Direct Observation of Fine Structure Transitions in a Paramagnetic Nickel(II) Complex Using Far-Infrared Magnetic Spectroscopy: A New Method for Studying High-Spin Transition Metal Complexes

Novel far-infrared (FIR) absorption spectroscopy in conjunction with
multiple, fixed external magnetic fields (FIR magnetic spectroscopy,
FIRMS) has been used to investigate pseudotetrahedral complexes
with the formula M(PPh3)2Cl2 (M = Ni, Zn; Ph = C6H5). Crystal
structures have been reported for the Ni complex; we report the
structure of the Zn complex. Transmission spectra at 5 K of Ni(PPh3)2Cl2 (S = 1) at zero magnetic field exhibit absorption bands
at 11.41, 15.28, and 23.0 cm-1. The two lower frequency bands
show great sensitivity to external magnetic field, and their field
dependence is as expected for electron spin transitions allowing
precise determination of the following parameters:  |D| =
13.35(1) cm-1, |E| = 1.93(1) cm-1, gx,y = 2.20(1), gz = 2.00(1).
Corresponding spectra of Zn(PPh3)2Cl2 (S = 0) exhibit bands only
at >20 cm-1, which show no field dependence. FIRMS is a
promising technique for direct investigation of the electronic
structure of high-spin transition metal complexes.