Co porphyrin

Annals of West University of Timisoara, Series Chemistry 13 (1) (2004) 9-20 9 SYNTHESES AND SPECTROSCOPIC CHARACTERIZATION OF CO(II) AND CO(III) MESO-TETRAPHENYLPORPHYRIN COMPLEXES D a n a V l a s c i c i a , A d r i a n C h i r i a c a , E u g e n i a Făgăd a r - C o s m a b , O t i l i a S p i r i d o n - B i z e r e a a , R a m o n a T u d o s e b a West University of Timisoara, Faculty of Chemistry – Biology – Geography, Inorganic Chemistry Department, Str. Pestalozzi 16, 300115 - Timisoara, Romania bInstitute of Chemistry Timisoara of Romanian Academy, Bd. M. Viteazul 24, 300223- Timisoara, Romania Received: 29 January 2004 Modified: 5 April 2004 Accepted: 15 May 2004 SUMMARY The present study is concerning about the syntheses of some metalloporphyrins, which are reported to be used as ionophores in ion selective membranes. That is why, tetraphenylporphyrin, H2(TPP), and the corresponding metalloporphyrins, spin free Co(II) and spin paired Co(III) complexes, CoII(TPP) and ClCoIII(TPP) were obtained. H2(TPP) is synthesized by the condensation of benzaldehyde and pyrrole, and the subsequent metallation of H2(TPP) is achieved with cobalt acetate in glacial acetic acid or chloroform as solvents. The compounds are analyzed by their electronic absorption spectra in the visible region, and by their IR spectra. Analysis of the electronic absorption spectra is presented on the basis of CoII(TPP) representing the class of hypsoporphyrins. The hypsochromic (blue) shifts of the CoII(TPP) complex and the bathochromic shifts of CoIII(TPP) are discussed. Keywords: meso-tetraphenylporphyrin, metalloporphyrins, UV-Vis spectroscopy, IR spectroscopy V L A S C I C I D . , C H I R I A C A . E T A L . 10 INTRODUCTION In connection with previous researches [1,2] concerning the correlative effects exhibited by some phosphorus (V) compounds on chlorophyll a and b contents in plants, and taking into consideration the major importance of chlorophylls, as natural porphyrins, we decided to extend our studies upon some other porphyrins focusing on their amazing properties. Porphyrins are a class of natural pigments containing a fundamental skeleton of four pyrrole nuclei united through the α-positions by four methine groups to form a macrocyclic structure [3]. Porphyrin is designated also with the nomenclature of porphine. 13 12 11 N 24 14 18 17 16 NH 23 19 15 3 2 1 N21 4 20 8 7 6 HN 22 9 10 5 pozitii meso (5, 10, 15, 20) pozitii α (1, 4, 6, 9, 11, 14, 16, 19) pozitii β (2, 3, 7, 8, 12, 1,3, 17, 18) Figure 1: The structure of the porphine macrocycle The porphyrin nucleus is a tetradentate ligand. When coordination occurs, two protons are removed from the pyrrole nitrogen atoms, leaving two negative charges. The porphyrin ring system exhibits aromatic character, containing 22 π-electrons, but only 18 of them are delocalized according to the Hückel’s rule of aromaticity (4n+2 delocalized π- electrons, where n=4). Simple porphyrins with identical substituents in ms- or β-positions are usually prepared by methods based on monopyrrole condensation (the Rothemund Method), when four identical pyrrole molecules are condensed into a porphyrin in one step. This technique firstly developed during the 1930’s was later improved in the 70’s by the Adler research group [4], as shown in equation 1, and represents also the first approach of our study. MESO-TETRAPHENYLPORPHYRIN COMPLEXES WITH CO(II) AND CO(III) 11 (1) The R-groups may indicate: alkyl-, alkoxy-, amino-, carboxyl-, carbomethoxyl- , halogeno- and nitro-groups. More complicated structures are prepared through intermediate di- or tetrapyrrole compounds [5, 6], in which the presence of the substituents leads to the possibility of formation of isomers around a substituent position, as shown in equation 2. (2) 1-3 4-7 X = H (1, 4, 5), 4-OCH3 (2, 6), 4-NO2 (3, 7); R = CH3 (4), C4H9 (5-7). The porphyrin complexes with transition metal ions are very stable [7]. Almost all metals have been combined with porphyrins, and studied in order to understand the V L A S C I C I D . , C H I R I A C A . E T A L . 