Structure and coordination properties of sterically strained meso-alkyl-substituted Zn porphyrin

The formation of molecular complexes of zinc 5,15-dipentyl-2,3,7,8,12,13,17,18-octamethylporphin (ZnP) with nitrogen bases (L = 2-methylimidazole (2-Me-Im), imidazole (Im), pyridine (Py), 3,5-dimethylpyrazole (DMP), and dimethylformanmide (DMF)) was studied by spectrophotometric titration and quantum-chemical calculations. The stability constant was found to increase linearly with the basicity of the extra ligand and to be proportional to the shift of the fundamental absorption bands in the UV/Vis spectra. The structure of the compound formed as a result of the intermolecular interaction of the macrocyclic complex with a base was determined. The structures of zinc porphyrin and its extra complexes were optimized by the PM3 quantum chemical technique. The geometric and energetic characteristics of the compounds were obtained. A correlation between the calculated interaction energy of the central metal atom and the nitrogen atom of the extra ligand, on the one hand, and the stability of Zn porphyrin extra complexes, on the other hand, was established. The dependence of the zinc-extra ligand bond strength on the basicity of the additional molecular ligand was established. An effect of steric strain on the coordination properties of the metal porphyrin was noted.     

Effect of steric strains in the macroring on the structure and properties of molecular complexes of (chloro)[5,15-(p-butoxyphenyl)-2,8,12,17-tetramethyl-3,7,13,17-tetrabutylporphinato]aluminum

The chelate (Cl)AlP was prepared by complexation of porphine (P) with aluminum(III) chloride in refluxing pyridine. Equilibrium coordination of nitrogen-containing ligands (L = 2-methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, dimethylformamide) with (Cl)AlP in benzene was studied by spectrophotometric titration and computer simulation. Quantitative and qualitative characteristics of the reaction were obtained. The structure of the mixed-ligand complex formed by intermolecular interaction of the metal porphyrin with a base was determined spectrophotometrically and by quantum-chemical calculations. An effect of additional molecular ligand and of steric strain in the macroring on the stability of the complex was noted. The stability constant (K _s) increases with an increase in the basicity (K _BH ⁺) of the extra ligand and is proportional to the shift of the main bands (?λ) in the electronic absorption spectra. The geometric and energy characteristics of hexacoordinated aluminum porphyrin were calculated by the PM3 method. Correlations were found between the calculated energy of the interaction of the aluminum atom with the base molecule (E _b) and stability of the mixed-ligand complexes (Cl)Al(L)P. The cis and trans effects in the complexes (Cl)Al(L)P were analyzed. The dependence of the strength of the Al-L bond on the nature of the porphyrin and the basicity of the additional molecular ligand was determined from the experimental data and calculation results.     

Regularities of Extra Coordination of Nitrogen-containing Ligands with an Anthracenyl-capped Zinc Porphyrin

3,3'-Dibutyl-4,4'-dimethylpyrrolylmethane was reacted with 9,10-bis(2-formylphenyloxymethyl)anthracene to synthesize a capped porphyrin, and its zinc complex was prepared. The coordination properties of the capped zinc porphyrin in extra coordination with N-methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, and dimethylformamide in o-xylene were studied. A correlation of the stability of the extra complexes and the basicity of the extra ligands was established. A correlation between the stability of the extra complexes and the shifts of their principal electronic absorption bands with respect to those of the zinc porphyrin was found. Deformations of the porphyrin ligand were noted to affect the strengyh of the metalextra ligand bond. The geometric and energetic characteristics of the fivecoordinate zinc porphyrin were obtained by quantum-chemical calculations. A correlation between the calculated energy of interaction of the central metal atom with the nitrogen atom of the extra ligand and the stability of the extra complexes of the capped Zn porphyrin was revealed.     

Coordination Properties of Sterically Stressed Zincporphyrins

Spectrophotometric titration and computer simulation were used to study how the nature of porphyrin and extra ligand affect the formation of extra complexes of zincporphyrins in o-xylene. The compounds under study were zincporphyrins (ZnP) with different substituents and phenyl radicals in meso-positions (zinc-5,15-(p-butyloxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetraethylporphyrin (ZnP¹), zinc-5,15-(p-butyloxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetrabutylporphyrin (ZnP²), zinctetraphenylporphine (ZnP³), and zinc complexes with overlapped porphyrin (ZnP⁴). N-Methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, and dimethylformamide were used as extra ligands (L). The strength of Zn–L bonding was found to decrease in extra complexes (L)ZnP in the series of ZnP as follows: ZnP⁴> ZnP¹> ZnP²> ZnP³. It was established that the stability constant (logK _st) for sterically nonstressed complexes (L)ZnP⁴linearly increases with growth in the extra ligand basicity (log ) and is proportional to the shift of the main absorption bands () in the electronic spectra of extra complexes of zinctetraphenylporphine. For spatially distorted (L)ZnP¹, (L)ZnP², and (L)ZnP³, the values of logK _stand log , as well as logK _stand , change symbatically. The geometric structure and energy characteristics of pentacoordinated zincporphyrins were calculated by quantum-chemical methods. Correlations were established between the calculated values of the energy of the interaction of the central metal atom with the extra ligand molecule and the stability of the extra complexes of zincporphyrins.     

