Versatile behaviour of the cyclohexane-1,2-dione bis(semicarbazone) ligand in mono- and di-nuclear metal complexes

Abstract

The chelating properties of cyclohexane-1,2-dione bis(semicarbazone)(H₂chds) were considered by means of IR spectroscopy and the crystal structures of [Co₂(H₂chds)₂(OH₂)₃(NO₃)][NO₃]₃1, [Ni(H₂chds)₂][NO₃]₂·2H₂O 2 and H₂chds·H₂O. The structure of 1 is triclinic, space group P, with a= 13.616(2), b= 12.694(2), c= 11.537(2)Å, α= 68.13(1), β= 63.37(1), γ= 70.01(1)°, Z= 2 and R= 0.0778. The crystals of 2 are also triclinic, space group P, a= 13.504(4), b= 13.221(5), c= 8.333(5)Å; α= 98.00(3), β= 77.71(4), γ= 106.43(3)°, Z= 2 and R= 0.0688. The H₂chds·H₂O molecule crystallizes in the space group P2₁/c with a= 7.350(1), b= 15.469(3), c= 10.270(3)Å; β= 93.98(2)°, Z= 4 and R= 0.0372. The behaviour of the ligand is different in each structure: in 1 nearly planar tetradentate and accommodated in the equatorial positions of pentagonal bipyramids; in 2 distorted-octahedral co-ordination is provided by two tridentate ligand molecules having one urea group free. The free molecule is nearly planar with a different conformation: its arms are folded in such a way that an intramolecular N–H ⋯ O hydrogen bond is allowed. The structure of 1 is quite original: dimers are formed by means of two carbonylic bridges; the apices of the two polyhedra are occupied by two water molecules and a nitrate ion and one water molecule respectively.