Thermochromism in nickel(II) complexes: thermal, solid state 1H NMR and single crystal X-ray analysis of bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate

Add time:08/20/2019    Source:sciencedirect.com

The complex bis-(N,N-dimethyl-1,2-ethanediamine) nickel(II) perchlorate undergoes a first-order thermochromic phase transition at ca. 476 K, changing its color from orange to red. The room temperature X-ray crystal structure determination showed that the nickel ion possesses a square-planar geometry with two five membered chelate rings, in the δλ conformation, forming the NiN4 chromophore. The broad-line 1H NMR indicates the onset of a dynamic disorder of diamine chelate rings at the phase transition temperature region, while T1 measurement of 1H affords the activation energy of the puckering metal chelate rings to be 26 kJ mol−1. The electronic spectrum revealed that a weakening of ligand field around the nickel is associated with the phase transition.

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