Structure and bonding in the neutral and anionic forms of dimethylglyoxime and its complexes

In order to permit a comparative study of the structure and bonding behaviour of dimethylglyoxime in its neutral and monoanionic forms, both ‘free’ and complexed to transition metals, redeterminations of the crystal structures of dimethylglyoxime, dmgH₂, and the complexes Cu(dmgH₂)Cl₂ and Cu(dmgH₂)Br₂ have been carried out, together with an initial determination of the structure of the hydrated sodium salt Na₂(dmg), 8H₂O. Crystals of dmgH₂ are triclinic, space group Pī, a 6·078(3), b 6·319(3), c 4·492(2) Å, α 122·69(3), β 91·71(4), γ 77·72(4)°, Z 1; the structure was refined to a residual of 0·049 for 748 ‘observed’ reflections. Crystals of Na₂(dmg), 8H₂O are monoclinic, P2₁c, a 11·317(7), b 12·995(7), c 4·901(4) Å, β 100·55(5)°, Z 2, the structure being refined to a residual of 0·040 for 942 ‘observed’ reflections. Crystals of Cu(dmgH₂)Cl₂ are triclinic, Pī, a 8·163(4), b 8·109(3), c 7·701(2) Å, α 110·88(3), β 101·31(3), γ 108·04(3)°, Z 2; for the isomorphous bromide a 8·628(3), b 8·276(4), c 7·757(2) Å, α 111·18(3), β 101·02(3), γ 108·55(3)°. The two structures were refined to residuals of 0·052 and 0·045 for 964 and 1597 ‘observed’ reflections respectively.