An Old Crystallization Technique as a Fast, Facile, and Adaptable Method for Obtaining Single Crystals of Unstable "Li2TCNQF4" and New Compounds of TCNQ or TCNQF4: Syntheses, Crystal Structures, and Magnetic Properties

Slavomíra Šterbinská; Mariia Holub; Erik Čižmár; Juraj Černák; Lawrence Rocco Falvello; Milagros Tomás

doi:10.1021/acs.cgd.3c00160

An Old Crystallization Technique as a Fast, Facile, and Adaptable Method for Obtaining Single Crystals of Unstable "Li₂TCNQF₄" and New Compounds of TCNQ or TCNQF₄: Syntheses, Crystal Structures, and Magnetic Properties

Cryst Growth Des. 2023 May 26;23(6):4357-4369. doi: 10.1021/acs.cgd.3c00160. eCollection 2023 Jun 7.

Authors

Slavomíra Šterbinská^{1

2}, Mariia Holub³, Erik Čižmár³, Juraj Černák¹, Lawrence Rocco Falvello², Milagros Tomás⁴

Affiliations

¹ Faculty of Sciences, Institute of Chemistry, Department of Inorganic Chemistry, P. J. Šafárik University in Košice, Moyzesova 11, 041 54 Košice, Slovakia.
² Instituto de Nanociencia y Materiales de Aragón (INMA) and Departamento de Química Inorgánica, CSIC-Universidad de Zaragoza, Zaragoza 50009, Spain.
³ Faculty of Sciences, Institute of Physics, P. J. Šafárik University in Košice, Park Angelinum 9, 041 54 Košice, Slovakia.
⁴ Instituto de Síntesis Quimica y Catálisis Homogénea (ISQCH), Departamento de Química Inorgánica, Pedro Cerbuna 12, University of Zaragoza-CSIC, E-50009 Zaragoza, Spain.

Abstract

Detailed structural information is essential for understanding the properties of TCNQ and TCNQF₄ compounds (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. Compound 3, previously described as "Li₂TCNQF₄," forms a one-dimensional (1D) ribbon. Compounds 1 and 2 can 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 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.