X-RAY STRUCTURE OF THERMOCHROMICBIS(N,N-DIETHYLETHYLENEDIAMINE)-COPPER(II)TETRAFLUOROBORATE

Abstract

The structure of a thermochromic complex, bis(N,N–diethylethylenediamine)copper(II) tetrafluoroborate [CuL₂(BF₄)₂] having the lowest transition temperature (24°c) amongst its isomorphous counterparts (ClO₄ ⁻ salts of Cu and Ni) has been determined at 22°c thus offering a unique opportunity to study near transition structural parameters. The Cu atom at the crystallographic centre of inversion has square planar coordination from four N–atoms of two centrosymmetrically related ligands [Cu[sbnd]N(secondary) = 2.061(5), Cu[sbnd]N(primary) = 2.003(6) Å, bite angle N[sbnd]Cu[sbnd]N = 84.6(2)°], the diethyl group orientations insulate the metal ion from anion coordination [closest approach (Cu…F3 = 3.621(4) Å)]. The thermal anisotropies of the chelate ring carbons are normal and do not indicate any disorder, although the structure is determined at a temperature (π22°c) very close to the transition. The highest thermal vibrations are shown by the BF₄ ⁻ anion and then to some extent by the terminal C-atoms of the diethyl groups. Factors involved in the thermochromic phase transition in these systems are discussed.