Electronic Structure and Magnetic Properties of a Low-Spin Cr Complex: -[CrCl(dmpe)] (dmpe = 1,2-Bis(dimethylphosphino)ethane).

Octahedral coordination complexes of the general formula -[MX(RECHCHER)] (M = Ti, V, Cr, Mn; E = N, P; R = alkyl, aryl) are a cornerstone of both coordination and organometallic chemistry, and many of these complexes are known to have unique electronic structures that have been incompletely examined. The -[CrCl(dmpe)] complex (dmpe = MePCHCHPMe), originally reported by Girolami and co-workers in 1985, is a rare example of a six-coordinate d system with an = 1 (spin triplet) ground state, as opposed to the high-spin ( = 2, spin quintet) state. The ground-state properties of = 1 systems are challenging to study using conventional spectroscopic methods, and consequently, the electronic structure of -[CrCl(dmpe)] has remained largely unexplored. In this present work, we have employed high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy to characterize the ground-state electronic structure of -[CrCl(dmpe)]. This analysis yielded a complete set of spin Hamiltonian parameters for this = 1 complex: = +7.39(1) cm, = +0.093(1) ( = 0.012), and = [1.999(5), 2.00(1), 2.00(1)]. To develop a detailed electronic structure description for -[CrCl(dmpe)], we employed both classical ligand-field theory and quantum chemical theory (QCT) calculations, which considered all quintet, triplet, and singlet ligand-field states. While the high density of states suggests an unexpectedly complex electronic structure for this "simple" coordination complex, both the ligand-field and QCT methods were able to reproduce the experimental spin Hamiltonian parameters quite nicely. The QCT computations were also used as a basis for assigning the electronic absorption spectrum of -[CrCl(dmpe)] in toluene.