) is introduced to enable energy-factored force fields to be estimated accurately for molecules where there are fewer (CO) frequencies than force constants in the force field ( underdetermined force fields). The symmetry classes of molecules covered are the tricarbonyls ( Fe(CO)(diene) and -Re(CO)(L-L)X), tricarbonyls (-M(CO)(L) M = Cr, Mo, W), tetracarbonyls ( Fe(CO)(L)), tetracarbonyls (-M(CO)(L) and Fe(CO)(L)) and pentacarbonyls ( M(CO)(L) M = Cr, Mo, W and M(CO)(X) M = Mn, Re). It is a relatively simple matter to extend the method to types of molecules not directly considered in this paper.

Infrared Dynamics of Iron Carbonyl Diene Complexes.

The temperature dependence of the low-frequency C-O bands in the IR spectrum of [(η-norbornadiene)Fe(CO)], reminiscent of signal coalescence in dynamic NMR, was interpreted by Grevels (in 1987) as chemical exchange due to very fast rotation of the diene group. Since then, there has been both support and objection to this interpretation. We discuss these various claims involving both one- and two-dimensional IR and, largely on the basis of new density functional theory calculations, furnish support for Grevels' original interpretation.

The Structure of [Fe(CO) ]-An Important New Chapter in a Long-Running Story.

The structure of the singlet state ( A ) of [Fe(CO) ] in the gas phase has been determined by a combination of laser photochemistry of [Fe(CO) ] and electron diffraction imaging. The ground state of [Fe(CO) ] is known to be a triplet species ( B ), and this is the species detected in picosecond time-resolved IR experiments with [Fe(CO) ] in solution. This is an appropriate moment to survey the state of knowledge on [Fe(CO) ], beginning from the first low-temperature matrix experiments.