Roncero-Barrero Cristina, Ribas-Ariño Jordi, Deumal Mercè, Moreira Ibério de P R
Departament de Ciència de Materials i Química Física, Universitat de Barcelona, c/Martí i Franquès 1-11, 08028 Barcelona, Spain.
Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, c/Martí i Franquès 1-11, 08028 Barcelona, Spain.
Phys Chem Chem Phys. 2022 May 25;24(20):12196-12207. doi: 10.1039/d2cp00415a.
Bisdithiazolyl radicals have furnished in recent years multiple examples of molecular materials with promising conductive and magnetic properties. The electronic band structure and magnetic ordering in four different isostructural pyridine-bridged bisdithiazolyl and Selenium substituted compounds have been studied by means of hybrid DFT based methods as implemented in the CRYSTAL code. The full rationalization of the properties of these multifunctional magnetic molecular materials requires a careful description of their complex open-shell electronic structure. The results describe the systems as narrow band (0.2-0.3 eV dispersion) open-shell semiconductors with a gap of 1.15-1.40 eV between the valence and conducting bands. The bands defining the insulating gap are dominated by orbital contributions arising from the heteroatoms sitting in the outer rings. A low energy closed-shell metallic solution is found at 0.25-0.35 eV above the magnetic solutions thus suggesting a complex mechanism for electric conduction with band and hopping contributions. The observed trend of the conductivity is in line with the variation of the insulating gap but more rigorous modelling is required to take into account the details of the band structure of the systems. For all the systems the spin density is well localised on the molecular units and is independent of the magnetic solution. Thus the system can be described as an ensemble of well-defined = 1/2 magnetic centres using a two-body Heisenberg-Dirac-van Vleck spin Hamiltonian. The lowest energy electronic solutions are in line with the observed magnetic behaviour at low temperature. The set of competing magnetic exchange interactions that emerges from using a suitable mapping to consistently describe the low energy magnetic solutions explains the variety of magnetic responses (absence of long-range magnetic order, antiferromagnetism or ferromagnetism) of the four studied compounds at low temperatures.
近年来，双二噻唑基自由基为具有潜在导电和磁性的分子材料提供了多个实例。通过CRYSTAL代码中实现的基于杂化密度泛函理论（DFT）的方法，研究了四种不同的同构吡啶桥联双二噻唑基和硒取代化合物中的电子能带结构和磁有序性。要全面合理地解释这些多功能磁性分子材料的性质，需要仔细描述其复杂的开壳层电子结构。结果表明，这些体系是窄带（色散为0.2 - 0.3 eV）开壳层半导体，价带和导带之间的能隙为1.15 - 1.40 eV。定义绝缘能隙的能带主要由外环中杂原子产生的轨道贡献主导。在比磁性解高0.25 - 0.35 eV处发现了一个低能量闭壳层金属解，这表明存在一种由能带和跳跃贡献组成的复杂导电机制。观察到的电导率趋势与绝缘能隙的变化一致，但需要更严格的建模来考虑体系能带结构的细节。对于所有体系，自旋密度很好地定域在分子单元上，并且与磁性解无关。因此，使用两体海森堡 - 狄拉克 - 范弗莱克自旋哈密顿量，可以将该体系描述为一组定义明确的S = 1/2磁性中心。最低能量的电子解与低温下观察到的磁行为一致。通过使用合适的映射来一致地描述低能量磁性解而出现的一组相互竞争的磁交换相互作用，解释了四种研究化合物在低温下的各种磁响应（不存在长程磁序、反铁磁性或铁磁性）。
