Molecular Structure of the trans and cis Isomers of Metal-Free Phthalocyanine Studied by Gas-Phase Electron Diffraction and High-Level Quantum Chemical Calculations: NH Tautomerization and Calculated Vibrational Frequencies

Peculiarities of electronic structure and chemical bonding in iron and cobalt metal complexes of porphyrazine and tetra(1,2,5-thiadiazole)porphyrazine

The geometrical and electronic structures of iron and cobalt metal complexes of porphyrazine and tetra(1,2,5-thiadiazole)porphyrazine in ground and low-lying excited electronic states were determined by DFT calculations and the complete active space (CASSCF) method with following accounting dynamic correlation by multiconfigurational quasidegenerate second-order perturbation theory (MCQDPT2). A geometrical structure of D[Formula: see text] symmetry has been obtained for all four complexes. According to data obtained by the MCQDPT2 method, the complexes of cobalt and iron possess the ground states 2A[Formula: see text] and 3A[Formula: see text], respectively, and wave functions of the ground states have the form of a single determinant. It is shown that the crystal field theory (CFT) can be used to describe the sequence of electronic states of the investigated complexes. The nature of the bonds between metal atoms and nitrogen atoms has been described using the analysis of the electron density distribution in the frame of Bader’s quantum theory of atoms in molecule (QTAIM).

Profiling energetics and spectroscopic signatures in prototropic tautomers of asymmetric phthalocyanine analogues

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) were used to explain discrepancies in UV-vis and MCD spectra of the metal-free tribenzo[b,g,l]thiopheno[3,4-q]porphyrazine (1), substituted tribenzo[b,g,l]porphyrazine (2), and 2,3-bis(methylcarboxyl)phthalocyanine (3). On the basis of gas-phase and polarized continuum solvation model (PCM) DFT and TDDFT calculations, it was suggested that both NH tautomers contribute to the spectroscopic signature of 1, whereas the Q-band region of 2 and 3 is dominated by a single NH tautomer. For all tested compounds, it was found that the combination of the BP86 exchange-correlation functional, 6-31G(d) basis set, and TDDFT-PCM approach provides the best accuracy in energies of the Q(x)- and Q(y)-bands of the individual NH tautomers as well as correctly describes their relative energy differences, which are important in understanding of experimental spectroscopy of the target systems.

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

The axial positions of planar metallomacrocycles are unoccupied. The positively charged metal is thus a potential binding site for electron-donating groups. The binding strength is affected by the central metal, the ligand, and the macrocycle. One ligand leads to the out-of-plane displacement of the central metal, whereas two ligands from two sides structurally neutralize each other. The axial ligand donates charge to the central metal and the macrocycle when the lone pair orients along the interaction axis. The frontier orbital levels are elevated because of the charge donated to the macrocycle. Even though the singlet-triplet gap and the absorption maximum do not change significantly upon binding, the redox chemistry is considerably affected by the shifts of orbital levels. The macrocyclic M-N bonds are weakened by the binding, but their natures remain almost unchanged. Calcium phthalocyanine is a special case, as the central calcium is too large to fit the cavity. Accordingly, multiple ligands facilely bind to the calcium from one side. The aluminum phthalocyanine halogen is another special case, as it has a halogen ligand coordinating to the aluminum through a nondative bond. This leads to some effects different from those caused by dative binding. When there is no considerable steric demand, the lone pair points along the interaction axis to facilitate the donation. When in a stacked dimer, the electron-rich group is part of a large molecule, and the orientation of the lone pair is approximately perpendicular to the interaction axis. This induces the charge loss of the central metal. Because metallomacrocycles are widespread in the biological, medical, and material sciences, the results from this study are expected to bring useful insights to these fields.

Molecular structures of chloro(phthalocyaninato)-aluminum(III) and -gallium(III) as determined by gas electron diffraction and quantum chemical calculations: quantum chemical calculations on fluoro(phthalocyaninato)-aluminum(III) and -gallium(III), chloro(tetrakis(1,2,5-thiadiazole)porphyrazinato)-aluminum(III) and -gallium(III) and comparison with their X-ray structures

The molecular structures of chloro(phthalocyaninato)aluminum(III) (ClPcAl) and chloro(phthalocyaninato)gallium(III) (ClPcGa) have been determined by using the gas electron diffraction (GED) method and augmented by quantum chemical calculations. The molecular structures of fluoro(phthalocyaninato)aluminum(III) (FPcAl), fluoro(phthalocyaninato) gallium(III) (FPcGa), chloro(tetrakis(1,2,5-thiadiazole)porphyrazinato)aluminum(III) (ClTTDPzAl), and chloro(tetrakis(1,2,5-thiadiazole)porphyrazinato)gallium(III) (ClTTDPzGa) have been optimized at the level B3LYP with basis sets 6-31G*, 6-311++G**, and cc-pVTZ, and the structures have been compared with those obtained by X-ray diffraction. Vibrational frequencies have been calculated for all six molecules at all basis sets combinations, except B3LYP/cc-pVTZ. These calculations predict that all molecules have C 4 v symmetry with the metal atom above the plane defined by the four inner cavity N atoms and an almost planar macrocycle. The most important structure parameters (GED|B3LYP/cc-pVTZ) are h (height of the metal atom above the inner cavity) h = 50.3(32)|44.9 pm, r(Al-Cl) = 214.5(16)|217.4 pm, r(Al-N) = 197.6(9)|198.7 pm, angle(Cl-Al-N) = 104.8(9)|103.1 degrees, angle(Al-N-C) = 124.2(7)|125.9 degrees for ClPcAl, and the corresponding values for ClPcGa are h = 53.1(28)|50.2 pm, r(Ga-Cl) = 218.9(14)|222.3 pm, r(Ga-N) = 200.6(8)|202.6 pm, angle(Cl-Ga-N) = 105.4(8)|104.3 degrees, angle(Ga-N-C) = 123.8(8)|125.0 degrees. Parenthesized values are estimated error limits defined as 2.5(sigma(2)(lsq) + (0.001 x r)(2))(1/2) for distances and 2.5sigma(lsq) for angles. The title compounds are all flexible molecules with about five vibrational frequencies below 100 cm(-1).