Metalloporphyrin receptors for bases

Abstract

The review summarizes data on the reversible addition of inorganic and organic biologi cally active bases at the coordination sites of mixed complexes containing the porphyrin dianion as one of ligands. An analysis of the thermodynamic parameters revealed new receptors for small cyclic molecules holding promise for analytical purposes and sensorics.Porphyrins (H 2 P) form simple and mixed coordina tion compounds (MP) with metal cations. 1-3 Simple complexes can have the cation : ligand composition 2 : 1, 1 : 1, 1 : 2, or 2 : 3. Complexes of the latter two composi tions have a sandwich structure. 4,5 The coordination spheres of mixed complexes contain, in addition to por phyrin, molecular, acido, or chelating ligands. Although sandwich complexes with a 2 : 3 stoichiometry belong to simple coordination compounds, each metal atom in these complexes is bound to two structurally different macro cyclic ligands (X ray diffraction data 6 ), viz., to the central planar ligand and the terminal dish shaped ligand.Among mixed complexes, complexes with aromatic macrocyclic ligands are distinguished by the nearly planar arrangement of the donor and other atoms of the macro cyclic ligand, a high charge density at the bonds in the coordinated aromatic ligand, and the delocalized elec tronic state of the latter. In other classes of mixed com plexes, cyclic ligands can contain only double and triple bonds or heteroatoms with several lone electron pairs as sterically rigid units, whereas the macrocycle in metallo porphyrins is rigid by itself. In other words, one of the ligands in mixed metalloporphyrins is characterized by the maximum steric rigidity. Upon coordination, the metal cation cannot impose stoichiometric constraints on this ligand corresponding to the optimal polyhedron of the complex. Hence, the overall coordination sphere of mixed porphyrin containing complexes is rather specific. Al though the specificity of the replacement of small (non macrocyclic) acido ligands in mixed porphyrin contain ing complexes of highly charged metal cations is well known, these reactions have received little quantitative study.Metalloporphyrins, in which the maximum possible coordination number of the metal cation is not achieved, can bind bases and form mixed coordination compounds.Until recently, these additional ligands in the coordina tion sphere have been commonly called extra ligands. 3,7 However, it is already evident that additional coordina tion processes is a special case of reactions of MP with bases. Nowadays, the coordination or replacement reac tions of ligands involving porphyrin complexes of highly charged metal cations (z > 3) are of considerable interest for coordination and applied chemistry, because these complexes not only have vacancies in the first coordina tion sphere but are also coordinatively unsaturated and are characterized by a high effective positive charge of the central atom due to high diversity of possible coordina tion polyhedra.In the overwhelming majority of cases, the coordina tion of inorganic and o...

Recent progress in organometallic porphyrin‐based molecular materials for optical sensing, light conversion, and magnetic cooling

“…Axial coordination bonding of heterocyclic molecules by MPs is studied using chemical thermodynamics/kinetics and spectrometry. [54] The porphyrin derivatives of the two charged metal cations were studied on axial complexation a long time ago. [55][56][57][58][59][60][61] The main conclusion from the research data was that the thermodynamic constants of substitution of the solvent molecules by the organic bases in MPs do not linearly correlate with the basicity constants in general case.…”

“…The data above were used in the works [12,91] [54][55][56][57][58][59][60] The influence of the base ). [92] Stability of the complexes with sterically hindered 2-MePy and 2,4,6-Me 3 Py is significantly lower than expected on the basis of pK BH + .…”

“…[ 50–52 ] Numerous researches of solid‐state receptors based on MPs predominantly with two charged metal cations, which were reviewed in the chapter, [ 53 ] have allowed receiving such characteristics as a concentration limit of sensitivity, time of response, and service life, but did not yield the new knowledge about the heterocyclic base–MP interaction characteristics and the MPL stability. Obtaining such characteristics in the solutions, [ 54 ] which are described below on an example MPXL as receptors of biologically active bases as imidazole, benzimidazole, pyridine, hydrogen sulfide, and piperidine, have allowed to define a way of the receptor structure optimization and to conduct the direct search in the practical purposes.…”

New Donor-Acceptor Porphyrin-Fullerene Dyades

“…[36] Были изучены также особые случаи, когда равновесие уста-навливалось достаточно быстро, но затем в системе на- Porphyrin-Fullerene Dyades блюдалась очень медленная необратимая реакция. [37,38] Для изучения таких реакций была разработана специ-альная методика, при которой экспериментально фикси-руется массив данных «оптическая плотность -концен-трация титранта -время». В случае реакции О=Мо(ОН) ТРР с Py 3 F равновесие устанавливается в течение 10 минут, однако затем наблюдается необратимый процесс, настолько медленный, что становится возможным с удо-влетворительной точностью определить константу уста-навливающегося вначале равновесия.…”

“…В ИК спектре продукта реакции обнаружены новые сигналы с частотами колебаний координированного Py 3 F -1426, 1190, 527 (колебания, относящиеся к фуллереновому каркасу С 60 ), [30] 1307(C=N пиридинового кольца), [31] 1122 и 995 (С-N пирролидинового кольца), [32] 481 (Мо-N) [39] , отсутствующие в спектре исходного комплекса. Благодаря наличию опубликованных в литературе [38,[40][41][42][43] данных по изучению реакций O=Mo(OH)TPP с другими аналогичными основаниями и основания Py 3 F с другими металлопорфиринами, можно провести анализ связи закономерностей образования донорно-акцепторных комплексов со структурой взаимодействующих молекул:…”