meso-5,10,15,20-Tetrakis(4-hydroxy-3-methoxyphenyl)porphyrin propionic acid monosolvate

In the title compound, C48H38N4O8·C3H6O2, the porphyrin molecule is centrosymmetric. The propionic acid solvent molecule is disordered over two sets of sites with equal occupancy factors. The porphyrin central core is almost planar, with an r.m.s. deviation of the fitted atoms of 0.045 Å. The substituent benzene rings make dihedral angles of 70.37 (4) and 66.95 (4)° with respect to the porphyrin core plane. The crystal structure is stabilized by an interesting network of hydrogen bonds. Porphyrin molecules are connected by O—H⋯O hydrogen bonds creating ribbons running along the [101] direction. Weak C—H⋯O hydrogen bonds connect separate molecular ribbons in the [110] direction, creating (-111) layers. Intramolecular N—H⋯N hydrogen bonds also occur. The propionic acid molecules are connected by pairs of —H⋯O hydrogen bonds, creating dimers.

This paper presents the crystal structure of meso-tetra(4-hydroxy-3-methoxyphenyl)porphyrin (I), which is good a candidate as a starting material for synthesis of a new potential anticancer photosensitizer. Compound (I) crystallizes in triclinic system with one porphyrin molecule in the unit cell. Crystal structure contains also one propionic acid solvent molecule per one porphyrin molecule (Fig.1). The solvent molecule is disordered and can occupy two positions in the unit cell with equal occupancy factors. Porphyrin molecule is centrosymmetric with two sets of benzene rings orientations. Central core of porphyrin molecule is approximately planar with r.m.s. deviation of fitted atoms equal to 0.045 Å. The largest distance from one atom (N1) to the average plane is 0.1057 (13) Å. The angles of substituent benzene rings with the porphyrin core plane are 70.37 (4)° and 66.95 (4)°. Porphyrin molecules occupy (596) planes creating π-π stacking structure. The distance between centroids of two pyrrolide ring and pyrrole rings is 4.232 Å. Two sets of methylene groups are almost coplanar with benzene rings with largest distance to average plane equal to 0.0982 (34) Å and 0.1053 (31) Å for atoms C23 and C24 respectively. The two torsion angles are as follows: C5-C6-O3-C24 = -4.5 (2)° and C22-C21-O4-C23 = 4.4 (2)°.

Experimental
Chemicals and solvents were purchased from commercial sources and used as received. Synthesis of meso-tetra(4-hydroxy-3-methoxyphenyl)porphyrin (I) was performed as fallows. 8.8 g (0.072 m) of vanillin was added into 300 ml of propionic acid. The mixture was boiled until the all aldehyde was dissolved. After this 5 ml (0.072 m) of pyrrole was added and the solution was boiled for 1.5 h. Then about 200 ml of propionic acid was distilled off, the residue was cooled to ambient temperature and neutralized with saturated solution of NaHCO 3 . The precipitate was filtered and washed with chloroform until the filtrate was colourless. The product of the reaction was purified by column chromatography (silica gel/chloroform:ethyl acetate).
The single crystals of (I) were obtained directly from precipitate after reaction procedure (before column chromatography purification).
All spectroscopic data were in accordance with literature [Bonar-Law, 1996].

Refinement
Non-hydrogen atoms were refined with anisotropic displacement parameters. The aromatic, methyl and hydroxyl hydrogen atoms were treated as "riding" on their parent carbon atoms with C-H = 0.96 Å, C-H = 0.98 Å and C-H = 0.84 Å respectively. Atomic displacement parameters of hydrogen atoms equal to 1.2 times the value of the equivalent atomic displacement parameters of the parent carbon atom (U iso (H) = 1.2U eq (C)) for aromatic hydrogen atoms and 1.5 times the value of the equivalent atomic displacement parameters of the parent carbon atom (U iso (H) = 1.5U eq (C)) for methyl and hydroxyl hydrogen atoms. Hydrogen atoms, which take part in hydrogen bonding, were located in a difference Fourier map (ΔF) and they were refined freely with isotropic displacement parameters. Similar-ADP restraint (SIMU) was applied to carbon atoms (C25, C26 and C27) in disordered propionic acid molecule.

Computing details
Data The molecular structure of compound (I), showing atom-labelling scheme. The molecule is centrosymmetric and only the unique atoms of the asymmetric unit are labelled. Ellipsoids representing displacement parameters are drown at the 50% probability level.

Figure 2
Scheme of network of hydrogen bonds in (I

Special details
Experimental. Absorption correction: CrysAlisPro, Agilent Technologies, Version 1.171.35.19 Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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. R-factors 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.