Crystal structure of bis-[trans-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ(4) N)bis-(thio-cyanato-κN)chromium(III)] tetra-chlorido-zincate from synchrotron data.

Dohyun Moon,Jong-Ha Choi,Keon Sang Ryoo

doi:10.1107/s205698901500746x

Abstract

The structure of the title compound, [Cr(NCS)2(cyclam)]2[ZnCl4] (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4), has been determined from synchrotron data. The asymmetric unit contains two independent halves of the Cr(III) complex cations and half of a tetra-chlorido-zincate anion. In each complex cation, the Cr(III) atom is coordinated by the four N atoms of the cyclam ligand in the equatorial plane and by two N-bound NCS(-) anions in a trans axial arrangement, displaying a distorted octa-hedral geometry with crystallographic inversion symmetry. The mean Cr-N(cyclam) and Cr-N(NCS) bond lengths are 2.065 (4) and 1.995 (6) Å, respectively. The macrocyclic cyclam moieties adopt centrosymmetric trans-III configurations with six- and five-membered chelate rings in chair and gauche configurations, respectively. The [ZnCl4](2-) anion, which lies about a twofold rotation axis, has a slightly distorted tetra-hedral geometry. The crystal packing is stabilized by hydrogen-bonding inter-actions between the N-H groups of the cyclam ligands, the S atoms of the NCS(-) groups and the Cl(-) ligands of the anion.

Highlights

1,4,8,11-tetraazacyclotetradecane, C10H24N4), has been determined from synchrotron data
The CrIII atom is coordinated by the four N atoms of the cyclam ligand in the equatorial plane and by two N-bound NCS anions in a trans axial arrangement, displaying a distorted octahedral geometry with crystallographic inversion symmetry
The crystal packing is stabilized by hydrogen-bonding interactions between the N—H groups of the cyclam ligands, the S atoms of the NCS groups and the Cl ligands of the anion

Summary

Chemical context

It has been found that cyclam (1,4,8,11-tetraazacyclotetradecane, C10H24N4) derivatives and their metal complexes exhibit anti-HIV activity (Ronconi & Sadler, 2007; De Clercq, 2010; Ross et al, 2012). The cyclam derivatives inhibit the entry of the virus into white cells by binding to CXCR4, a chemokine receptor in the outer membrane. The strength of binding to the CXCR4 receptor correlates with the anti-HIV activity. E71, 540–543 research communications structure, and can adopt both planar (trans) and folded (cis) configurations (Poon & Pun, 1980). The trans-V configuration can fold to form the cis-V isomer (Subhan et al, 2011). The thiocyanate anion can be present in complexes as either a ligand or a non-coordinating anion (Moon et al, 2013). We describe here the synthesis and structural characterization of trans[Cr(NCS)2(cyclam)]2[ZnCl4], (I)

Structural commentary

Supramolecular features

Database survey

Synthesis and crystallization

Findings

Refinement