Abstract
The structure of the complex salt, cis-[Cr(NCS)2(cyclam)]2[Cr2O7]·H2O (cyclam= 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4), has been determined from synchrotron data. The asymmetric unit comprises of one [Cr(NCS)2(cyclam)]+ cation, one half of a Cr2O72- anion (completed by inversion symmetry) and one half of a water mol-ecule (completed by twofold rotation symmetry). The CrIII ion is coordinated by the four cyclam N atoms and by two N atoms of cis-arranged thio-cyanate anions, displaying a distorted octa-hedral coordination sphere. The Cr-N(cyclam) bond lengths are in the range 2.080 (2) to 2.097 (2) Å while the average Cr-N(NCS) bond length is 1.985 (4) Å. The macrocyclic cyclam moiety adopts the cis-V conformation. The bridging O atom of the dichromate anion is disordered around an inversion centre, leading to a bending of the Cr-O-Cr bridging angle [157.7 (3)°]; the anion has a staggered conformation. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the cyclam N-H groups and water O-H groups as donor groups, and the O atoms of the Cr2O72- anion and water mol-ecules as acceptor groups, giving rise to a three-dimensional network.
Highlights
The CrIII ion is coordinated by the four cyclam N atoms and by two N atoms of cis-arranged thiocyanate anions, displaying a distorted octahedral coordination sphere
The Cr—N(cyclam) bond lengths are in the range 2.080 (2) to
The bridging O atom of the dichromate anion is disordered around an inversion centre, leading to a bending of the Cr—O—Cr bridging angle [157.7 (3) ]; the anion has a staggered conformation
Summary
It has been established that cyclam (1,4,8,11-tetraazacyclotetradecane, C10H24N4) derivatives and their complexes can exhibit anti-HIV effects or stimulate the activity of stem cells from bone marrow (Ronconi & Sadler, 2007; De Clercq, 2010; Ross et al, 2012). There are five configurational trans isomers for the macrocycle, which differ in the chirality of the sec-NH sites (Choi, 2009). The configuration of the macrocyclic ligand and the influence of the counter-anion are important factors in developing new highly effective anti-HIV drugs. Since counter-anionic species play an important role in coordination chemistry (Martınez-Máñez & Sancenón, 2003; Fabbrizzi & Poggi, 2013), it may be possible that the [Cr(NCS)2(cyclam)]+ cation is suitable to bind to an oxoanion. E73, 72–75 research communications mate salt, [Cr(NCS)2(cyclam)]2(Cr2O7)H2O, (I), and its structural characterization by synchrotron single-crystal X-ray diffraction
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