ABSTRACT
The position of the experimentally observed (in the UV-vis and magnetic circular dichroism (MCD) spectra) low-energy metal-to-ligand charge-transfer (MLCT) band in low-spin iron(II) phthalocyanine complexes of general formula PcFeL2, PcFeL'Lâ³, and [PcFeX2]2- (L, L', or Lâ³ are neutral and X- is an anionic axial ligand) was correlated with the Lever's electrochemical EL scale values for the axial ligands. The time-dependent density functional theory (TDDFT)-predicted UV-vis spectra are in very good agreement with the experimental data for all complexes. In the majority of compounds, TDDFT predicts that the first degenerate MLCT band that correlates with the MCD A-term observed between 360 and 480 nm is dominated by an eg (Fe, dπ) â b1u (Pc, π*) single-electron excitation (in traditional D4h point group notation) and agrees well with the previous assignment discussed by Stillman and co-workers[ Inorg. Chem. 1994, 33, 573-583]. The TDDFT calculations also suggest a small energy gap for b1u/b2u (Pc, π*) orbital splitting and closeness of the MLCT1 eg (Fe, dπ) â b1u (Pc, π*) and MLCT2 eg (Fe, dπ) â b2u (Pc, π*) transitions. In the case of the PcFeL2 complexes with phosphines as the axial ligands, additional degenerate charge-transfer transitions were observed between 450 and 500 nm. These transitions are dominated by a2u (Pc + L, π) â eg (Pc, π*) single-electron excitations and are unique for the PcFe(PR3)2 complexes. The energy of the phthalocyanine-based a2u orbital has large axial ligand dependency and is the reason for a large energy deviation for B1 a2u (Pc + L, π) â eg (Pc, π*) transition. The energies of the axial ligand-to-iron, axial ligand-to-phthalocyanine, iron-to-axial ligand, and phthalocyanine-to-axial ligand charge-transfer transitions were discussed on the basis of TDDFT calculations.
ABSTRACT
The electronic structures and, particularly, the nature of the HOMO in a series of PcFeL2, PcFeL'Lâ³, and [PcFeX2]2- complexes (Pc = phthalocyaninato(2-) ligand; L = NH3, n-BuNH2, imidazole (Im), pyridine (Py), PMe3, PBu3, t-BuNC, P(OBu)3, and DMSO; L' = CO; Lâ³ = NH3 or n-BuNH2; X = NCO-, NCS-, CN-, imidazolate (Im-), or 1,2,4-triazolate(Tz-)) were probed by electrochemical, spectroelectrochemical, and chemical oxidation as well as theoretical (density functional theory, DFT) studies. In general, energies of the metal-centered occupied orbitals in various six-coordinate iron phthalocyanine complexes correlate well with Lever Electrochemical Parameter EL and intercross the phthalocyanine-centered a1u orbital in several compounds with moderate-to-strong π-accepting axial ligands. In these cases, an oxidation of the phthalocyanine macrocycle (Pc(2-)/Pc(1-)) rather than the central metal ion (Fe(II)/Fe(III)) was theoretically predicted and experimentally confirmed.
ABSTRACT
Density Functional Theory (DFT) calculations coupled with several exchange-correlation functionals were used for the prediction of Mössbauer hyperfine parameters of 36 bis-axially coordinated iron(II) phthalocyanine complexes with the general formulas PcFeL2, PcFeL'Lâ³, and [PcFeX2]2-, including four new compounds. Both gas-phase and PCM calculations using BPW91 and MN12L exchange-correlation functionals were found to accurately predict both Mössbauer 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 â¼40 exchange-correlation functionals tested, only MN12L was found to correctly reproduce quadrupole splitting trends in the PcFeL2 complexes coordinated with phosphorus-donor axial ligands (i.e., P(OnBu)3 ≈ P(OEt)3 < PMe3 < P[(CH2O)2CH2]-p-C6H4NO2 < PEt3 ≈ PnBu3). 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 3dz2 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-Lax interactions. The first X-ray crystal structure of a PcFeL2 complex with axial phosphine ligands is also reported.
ABSTRACT
Adsorption of actinide (Ac = U, Np, Pu) complexes with environmentally relevant ligands on silicene and germanene surfaces has been investigated using density functional theory to determine the geometrical, energetic, and electronic properties. Three types of ligands for each central metal atom are considered: OH-, NO3-, and CO32- with common oxo ligands in all cases. Among these, carbonate complexes show the strongest adsorption followed by hydroxide and nitrate. Two types of model, cluster and periodic models, have been considered to include the short- and long-range effects. The cluster and periodic models are complementary, although the former has not yet been widely used for studies of 2D materials. Two cluster sizes have been investigated to check size dependency. Calculations were performed in the gas phase and water solvent. On the basis of the adsorption energy, for the CO32- and OH- ligands, the bond position between two Si atoms in the silicene sheet is the most strongly adsorbed site in the cluster model for silicene whereas in the periodic model these complexes exhibit strong binding on the Si atom of the silicene surface. The Ac complexes with the NO3- ligand show strong affinity at the hollow space at the center of a hexagonal ring of silicene in both models. The H site is most favorable for the binding of complexes on the germanene cluster whereas these sites vary in the periodic model. Electronic structure calculations have been performed that show a bandgap range from 0.130 to 0.300 eV for the adsorption of actinide complexes on silicene that can be traced to charge transfer. Density of states calculations show that the contribution of the nitrate complexes is small near the Fermi level, but it is larger for the carbonate complexes in the silicene case. Strong interactions between Ac complexes and silicene are due to the formation of strong Si-O bonds upon adsorption which results in reduction of the actinide atom. Such bonding is lacking in germanene.
