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

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.