The N–M–N bond angle in the chelate ring of ethylenediamine. The crystal structure of tetra-aqua(ethylenediamine)nickel(II) nitrate

Abstract

The crystal structure of [Ni(en)(OH₂)₄][NO₃]₂ is reported (en = ethylenediamine). The mean Ni–N bond length is 2.065 A, and N–Ni–N bond angle 83.6°. N–M–N angles in en complexes, and O–M–O angles in acetylacetonates, are discussed in terms of their relation to M–N or M–O bond length. A conformational analysis of tris-en complexes is carried out so as to compare the predicted effect on the N–M–N angle of varying the M–N bond length with the observed relation between N–M–N angle and M–N length.