12 biosynthetic formation and biological activity of natural compounds (photosynthesis, dioxygen transport and storage). It is well known that porphyrin is also a high sensitive chromogenic reagent. Porphyrins and their metal chelates generally exhibit characteristic sharp and intensive absorption bands in the visible region. Various metalloporphyrins have shown a potentiometric response to anions with selectivity sequences solely dependent on the centrally bonded metal [8]. The metalloporphyrins have rich redox chemistry since they have the advantage of including coordination of additional ligands above and below the porphyrin plane. These two last mentioned properties are representing the main interest of our further researches. Porphyrins and metalloporphyrins have found numerous applications in chemical analysis, especially in spectroscopy, chromatography and electroanalytical chemistry. They are also used as field-responsive materials, particularly for optoelectronic applications. The facile substitution of the periphery of various porphyrins has generated a series of unusual liquid crystalline materials. The porphyrin ligands are the base for special materials exhibiting large dipole moments, polarizabilities, and hyperpolarizabilities. The nonlinear optical properties of these materials are of special interest in optical communications, data storage and electrooptical signal processing [9]. MATERIALS AND METHODS • Synthesis of tetraphenylporphyrin, H2(TPP) [10]. 180 ml propionic acid is heating to reflux. 4,8 ml benzaldehyde is added into the top of the water condenser. To the resulting solution 3,4 ml of freshly distilled pyrolle was added, and the solution was refluxed for 30 minutes. After refluxing, the reaction mixture was cooled to ambient temperature and decanted into a flask containing ca. 100 ml methanol. H2(TPP) was filtered and washed with methanol, followed by hot distilled water. The purified meso- tetraphenylporphyrin is presenting as dark-violet crystals, mp=194oC, η=21%. • Synthesis of tetraphenylporphyrinatocobalt(II), CoTPP [11]. 0.2 g (0.33 mmol) H2TPP were placed in a 250 mL 2-necked round bottom flask. 80 mL of fresh (newly opened bottle or freshly distilled) chloroform were added, and the mixture was MESO-TETRAPHENYLPORPHYRIN COMPLEXES WITH CO(II) AND CO(III) 13 stirred to dissolve the H2TPP, and than heated. While this is taking place, a solution consisting of 1.0 g (4.0 mmol) of cobalt acetate tetrahydrate in 50 mL methanol was made and heated to near boiling, until the Co(II) acetate was dissolved. The methanol solution of cobalt acetate was poured in the round bottom flask and heated to reflux. Refluxing and stirring was continued for 30-60 minutes, occasionally checking for the disappearance of strong red fluorescence under long-wave UV light (CoTPP does not fluoresce, while the free-base does). Insertion of Co(II) is complete when no spot of the free base porphyrin can be detected. When metal insertion was complete, the solution was cooled to room temperature. About 100 mL of distilled water was placed in a separatory funnel, and poured the cooled reaction mixture in on top of it. The chloroform will sink to the bottom, while the methanol and excess inorganic salt will dissolve in the water. After repeating this operation, most of the inorganic salts, and most of the methanol, have been removed, and the chloroform solution of the cobalt porphyrin can be washed several additional times (now with shaking of the separatory funnel) with fresh water. The chloroform solution was dried over Na2SO4, the drying agent was filtered off, and than the filtrate was evaporated to dryness. The CoTPP is separated as dark-red crystals, η=87% with respect to porphyrin. • Synthesis of chloro-tetraphenylporphyrinatocobalt(III), ClCoTPP [12]. 