Features of Formation of Mixed-Ligand Complexes of Aluminum Tetraphenylporphine

Formation of extra complexes of aluminum tetraphenylporphine was studied by spectrophotometric titration. The effect of the nature of acido ligands on the stability of mixed-ligand complexes of aluminum tetraphenylporphine was determined. The stability constant (log K _st) of sterically unstrained complexes (Cl)Al(L)TPP and (OH)Al(L)TPP increases linearly with increasing basicity of the extra ligand (log KBH⁺); in the case of sterically distorted complexes (OAc)Al(L)TPP and (Acac)Al(L)TPP changes in log K _st and log KBH⁺ vary in the same direction. The geometries and energy characteristics of six-coordinate complexes of aluminum porphyrins were calculated quantum-chemically. The calculated enthalpies and Gibbs energies of formation of the complexes are consistent with the experiment. The possibility of the bidentate coordination of acetate and acetylacetonate in the porphyrin extra complexes was proved.     

Effect of macrocycle deformation and electronic effects of substituents on the stability of zinc-5,15-di(o-nitrophenyl)octaalkylporphyrin molecular complexes

The process of intermolecular interaction of zinc-5,15-di(o-nitrophenyl)-octaalkylporphyrin with nitrogen-containing bases of various sturctures was studied using the method of absorption spectroscopy. A dependence of stability of axial zinc-porphyrin complex on electronic effects of nitro groups and basic properties of extra ligand is revealed. By quantum-chemical PM3 method geometric structure and energetic characteristics of optimized molecules of zinc-porphyrin and its axial complexes was calculated. The influence of conformational effects of the porphyrin ligands on the strength of σ-bond of zinc with nitrogen atom of the nitrogen base (Zn-N_L) was revealed. It was established that the formation of the Zn-N_L bond proceeded with the change in the type and degree of deformation of the macrocycle in the molecular complex. Correlations between the calculated values of energy of Zn-N_L bond and stability of the axial complexes were found.

     

Thermal oxidative destruction of complexes of heterocyclic N-oxides with Zn(II)tetra-phenylporphyrin

Thermogravimetry, differential thermal analysis and differential scanning calorimetry were applied for investigation of molecular complexes of heterocyclic N-oxide with zinc(II)tetraphenylporphyrin. The kinetic characteristics of the process of the thermal oxidative destruction for individual compounds and their molecular complexes have been calculated. The obtained results indicate that the complex formation of ZnTPhP with heteroaromatic N-oxides leads to an increase of the thermal stability both the metalloporphyrin and the ligands. It has been shown that the stability of the molecular complexes of ZnTPhP with heteroaromatic N-oxides depends on basicity of the coordinated ligand.     

Chromium(III) and Chromium(IV) Tetraphenylporphine Complexes

Stable chromium complex (AcO)CrTPP was synthesized through the reaction of meso-tetraphenylporphine with chromium(III) acetate in boiling phenol. Coordination properties of chromium porphyrin in reaction with imidazole and pyridine in o-xylene were studied by electronic absorption spectroscopy and computer modeling. A single-electron oxidation of chromium(III) complex was found to be affected by peroxide compounds. The stability of an extra complex depends on the basic properties of the extra ligand and oxidation number of the central metal atom. The complex stability correlates with the calculated energy of formation of the metal–extra ligand bond. The geometrical structure and energy parameters of hexacoordinated chromium porphyrins were calculated using the quantum-chemical method. The effect of the cis and trans position of ligands in the composition of a macrocyclic compound was established to be significant only in the extra complexes (AcO)CrTPP.     

