Effect of Halogen Substituents on Ligand-to-Ligand Charge Transfer Energy in Distorted Octahedral Tin(IV) Complexes with 3,6-Di‑tert‑butyl‑o‑benzoquinone and Diimines

New dihalogenotin(IV) complexes with 3,6-di-tert-butyl-o-benzoquinone and diimine ligands, pyrazino[2,3-f][1,10]phenanthroline (DPQ) and dipyrido[3,2-a:2'3'-с]phenazine (DPPZ), are synthesized and structurally characterized. The complexes have the distorted octahedral coordination environment in which the catecholate and diimine ligands are mutually cis-oriented. The electronic absorption spectra of the synthesized compounds exhibit the charge-transfer bands between the donor catecholate and acceptor nitrogen-containing ligands in the range of 400–650 nm causing their intense color. The position of the maximum in the absorption spectra depends on the nature of the halogen substituent and extent of π-conjugation of the diimine ligand. The reaction of the starting 3,6-di-tert-butylcatecholatodichloridotin(IV) complex with 2,2'-azobis(pyridine) is accompanied by a complete two-electron transfer from the catecholate ligands to the nitrogen-containing ligand with the formation of the biradical binuclear system. An analysis of the absorption spectrum demonstrates a series of electronic transitions in a range of 700–1400 nm attributed to the charge transfer between the organic ligands of the complex.