Tris(2,2′-bipyridine-κ2 N,N′)cobalt(III) tris(oxalato-κ2 O 1,O 2)ferrate(III) monohydrate

The title compound, [Co(C10H8N2)3][Fe(C2O4)3]·H2O, consists of two discrete tris(chelate) metal ions (CoIIIN6 and FeIIIO6 chromophores) and a water molecule. The structure is highly symmetrical; the CoIII and FeIII ions occupy positions with site symmetry 3.2. The coordination polyhedra of the metal atoms have a nearly octahedral geometry with noticeable trigonal distortions. The Co—N and Fe—O bond lengths are equal by symmetry, viz. 1.981 (2) and 1.998 (4) Å, respectively. The cations and anions are arranged alternately along their threefold rotation axes parallel to [001], forming chains that are packed in a hexagonal manner. The water molecules occupy voids between the chains. The crystal under investigation was an inversion twin.

The title compound, [Co(C 10 H 8 N 2 ) 3 ][Fe(C 2 O 4 ) 3 ]ÁH 2 O, consists of two discrete tris(chelate) metal ions (Co III N 6 and Fe III O 6 chromophores) and a water molecule. The structure is highly symmetrical; the Co III and Fe III ions occupy positions with site symmetry 3.2. The coordination polyhedra of the metal atoms have a nearly octahedral geometry with noticeable trigonal distortions. The Co-N and Fe-O bond lengths are equal by symmetry, viz. 1.981 (2) and 1.998 (4) Å , respectively. The cations and anions are arranged alternately along their threefold rotation axes parallel to [001], forming chains that are packed in a hexagonal manner. The water molecules occupy voids between the chains. The crystal under investigation was an inversion twin.  Yanagi et al. (1981); Zhang et al. (2009). For measuring of trigonal distortion angles, see: Muetterties & Guggenberger (1974).
In the crystal cobalt and iron complex ions are arranged alternately along their C 3 -axes parallel to [001] direction forming chains (Fig. 2) with the closest Co···Fe separation of ca 6.2 Å. The chains are packed in a hexagonal manner ( Fig. 3) and the water molecules occupy voids inside the hexagonal channels. Hydrogen atoms of water molecules are disordered to three positions accordingly to the symmetry of the channels.
The bond valence sum analysis applied to the appropriate bond lengths leads to the +3 oxidation states for both metals: 3.22 (Co) and 3.00 (Fe) using the bond valence parameters from http://www.iucr.org/resources/data/datasets/bondvalence-parameters.

Refinement
All hydrogen atoms were located from difference Fourier map and refined within the riding model approximation with U iso (H)= 1.5Ueq(C) for hydrogen atoms of the water molecule, and C-H = 0.93 (1)Å and U iso (H)= 1.2Ueq(C) for aromatic hydrogen atoms. Flack parameter value (Flack, 1983) of 0.57 (3) was obtained in the final structure factor calculation for enanthiopure chiral structure, that indicates presence of the both enanthiomers in the particular crystal examined. Futher full-matrix refinement of the Flack parameter slightly improved the agreement index R (from 0.0676 to 0.0625). Content of the the major enanthiomer in the refined racemic twin structure is 57 (3)%. Several isolated electron density peaks were located during the refinement, which were believed to be a solvent molecule. Large displacement parameters were observed modeling the disordered oxygen atom. SQUEEZE procedure of PLATON (Spek, 2009) indicated a solvent cavity of volume 161 Å 3 centered at (0,0,0), containing approximately 21 electron. In the final refinement, this contribution was removed from the intensity data that produced better refinement results.

Computing details
Data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell refinement: CrysAlis RED (Oxford Diffraction, 2009); data reduction: CrysAlis RED (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).    The packing of the title compound demonstrating hexagonal arrangment of the cation-anion chains and water molecules occupying voids in the interchain channels. The hydrogem atoms of water molecules are disordered into three positions. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.