The electronic structure of transition metal compounds

Abstract

This chapter addresses a particular problem of transition metal chemistry: the bonding between a transition metal and a main group metal. Recently, transition metal carbonyl complexes of Al I - and Ga 1 -fragments—for example, [(CO) 5 Cr-Ga(C 2 H 5 )L 2 ] (L 2 = tmeda), [(CO) 4 Fe-A1Cp*], and [(CO) 5 W-AlClL 2 ] (L 2 = tmeda) could be synthesized and characterized by X-ray analysis. The position of the v(CO)-IR-bands has been taken as indication against the extreme description of the complexes as contact ion pairs. The overall structures suggest an interpretation of the interaction between the transition metal and the main group metal as a donor–acceptor bond. The study of the compounds [(CO) 5 W-XCl n (NH 3 ) m ] x– discussed in the chapter gives a thorough description of the bonding between a main group metal and a transition metal for a wide range of main group elements. The MP2 optimized geometry of model system [(CO) 5 W-AlCl(NH 3 ) 2 ] is in agreement with the X-ray structure of the recently synthesized [(CO) 5 W-A1C1L 2 ] (L2 = tmeda). The analysis of the electronic structure using the natural bond orbital (NBO) analysis and the newly developed charge decomposition analysis (CDA) clearly shows that the free electron pair of aluminum forms a donor bond to tungsten and, therefore, [(CO) 5 W-A1CI(NH 3 ) 2 ] is best understood as a donor–acceptor complex.