Polymorphism in [Cu(cyclam)(TCNQ)₂](TCNQ) Stacked Systems (cyclam = 1,4,8,11-Tetraazacyclotetradecane, TCNQ = 7,7,8,8-Tetracyanoquinodimethane)

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Abstract

The compound [Cu(cyclam)(TCNQ)2](TCNQ) (cyclam = 1,4,8,11-tetraazacyclotetradecane, TCNQ = 7,7,8,8-tetracyanoquinodimethane) has been obtained in two different crystallographic forms, isomers 1 and 2. Crystal data for isomer 1: triclinic, P1̄, a = 7.855(6) Å, b = 10.267(2) Å, c = 14.424(3) Å, α = 95.42(2)°, β = 102.18(5)°, γ = 109.74(3)°, Z = 1. Crystal data for isomer 2: triclinic, P1̄, a = 8.165(1) Å, b = 9.918(3) Å, c = 13.278(3) Å, α = 83.91(2)°, β = 78.31(2)°, γ = 79.22(2)°, Z = 1. Both isomers show the same copper environment and oxidation states in the TCNQ molecules, and the only difference is observed in the stacking of the latter groups. The main common feature is the presence of parallel chains of copper macrocycle units linked by dimeric (TCNQ)22-, which coordinates to the metal. These chains are joined in isomer 1 by one neutral TCNQ molecule oriented parallel to the anionic TCNQ dimers and overlapping with two of them creating a bidimensional network. In contrast, the neutral TCNQ in isomer 2 is rotated about 70° relative to the anionic dimers and overlaps with four different chains, extending the interaction in a tridimensional way. The spectral and solid state conductivity data show electronic localization on the dimers (TCNQ)22- in both isomers with a weak semiconducting behavior. The magnetic behavior of both isomers can be interpreted as the sum of contributions from the metal and a thermally activated triplet state for the dimerized anions. The latter contribution is favored by the π overlap of the neutral TCNQ molecules, since the analogous derivative [Cu(cyclam)(TCNQ)2], only with anionic dimers, shows a strong antiferromagnetic coupling inside the dimers and no appreciable contribution to the bulk magnetic susceptibility is observed.

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