Three-, four-, and five-co-ordination modes of a potentially quinquedentate ‘nitrogen–sulphur’ macrocyclic ligand: the crystal and molecular structures of two copper(II) complexes

Abstract

The 17-membered Schiff-base ‘N₃S₂’ macrocycle (L) derived from the cyclic condensation of 2,6-diacetylpyridine with 1,10-diamino-4,7-dithiadecane forms complexes with Cu^II of formulae CuLXY and CuLY₂ where X = Cl, Br, or NCS and Y = ClO₄, BPh₄, or NCS. The crystal and molecular structures of two of the complexes have been determined: [CuL][ClO₄]₂ is orthorhombic, space group P2₁cn(no. 33), with a= 11.934(5), b= 13.528(6), c= 14.581(7)Å, and Z= 4; [CuL(NCS)][ClO₄]·0.5H₂O is monoclinic, space group C2/c, with a= 37.831(30), b= 8.187(5), c= 16.364(11)Å, β= 102.9(1)°, and Z= 8. Diffraction data for both crystals have been refined by full-matrix least squares (1 364 reflections to R 0.068 and 1 196 reflections to R 0.082, respectively). Both structures have a distorted square-pyramidal structure in which the trimethine unit of the macrocycle occupies three positions of the square plane [Cu–N 1.93–2.08 Å]. In [CuL][ClO₄]₂ the fourth position is occupied by one sulphur atom of the macrocycle [Cu–S 2.377(4)Å], the other sulphur atom being axially sited at 2.470(4)Å. In [CuL(NCS)][ClO₄]·0.5H₂O the square plane is completed by the thiocyanate group [Cu–N 1.854(19)Å], the axial position being occupied by one ligand sulphur atom at 2.745(5)Å, the other sulphur atom being unco-ordinated. In both structures there is a weak interaction with a perchlorate oxygen in the axial position trans to the sulphur atom. Infrared and e.s.r. spectra suggest that [CuL(NCS)][BPh₄] has a dimeric (NCS-bridged) structure in the solid state whereas solid [CuL(NCS)₂] appears to contain both bridging and terminally N-bonded NCS groups, with neither of the macrocycle sulphur atoms co-ordinated.