On Ligand Binding Energies in Porphyrinic Systems

Abstract

Porphyrins / Phthalocyanins / Energy Decomposition Analysis / Bond Properties / Solvent-Metal Complexation / Metal CoordinationEnergy decomposition analysis is a powerful tool to study the bond properties of molecules. Here, we used a recent implementation by P. Su and H. Li (J. Chem. Phys. 131 (2009) 014102) to test the method for investigations of ligand binding to medium sized molecules (30-40 atoms). We studied the properties of the bond between porphyrins or phthalocyanines with central metals without (Mg) or with a closed d shell (Zn and Cd) to ligands binding via various row II and III atoms (nitrogen, oxygen, phosphorus and sulphur) using various methods and basis sets. Several interesting results could be deduced: In the porphyrins, ligands binding via a nitrogen atom were preferred to those binding via oxygen and sixfold coordination was readily available for magnesium as central metal atom as opposed to zinc and cadmium derivatives which also showed a weaker bond strength. In phthalocyanines, a tendency to form fivefold coordination was also seen for magnesium compounds and bonds to nitrogen and oxygen had the same strength. Ligation to row III elements created only weak bonds that were prone to fluctuations.

Ultrafast Dynamics of meso‐Tetraphenylmetalloporphyrins: The Role of Dark States

“…The CdTPP spectra in anhydrous toluene and THF showed only a very small bathochromic shift of the two Q bands from λ =568 to 573 nm and from λ =609 to 615 nm, respectively, which we assigned to a solvatochromic effect (see Figure S5). For MgTPP, especially in THF, five‐coordinated species should be prevalent, in addition to the six‐coordinated one 13. A four‐coordinated Mg species within porphyrins and (bacterio)chlorophylls has never been encountered experimentally in crystal structures owing to them being unstable and coordinatively unsaturated.…”

“…Its symmetry is supposed to be close to D 4 h . However, in the minimum energy geometry, the four peripheral phenyl rings are known to be twisted by 65–70° with respect to the porphyrin skeleton;10–13 this lowers the symmetry to C 2 v . In coordinating solvents, magnesium atoms in chlorophylls or porphyrins become five‐ or even sixfold coordinated, which reduces the symmetry further.…”

Effects of Center Metals in Porphines on Nanomechanical Gas Sensing

“…Importantly, iron porphine maintained its sensitivity for most of the measured gases, owing to its two strong axial coordination sites. These different behaviors between zinc and iron porphines can be supported by two separate studies by Schalk [ 35 ] and Kang [ 42 ]. They calculated the binding energies of water molecules to zinc and iron porphyrinic systems and showed that zinc porphine has a higher affinity to water molecules than that of iron porphine.…”

“…However, it can be seen from Figure 4 that the intensity ratio slightly deviated from 1.0, reflecting the altered porphine-gas interaction by zinc insertion. Zinc porphine generally had a strong pentadentate coordination mode, which allowed one axial ligand to be complexed to the central zinc atom [ 35 ]. When two ligands were coordinated to the zinc center, zinc porphine showed a six-coordinated structure with two axial ligands, in which the binding energy of a second complexation was much lower than that of the first [ 36 ].…”

On the origin of high transient anisotropies: An exemplification in a Cd-porphyrin

“…An anisotropy of 0.1 for SE represents the dephased case, which is reasonable to assume since we do not observe any fast components which might be due to the distorted shape of CdTPP as compared with the highly symmetric MgTPP. 33 Now consider ESA as being wavelength independent and having a fixed value of r ESA . Moreover, define …”