Effects induced by axial ligands binding to tetrapyrrole-based aromatic metallomacrocycles

Spin Crossover in Nickel(II) Tetraphenylporphyrinate via Forced Axial Coordination at the Air/Water Interface

Coordination-induced spin crossover (CISCO) in nickel(II) porphyrinates is an intriguing phenomenon that is interesting from both fundamental and practical standpoints. However, in most cases, realization of this effect requires extensive synthetic protocols or extreme concentrations of extra-ligands. Herein we show that CISCO effect can be prompted for the commonly available nickel(II) tetraphenylporphyrinate, NiTPP, upon deposition of this complex at the air/water interface together with a ruthenium(II) phthalocyaninate, CRPcRu(pyz)₂, bearing two axial pyrazine ligands. The latter was used as a molecular guiderail to align Ni···Ru···Ni metal centers for pyrazine coordination upon lateral compression of the system, which helps bring the two macrocycles closer together and forces the formation of Ni–pyz bonds. The fact of Ni(II) porphyrinate switching from low- to high-spin state upon acquiring additional ligands can be conveniently observed in situ via reflection-absorption UV-vis spectroscopy. The reversible nature of this interaction allows for dissociation of Ni–pyz bonds, and thus, change of nickel cation spin state, upon expansion of the monolayer.

Water-Involved Hydrogen Bonds in Dimeric Supramolecular Structures of Magnesium and Zinc Phthalocyaninato Complexes

Two dimeric supramolecular structures {MgPc(H2O)·4-methylmorpholine}2-(1) and {ZnPc(H2O)·4-methylmorpholine}2-(2) formed from two molecules of magnesium and zinc aquaphthalocyanines in 4-methylmorpholine solution were revealed by single-crystal X-ray diffraction. Coordinated H2O molecules to the metal center of respective Mg or Zn phthalocyanines oriented face-to-face to form two hydrogen bonds, one of them connecting via O-H···N-azamethine atom to form a dimeric structure in the crystals with ring-to-ring distances of 3.412(3) Å in 1 and 3.403(5) Å in 2, whereas the second hydrogen bonds link the solvent 4-methylpholine molecules to form supramolecular dimeric {MgPc(H2O)·4-methylmorpholine}2-(1) and {ZnPc(H2O)·4-methylmorpholine}2-(2) structures. The interaction of the metal center of MgPc or ZnPc with O atom of the water molecule results its displacement of ∼0.5 Å from the N4-isonodole plane of the phthalocyaninate(2-) macrocycle that adopts a saucer-shape form. To better understand the interactions leading to the existence of the dimeric structures in the crystals, theoretical calculations of dimer stabilization energy composed of two monomers (MgPcH2O and ZnPcH2O), as well as three-dimensional molecular electrostatic potentials, have been performed using the density functional theoretical method. The calculated absorption spectra of both supramolecular monomers and dimers were compared with the experimental ones in 4-methylmorpholine solution. The water axial ligation of MgPc and ZnPc and the formation of the monomeric and dimeric supramolecular structures only slightly change the energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital levels that is compared with those of the parent MgPc and ZnPc pigments.

Beryllium subphthalocyanines self-assembling properties

Beryllium subphthalocyanines have been recently shown to be suitable candidates for photochemical devices if combined with appropriate donor systems. The ability of beryllium subphthalocyanines to self-assemble is explored for the first time by means of density functional theory calculations. Free dimers of beryllium subphtalocyanine and their corresponding complexes with water and pyridine are computed at the wB97X-D/6-311+G(d,p) level of theory. In contrast with the behavior reported for beryllium phthalocyanines, for beryllium subphtalocyanines, beryllium–aza–nitrogen intermolecular interactions are observed, suggesting that these species are likely to self-assemble. Aggregates of related structures such as beryllium subporphyrazines with axial groups confirm the importance of hydrogen bonds in the stacking.

Theoretical calculations of π-type pnicogen bonds in the triad intermolecular complexes

The pnicogen bonding interactions of PCl3and π-electron systems (acetylene, ethylene, benzene) were calculated by using MP2/aug-cc-pVDZ method and the effect of hydrogen bond on pnicogen bond systems were investigated. It has been indicated that the hydrogen bonding and the pnicogen bonding interactions have influence on each other and the positively cooperative effect has been detected. The interaction energies of pnicogen bonded supramolecular system were also calculated by using DFT method (M06-2X) and some simple comparisons with those by using MP2 method were made. It has been disclosed from natural bond orbitals (NBO) analysis that more the amount of charge transfer of pnicogen bonding interaction, the greater the stability of the corresponding complex. Through AIM topological analysis, it has been revealed that the electron density of pnicogen bond BCP point is positively correlated with the stability of trimeric complex. Electron localization function (ELF) was also adopted to analyze the nature of pnicogen bonding interactions. Furthermore, density difference function (DDF) method was adopted to analyze the variation of electron density of pnicogen bond system because of hydrogen bond.

Ultrafast charge separation and charge stabilization in axially linked ‘tetrathiafulvalene–aluminum(iii) porphyrin–gold(iii) porphyrin’ reaction center mimics

Sequential electron transfer leading to charge stabilization in newly synthesized vertically aligned ‘tetrathiafulvalene–aluminum(iii) porphyrin–gold(iii) porphyrin’ supramolecular triads is reported.