Accurate Prediction of Mössbauer Hyperfine Parameters in Bis-Axially Coordinated Iron(II) Phthalocyanines Using Density Functional Theory Calculations: A Story of a Single Orbital Revealed by Natural Bond Orbital Analysis

Abstract

Density Functional Theory (DFT) calculations coupled with several exchange-correlation functionals were used for the prediction of Mossbauer hyperfine parameters of 36 bisaxially coordinated iron(II) phthalocyanine complexes with the general formulas PcFeL 2 , PcFeL′L″, and [PcFeX 2 ] 2− , including four new compounds. Both gas-phase and PCM calculations using BPW91 and MN12L exchange-correlation functionals were found to accurately predict both Mossbauer quadrupole splittings and the correct trends in experimentally observed isomer shifts. In comparison, hybrid exchange-correlation functionals underestimated quadrupole splittings, while still accurately predicted isomer shifts. Out of ∼40 exchange-correlation functionals tested, only MN12L was found to correctly reproduce quadrupole splitting trends in the PcFeL 2 complexes coordinated with phosphorus-donor axial ligands (i.e., P(OnBu) 3 ≈ P(OEt) 3 < PMe 3 < P[(CH 2 O) 2 CH 2 ]-p-C 6 H 4 NO 2 < PEt 3 ≈ PnBu 3 ). Natural Bond Orbital (NBO) analysis was successfully used to explain the general trends in the observed quadrupole splitting for all compounds of interest. In particular, the general trends in the quadrupole splitting correlate well with the axial ligand dependent, NBO-predicted population of the 3d z2 orbital of the Fe ion and are reflective of the hypothesis proposed by Ohya and co-workers (Inorg. Chem., 1984, 23, 1303 on the adaptability of the phthalocyanine's π-system toward Fe-L ax interactions. The first X-ray crystal structure of a PcFeL 2 complex with axial phosphine ligands is also reported.

Application of Lever’s EL Parameter Scale toward Fe(II)/Fe(III) versus Pc(2-)/Pc(1-) Oxidation Process Crossover Point in Axially Coordinated Iron(II) Phthalocyanine Complexes

“…Indeed, as we recently demonstrated using NMR spectroscopy, the PcFe II (PR 3 ) 2 complexes are stable in solution for prolonged times. 63 In addition, unlike [PcFe II X 2 ] 2− systems (X = NCO − and NCS − ), the PcFe II (PR 3 ) 2 complexes are not sensitive toward the nature of the supporting electrolyte, which is also indicative of the relatively low mobility of the axial ligands in these systems. The ion pairing of electrolyte anions to the cationic [PcFe III (PR 3 ) 2 ] + complexes, which might cause a small splitting of the Q-band, is also unlikely as such Q-bands were observed in DCM/0.3 M TBAP and DCM/0.15 M TFAB systems.…”

“…All phthalocyanine complexes were prepared as described previously. ,,,, A tetrabutylammonium tetrakis­(pentafluorophenylborate) (TFAB) electrolyte was prepared following the reported protocol . Dimethyl sulfoxide (DMSO, anhydrous, ≥99.9%), DriSolv anhydrous dichloromethane (DCM, ≥99.8%), pyridine (Py, anhydrous, 99.8%), potassium cyanate (KNCO, 96%), and tetrabutylammonium perchlorate (TBAP, for electrochemical analysis, ≥99.0%; caution: perchlorate salts are potentially explosive and should be handled with care) were all purchased from Sigma-Aldrich and used as received.…”

“…Vibrational frequencies were calculated to ensure that all geometries were local minima. Since the nature of the frontier molecular orbitals in the currently investigated complexes was expected to have some dependency on the utilized exchange-correlation functional, ,,, single-point calculations were conducted using TPSSh, , O3LYP, and MPWLYP exchange-correlation functionals. All computations were solution-phase calculations conducted using the PCM model with DCM as the solvent to make an accurate comparison between all complexes.…”

“…In light of Lever’s work and the considerable academic and industrial interest surrounding iron phthalocyanine (PcFe II ) derivatives, − this work focuses on expanding the already rich chemistry of these complexes. Indeed, iron phthalocyanine complexes have been studied as catalysts for C–H bond activation, − electrocatalysts for the oxygen reduction reaction, − active components for catalytic cancer therapy, , platforms for optical detection of small molecules, − and composite materials for electrochemical detection of biologically relevant species. − The axial coordination of nitrogen bases, − phosphines and phosphites, − nitroso compounds, sulfoxides and sulfides, − carbon monoxide, − and isonitriles − to iron­(II) phthalocyanine was studied by UV–visible, NMR, and Mössbauer spectroscopies as well as by crystallography. Based on early electrochemical, spectroelectrochemical, chemical, , and photochemical oxidation data, it was always assumed that the highest occupied m...…”

Understanding the Electronic Interactions, Vertical Excitation Analysis, and the Photovoltaic Properties of 5-(2-ethylhexyl)-1,3-di(furan-2-yl)-4H-thieno[3,4-c]pyrrole-4,6-dione

“…NBO studies afford us with the nature of donor and virtual acceptor orbitals, the interaction between them and their occupancies. These interactions through the delocalization of mobile electrons from occupied Lewis orbitals to vacant (virtual) non-Lewis molecular orbitals to improve the presence of electrons, hence the occupancies [22,[73][74]. The magnitude of the interactions between molecular orbitals contributes fractionally to the overall stability of the molecule.…”