Bis[trans-difluoridotetrakis(pyridine-κN)chromium(III)] sodium tetrachloridozincate perchlorate from synchrotron data

The title salt, Na[CrF2(C5H5N)4]2[ZnCl4]ClO4, consists of two cationic CrIII complexes, an Na+ cation, one [ZnCl4]2− anion and one ClO4 − anion. The CrIII atoms are coordinated by four pyridine (py) N atoms and two F atoms in a trans arrangement, displaying a distorted octahedral geometry. The mean Cr—N(py) and Cr—F bond lengths are 2.086 (8) and 1.864 (14) Å, respectively. The [ZnCl4]2− anion has a distorted tetrahedral geometry. The most notable feature of the crystal packing is the formation of weak pyridine–perchlorate C—H⋯O hydrogen bonds, resulting in supramolecular chains along the b-axis direction. The perchlorate anion was disordered over two sets of sites in a 0.868 (3):0.132 (3) ratio.

The experiment at PLS-II 2D-SMC beamline was supported in part by MEST and POSTECH. tetrachloridozincate perchlorate from synchrotron data Dohyun Moon, Keon Sang Ryoo and Jong-Ha Choi

Structural commentary
The preparation and characterization of novel chromium(III) systems have received much attention because chromium(III) doped crystals are promising materials for tunable solid state laser in the spectral region between 600 and 1100 nm (Powell, 1998). Anionic species also play a very important role in chemistry, medicine and in biology, yet their binding characteristics have not received much recognition. The study of the anion effect and geometrical isomer in octahedral transition metal complexes may be expected to yield a great variety of new structures and properties of both chemical and biological significance. The [Cr(py) 4 X 2 ] n+ (X = monodentate; py = pyridine) cation can be either trans or cis geometric isomers.
In this communication, we report the synthesis and structure of 2[Cr(C 5 H 5 N) 4 F 2 ] + [ZnCl 4 ] 2-Na + ClO 4in order to confirm the arrangement of four py molecules and two F ligands in the complex. This is another example of a trans-[Cr(py) 4 F 2 ] + complex but with a different counter anion (Fochi et al., 1991;Moon & Choi, 2013). The asymmetric unit of the title salt contains discrete two trans-[Cr(py) 4 F 2 ] + , one [ZnCl 4 ] 2-, one Na cation and one disordered ClO 4anion.
The structural analysis shows that there are two independent Cr(III) complex cations in which the four nitrogen atoms of four py ligands occupy the equatorial sites and the two F atoms coordinate to the Cr atom in trans configuration. An ellipsoid plot (60% probability level) of the title compound, together with the atomic labelling, is depicted in Fig. 1 Å and the Cl-Zn-Cl angles of 100.05 (6)-121.91 (3)° are observed, respectively. The ClO 4also has distorted tetrahedral geometry due to the influence of hydrogen bonding and connecting Na + ion on the Cl-O lengths and the O-Cl-O angles. In the title complex, the crystal lattice is stabilized by weak hydrogen bonding interactions between the C-H groups of the py ligand and the O atoms of the ClO 4 anion ( Table 1).

Synthesis and crystallization
All chemicals were reagent grade materials and used without further purification. As starting material, trans-[Cr(py) 4 F 2 ]NO 3 was prepared as described previously (Glerup et al., 1970). The crude [Cr(py) 4 F 2 ]NO 3 (0.2 g) was dissolved in 10 ml water at 60 °C. The 10 ml solution of 1M HCl containing 0.1 g sodium perchlorate and 0.5 g of ZnCl 2 was gradually added. The unreacted materials were removed by filtration and allowed to stand at room temperature for several days to give purple crystals of the title compound suitable for X-ray structural analysis.

Refinement
C-bound H-atoms were placed in calculated positions (C-H = 0.95) and were included in the refinement in the riding model approximation with U iso (H) set to 1.2U eq (C). The perchlorate anion was distorted over two positions in a 0.868 (3):0.132 (3) ratio.

Figure 1
A perspective view of the molecular structures of the asymmetric unit in the title compound