Thermal Behavior of the “α‐Diimine‐NiII‐Catecholate” Chromophores

Study of the thermal behavior were performed for the first time for a series of ligand‐to‐ligand charge transfer complexes of “α‐diimine‐Ni II ‐catecholate” type: Ni II (3,6‐Cat)(bipy) ( 1 ), Ni II (3,6‐Cat)(bipy t Bu ) ( 2 ) and Ni II (3,6‐Cat)(DAD dipp ) ( 3 ), where 3,6‐Cat is 3,6‐di‐ tert ‐butyl‐catecholate, bipy and bipy t Bu are 2,2′‐bipyridine and its 4,4′‐di‐ tert ‐butyl‐substituted analog, DAD dipp is 1,4‐bis(2,6‐di‐ iso ‐propylphenyl)‐1,4‐diaza‐1,3‐butadiene. The phase transition behavior, vapor phase composition, volatility, and thermodynamics of the sublimation process (enthalpy and entropy calculations) of chromophores 1 – 3 were examined using DSC, TGA, EI‐MS, and the Knudsen effusion method with weight registration of the sublimated substance. The Hirshfeld surface analysis was implemented to establish a relationship between the characteristics of the crystal packing, and the thermal properties. The compounds 1 – 3 are distinguished by the high thermal stability and good volatility, as well as the completeness of the transition to the gas phase under low pressure conditions. An increase in ligand's bulkiness leads to a “rarefaction” of the crystal packing of the chromophore, and a corresponding rise of volatility in the order 1 ≤ 2 < 3 .