X-Ray structures, Mössbauer hyperfine parameters, and molecular orbital descriptions of the phthalocyaninato iron(II) azole complexes

Abstract

The electronic structures of a set of PcFe(azole)2 complexes (azole = imidazole, [Formula: see text]-methylimidazole, pyrazole, isoxazole, thiazole, 1,2,4-triazole, 3-amino-1,2,4,-triazole, and 5-amino-1,2,3,4-tetrazole) were examined by Mössbauer spectroscopy and Density Functional Theory (DFT) calculations. In addition, the geometric distortions in these compounds were elucidated by X-ray crystallography for imidazole, pyrazole, and thiazole-containing compounds. Predicted by DFT calculations, Mössbauer hyperfine parameters for all compounds are in reasonable agreement with experimental results, and the influence of the [Formula: see text]-donor and [Formula: see text]-acceptor properties of the axial azoles on the electronic structure of the PcFe(azole)2 complexes is demonstrated by comparison with the reference PcFePy2 compound.

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

“…These can be rationalized by the linkage isomerism expected for this compound. Indeed, our DFT calculations discussed below are indicative of only small energy differences between the 1Tz – and 4Tz – linking isomers (Chart ), which can coexist in solution and are responsible for the rather broad quadrupole splitting observed in the Mössbauer spectrum of the PcFe II (Tz) 2 complex . In our case, we speculate that the three overlapping oxidation waves belong to [PcFe II (1Tz – ) 2 ] 2– , [PcFe II (4Tz – ) 2 ] 2– , and [PcFe II (1Tz – )­(4Tz – )] 2– linkage isomers (Chart ).…”

“…Indeed, our DFT calculations discussed below are indicative of only small energy differences between the 1Tz − and 4Tz − linking isomers (Chart 1), which can coexist in solution and are responsible for the rather broad quadrupole splitting observed in the Mossbauer spectrum of the PcFe II (Tz) 2 complex. 44 In our [PcFe II (4Tz − ) 2 ] 2− is ∼0.140 eV for all three tested exchangecorrelation functionals (Table 3). This correlates well with ∼210 mV difference observed between the first and third oxidation waves in the [PcFe II (Tz − ) 2 ] 2− complex (Table 2).…”

“…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...…”

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

“…37−41 The most diverse group of iron phthalocyanine derivatives are bis-axially coordinated iron(II) compounds, which have the general formulas PcFeL 2 , PcFeL′L″, or [PcFeX 2 ] 2− (where L, L′, and L″ are neutral ligands and X − are anionic ligands). 42−44 Axial ligands such as nitrogen bases (ammonia, 45 organic amines, 10,42−44,46−48 azoles, 49,50 pyridines, 51−53 and other heterocyclic nitrogen donors 54−60 ), isonitriles, 61−67 carbon monoxide, 68−70 sulfides and sulfoxides, 69−71 cyanide, 44,52,53,72,73 phosphines and phosphites, 74−77 and oxygen donors 68−70 57 Fe Mossbauer spectroscopic characterization of PcFeL 2 complexes was first reported in the late 1960s, 42,43,78,79 and several attempts to rationalize the hyperfine parameters in these compounds have been undertaken since that time. 46,70 These include empirical observations, 42,70 the combination of semiempirical calculations of ligand properties including steric effects, 46 as well as direct semiempirical calculations, 47,80 ab initio, 47 and Density Functional Theory (DFT) 47,81 calculations on iron phthalocyanine complexes.…”

“…46,70 These include empirical observations, 42,70 the combination of semiempirical calculations of ligand properties including steric effects, 46 as well as direct semiempirical calculations, 47,80 ab initio, 47 and Density Functional Theory (DFT) 47,81 calculations on iron phthalocyanine complexes. We recently reported 57 Fe Mossbauer spectra of PcFe(azole) 2 complexes 49 and found that when using the theoretical approach for the prediction of 57 Fe Mossbauer hyperfine parameters developed in our lab in 2006, 81 the general trends in quadrupole splitting for these complexes can be reproduced well; however, the DFT-predicted absolute values for quadrupole splitting deviate from the experimental values quite significantly (∼0.2−0.25 mm/s). Moreover, this methodology failed to accurately predict the quadrupole splitting for PcFe(CNR) 2 , [PcFe-(CN) 2 ] 2− , and phosphorus donor atom-containing PcFeL 2 complexes.…”