Crystal structure of an unknown solvate of (piperazine-κN){5,10,15,20-tetrakis[4-(benzoyloxy)phenyl]porphyrinato-κ4 N}zinc

The molecular structure of the piperazine[5,10,15,20-(tetraphenylbenzoate)porphyrinato-κ4 N]zinc(II) complex is composed of parallel pairs of layers with an interlayer distance of 4.100 Å while the distance between two pairs of layers is 4.047 Å.

The title compound, [Zn(C 72 H 44 N 4 O 8 )(C 4 H 10 N 2 )] or [Zn(TPBP) (pipz] (where TPBP and pipz are 5,10,15,phenyl]porphyrinato and piperazine ligands respectively), features a distorted square-pyramidal coordination geometry about the central Zn II atom. This central atom is chelated by the four N atoms of the porphyrinate anion and further coordinated by a nitrogen atom of the piperazine axial ligand, which adopts a chair confirmation. The average Zn-N(pyrrole) bond length is 2.078 (7) Å and the Zn-N(pipz) bond length is 2.1274 (19) Å . The zinc cation is displaced by 0.4365 (4) Å from the N 4 C 20 mean plane of the porphyrinate anion toward the piperazine axial ligand. This porphyrinate macrocycle exhibits major saddle and moderate ruffling deformations. In the crystal, the supramolecular structure is made by parallel pairs of layers along (100), with an interlayer distance of 4.100 Å while the distance between two pairs of layers is 4.047 Å . A region of electron density was treated with the SQUEEZE [Spek (2015). Acta Cryst. C71, 9-18] procedure in PLATON following unsuccessful attempts to model it as being part of disordered n-hexane solvent and water molecules. The given chemical formula and other crystal data do not take into account these solvent molecules.

Chemical context
The Zn II ion is one of the most prevalent metal ions as the metal center of a metalloporphyrin. Indeed, zinc porphyrin complexes provide simpler systems than those of iron, cobalt, or other d transition metals to evaluate the influence of a wide range of different ligands on the spectroscopic and structural properties of complexed porphyrins. The metal ion is unambiguously in the +II oxidation state; in most cases, fourcoordinate (porphyrinato) zinc complexes will accept one axial ligand to form complexes with a coordination number of five for the metal (Denden et al., 2015). Nevertheless, zinc porphyrins with a coordination number of six for the metal have also been reported (Shukla et al., 2000;Oberda et al., 2013). ISSN 2056-9890 In the literature, an important number of zinc-pyridine (and substituted pyridines) metalloporphyrins have been reported, e.g. [Zn(TPP)(py)] (TPP = 5,10,15,20-tetraphenylporphyrinato) (Devillers et al., 2013). This is also the case for other related cyclic N-donor ligands such as dabco (1,4-diazabicyclo[2.2.2]octane) and pyz (pyrazine), e.g. [Zn(OEP) (dabco)] (OEP = octaethylporphyrinato) (Konarev et al., 2009) and [Zn(TPP) (pyz)] (Byrn et al., 1993). Notably, to date no zinc-piperazine porphyrin structure has been reported in the literature. In this work, we have focused on the crystal struc-ture and the UV-visible characterizations of the new zinc porphyrin title complex, namely the (piperazine) {5,10,15,20tetrakis[4-(benzoyloxy)phenyl]porphyrinato}zinc complex (I).

Structural commentary
The Zn II cation is chelated by four pyrrole-N atoms of the porphyrinate anion and coordinated by a nitrogen atom of the piperazine axial ligand in a distorted square-pyramidal geometry. The piperazine ligand adopts the usual chair conformation (Fig. 1). The Zn __ N(pipz) bond length [2.1274 (19) Å ] is considerably longer than the related nonporphyrinic zinc-pipz distances which are in the range 2.039 (3)-2.064 (2) Å (Suen et al., 2002;Nguyen et al., 2006) but shorter than that of the zinc-dimethylpiperazine [2.250 (2) Å ; Konarev et al., 2007]. The average equatorial zinc-N(pyrrole) distance (Zn-Np) is 2.078 (7) Å , which is close to those of related zinc metalloporphyrins of type [Zn(Porph)(L)] (Porph and L are a porphyrinato and a monodentate neutral ligand, respectively; Byrn et al., 1993;Lipstman et al., 2006). Fig. 2 is a formal diagram of the porphyrinato core atoms of (I) showing the displacements of each atom from the mean plane of the 24atom porphyrin macrocycle in units of 0.01 Å . The zinc atom is displaced by 0.4365 (4) Å from the 24-atom porphyrin mean plane (P C ). This Zn __ P C distance is close to those of [Zn(OEP)(dabco)] (Konarev et al., 2009) and [Zn(TPP)(pyridine)] which are 0.572 and 0.418 Å , respectively (Furuta et al., 2002). The porphyrin core presents a major saddle and a moderate ruffling distortion (Scheidt & Lee, 1987). 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.

