Structural, optical and magnetic properties of a new metal-organic Co^II-based complex

A mononuclear cobalt(ii) complex [C₅H₈N₃]₂[CoCl₄(C₅H₇N₃)₂] (I) was synthesized and structurally characterized. Single crystal X-ray diffraction analysis indicates that monometallic Co(ii) ions acted as coordination nodes in a distorted octahedral geometry, giving rise to a supramolecular architecture. The latter is made up of a ½ unit form composed of an anionic element [Co_0.5Cl₂(C₅H₇N₃)]⁻ and one 2-amino-4-methylpyrimidinium cation [C₅H₈N₃]⁺. The crystalline arrangement of this compound adopts the sandwich form where inorganic parts are sandwiched between the organic sheets following the [100] direction. More information regarding the structure hierarchy has been supplied based on Hirshfeld surface analysis; the X⋯H (X = N, Cl) interactions play a crucial role in stabilizing the self-assembly process of I, complemented by the intervention of π⋯π electrostatic interaction created between organic entities. Thermal analyses were carried out to study the thermal behavior process. Static magnetic measurements and ab initio calculations of compound I revealed the easy-axis anisotropy character of the central Co(ii) ion. Two-channel field-induced slow-magnetic relaxation was observed; the high-frequency channel is characterized by underbarrier relaxation with U_eff = 16.5 cm⁻¹, and the low-frequency channel involves a direct relaxation process affected by the phonon-bottleneck effect.