Charge transfer, proton transfer and clathrate compounds of dihydrotetracyanodiphenoquinodimethane (H(2)TCNDQ) having highly acidic protons

Dihydrotetracyanodiphenoquinodimethane (H(2)TCNDQ) is a multifunctional molecule capable of behaving both as a weak electron acceptor (E-1/2(1) = -1.50 V, vs. SCE, in CH3CN) and a dibasic Bronsted acid (pK(a1) = 4.92, pK(a2) = 6.46 in ethanol-water (3 : 1)). H(2)TCNDQ affords three kinds of molecular compounds depending on the predominant intermolecular interactions; namely, 1) proton transfer (PT) complexes with amines of strong basicity (pK(a) > 4.7), 2) neutral clathrate complexes with amines of weak basicity (pK(a) < 4.7) or donors containing a TTF system without any charge transfer (CT) and PT interactions and 3) anion radical salts with amines of intermediate basicity. The last is derived from the PT complexes containing dianion TCNDQ(2-), which can be oxidized to monoanion radical TCNDQ(-center dot) by air. In the neutral clathrate complexes, C-H center dot center dot center dot X (X = N, O, pi) hydrogen bonds with the dicyanomethyl proton of H(2)TCNDQ play an important role, and construct a self-assembled structure.