Abstract

Dihydrotetracyanodiphenoquinodimethane (H₂TCNDQ) is a multifunctional molecule capable of behaving both as a weak electron acceptor (E¹_1/2 = −1.50 V, vs. SCE, in CH₃CN) and a dibasic Brönsted acid (pK_a1 = 4.92, pK_a2 = 6.46 in ethanol–water (3 ∶ 1)). H₂TCNDQ 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 TCNDQ²⁻, which can be oxidized to monoanion radical TCNDQ⁻˙ by air. In the neutral clathrate complexes, C–H⋯X (X = N, O, π) hydrogen bonds with the dicyanomethyl proton of H₂TCNDQ play an important role, and construct a self-assembled structure.