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)(2)Cl-2 (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)(2)Cl-2 (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(l) cm(-1), \E\ = 1.93(l) cm(-1), g(x,y) = 2.20(l), g(z) = 2.00(l). Corresponding spectra of Zn(PPh3)(2)Cl-2 (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.