Restricting Chelate Ring Flipping in Cu^II Complexes. I. Non-Thermochromic Bis(o-phenylenediamine-N,N')copper(II) Bis(tetrafluoroborate)

The title complex, [Cu(C₆H₈N₂)₂](BF₄)₂, is the first in a series where the phenylenediamine collar restricts the `flipping' of the chelate ring C atoms, which is the mechanism responsible for the thermochromic transition in N,N-diethylethylenediamine complexes. The Cu^II ion has tetragonally distorted octahedral geometry with four short equatorial Cu—N bonds [2.023 (3) and 1.990 (3) Å], and two long, mutually trans, axial Cu...F interactions [2.546 (2) Å]. The features of molecular packing, namely the shorter metal-to-anion contacts and stronger N-H...F hydrogen bonds as compared to those in their thermochromic analogues, seem to be associated with the non-thermochromic behaviour.

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