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.

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(2 ampy ) 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/2 ampy . 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.