0,3 g Co(II)TPP was suspended in methanol (297 ml) containing concentrated hydrochloric acid (3 ml). When the suspension was stirred at room temperature in an open flask for several hours, the solution gradually changed to reddish purple, and then the whole became a clear solution. The solution was filtered and concentrated under reduced pressure al about 50oC. The separated crystalline precipitates were collected, washed with water, and then with a small amount of methanol-water mixture, dried at room temperature, and recrystallized from methanol and then chloroform-ether. The purified ClCoTPP is obtained as nice violet crystals, η=75% with respect to CoTPP. • UV-Vis spectra were registered on Perkin Elmer Lambda 12, UV-Vis spectrophotometer, and the thickness of the used cuvette being of 1 cm. • IR spectra were determined on SPECORD M80 JENA as KBr pellets. • Melting point was determined on a Boetius apparatus and is uncorrected. • Reactions, reagents and all sensitive operations were carried out with protection from atmospheric moisture, purging inert gas. V L A S C I C I D . , C H I R I A C A . E T A L . 14 • Propionic acid (97%), benzaldehyde, pyrolle, methanol, chloroform, cobalt acetate tetrahydrate, hydrochloric acid were achieved from Sigma Aldrich Division, Germany. All chemicals used were dried and distilled from appropriate drying agents, according to Perrin [13]. RESULTS AND DISCUSSION The most characteristic physical property of a metalloporphyrin is its absorbtion spectrum. The UV –visible absorption bands of the porphyrins are due to the electronic transitions from the ground state (So) to the lowest singlet excitated states S1 (Q state) and S2 (B state). The So→S1 transition gives rise to the weak Q bands in visible region (550-650 nm) while So→S2 transition produces the strong B band (Soret Band) in near UV region (380-450 nm) [14]. The region from 400 to 500 nm, which is called the Soret band, is widely used for spectrophotometric determination of metalloporphyrins because shows the most intensive absorption (molar absorptivities of the order of 105). Gouterman[15] has developed a molecular orbital theory which has been quite successful in explaining the occurrence and effects of substituents and metal coordination on so-called Q and B bands of porphyrins and metalloporphyrins. In this terminology of the four-orbital model, the transitions that give rise to the characteristic porphyrin spectra bands are A2u(π)→Eg(π*) and A1u(π)→Eg(π*). The lowest energy exited singlet state Q(0,0) is split into Qx(0,0) and Qy(0,0) by the D2h symmetry of the free base porphyrins. Each band has a vibronic overtone, Qx(1,0) and Qy(1,0). The second excited singlet state B(0,0) gives rise to the B band (Soret band) which is not split due to the nodes that occur at the nitrogen atoms of the A1u(π) orbital. The UV-visible spectra of meso-tetraphenylporphyrin (H2TPP), CoTPP, and ClCoTPP were performed in EtOH, according to Figures 2-4 and in hexane, according to Figures 5-7. Some changes in λ due to solvent polarity are to be seen. The π →π* transitions would be red-shifted (to lower energy) in all spectra determined in ethanol (Figures 2-4), as a polar solvent, comparatively to that performed in hexane (Figures 5-7), due to the higher stabilization of the π* orbital, relative to that of the π orbital. MESO-TETRAPHENYLPORPHYRIN COMPLEXES WITH CO(II) AND CO(III) 15 X10 Figure 2. UV-Vis spectrum of H2TPP in EtOH 353 380 400 420 440 460469 0.2 1.0 1.5 2.0 2.5 3.0 3.6 nm A 427.90, 2 417.51, 3.25413.09, 3.30 502 600 700 801 0.17 0.20 0.25 0.30 0.35 0.40 0.45 0.51 nm A 583 0.2598 778.24, 644.88, 0.21 532.52, 0.47 Figure 3. UV-Vis spectrum of CoTPP in EtOH It can be seen that the spectrum of CoTPP (Figure 3) is broadened compared with that of H2TPP (Figure2.), which implies the possible formation of an aggregate. The unusual nature of electronic spectra of CoII porphyrin can be explained on basis of the effect of the solvent. Regarding the UV-Vis spectrum of Co(III)-porphyrin, the red shift of both the Soret and Q band is becoming preeminent comparatively to meso- tetraphenylporphyrin and CoTPP UV- Vis spectra in alcohol. 