Di-μ-cyanido-1:2κ2 C:N,2:3κ2 N:C-hexacyanido-1κ3 C,3κ3 C-tetrakis(1,10-phenanthroline)-1κ2 N,N′;2κ4 N,N′;3κ2 N,N′-1,3-dicobalt(III)-2-iron(II) tetrahydrate

The hydrothermal reaction of CoCl2·6H2O, 1,10-phenanthroline (phen) and K3[Fe(CN)6] in deionized water yielded the title cyanide-bridged trinuclear cluster, [Co2Fe(CN)8(C12H8N2)4]·4H2O or [{CoIII(phen)(CN)4}2{FeII(phen)2}]·4H2O, which contains two CoIII centers and one FeII center linked by cyanide bridges. The combination of coordinative bonds, O—H⋯N and O—H⋯O hydrogen bonds and π–π stacking interactions [centroid–centroid distance = 3.630 (2) Å] results in the stabilization of a supramolecular structure. All uncoordinated water molecules are disordered. Thermogravimetric analysis reveals that the title complex loses the four crystal water molecules at about 333 K, then the anhydrous phase loses no further mass up to about 573 K, above which decomposition occurs.

Bearing this in mind, we introduced CoCl 2 .6H 2 O, 1,10-phenanthroline (phen), and K 3 [Fe(CN) 6 ] (or Na 2 [Fe(CN) 5 NO].2H 2 O) into the reaction in order to obtain a Co-Fe bimetallic monometallic complex. It is interesting that a novel cyanide-bridged trinuclear cluster [{Co III (phen)(CN) 4 } 2 {Fe II (phen) 2 }].4H 2 O, was obtained. It should be noted here that, to the best of our knowledge, the title complex is the first example of a trinuclear cluster prepared by hydrothermal method in the cyanide-based system.
The asymmetric unit of the structure of the title complex is given in Fig. 1. Selected bond lengths and angles are listed in Table 1. Within the neutral [{Co III (phen)(CN) 4 } 2 {Fe II (phen) 2 }] unit, there are one Fe II center and two Co III centers, with {FeN6} and {CoN2C4} coordination environments, respectively. The Fe center is six-coordinate and adopts a distorted slightly octahedral geometry. Each Fe center is coordinated with two coordinated phen ligands and two bridging cyanide groups in a cis arrangement with the angle N1-Fe1-N2 = 89.63 (6)°. The dihedral angle between the planes of chelating phen ligands with the Fe1 atom is ca 85°. The mean basal plane is constructed by three N atoms (N9, N11, and N12) from two phen ligands and N1 atom from one bridging cyanide group, while the axial positions are occupied by N10 atom from one phen ligand and N2 atom of the other bridging cyanide group. The geometrical data of the [Fe II (phen) 2 (CN) 2 ] unit in the title complex are similar to those found for the [Fe II (phen) 2 (CN) 2 ] unit in the one-dimensional complex [Cu 2 Fe II (CN) 4 (phen) 3 ] n .0.5nH 2 O (He et al., 2005), the [Fe II (bipy) 2 (CN) 2 ] unit in the two-dimensional complex [Fe II (bipy) 2 (CN) 4 Cu 2 ] (Colacio et al., 2003), and three-dimensional complex [Fe II (CN) 4 (phen) 2 Cu 2 ] .
The Co III centers (Co1 and Co2) are both coordinated by two N atoms from one phen ligand, one C atom from one bridging cyanide ligand, and three C atoms from three terminal cyanide ligands. For the Co III centers, the basal plane is formed by two N atoms of one phen ligand and two C atoms of two terminal cyanide groups, while the axial sites are occupied supplementary materials sup-2 by two C atoms of the other two cyanide groups. As in all other cyanide-bridged complexes, the M-C bond is much shorter than the M-N bond (Table 1). Furthermore, the Co-C-N angles are closed to be linear with the angles spanning from 171° to 179°, which are comparable with those observed for the complexes obtained by hydrothermal methods (Colacio et al., 2003;He et al., 2005;Mao et al., 2005;Colacio et al., 2005), based on [Fe(CN) 6 ] 3as the building block.
Thus, cyanide bridges connect one Fe II atom to two Co III atoms in cis arrangement, giving rise to a Co III 2 Fe II trinuclear cluster with a Fe1 ··· Co1 distance of 5.052 Å and a Fe1 ··· Co2 distance of 5.056 Å. It is noteworthy that the structure of the title complex is distinguished from that of cyanide-based mixed-valence Co II /Co III complexes (Halbauer et al., 2008;Guo et al., 2007), and mixed-valence Fe II /Fe III (Zhao et al., 2008;Overgaard et al., 2004;Brewer et al., 2007;Xie et al., 2007;Fernández-Armas et al., 2007;Paredes-García et al., 2006) complexes belonging to other systems.
The crystallized water molecules are hydrogen-bonded to each other and terminal cyanide groups. The probable hydrogen bonding interactions are given in Table 2. In addition, weak face-to-face π-π interactions between the aromatic rings of adjacent phen ligands from neighboring trinuclear clusters also play important roles in the formation and stabilization of the three-dimensional supramolecular structure (Fig. 2). The distance between two adjacent aromatic ring center is ca 3.63 Å.
The IR spectrum ( Fig. 3) of the title complex exhibits two strong peaks at 2080 cm -1 and 2133 cm -1 , and one weak peak at 2171 cm -1 , which indicates the existence of different types of cyanide bridges in the structure. The lower frequencies at 2080 cm -1 and 2133 cm -1 are reasonably assigned to the terminal cyanide stretching vibrations, while the higher one of 2171 cm -1 confirms the presence of bridging cyanide groups.
There is a broad band at the wavenumber range of 3700-2900 cm -1 ascribed to the O-H stretching absorption (ν O-H ) in H 2 O molecules. The IR spectrum exhibits characteristic strong bands of the coordinated phen ligands at 1638, 1521, 1425, 844, and 722 cm -1 (δ C-H benzene ring). The bands at 1521, 1425 and 722 cm -1 are shifted from their positions for the free phen ligands (1503, 1420 and 737 cm -1 ), indicating nitrogen coordination. The IR feature has been confirmed by single-crystal X-ray crystallographic analysis.
Thermogravimetric analysis (Fig. 4) is performed to study the thermal stability of the title complex, which shows the title complex loses four crystallized water molecules at above 333 K with a weight loss of 6.29% (Calc. 6.17%). The anhydrous phase loses no further mass up to about 573 K, above which thermal decomposition occurs.

Experimental
All starting reagents were of analytical grade quality, obtained from commercial sources and used without further purification. A mixture of CoCl 2 .6H 2 O (0.1071 g, 0.45 mmol), 1,10-phenanthroline (phen, 0.0892 g, 0.45 mmol), K 3 [Fe(CN) 6 ] (0.1482 g, 0.45 mmol) in a molar ratio of 1:1:1 combined with 10 ml deionized water was stirred for 20 min at room temperature and then transferred into a 25 ml Teflon-lined stainless-steel vessel. The mixture was heated hydrothermally at 413 K for two days under autogenous pressure. Slow cooling of the resulting solution to room temperature afforded dark red, prism-shaped crystals suitable for single-crystal X-ray structure analysis. Yield: 30% (based on Fe). These crystals were separated, washed thoroughly with deionized water and finally with ethanol, and dried. Analysis calculated for