An Old Crystallization Technique as a Fast, Facile, and Adaptable Method for Obtaining Single Crystals of Unstable “Li(2)TCNQF(4)” and New Compounds of TCNQ or TCNQF(4): Syntheses, Crystal Structures, and Magnetic Properties

[Image: see text] Detailed structural information is essential for understanding the properties of TCNQ and TCNQF(4) compounds (TCNQ = 7,7,8,8-tetracyanoquinodimethane; TCNQF(4) = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane). The ineludible requirement of obtaining crystals of a size and quality sufficient to yield a successful X-ray diffraction analysis has been challenging to satisfy because of the instability of many of these compounds in solution. Crystals of two new complexes of TCNQ, [trans-M(2ampy)(2)(TCNQ)(2)] [M = Ni (1), Zn (2); 2ampy = 2-aminomethylpyridine], as well as unstable [Li(2)(TCNQF(4))(CH(3)CN)(4)]·CH(3)CN (3), can be prepared in minutes by a horizontal diffusion technique and can be harvested easily for X-ray structural studies. Compound 3, previously described as “Li(2)TCNQF(4),” forms a one-dimensional (1D) ribbon. Compounds 1 and 2 can also be obtained as microcrystalline solids from methanolic solutions of MCl(2)/LiTCNQ/2ampy. Their variable-temperature magnetic studies confirmed a contribution of strongly antiferromagnetically coupled pairs of TCNQ(•—) anion radicals at higher temperatures with exchange coupling J/k(B) = −1206 K and J/k(B) = −1369 K for 1 and 2, respectively, estimated using a spin dimer model. The presence of magnetically active anisotropic Ni(II) atoms with S = 1 in 1 was confirmed, and the magnetic behavior of 1, representing an infinite chain of alternating S = 1 sites and S = 1/2 dimers, was described by a spin-ring model suggesting ferromagnetic exchange coupling between Ni(II) sites and anion radicals.