Synthesis, crystal polymorphism and spin crossover behavior of adamantylboron-capped cobalt(ii) hexachloroclathrochelate and its transformation into the CoIIICoIICoIII-bis-macrobicyclic derivative

Fast crystallization of the monoclathrochelate cobalt(ii) intracomplex [Co(Cl(2)Gm)(3)(BAd)(2)] (where Cl(2)Gm(2-) is a dichloroglyoxime dianion and BAd is an adamantylboron capping group, 1), initially obtained by the direct template condensation of the corresponding chelating alpha-dioximate and cross-linking ligand synthons on the Co2+ ion as a matrix, from benzene or dichloromethane afforded its structural triclinic and hexagonal polymorphs. Its prolonged recrystallization from dichloromethane under air atmosphere and sunlight irradiation unexpectedly gave the crystals of the (CoCoCoIII)-Co-III-Co-II-trinuclear dodecachloro-bis-clathrochelate intracomplex [[Co-III(Cl(2)Gm)(3)(BAd)](2)Co-II] (2), the molecule of which consists of two macrobicyclic frameworks with encapsulated low-spin (LS) Co3+ ions, which are cross-linked by a mu(3)-bridging Co2+ ion as a bifunctional Lewis-acidic center. The most plausible pathway of such a 1 -> 2 transformation is based on the photoinitiated radical oxidation of dichloromethane with air oxygen giving the reactive species. Cobalt(ii) monoclathrochelate 1 was found to undergo a temperature-induced spin crossover (SCO) both in its solutions and in the solid state. In spite of the conformational rigidity of the corresponding quasiaromatic diboron-capped tris-alpha-dioximate framework, the main parameters of this SCO transition (i.e., its completeness and gradual character) are strongly affected by the nature of the used solvent (in the case of its solutions) and by the structural polymorphism of its crystals (in the solid state). In the latter case, the LS state (S = 1/2) of this complex is more thermally stable and, therefore, the cobalt(ii)-centered 1/2 -> 3/2 SCO is more gradual than that in solutions.

Automated summary

This study investigates the fast crystallization and structural transformation of a cobalt (II) complex. The complex undergoes a temperature-induced spin crossover and its behavior is influenced by solvent and crystal polymorphism. The findings provide insights into the synthesis and properties of cobalt complexes.