Synthesis, crystal structure and characterizations of di-μ-cyanido-1:2κ2 N:C;2:3κ2 C:N-bis(4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane)-1κ8 N 1,N 10,O 4,O 7,O 13,O 16,O 21,O 24;3κ8 N 1,N 10,O 4,O 7,O 13,O 16,O 21,O 24-[5,10,15,20-tetrakis(4-chlorophenyl)porphyrinato-2κ4 N]-2-iron(II)-1,3-dipotassium(I) tetrahydrofuran disolvate with an unknown solvent

In the title compound, the central FeII ion is coordinated by four pyrrole N atoms of the porphyrin core and two C atoms of the cyano groups in a slightly distorted octahedral coordination environment. The complex molecule has a distorted porphyrin core.


Chemical context
The cyanide ion, CN À , a well-known acute chemical poison, acts by inhibiting the enzyme cytochrome c oxidase, which catalyses the conversion of O 2 to H 2 O along with the captured biological energy necessary to sustain life (Li et al., 2015). It is often used as a ligand in ferric heme proteins in order to prepare low-spin (S = 1/2) ferric derivatives. These studies have raised questions about the geometry of the CN À ligand when bound to iron in proteins (Schappacher et al., 1989). The first cyano iron porphyrin structure, bis(tert-butylisocyanide)octaethyloxophlorinatoiron(II), was reported by Jameson & Ibers (1979). However, since the reaction of cyanide with ferrohemes has been relatively little studied owing to the low stability of the complexes even at alkaline pH values (up to ISSN 2056-9890 9.4) (Yoshikawa et al., 1985), only seven low-spin bis(cyano)iron(II) porphyrinates have since been characterized. Herein, the crystal structure of an iron(II) porphyrin complex, [K(222)] 2 [Fe II (TpClPP)(CN) 2 ]Á2THF is reported where TpClPP is 5, 10,15,20-tetrakis(p-chlorophenyl) porphyrinato-4 N and 222 is 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosane and is used to stabilize the K + cation.

Structural commentary
In the title compound ( Fig. 1), the asymmetric unit contains one six-coordinated iron(II) porphyrin in which the carbon atoms C27 and C28 of the cyanide ligands ligate to the central Fe II ion, two cyano-bound [K(222)] + ligands and two tetrahydrofuran solvent molecules. Additional quantitative information on the structure is given in Fig. 2, which shows the displacement of each porphyrin core atom (in units of 0.01 Å ) from the 24-atom mean plane. Averaged values of the chemically unique bond lengths (in Å ) and angles (in ) are also shown. The average Fe-N p (N p is the porphyrin nitrogen atom) bond length is 1.964 (10) Å , similar to the distances in other reported bis(cyano)iron(II) porphyrinates [1.967 (12)-2.004 (5) Å ; Li et al., 2007). The mean axial Fe-C(cyano) bond length is 1.990 (2) Å , similar to 1.990 (5) Å for [PPN][Fe(TMP)(CN) 2 ] (Bartczak et al., 1998). The mean ligand C N bond length is 1.160 (1) Å . The average Fe-C-N angle involving the cyanide C and N atoms is nearly linear at 178.7 (1) . The Fe II ion is displaced slightly from the porphyrin core towards the axial ligand, as illustrated by the displacement of the metal atom from the 24-atom mean plane. The title compound shows a distorted porphyrin core conformation. The mean absolute core-atom displacements C a , C b , C m and C av are 0.32 (3), 0.22 (3), 0.56 (2) and 0.37 (14) Å , respectively. The molecular packing is shown in Fig. 3.

Supramolecular features
In order to represent clearly the interactions between [K(222)] + and the porphyrin core in the title compound, the distances between the carbon atoms (hydrogen atoms) of [K(222)] + and the close pyrrole ring centroids are shown in Fig. 4, and the geometrical parameters are listed in Table 1; all are in the range of C-HÁ Á Á interactions (Takahashi et al., 2001).

