Copper(II) Complexes of N,N-Diisopropylpicolinamide – Solvatochromic and Thermochromic Phase Change of a Monomeric Complex to a Ferromagnetically Coupled Dimeric Complex



The synthesis and characterization of mononuclear [Cu(L)2(Cl)2] (1), dinuclear [{CuCl(L)}2(μ-Cl)2] (2), and another mononuclear complex [Cu(L)2(ClO4)2] (3) with a bidentate N,N-diisopropylpicolinamide ligand (abbreviated L) are described. Complexes 1 and 2 were obtained from the same reaction mixture and show thermo- and solvatochromic behavior. Complex 1 shows irreversible thermochromism by changing into 2 upon heating at 160 °C. These two complexes also show solvatochromism in various solvents. The coordination geometry of the metal ions in 1 and 3 is distorted octahedral, whereas 2 has CuII ions in a distorted square-pyramidal geometry. Variable-temperature magnetic susceptibility measurements for the dinuclear copper complex show a ferromagnetic interaction between the CuII ions. The chromotropism has been attributed to a change in geometry from octahedral with terminal chloride ligands to a distorted square-pyramidal coordination with bridging chloride ions.