Charge-Transfer Complexes of 3a,6a-Diaza-1,4-Diphosphapentalenes With the Organic π-Acceptor 2,3-Dicyanopyrazine and Its Derivatives

Abstract

2,3-Dicyanopyrazine (DCNP) was first utilized as a π-acceptor to form charge-transfer complexes with strong π-donors, 3a,6a-diaza-1,4-diphosphapentalenes (RR’DDP), bearing peripheral methyl and annelated cyclohexyl substituents. The donor and acceptor molecules form mixed D–A–D–A stacks irrespective of the component ratio. The study of electron density topology indicated that each DCNP molecule accepts 0.22–0.24 electron charges in the crystal. The intermolecular interaction energy between donor and acceptor molecules ranges from 3.8 to 5.0 kcal/mol. An evaluation of the dark conductivity of the (cHexDDP•DCNP) sample showed an increase in current by ~5 orders of magnitude upon raising the temperature from 233 to 283 K. When RR’DDP interacts with acenaphthene- and cyclohexane-annelated 2,3-dicyanopyrazines, complexation is observed in solution, but CTC crystals do not form.