211 300 400 491 -0.1 0.2 0.4 0.6 0.8 1.0 1.2 nm A 413.62, 1 274.48, 0.07 228.01, 0.17 442 600 800 1000 1110 0.020 0.025 0.030 0.035 0.040 0.045 0.050 0.055 0.060 0.065 0.071 nm A 646.71, 0.03 589.17, 0.03 545.46, 0.04 512.07, 0.06 V L A S C I C I D . , C H I R I A C A . E T A L . 16 300 400 500 600 700 800 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 nm A 543.42489.79 428.41 363.84 Figure 4. UV-Vis spectrum of ClCoTPP in Et OH The main results from UV-Vis Spectroscopy (EtOH) - λ max(log ε), are given below: • H2TPP: 413.62 (4.83), 512.07( 3.22), 545.46 ( 2.93), 589.17 ( 2.69), 646.71 ( 2.66) • CoTPP: 413.09 (3.98), 417.50(3.92), 4.27.90( 3.79), 532.52 (2.17), 644.88(1.65), 778.24 (2.08) • ClCoTPP: 428.41 (3.97), 543.42 (1.99) 300 400 500 600 700 800 0.0 0.5 1.0 1.5 2.0 2.5 3.0 nm A 511.30 460.98 417.93 Figure 5. UV-Vis spectrum of H2TPP in hexane Comparatively with the Soret band from UV-Vis spectrum of meso- tetraphenylporphyrin in hexane (Figure 5), the Soret band from UV-Vis spectrum of Co (II)- MESO-TETRAPHENYLPORPHYRIN COMPLEXES WITH CO(II) AND CO(III) 17 porphyrin (Figure 6) is significant blue shifted. The hypsochromic effect registered is about 8 nm. In the same solvent, the comparison of UV-Vis spectrum of Co (III)- porphyrin with UV-Vis spectrum of Co (II)- porphyrin revealed a significant bathochromic effect of the former, regarding both the Soret band and the Q band. 300 400 500 600 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 nm A 523.00486.11 406.11 343.47 Figure 6. UV-Vis spectrum of CoTPP in hexane 300 400 500 600 700 800 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 nm A 628.07 527.86 495.56 413.55 Figure 7. UV-Vis spectrum of ClCoTPP in hexane V L A S C I C I D . , C H I R I A C A . E T A L . 18 The main results from UV-Vis Spectroscopy (Hexane) - λ max(log ε) are given below: • CoTPP : 406.11(3.94), 523.00(2.17) • ClCoTPP : 413.55(3.86), 527.86 (2.33) The main results from IR-spectra (KBr-pellet)- cm-1, are presented: • H2TPP: 3432(νNH), 3052 –3030 (ν ArH), 1594, 1570, 1470, 1440, (plane skeletal vibrations), 1178, 1000, 974, 798, 712 (γ NH), 698, 622. • CoTPP: 1600, 1442, 1348, 1070, 1004, 796, 750, 700, 464 • ClCoTPP: 3056, 1596, 1440, 1362, 1072, 1002, 800, 752, 704, 432 CONCLUSIONS 1. Tetraphenylporphyrin, H2(TPP), and the corresponding metalloporphyrins, spin free Co II and spin paired Co III complexes, CoII(TPP) and ClCoIII(TPP) were obtained. H2(TPP) was synthesized by the condensation of benzaldehyde and pyrrole, and the subsequent metallation of H2(TPP) was achieved with cobalt acetate in glacial acetic acid or chloroform as solvents. The obtaining of ClCoIII(TPP) was done by treatment of CoTPP with concentrated hydrochloric acid. 2. The compounds are analyzed by their electronic absorption spectra in the visible region, and by their IR spectra. 3. For the same compound, the spectra worked up in ethylic alcohol are red shifted compared to those taken in hexane, probably because in polar solvents the higher stabilization of the π* orbital, relative to that of the π orbital is occurring. 4. Comparatively with the Soret band from UV-Vis spectrum of meso- tetraphenylporphyrin in hexane, the Soret band from UV-Vis spectrum of Co (II)- porphyrin is significant blue shifted. The hypsochromic effect registered is about 8 nm. Regarding the Q band, it is red shifted even in this compound. MESO-TETRAPHENYLPORPHYRIN COMPLEXES WITH CO(II) AND CO(III) 19 5. In the same solvent, the comparison of UV-Vis spectrum of Co (III)- porphyrin with UV-Vis spectrum of Co (II)- porphyrin revealed a significant bathochromic effect of the former, regarding both the Soret band and the Q band. 6. 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