Synthesis and coordination properties of the zinc complex of dimeric porphyrin in reactions with imidazole, 2-methylimidazole, and the pyridine in benzene

Dimeric porphyrin(2,6-bis[15′-(3″,5″-di-tert-butylphenol)-3′,7′,13′,17′-tetramethyl-2′,8′,12′,18-tetraethylporphin-5′-yl]-4-tert-buthylphenol) and its binuclear zinc complex were obtained from 4,4′-dimethyl-3,3′-diethyldipyrrolylmethane, 2,6-diformyl-4-tert-butylphenol and 3,5-di-tert-buthylbenzaldehyde. Coordina-tion properties of dimeric zincporphyrin in the intermolecular reaction with nitrogen-containing bases (imidazole, 2-methylimidazole, and pyridine) in benzene were studied. Geometry and electronic structure of the zincporphyrin and its molecular complexes were calculated by a quantum-chemical method. Energy characteristics of the intermolecular reaction of the dimeric zincporphyrin with bases were determined. The calculated energies of the central metal atom interaction with the nitrogen atom of an extra-ligand agree well with the stability of the Zn-porphyrin molecular complexes. The influence of the deformation distortions of the porphyrin ligand on the strength of the metal-extra-ligand σ-bond was established.     

Coordination properties of zinc 5,15-di(<Emphasis Type="Italic">ortho</Emphasis>-aminophenyl)octaalkylporphyrin in reactions with mono- an dibasic nitrogen bases

The coordination properties of zinc 5,15-di(ortho-aminophenyl)octaalkylporphyrin in reactions with mono- and dibasic nitrogen bases in benzene are studied by means of computational modeling and spectrophotometric titration. The stability of molecular zinc porphyrinate complexes in solution is estimated and their structure is determined. The correlation between the coordination properties of the compound under investigation and electronic and conformational factors of the macrocycle is established. The base nature is shown to affect the stability of zinc porphyrinate complexes. The correlations between the calculated σ bond energy of the zinc atom with the nitrogen atom of the base (E _b) and the equilibrium constant of the axial coordination reaction are obtained. It is demonstrated that the reaction is accompanied by an increase in steric hindrance and a change in the type of deformation of the porphyrin ligand.     

Thermal properties and photostability of zinc(II) complexes with alkyl- and aryl-substituted dipyrrins and azadipyrrin

The results of studies and comparative analysis of thermal properties and photostability of zinc(II) complexes with tetramethyl- and tetraphenyl-substituted dipyrrins and tetraphenyl-meso-azadipyrrin are reported. The thermal decomposition of complexes starts in the temperature range between 293 and 481°C depending on the molecular structure. Tetraphenyl-substituted zinc(II) dipyrrinate shows the highest photoand thermal stability. The substitution of phenyl moieties in the ligand structure with methyl groups and replacement of the methine spacer with a nitrogen atom reduces thermal stability and photostability of the complexes.     

Ethylphosphinediacetic acid: synthesis,characterization and coordinating behaviour towards Ca(II), Ni(II) and Hg(II) ions in solution

The new ligand, ethylphosphinediacetic acid, H₂Z, was synthesized and characterized by spectral methods. The Z^2? anion is protonated in three steps with the pK values of 6.10 (phosphorus atom), 2.75 and 0.9 (carboxyl groups). The ligand is highly selective for soft metal ions as demonstrated by the stability constants of the water-soluble complexes CaHZ-(logβ_CaHZ^HZ 0.73), NiZ₂^2? (log β₂ 9.06) and HgZ₄^6? (log β₄ 40.9). The di in behaviour compared to related phosphineacetic acids are mainly consequences of the high basicity of the phosphorus atom.     

Synthesis and investigation of 2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl-5,15-bis(2-thienyl)-21H,23H-porphin and its complexes with manganese (III) acetate and chloride

2,8,12,18-Tetrabutyl-3,7,13,17-tetramethyl-5,15-bis(2-thienyl)-21H,23H-porphin and its complexes with manganese(III) with additional acetate and chloride acido ligands were synthesized. Basing on the UV, IR, and NMR spectra and the kinetic properties of the proton transfer and the dissociation of free and coordinated porphyrin respectively it was established that in the change of porphyrin basicity at thienyl substitution the effect of the sulfur atom vacant d-orbitals involved in the conjugation was predominant. The stability of thienyl-substitued complexes of manganese(III) rises when the axial Cl^? is replaced by acetate ion.     

