Splitting of the 2nd d–d Band of trans-[CoCl2N4]X-Type Complexes Observed in the Solid State at 113 K

Abstract
The electronic spectra of trans-[CoCl2(NH3)4]Cl and its analogues measured in the solid state at 113 K show four ligand field bands assignable to the Ia(1Ega← 1A1g), Ib(1A2g← 1A1g), IIa(1B2g← 1A1g), and IIb(1Egb← 1A1g) transitions in D4h approximation. The ligand field parameters obtained from the observed data are; eσ(N)=7400–8000 cm−1, eσ(Cl)=4500–5400 cm−1, eπ(Cl)=300–830 cm−1, and the Racah’s parameter C estimated with the assumption of C=4B is ca. 2000 cm−1. A nearly linear relationship is obtained between the eσ(Cl) and eπ(Cl) values; the stronger the coordination of Cl− to Co(III), the stronger the π interaction of Cl− with Co(III).