FTIR spectroscopy
The FTIR spectra were recorded on a Nicolet 6700 spectrometer as Nujol mulls. The IR spectroscopy of the title compound (KBr, cm À1 ) is shown in Fig. 5. Strong C-N bondstretching frequencies of the cyanide ligand were observed at 2076 cm À1 , which is comparable with reported values (He et al., 2016;Scheidt et al., 1983.) Table 2 Comparison of selected bond lengths and angles (Å , ) in the title compound with those in related compounds with bis(cyano) ligands.

Figure 2
Scheme of the porphyrin core of the title compound. Averaged values of the chemically unique bond lengths (in Å ) and angles (in ) are shown. The numbers in parentheses are the s.u. values calculated on the assumption that the averaged values are all drawn from the same population. The perpendicular displacements (in units of 0.01 Å ) of the porphyrin core atoms from the 24-atom mean plane are also displayed. Positive values of the displacement are towards the C atoms of the axial ligand.

Figure 3
A view of the molecular packing of the title compound in the crystal structure. Hydrogen atoms have been omitted for clarity. Unjoined atoms are the sites of the minor components of disorder.

Figure 4
Diagram showing the distances between carbon atoms of [K(222)] + and the centroids of pyrrole rings, which are involved in weak C-HÁ Á Á 6. Synthesis and crystallization 6.1. General procedure All reactions were performed using standard Schlenk techniques unless otherwise specified. All solvents were freeze/pump/thaw/degassed prior to use. Tetrahydrofuran was refluxed in the presence of sodium and benzophenone under argon until the solution was blue. Hexanes (Beijing Chemical Works) were stored over potassium-sodium alloy and chlorobenzene (Sinopharm Chemical Reagent) over P 2 O 5 (Sinopharm Chemical Reagent) under nitrogen. 2,6-dimethylpyridine (Aladdin) and ethanethiol (Aladdin) were purified by distillation before use. KCN was recrystallized and purified by a literature procedure (Armarego et al., 2009 (Adler et al., 1967;Fleischer & Srivastava, 1969) .

Synthesis of the title compound
The purple powder [Fe III (TpClPP)] 2 O (10.0 mg, 0.006 mmol) was dried under vacuum for 1 h in a Schlenk tube. Chlorobenzene ($5 mL) was transferred into the Schlenk tube by cannula and ethane thiol ($2 mL, 0.028 mol) was added via syringe. The mixture was stirred under argon at ambient temperature for 48 h. Vacuum evaporation of the solvent yielded a dark-purple solid to which [K(222)(CN)] (0.012 mmol) in THF ($8 mL) was added by cannula and the mixture was stirred overnight. X-ray quality crystals were obtained in 8 mm Â 500 mm sealed glass tubes by liquid diffusion using hexanes as non-solvent.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All hydrogen atoms were placed in calculated positions (C-H = 0.95, 0.98 and 0.99 Å for aryl, methyl and methlyene H atoms, respectively) and refined using a riding model with U iso (H) = 1.5U eq (C) for methyl H atoms or U iso (H) = 1.2U eq (C) otherwise. One of the THF molecules is disordered and was modelled over two sets of sites with relative occupancies of 0.619 (5) and 0.381 (5). One of the O atoms and several C atoms of one of the 222 molecules were refined as disordered over two sets of sites with refined occupancy ratios of 0.739 (6):0.261 (6) for O6/O6A, C61/C61A, C62/C62A and 0.832 (4):0.168 (4) for C52/C52A, C58/C58A, C64/C64A. Five reflections that were obscured by the beam stop were omitted in the last cycles of refinement. A region of electron density, most probably disordered THF possibly overlain with hexane, occupying voids of ca 372 Å 3 for an electron count of 83, was removed with the SQUEEZE procedure in PLATON (Spek, 2015) following unsuccessful attempts to model it as plausible solvent molecules.

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.