Theoretical study of complexes of Ti-doped aluminide cluster Al@Al11Ti with ligands L containing multiple bonds

The Al₁₂Ti(π-L) complexes with ligands L = C₂H₂, C₂H₄, HCN, N₂H₂, C₆H₆, and N₂ in the singlet and triplet states have been calculated within the B3LYP approximation of the density functional theory using the 6–31G* basis set. Their calculated structures and properties have been compared with the results of analogous calculations of the titanium porphyrin complexes with the same ligands L. It has been demonstrated that, in both series of compounds, the side-on coordination of the ligands (through the multiple bond, π type) to the titanium atom is accompanied by the weakening and elongation of the C-C, C-N, and N-N bonds by 0.05–0.20Å and the long-wavelength shift of the stretching vibration modes ν_str(CC), ν_str(CN), and ν_str(NN) by a few hundreds of cm^?1. For the Ti aluminide complexes, these activation effects are much more clearly pronounced than for their Ti porphyrin analogues. The aluminide complexes (except the nitrogenyl one) have the singlet ground state; however, the nearest triplet is close lying to the singlet (within 1–14 kcal/mol). The singlet is characterized by the considerable electron density transfer from the Al₁₂Ti cluster to the ligand L, the displacement of the Ti atom from the aluminum cage to the ligand, and the distortion of the Al₁₂ cage. In the triplet states, the ligand activation depends on the character of spin density delocalization between the ligand, the Ti atom, and the Al₁₂ cage. If the spin density is distributed between the Ti atom and the Al₁₂ cage or if both unpaired electrons are localized on the Ti atom, then the structure, stability, and spectroscopic properties of the “active” Ti-L moiety in these triplets differ only slightly from those in the singlet state. If the spin density is distributed between the Ti atom and the ligand, the singlet-triplet excitation is accompanied by the elongation and weakening of the Ti-ligand bond and the decrease in the ligand activation effect. Complexes with several ligands L coordinated to the Ti atom in the Al₁₂Ti cluster have been calculated. There are some trends in the change in the molecular characteristics of the Ti-ligand bonds in different series of the complexes.     

Synthesis,spectroscopic studies,thermal analyses,biological activity of tridentate-coordinated transition-metal complexes [M(L)X2] and crystal structure of [ZnBr2(2,6-bis(tert-butylthiomethyl)pyridine)]

A new terdentate acyclic pincer ligand, 2,6-bis(tert-butylthiomethyl)pyridine (tbtmp), was synthesized and reacted with several complexes of iron, zinc, nickel, cobalt, and copper. The ligand and its coordination compounds were characterized using elemental analysis, infrared, ¹H- and ¹³C-NMR-spectroscopy, thermal analyses, plus—for the Zn complex—single-crystal X-ray diffractometry. The structure of [Zn(L)Br₂] was solved in the tetragonal crystal system, chiral space groups P4₁2₁2 and P4₃2₁2 (No. 92 and No. 96, a = 947.2(1) pm, c = 2265.2(5) pm), revealing five-fold coordination of the metal atoms. According to spectroscopy, all complexes share the same coordination environment around the metal atoms, consisting of two halide anions and a sulfur-methylene-pyridine-methylene-sulfur entity; tbtmp acts as a tridentate ligand with the pyridine N atom and both tert-butylthio S atoms coordinating to the metal ions (NS2). The analysis results indicate that the metal ions are coordinated as distorted pseudo-bipyramids, LMX₂, with the chelate ligand meridionally arranged. One of the complexes contains ethanol as an additional ligand, resulting in a pseudo-octahedral coordination sphere [Ni(L)Cl₂EtOH]. The latter was obtained in the form of green crystals, which turn into a red powder with loss of the ethanol molecule. Fe (III), Co(II), Ni(II) and Cu(II) metal complexes [M(L)Cl₂] were screened for their antibacterial activity against B. subtilis G(+) and Escherichia coli G(−) bacteria, and fungus (Candida albicans and Aspergillus flavus).     

Synthesis and Thermodynamic Investigation of 4-Amino-6-Hydroxy-2-Mercapto Pyrimidine (AHMP) Complexes with Some Selected Divalent Metal(II) Ions

The synthesis and characterization of zinc(II), cadmium(II), lead(II), mercury(II) and phenylmercury(II) complexes of 4-amino-6-hydroxy-2-mercapto pyrimidine (AHMP) are reported. The stoichiometry of the complexes was found to be 1:2 except for the phenylmercury(II) complex where the ratio is 1:1. Characterization of these complexes was carried out by means of elemental analyses, IR and ¹H NMR measurements. In these complexes the ligand is bonded to the metal through its sulfur atom. The potentiometric results showed the formation of 1:1 and 1:2 complexes and the corresponding stability constants were determined for both Zn(II) and Cd(II) ions. The high insolubility of mercury(II), phenylmercury(II) and lead(II) complexes prevented the determination of their stability constants. The concentration distribution of the complexes in solution was evaluated. The effect of temperature on the dissociation constant of AHMP and the formation constants of both the Zn-AHMP and Cd-AHMP complexes were studied and the thermodynamic parameters were calculated.     

