Synthesis and crystal structure of three mixed-ligand copper(II) complexes with nitrilotriacetic acid

The synthesis and X-ray diffraction study of three Ca[CuX(Nta)] · 2H2O complexes, where X = Cl (I) or Br (II and III are the monoclinic and orthorhombic modifications, respectively), are performed. Structures I–III are built of [CuX(Nta)]2− anionic complexes and hydrated Ca2+ cations, which are linked by Ca-O bonds into a three-dimensional framework. In I–III, the coordination of the Cu atom includes the N atom and three O atoms of the tetradentate chelate Nta3− ligand and the X− anion in the trans position with respect to N. The Cu-O bond lengths vary in the ranges 1.971–2.268 Å in I, 1.958–2.289 Å in II, and 2.040–2.110 Å in III. The Cu-X bond lengths are 2.223, 2.364, and 2.354 Å in I, II, and III, respectively. In I and II, the coordination polyhedron of the Cu atom is approximated by a distorted square pyramid with an O atom at the apical vertex, whereas in III, the polyhedron is described as a distorted trigonal bipyramid with the N and Br atoms at the axial sites. The structures are additionally stabilized by O(w)-H…O and O(w)-H…X hydrogen bonds.