Crystal structure of (4-cyanopyridine-κN){5,10,15,20-tetrakis[4-(benzoyloxy)phenyl]porphyrinato-κ4 N}zinc–4-cyanopyridine (1/1)

In the crystal, the ZnII cation is chelated by four pyrrole-N atoms of the porphyrinate anion and coordinated by a pyridyl-N atom of the 4-cyanopyridine axial ligand in a distorted square-pyramidal geometry. The non-coordinating 4-cyanopyridine molecule is disordered over two positions in the supramolecular channel formed by complex molecules.


Chemical context
During the last two decades, renewed attention to zinc metalloporphyrins has been noted for their applications in different fields e.g. solar energy harvesting and artificial photosynthesis (Aratani et al., 2009;Panda et al., 2012) and as building blocks of assemblies (Diskin-Posner et al., 2002). Many structures of five-coordinate zinc porphyrins of the type [Zn(Porph)(L)] (Porph = is a porphyrinato ligand and L is a neutral unidentate ligand N-bonded to the zinc cation) are known in the literature. However, only three structures of zinc-4-NCpy non-porphyrinic species [CSD refcodes CYPYZN (Steffen & Palenik, 1977); LIMWUZ (Clegg et al., 1995) and QIDXAD (Huang et al., 2007; CCD Version 5.35 (Groom & Allen, 2014)] and one structure of a zinc-4-NCpyporphyrin derivative are reported in the literature (CSD refcode IRAFIR; Brahma et al., 2011). To gain more insight into the structural and spectroscopic properties of Zn II -Ndonor monodentate neutral ligand metalloporphyrins in general and Zn II -cyanopyridine porphyrin derivatives in particular, we report herein the synthesis, the molecular structure and the spectroscopic data of the title compound with the formula [Zn(TPBP)(4-CNpy)]Á(4-CNpy) (I). ISSN 2056-9890
The saddle deformation is due to the displacement of the pyrrole rings alternately above and below the mean porphyrin macrocycle so that the pyrrole nitrogen atoms are out of the mean plane. The ruffling distortion is indicated by the high values of the displacement of the meso-carbon atoms above and below the porphyrin mean plane while the doming deformation is originated by the displacement of the metal atom out of the mean plane, and the nitrogen atoms are displaced toward the axial ligand. Generally, for hemoproteins and metalloporphyrins, the plane of the axial ligand (i.e., imidazole, pyridine) nearly bisects the 'cis' Np-Fe-Np angle, which is also the case for the title zinc-4-CNpy derivative (I) where the dihedral angle between the plane of the 4-CNpy ligand and the N4-Zn-N5 plane is 36.33 (12) (Fig. 2).

Supramolecular features
Within the crystal structure of (I) (Fig. 3), the [Zn(TPBP)(4-CNpy)] complexes are linked together via weak non-classical C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and by C-HÁ Á Á interactions (Table 1) An ORTEP view of the molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. H atoms have been omitted for clarity.

Figure 3
A partial view of the crystal packing of (I) showing the link between the [Zn(TPBP)(4-cyano)] complexes via non-classical C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and by C-HÁ Á Á interactions. The non-coordinating 4-cyanopyridine molecules are omitted for clarity.

Figure 4
The crystal structure of the title compound plotted in projection along [001] showing the disordered non-coordinating 4-cyanopyridine molecules occupying the channels between the [Zn(TPBP)(4-CNpy)] complex molecules. H atoms have been omitted. stirred for another 40 min. The mixture was cooled overnight at 277 K and filtered under vacuum. The crude product was purified using column chromatography (chloroform/petroleum ether 4/1 v/v as an eluent). A purple solid was obtained and dried under vacuum (1.18 g, yield 21%).

Synthesis and crystallization of the title complex (I)
To a solution of [Zn(TPBP)] (100 mg, 0.086 mmol) in dichloromethane (5 mL) was added an excess of 4-cyanopyridine (200 mg, 0.192 mmol). The reaction mixture was stirred at room temperature for 2 h. Single crystals of the title complex were obtained by diffusion of hexanes through the dichloromethane solution.

FT-IR spectroscopy
The FT-IR spectrum of [Zn(TPBP)(4-CNpy)]Á(4-CNpy) (I) ( Fig. 6) was recorded in the 4000-400 cm À1 domain using a Perkin-Elmer Spectrum Two FTIR spectrometer. The spectrum presents characteristic IR bands of the TPBP porphyrinato moiety. The C-H stretching frequencies of the porphyrin are in the range 3060-2860 cm À1 , the ester group of the meso-substituents of this porphyrin are identified by a strong band at 1736 cm À1 , (C O) stretch and by two strong bands at 1264 and 1061 corresponding to the (C-O) stretching vibration. The IR spectrum of (I) also shows a very weak absorption band at 2238 cm À1 attributed to the nitrile stretching frequency (C N). The value of this band is almost identical to the one of the free 4-cyanopyridine (2236 cm À1 ) which could be attributed both to the 4-CNpy ligand or the free 4-CNpy molecule in (I) because this band is usually not affected by the coordination of the 4-cyanopyridine (Singh et al., 2000). On the other hand, the IR spectrum of the title compound exhibits several absorption bands at 1907 cm À1 (vw: very weak), 1523 cm À1 (vw), 1505 cm À1 (w: weak), 1406 cm À1 (m: medium), 996 cm À1 (s: strong), 707 cm À1 (m), 685 cm À1 (m) and 538 cm À1 (w) attributed to the pyridyl group of the coordinating and the free 4-cyanopyridine species (Singh et al., 2000).    (Sheldrick, 2015), ORTEPIII (Burnett & Johnson, 1996) and WinGX publication routines (Farrugia, 2012).