Construction and photophysics study of supramolecular complexes composed of three-point binding fullerene-trispyridylporphyrin dyads and zinc porphyrin

A series of novel supramolecular complexes composed of a three-point binding C(60)-trispyridylporphyrin dyad (1) or C(70)-trispyridylporphyrin dyad (2) and zinc tetraphenylporphyrin (ZnP) were constructed by adopting a "covalent-coordinate" bonding approach, composed of three-point binding. The dyads and self-assembled supramolecular triads or pentads formed by coordinating the pyridine groups located on the dyads to ZnP, have been characterized by means of spectral and electrochemical techniques. The formation constants of ZnP-1 and ZnP-2 complexes were calculated as 1.4 × 10(4) M(-1) and 2.0 × 10(4) M(-1), respectively, and the Stern-Volmer quenching constants K(SV) were founded to be 2.9 × 10(4) M(-1) and 5.5 × 10(4) M(-1), respectively, which are much higher than those of other supramolecular complexes such as previously reported ZnP-3 (N-ethyl-2-(4-pyridyl)-3,4-fulleropyrrolidine). The electrochemical investigations of these complexes suggest weak interactions between the constituents in the ground state. The excited states of the complexes were further monitored by time-resolved fluorescence measurements. The results revealed that the presence of the multiple binding point dyads (1 or 2) slightly accelerated the fluorescence decay of ZnP in o-DCB relative to that of the "single-point" bound supramolecular complex ZnP-3. In comparison with 1 and 2, C(70) is suggested as a better electron acceptor relative to C(60). DFT calculations on a model of supramolecular complex ZnP-1 (with one ZnP entity) were performed. The results revealed that the lowest unoccupied molecular orbital (LUMO) is mainly located on the fullerene cage, while the highest occupied molecular orbital (HOMO) is mainly located on the ZnP macrocycle ring, predicting the formation of radical ion pair ZnP(+)˙-H(2)P-C(60)(-)˙ during photo-induced reaction.     

Crystal solvates of carboxy-substituted Zn(II) phthalocyaninates with pyridine

Physicochemical characteristics (composition, energetic and chemical stability) of the molecular complexes of carboxy-substituted Zn(II) phthalocyaninates with pyridine were determined. It was found that the carboxyl substituents in positions 4 and 5 of the complex Zn(4,5-COOH)₈Pc favor the formation of the most stable molecular complexes with pyridine. The carboxyl substituents in the composition of Zn(3-COOH)₄Pc are not solvated with pyridine due to steric hindrances and the formation of the hydrogen bond between the carboxyl H atom and the meso-nitrogen atom; the molecular complexes of a tetrasubstituted Zn(4-COOH)₄Pc with pyridine are unstable.     

Coordination compounds of CuCl<Subscript>2</Subscript> with 1-(<Emphasis Type="Italic">N</Emphasis>-heterylmethyl)silatranes

Reactions of CuCl₂ with 1-(N-indolylmethyl)and 1-(N-carbazolylmethyl)silatranes (L) afforded new complexes CuCl2?L. Quantum chemical calculations of these complexes and a Cu^II complex with 1-(N-pyrrolylmethyl)silatrane showed that the Cu atom is coordinated to both the equatorial O atom of the silatranyl group and the π-system of the ligand? heterocycle.     

Synthesis of 5-acetyl-4,6-dimethyl-1,2,3,4-tetrahydropyrimidine-2-thione and structural characterization of its polymorphs and complexes with 12-group metal iodides

A novel cyclic thiourea, 5-acetyl-4,6-dimethyl-1,2,3,4-tetrahydropyrimidine-2-thione (L), was synthesized by the reaction of N-(1-tosylethyl)thiourea with potassium enolate of acetylacetone followed by acid-catalyzed dehydration of the obtained 5-acetyl-4-hydroxy-4,6-dimethylhexahydropyrimidine-2-thione. Its polymorphs and complexes with zinc, cadmium, and mercury iodides were studied by X-ray diffraction. Two polymorphs of 5-acetyl-4,6-dimethyl-1,2,3,4-tetrahydropyrimidine-2-thione differ in ring conformation and packing manner. In the monomeric cadmium complex [CdL₂I₂], the central atom is tetrahedrally coordinated in the standard manner by iodine and thiocarbonyl S atoms, while in the dimeric mercury complex [Hg₂L₂I₄], every mercury atom is coordinated by two bridging I atoms, one terminal I atom and one thiocarbonyl S atom of the ligand. In the polymeric zinc complex [ZnLI₂], the zinc tetrahedra are linked by the bidentate bridging 5-acetyl-4,6-dimethyl-1,2,3,4-tetrahydropyrimidine-2-thione molecules through thiocarbonyl S atom and acetyl O atom.