Structural and Magnetic Properties of M(mnt)₂ Salts (M = Ni, Pt, Cu) with a Ferrocene-Based Cation, [FcCH₂N(CH₃)₃]⁺. Interplay between M···M and M···S Intermolecular Interactions

A series of metal bis-mnt complexes (mnt = 1,2-dithiolatomaleonitrile) with the trimethylammonium methylferrocene cation have been synthesized and characterized using X-ray diffraction, magnetic susceptibility, and differential scanning calorimetry measurements. The complexes have the formulas (FcCH2NMe3)[Ni(mnt)2] (2), (FcCH2NMe3)[Pt(mnt)2] (3), and (FcCH2NMe3)2[Cu(mnt)2] (4) (where Fc = ferrocene). At 300 K, the crystal structures of 1:1 complexes 2 and 3 are very similar. They consist of pairs of [M(mnt)2]- in a slipped configuration packed in stacks. Each [M(mnt)2]- stack is separated from adjacent stacks by two columns of cations. Within the pairs, the [M(mnt)2]- anions interact via short M···S contacts, while there are no short contacts between the pairs. Complex 4, which has a 2:1 stoichiometry, exhibits a markedly different packing arrangement of the anionic units. Due to the special position of the Cu atom in the asymmetric unit cell, [Cu(mnt)2]2- dianions are completely isolated from each other. The magnetic susceptibility behavior of the nickel complex is consistent with the presence of magnetically isolated, antiferromagnetically (AF) coupled [Ni(mnt)2]- pairs with the AF exchange parameter, J = −840 cm-1. The platinum complex undergoes an endothermic structural phase transition (Tp) at 247 K. Below Tp its structure is characterized by the formation of magnetically isolated [Pt(mnt)2]22- dimers in an eclipsed configuration with short Pt···Pt and S···S contacts between monomers. In the magnetic properties, the structural changes reveal themselves as an abrupt susceptibility drop implying a substantial increase of the AF exchange parameter. A mechanism of the phase transition in the platinum compound is proposed. For compound 4, paramagnetic behavior is observed.本研究合成了一系列带有二茂铁甲基三甲基铵阳离子的金属双-mnt配合物（mnt：1,2-二硫代马来二腈），并通过X射线衍射、磁化率测试以及差示扫描量热法对其进行了表征。该系列配合物的分子式分别为(FcCH2NMe3)[Ni(mnt)2] (2)、(FcCH2NMe3)[Pt(mnt)2] (3)以及(FcCH2NMe3)2[Cu(mnt)2] (4)（其中Fc为二茂铁（ferrocene））。 在300 K下，1:1型配合物2和3的晶体结构极为相似。二者均以滑移构型的[M(mnt)2]-二聚体为结构单元并堆积成柱；每一列[M(mnt)2]-堆叠柱均通过两列阳离子与相邻堆叠柱分隔开。在二聚体内部，[M(mnt)2]-阴离子之间通过短程M···S相互作用产生耦合，而不同二聚体之间则不存在短程接触。 具有2:1化学计量比的配合物4则呈现出显著不同的阴离子单元堆积模式。由于铜原子在不对称晶胞中的特殊占位，[Cu(mnt)2]2-二价阴离子彼此之间完全相互隔离。 镍配合物的磁化率行为与磁孤立的反铁磁（AF）耦合[Ni(mnt)2]-二聚体相符，其反铁磁交换常数J = −840 cm⁻¹。 铂配合物在247 K处发生吸热型结构相变（相变温度记为Tp）；在Tp以下，其晶体结构形成了重叠构型的磁孤立[Pt(mnt)2]22-二聚体，单体之间存在短程Pt···Pt与S···S相互作用。在磁性能方面，该结构变化表现为磁化率的突变下降，意味着反铁磁交换参数显著增强。研究人员提出了该铂基化合物的相变机理。 对于配合物4，观测到其呈现顺磁行为。