Structural Variety in Mn(NCS)₂ 4-Cyanopyridine Coordination Compounds: Synthesis, Structures, Isomerism, and Magnetic Properties

Abstract

The reaction of Mn­(NCS)2 with 4-cyanopyridine (CNpy) leads to the formation of discrete complexes with the composition [Mn­(NCS)2(CNpy)4] (1), [Mn­(NCS)2(H2O)2(CNpy)2] (2-I and 2-II), and [Mn­(NCS)2(H2O)2(CNpy)2]·xCNpy (x = 4, 3; x = 2, 4), in which the Mn­(II) centers are octahedrally coordinated by two terminal N-bonded thiocyanate anions and by four (1) or two CNpy coligands and two water molecules (2-I, 2-II, 3, and 4). If an excess of Mn­(NCS)2 is used, two additional compounds with the compositions [Mn­(NCS)2(CNpy)2] n (5) and [Mn­(NCS)2(CNpy)] n (6-I and 6-II) are obtained. In all compounds the Mn­(II) cations are octahedrally coordinated and linked into linear chains (5), into layers (6-I), or into a 3D network (6-II) by the thiocyanate anions. Investigations using TG-DTA and temperature-dependent powder X-ray diffraction prove that the discrete complexes 2-II, 3, and 4 decompose in several steps, leading to the formation of Mn­(NCS)2 via 5 and 6-I as intermediates. For compounds 2-II, 4, and 6-II only one batch was obtained, indicating that these compounds are metastable. Magnetic measurements for compounds 5 and 6-I reveal dominating antiferromagnetic interactions and maxima in the susceptibility curve at 20 K (5) and 24 K (6-I), which are reproduced by quantum Monte Carlo simulations. The specific heat proves magnetic ordering at 2.8 K (5) and 12.4 K (6-I). The ordering of 6-I is associated with a weak ferromagnetism.

Comparison of the crystal structures of the low- and high-temperature forms of bis[4-(dimethylamino)pyridine]dithiocyanatocobalt(II)

“…Because in such a case the composition of the different forms is identical, all changes in the physical properties can be directly correlated with the structural changes. One class of compounds in which polymorphism and especially isomerism is observed are coordination compounds based on transitionmetal thiocyanates, because this anionic ligand shows several different coordination modes leading to a large structural variability (Bo ¨hme et al, 2020;Jochim et al, 2020;Mautner et al, 2018;Neumann et al, 2020a;Wellm et al, 2020a;Werner et al, 2015;Buckingham, 1994;Barnett et al, 2002).…”

Transformation of One-Dimensional Ladders into Two-Dimensional Networks via Simple Solvate Exchange in Single-Crystal-to-Single-Crystal Mode

“…Studies on self-assembly and related synthetic methodologies have provided information useful to the structural control and development of metal–ligand framework materials. − Tuning of supramolecular isomers, a challenging issue, can aid fundamental understanding and facilitate development of functional molecular coordination materials. − Such an efficient methodology for construction of desirable molecular coordination materials from building blocks is a hot topic and has already yielded exciting advances in various task-specific practical functionalities such as photoelectronic devices, ion exchangers, desiccants, molecular sieves, sensors, catalysts, negative Poisson’s ratio materials, guest-preorganizers, and state-transition materials. − Generally, self-assembly of metal ions with designed organic ligands gives rise to serendipitous products containing supramolecular isomers − owing to the intrinsic presence of unusually weak interactions − and reaction conditions related to solvent, temperature, pH, photoenergy, and the crystallization method. − As for the diverse supramolecular isomers possibly obtainable from identical building blocks, research into selective product formation is keenly required and can provide a good opportunity for investigation of the detailed structure–property relationships of functional coordination polymers. − …”