Supramolecular features
In the crystal of compound (I), the [Zn(TPBP)(pipz)] molecules are linked together in such way to make a pair of layers, parallel to (100), which are parallel to other pairs. The overall supramolecular architecture in (I) is two-dimensional (Fig. 3). The distance between two layers is 4.100 Å while the pairs of layers are spaced apart by 4.047 Å . Within a layer, the linkage of the [Zn(TPBP)(pipz)] molecules is accomplished by C __ HÁ Á Á interactions between the carbon atom C56 of a phenyl ring of one TPBP porphyrinate and the centroid Cg10 of a phenyl ring of an adjacent TPBP species [C56 __ H56Á Á ÁCg10 = 3.623 (3) Å ;  [Zn(TPBP)] starting complex were synthesized using modified reported methods (Adler et al., 1967;Oberda et al., 2011). The packing of (I) viewed along [010] showing the two-dimensional superstructure formed by pairs of layers.

Figure 2
Formal diagram of the porphyrinate core illustrating the displacements of each atom from the 24-atom core plane in units of 0.01 Å . Table 1 Hydrogen-bond geometry (Å , ).

UV-visible spectra
The UV-visible spectra (CHCl 3 solution/solid state) were recorded on a WinASPECT PLUS (validation for SPECORD PLUS version 4.2) scanning spectrophotometer. Fig. 6 illustrates the electronic spectra of the solid [Zn(TPBP)] complex, used as starting material, and complex (I) which shows that the Soret and Q band of the latter species is red-shifted compared to those of the starting material. Thus, the max (in nm) values of the Soret and Q bands of [Zn(TPBP)] and (I) are 438/445, 563/568 and 606/609 respectively. By the other hand, for (I), the values of theses absorption bands in chloroform are blue-shifted compared to those in the solid state. In fact the max (in nm) values are 430/445 for the Soret band and 563/568 and 603/609 for the Q bands.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. In the final refinement of (I) four reflections, viz. The packing of (I) viewed along [100] showing the intermolecular interactions between two layers and between two pairs of layers.

Figure 5
owing to poor agreements between observed and calculated intensities.
All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.99 Å (methylene) and 0.95 Å (aromatic) with U iso (H) = 1.2U eq (C). The two H atoms of the piperazine axial ligand were found in the difference Fourier map and the hydrogen atom of the nitrogen N5 of the piperazine ligand coordinating to the Zn 2+ atom was freely refined while the hydrogen atom of the second nitrogen (N6) of the piperazine ligand was refined with fixed isotropic displacement parameters with U iso =1.2U eq (N6). The bond length N5 __ H5 of the piperzine axial ligand was restrained to ensure proper geometry using DFIX instruction of SHELXL2014 (Sheldrick, 2015). The anisotropic displacement ellipsoids of the carbon and nitrogen atoms of the same piperazine ligand were very elongated, which indicates static disorder. For these atoms, a SIMU restraint was applied (McArdle, 1995;Sheldrick, 2008). An unknown n-hexane and water disordered molecules were difficult to model, therefore solvent contributions to the scattering have been removed  using the SQUEEZE procedure (Spek, 2015) in PLATON (Spek, 2009). SQUEEZE calculated a void volume of approximately 530 Å 3 occupied by 60 electrons per unit cell, which points to the presence of approximately a half n-hexane and a water molecule per formula unit. Fig. 7 shows the positions of the voids within the unit cell.   Data collection: SAINT (Bruker, 2015); cell refinement: APEX3 (Bruker, 2015) and SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SIR2004-1.0 (Burla et al., 2005); program(s) used to refine structure: SHELXL2015 (Sheldrick, 2015); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX publication routines (Farrugia, 2012).

(Piperazine-κN){5,10,15,20-tetrakis[4-(benzoyloxy)phenyl]porphyrinato-κ 4 N}zinc unknown solvate
Crystal data [Zn(C 72   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.