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 (ClO 4 ) 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 Cu II ions in a distorted square‐pyramidal geometry. Variable‐temperature magnetic susceptibility measurements for the dinuclear copper complex show a ferromagnetic interaction between the Cu II 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.