Structural Trends in Potential Organic Conductors Based on (Donor-CH2)(2) Tetracyanoquinodimethane Molecules

The stoichiometry of electron donor-acceptor (EDA) complexes with potential electrical conductivity may be predetermined by preparing compounds in which D(s) and A(s) are chemically linked. The structural properties of three compounds comprised of two identical Ds bonded to one A (TCNQ; i.e., D center dot center dot center dot A center dot center dot center dot D) are reported here. The three compounds are isostructural; monoclinic, space group P2(1)/a, Z = 2. D = C6H5: a = 13.999 (6), b = 10.760 (2), c = 6.970 (2) angstrom, beta = 102.51 (3)degrees. D = p-C6H4OCH3 Zeta: a = 16.887 (6), b = 10.235 (6), c = 7.172 (4) angstrom, beta = 107.80 (4)degrees. D = beta-naphthyl: a = 16.93 (4), b = 11.676 (8), c = 7.093 (9) angstrom, beta = 114.3 (1)degrees. The structure of the last compound has also been determined at 93 K: a = 16.816 (5), b = 11.438 (4), c = 7.086 (1) A, beta = 115.21 (3)degrees. The outstanding common structural feature is the tendency to form infinite segregated stacks of A along the c axis, thus achieving a condition necessary for electrical conductivity. The charge-transfer interaction is achieved by the formation of previously not observed D center dot center dot center dot A center dot center dot center dot D triplets along both the A stacks and linking screw-related stacks. Details of the interactions leading to this unusual architecture are investigated with the aid of lattice energy calculations.