Crystal structure of bis[cis-(1,4,8,11-tetraazacyclotetradecane-κ4 N)bis(thiocyanato-κN)chromium(III)] dichromate monohydrate from synchrotron X-ray diffraction data

The asymmetric unit of the title compound comprises of one complex cation, one half of a Cr2O7 2− anion and one half of a water molecule. The CrIII ion has a distorted octahedral coordination by four N atoms of the cyclam ligand and by two N-bonded NCS groups in cis positions; the conformation of the dichromate anion is staggered.

The structure of the complex salt, cis-[Cr(NCS) 2 (cyclam)] 2 [Cr 2 O 7 ]ÁH 2 O (cyclam = 1,4,8,11-tetraazacyclotetradecane, C 10 H 24 N 4 ), has been determined from synchrotron data. The asymmetric unit comprises of one [Cr(NCS) 2 (cyclam)] + cation, one half of a Cr 2 O 7 2À anion (completed by inversion symmetry) and one half of a water molecule (completed by twofold rotation symmetry). The Cr III 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 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 intermolecular hydrogen bonds involving the cyclam N-H groups and water O-H groups as donor groups, and the O atoms of the Cr 2 O 7 2À anion and water molecules as acceptor groups, giving rise to a three-dimensional network.

Chemical context
Recently, it has been established that cyclam (1,4,8,11-tetraazacyclotetradecane, C 10 H 24 N 4 ) 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). Cyclam has a moderately flexible structure and can adopt both planar (trans) and folded (cis) conformations (Poon & Pun, 1980). There are five configurational trans isomers for the macrocycle, which differ in the chirality of the sec-NH sites (Choi, 2009). The trans-I, trans-II and trans-V configurations also can fold to form cis-I, cis-II and cis-V isomers, respectively (Subhan et al., 2011). The configuration of the macrocyclic ligand and the influence of the counter-anion are important factors in developing new highly effective anti-HIV drugs.
The dichromate anion is environmentally important due to its high toxicity (Yusof & Malek, 2009), and its use in industrial processing (Goyal et al., 2003). Since counter-anionic species play an important role in coordination chemistry (Martínez-Má ñ ez & Sancenó n, 2003;Fabbrizzi & Poggi, 2013), it may be possible that the [Cr(NCS) 2 (cyclam)] + cation is suitable to bind specifically to an oxoanion. In this context, we report here on the synthesis of a new chromium(III)-dichro-mate salt, [Cr(NCS) 2 (cyclam)] 2 (Cr 2 O 7 )ÁH 2 O, (I), and its structural characterization by synchrotron single-crystal X-ray diffraction. Fig. 1 displays the molecular components of (I). The structure is another example of a [Cr(NCS) 2 (cyclam)] + cation (Friesen et al., 1997;Moon et al., 2013) but with a different counteranion. The asymmetric unit comprises of one [Cr(NCS) 2 (cyclam)] + cation, one half of a Cr 2 O 7 2À anion (completed by inversion symmetry) and one half of a water molecule (completed by twofold rotation symmetry). In the complex cation, the Cr III ion is coordinated by the N atoms of the cyclam ligand in the folded conformation. The nitrogen atoms of two NCS À ligands coordinate to the chromium atoms in a cis arrangement. The cyclam moiety adopts the cis-V (antianti) conformation (Subhan et al., 2011) (Choi et al., 2004b;Moon et al., 2013;Subhan et al., 2011;Choi et al., 2004a;Meyer et al., 1998;Forsellini et al., 1986, respectively).

Supramolecular features
Two O-HÁ Á ÁO hydrogen bonds link the water molecule to neighboring Cr 2 O 7 2À anions while N-HÁ Á ÁO hydrogen bonds interconnect [Cr(NCS) 2 (cyclam)] + cations with both the anions and water molecules (Table 1; Figs. 1 and 2) . An extensive array of these contacts generates a three-dimensional network of molecules stacked along the c-axis. The molecular components in the structure of (I) with displacement ellipsoids drawn at the 30% probability level. Only one orientation of the disordered anion is shown; primed atoms are related by symmetry code (Àx, Ày + 1, Àz À 1

Synthesis and crystallization
Cyclam was purchased from Stream Chemicals and used as provided. All chemicals were reagent-grade materials and used without further purification. The starting material, cis-[Cr(NCS) 2 (cyclam)]SCN was prepared according to a literature protocol (Ferguson & Tobe, 1970). The thiocyanate salt (0.513 g) was dissolved in 15 mL water at 347 K. The filtrate was added to 5 mL of water containing solid K 2 Cr 2 O 7 (0.02 g).
The resulting solution was evaporated slowly at room temperature until formation of crystals. The obtained blocklike orange crystals of the dichromate salt were washed with small amounts of 2-propanol and dried in air before collecting the synchrotron data. Elemental analysis calculated for [Cr(NCS) 2 (C 10 H 24 N 4 )] 2 (Cr 2 O 7 )ÁH 2 O: C, 29.69; H, 5.19; N, 17.31%; found C, 29.84; H, 4.90; N, 17.28%.
lography experiment at PLS-II BL2D-SMC beamline was supported in part by MSIP and POSTECH.   (Putz & Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip,2010).  (Sheldrick 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0074 (7) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.