A one-dimensional polymeric cobalt(III)–potassium complex with 18-crown-6, cyanide and porphyrinate ligands

The reaction of CoII(TpivPP) {TpivPP is the dianion of 5,10,15,20-tetrakis[2-(2,2-dimethylpropanamido)phenyl]porphyrin} with an excess of KCN salts and an excess of the 18-crown-6 in chlorobenzene leads to the polymeric title compound catena-poly[[dicyanido-2κ2 C-(1,4,7,10,13,16-hexaoxacyclooctadecane-1κ6 O){μ3-(2α,2β)-5,10,15,20-tetrakis[2-(2,2-dimethylpropanamido)phenyl]porphyrinato-1κO 5:2κ4 N,N′,N′′,N′′′:1′κO 15}cobalt(III)potassium] dihydrate], {[CoK(CN)2(C12H24O6)(C64H64N8O4]·2H2O}n. The CoIII ion lies on an inversion center, and the asymmetric unit contains one half of a [CoIII(2α,2β-TpivPP)(CN)2]− ion complex and one half of a [K(18-C-6]+ counter-ion (18-C-6 is 1,4,7,10,13,16-hexaoxacyclooctadecane), where the KI ion lies on an inversion center. The CoIII ion is hexacoordinated by two C-bonded axial cyanide ligands and the four pyrrole N atoms of the porphyrin ligand. The KI ion is chelated by the six O atoms of the 18-crown-6 molecule and is further coordinated by two O atoms of pivalamido groups of the porphyrin ligands, leading to the formation of polymeric chains running along [011]. In the crystal, the polymeric chains and the lattice water molecules are linked by N—H⋯O and O—H⋯N hydrogen bonds, as well as weak C—H⋯O, O—H⋯π and C—H⋯π interactions into a three-dimensional supramolecular architecture.


Comment
In the Cambridge Structural Database (CSD, Version 5.35;Allen, 2002) there are more than ninety structures of cyanometalloporphyrins. This large number of structures reflects the importance of this type of compounds. Nevertheless, only one structure of cyano-porphyrin species with a cobalt as central ion is known (Hoshino et al.., 2000). The cyano-cobalt porphyrin derivatives are good model for the B12 vitamin called cobalamin, which is a cobalt porphyrin-like protein responsible, inter alia, of the formation of blood.
We reports herein the crystal structure of the poly [(1,4,7,10,13,16-hexaoxacyclooctadecane) In this complex, the cobalt is coordinated to the four N atoms of the porphyrin ring and the carbons of the two trans cyano axial ligands (Fig. 1).
It has been noticed that there is a relationship between the ruffling of the porphyrinato core and the mean equatorial Co -N p distance; the porphyrinato core is ruffled as the Co-N p distance decreases (Iimuna et al., 1988 The crystal packing features weak C-H···π interactions between the 1D polymer chains (Table 1 and Fig. 2).

Experimental
To a solution of [Co II (TpivPP)] (Collman et al., 1978) (100 mg, 0.067 mmol) in chlorobenzene (10 mL) was added an excess of 18-crown-6 (150 mg, 0.567 mmol) and potassium cyanide (100 mg, 0.378 mmol). A rapid color change from orange-red to green occurred. The resulting material was crystallized by diffusion of hexanes through the chlorobenzene .2H 2 O} n crystals as synthesis product.

Refinement
The two hydrogens of the water molecule were found in the difference Fourier map and were included in the refinement using restraints (O-H = 0.85 (1) Å) with U iso (H) = 1.2U eq (O6). Other H atoms attached to C and N atoms were fixed geometrically and treated as riding with C-H = 0.99 Å (methylene), 0.95 Å (aromatic) and 0.98 Å with U iso (H) = 1.2U eq (C aromatic, methylene, methyl ) and N-H = 0.88 Å with U iso (H) = 1.2U eq (N).

Computing details
Data  The crystal structure of the title compound plotted in projection along [100]. H atoms have been omitted. Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. 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. Rfactors 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.