Detailed structural information is essential for understanding
the properties of TCNQ and TCNQF4compounds (TCNQ = 7,7,8,8-tetracyanoquinodimethane;
TCNQF4= 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 [Li2(TCNQF4)(CH3CN)4]·CH3CN (3), can be prepared
in minutes by a horizontal diffusion technique and can be harvested
easily for X-ray structural studies. Compound3, previously
described as “Li2TCNQF4,” forms
a one-dimensional (1D) ribbon. Compounds1and2can also be obtained as microcrystalline solids from methanolic
solutions of MCl2/LiTCNQ/2ampy. Their
variable-temperature magnetic studies confirmed a contribution of
strongly antiferromagnetically coupled pairs of TCNQ•—anion radicals at higher temperatures with exchange couplingJ/kB= −1206 K andJ/kB= −1369 K for1and2, respectively, estimated using a spin
dimer model. The presence of magnetically active anisotropic Ni(II)
atoms withS= 1 in1was confirmed,
and the magnetic behavior of1, representing an infinite
chain of alternatingS= 1 sites andS= 1/2 dimers, was described by a spin-ring model suggesting ferromagnetic
exchange coupling between Ni(II) sites and anion radicals.