Synthesis, FT–IR characterization and crystal structure of aqua(5,10,15,20-tetraphenylporphyrinato-κ4 N)manganese(III) trifluoromethanesulfonate

This porphyrinate macrocycle of the title compound exhibits a strong saddle and moderate ruffling deformations. In the crystal, the individual manganese porphyrin complex cations and the trifluoromethanesulfonate anions are arranged in alternating planes stacked along [001].

In the title salt, [Mn(C 44 H 28 N 4

)(H 2 O)](CF 3 SO 3 ) or [Mn III (TPP)(H 2 O)]-
(CF 3 SO 3 ) (where TPP is the dianion of 5,10,15,20-tetraphenylporphyrin), the Mn III cation is chelated by the four pyrrole N atoms of the porphyrinate anion and additionally coordinated by an aqua ligand in an apical site, completing the distorted square-pyramidal coordination environment. The average Mn-N(pyrrole) bond length is 1.998 (9) Å and the Mn-O(aqua) bond length is 2.1057 (15) Å . The central Mn III ion is displaced by 0.1575 (5) Å from the N 4 C 20 mean plane of the porphyrinate anion towards the apical aqua ligand. The porphyrinate macrocycle exhibits a moderate ruffling and strong saddle deformations. In the crystal lattice, the [Mn III (TPP)(H 2 O)] + cation and the trifluoromethanesulfonate counter-ions are arranged in alternating planes packed along [001]. The components are linked together through O-HÁ Á ÁO hydrogen bonds and much weaker C-HÁ Á ÁO and C-HÁ Á ÁF interactions. The crystal packing is further stabilized by weak C-HÁ Á Á interactions involving the pyrrole and phenyl rings of the porphyrin moieties.

Chemical context
While the role of manganese porphyrins in biological processes has not been unambiguously established (Boucher et al., 1972), synthetic manganese porphyrin complexes have been used extensively as models for monoxygenases enzymes (Meunier et al., 1988;Groves & Nemo, 1983) or as DNA cleavage agents (Rodriguez & Bard, 1992;Bernadou et al., 1989). The latter can also be considered as potential contrast enhancement agents for magnetic resonance imaging (Fawwaz et al., 1990). ISSN 2056-9890 In most Mn III -porphyrin complexes, the metal is fivecoordinate and is in its high-spin state whereby polar solvents readily can displace the coordinating anionic ligand to yield solvated complexes (Godziela et al., 1986;Janson et al., 1973). In our case, the reaction of chlorido-(5,10,15,20-tetraphenylporphyrinato)manganese(III) with hygroscopic silver triflate let to the formation of an aqua- [5,10,15,20-tetraphenylporphyrinato)]manganese(III) salt, [Mn(C 44 H 28 N 4 )(H 2 O)]-(CF 3 SO 3 ), (I) or [Mn III (TPP)(H 2 O)](CF 3 SO 3 ) (where TPP is the dianion of 5,10,15,20-tetraphenylporphyrin). The coordination of a water molecule instead of the triflate ion to Mn III can be explained, as mentioned above, by the weak affinity of manganese(III) to an ionic ligand and in particular by the triflate anion which is known to be a weakly coordinating ligand.
In order to gain more insight into the structure of aqua-Mn III metalloporphyrins, we report herein the synthesis, crystal structure and the spectroscopic data of compound (I).

