Crystal structures of the complexes containing macrocyclic cations [M(cyclam)]2+ (M = Ni, Zn) and tetraiodidocadmate(2–) anion

Abstract

The asymmetric units of the isostructural compounds (1,4,8,11-tetraazacyclotetradecane-κ4 N)nickel(II) tetraiodidocadmate(II), [Ni(C10H24N4)][CdI4] (I), and triiodido-1κ3 I-μ-iodido-(1,4,8,11-tetraazacyclotetradecane-2κ4 N)cadmium(II)zinc(II), [CdZnI4(C10H24N4)] (II) (C10H24N4 = 1,4,8,11-tetraazacyclotetradecane, cyclam, L), consist of the centrosymmetric macrocyclic cation [M(L)]2+ [M = NiII or ZnII] with the metal ion lying on a twofold screw axis, and the tetraiodocadmate anion [CdI4]2− located on the mirror plane. In I, the anion acts as an uncoordinated counter-ion while in II it is bound to the ZnII atom via one of the iodide atoms, thus forming an electroneutral heterobimetallic complex [Zn(L)(CdI4)]. The NiII and ZnII ions are coordinated in a square-planar manner by the four secondary N atoms of the macrocyclic ligand L, which adopts the most energetically stable trans-III conformation. The [CdI4]2− anions in I and II are structurally very similar and represent slightly deformed tetrahedrons with average Cd—I bond lengths and I—Cd—I angles of ca 2.79 Å and 109.6°, respectively. The supramolecular organization of the complexes under consideration in the crystals is very similar and is determined by the hydrogen-bonding interactions between the secondary amino groups of the ligand L in the [M(L)]2+ cations and iodide atoms of the [CdI4]2− anion. In particular, the alternating cations and anions form chains running along the b-axis direction that are arranged into di-periodic sheets oriented parallel to the (101) and (\overline{1}01) planes. Because both kinds of sheets are built from the same cations and anions, this feature provides the three-dimensional coherence of the crystals of I and II.