(Tetramethylporphyrinato)nickel 7,7,8,8-Tetracyanoquinodimethane, Ni(TMP)TCNQ. Synthesis, Structure, and Physical Properties

Single crystals of the 1:1 charge-transfer complex (tetramethylporphyrinato)nickel(II) 7,7,8,8-tetracyanc-p-quinodimethane, Ni(TMP)TCNQ, were afforded by the reaction of Ni(TMP) in benzene with TCNQ in acetonitrile. The compound crystallizes in the space group C_2h⁵−P2₁/n of the monoclinic system with four formula units in a cell of dimensions a = 17.542 (11) Å, b = 6.868 (5) Å, c = 22.597 (13) Å, and β = 98.42 (2)° at 116 K. Full-matrix least-squares refinement of 407 variables gives a final value of the conventional R index (on F²) of 0.093 for 5190 observations. The conventional R index on F for 3095 reflections having F_o² > 3σ(F_o²) is 0.053. The structure consists of stacks of alternating, parallel Ni(TMP) and TCNQ molecules which are tilted with respect to the stacking axis. The short intrastack interplanar spacing between Ni(TMP) and TCNQ molecules (∼3.30 Å) and the presence of two broad charge-transfer bands at 9100 and 11100 cm⁻¹ suggest that there is some charge-transfer interaction in the complex. The visible and middle-infrared spectrum of Ni(TMP)TCNQ is essentially a superposition of the spectra of the individual neutral component molecules, so the degree of charge transfer in Ni(TMP)TCNQ is small. An analysis of the bond distances in the TCNQ molecule indicates that the amount of charge transfer is less than 0.2 e. The Ni(TMP)TCNQ complex is diamagnetic, and the conductivity along the single-crystal needle axis is low (<10⁻⁵ Ω⁻¹ cm⁻¹).