Synthesis, structure and magnetism of homodinuclear complexes of Co, Ni and Cu supported by a novel bitriazine scaffold

Abstract

Btzn (1), an amine-functionalized bi(1,3,5-triazine) 4,4′-(NH₂)₂-6,6′-(NHC₆H₅)₂-2,2′-(1,3,5-C₃N₃)₂, is reported, and its coordination with Co, Ni and Cu is explored. Reactions of metal salts (2 equiv) with Btzn (1 equiv) result in dimeric species [(Btzn)Co₂(NCS)₄(EtOH)₂(DMF)₂], (2), [(Btzn)Ni₂(η¹-ONO₂)₂(MeOH)₄(DMF)₂]·2[NO₃], (3), [(Btzn)Cu₂Cl₄(DMF)₂], (4), and [(Btzn)Cu₂(η²-O₂NO)₂(OH₂)₂(DMF)₂]·2[NO₃], (5). These complexes are the first examples of the coordination of transition metals with bi(1,3,5-triazine) ligands. Their structures display a bridging bis-bidentate coordination mode for Btzn. Variable-temperature magnetic susceptibility of the complexes reveals antiferromagnetic exchange between the spin carriers, with calculated exchange coupling values (J) of −4.7 cm⁻¹ for 3, −18.2 cm⁻¹ for 4, and −5.5 cm⁻¹ for 5. An in-depth evaluation of the metal geometry highlights the inefficient overlap of the magnetic d-orbitals through the bridging ligand, most likely leading to reduced delocalization and coupling.