Structural commentary
The central Mn III cation of the complex [Mn III (TPP)(H 2 O)] cation exhibits a distorted square-pyramidal coordination environment (Fig. 1). The equatorial plane is formed by four nitrogen atoms of the porphyrin ligand while the apical position is occupied by the aqua ligand. The asymmetric unit of (I) is completed by one CF 3 SO 3 À counter-ion. The Mn-O(aqua) bond length of 2.1057 (15) Å is considerably shorter than those of other aqua-Mn III metalloporphyrins which range from 2.166 to 2.258 Å (Dawe et al., 2005;Turner, et al., 1996). The average equatorial manganese-N(pyrrole) distance is 1.998 (9) Å , which is close to related [Mn III (Porph)(X)] + ion complexes (Porph and X are a porphyrinato and a monodentate neutral ligand, respectively), e.g. [Mn III (TClPP)(py)] + (TClPP is 5,10,15,20-(tetra-4-chlorophenyl)porphyrinato) where the average Mn-N(pyrrole) bond length is 2.007 (2) Å (Rittenberg et al., 2000). In Fig. 2, the displacements of each atom in (I) from the mean plane of the 24-atom porphyrin macrocycle in units of 0.01 Å is illustrated. The Mn III ion is displaced by 0.158 (5) Å from the 24-atom porphyrin mean plane (P C ) which is slightly higher than in the [Mn III (DBHPP)(H 2 O)] + (DBHPP = 5,10,15,porphyrinato) species (Mn-P C = 0.122 Å ), but smaller than in the [Mn III (TPP)(py)] + ion complex (Mn-P C = 0.199 Å ;Dawe et al., 2005). As can be seen in Fig. 2, the porphyrin core presents (i) high saddle distortions as seen by the displacements of the pyrrole rings alternately above and below the mean porphyrin macrocycle and (ii) a moderate ruffling which is indicated by the high values of the displacements of the meso-C atoms above and below the porphyrin mean plane (Scheidt & Lee, 1987). The structures of the molecular entities in compound (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms except those of the aqua ligand have been omitted for clarity.

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

Supramolecular features
In the crystal packing of (I), the manganese porphyrin complex cations and the triflate anions are arranged in alternating planes packed along [001] (Fig. 3)

Synthesis and crystallization
To a solution of [Mn III (TPP)Cl] (100 mg, 0.142 mmol) (Cheng & Scheidt, 1996) in chloroform (10 ml) was added an excess of one equivalent of silver triflate (100 mg, 0.389 mmol). The reaction mixture was stirred at room temperature for 12 h. Crystals of the title complex were obtained by diffusion of hexanes through the chloroform solution. We assume that water was delivered from the hygroscopic silver triflate salt. Spectroscopic analysis: UV-vis spectrum in chloroform: max (nm) 386, 474, 570 and 604.

FT-IR spectroscopy
The FT-IR spectrum of (I) (Fig. 5) was recorded in the 4000-400 cm À1 range using a PerkinElmer Spectrum Two FTIR spectrometer. The spectrum presents characteristic vibrational bands of the TPP porphyrinato moiety. The C-H stretching frequencies of the porphyrin molecule are in the range 3060 to 2860 cm À1 , the C C and C N stretching frequencies are assigned at 1728 cm À1 and 1654 cm À1 , respectively. A strong 722 Harhouri et al. [Mn(C 44 The crystal packing of (I), viewed down [100], showing the weak C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds and the C-HÁ Á Á intermolecular interactions.

Figure 3
The crystal structure of the title compound in a projection approximately along [010]. H atoms have been omitted.

Figure 5
The FT-IR spectrum of (I).
band attributed to the bending vibration of the CCH moieties of the porphyrin core is centred around 1010 cm À1 . The two absorption bands at 3456 cm À1 and 3242 cm À1 are attributed to the antisymmetric and symmetric OH stretching frequencies of the aqua ligand, while the bending vibration of the same ligand is at 1629 cm À1 . The presence of the triflate counter-ion is confirmed by the following absorption bands: a medium-strong band at 1308 cm À1 attributed to the asymmetric stretching frequency of the SO 3 group, a strong band at 1231 cm À1 corresponding to the symmetric stretching frequency of the CF 3 moiety, a medium-strong band at 1162 cm À1 attributed to as (CF 3 ), a strong band at 1027 cm À1 corresponding to s (SO 3 ), a strong band at 633 cm À1 attributed to the bending vibration of the SO 3 group and a weak and a medium-strong band at 576 cm À1 and 515 cm À1 corresponding to as (CF 3 ) and as (SO 3 ) vibrations, respectively.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. Carbon-bound hydrogen atoms were placed in calculated positions and refined as riding atoms with C-H = 0.93 Å with U iso (H) = 1.2U eq (C). The two hydrogen-atom positions of the aqua ligand were discernible from difference maps. However, for the final model these positions were calculated by using the CALC-OH program (Nardelli et al., 1999) and were modelled with fixed isotropic displacement parameters. Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

Aqua(5,10,15,20-tetraphenylporphyrinato-κ 4 N)manganese(III) trifluoromethanesulfonate
Crystal data [Mn(C 44  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.