Transition metal complexes with open d-shell in semiempirical context. Application to analysis of Mössbauer data on spin–active iron(II) compounds (original) (raw)
Related papers
Journal of Computational Chemistry, 2003
A computational method targeted to Werner-type complexes is developed on the basis of quantum mechanical effective Hamiltonian crystal field (EHCF) methodology (previously proposed for describing electronic structure of transition metal complexes) combined with the Gillespie-Kepert version of molecular mechanics (MM). It is a special version of the hybrid quantum/MM approach. The MM part is responsible for representing the whole molecule, including ligand atoms and metal ion coordination sphere, but leaving out the effects of the d-shell. The quantum mechanical EHCF part is limited to the metal ion d-shell. The method reproduces with reasonable accuracy geometry and spin states of the Fe(II) complexes with monodentate and polydentate aromatic ligands with nitrogen donor atoms. In this setting a single set of MM parameters set is shown to be sufficient for handling all spin states of the complexes under consideration.
Theoretical Investigation of the Electronic Structure of Fe(II) Complexes at Spin-State Transitions
Journal of Chemical Theory and Computation, 2012
The electronic structure relevant to low spin (LS)high spin (HS) transitions in Fe(II) coordination compounds with a FeN 6 core are studied. The selected [Fe(tz) 6 ] 2+ (1) (tz=1Htetrazole), [Fe(bipy) 3 ] 2+ (2) (bipy=2,2'-bipyridine) and [Fe(terpy) 2 ] 2+ (3) (terpy=2,2':6',2''terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT) and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS-HS states (ΔE HL) applying the above methods, and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d 6 states along the 1 mode(s) that connect the LS and HS states. The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔE HL. In addition, a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves. Although the TD-DFT results might differ in some respect (in our case, we found a discrepancy at the triplet states), our results suggest that this approach, with due care, is very promising as an alternative for the very expensive CASPT2 method. Finally, the two dimensional (2D) potential energy surfaces above the plane spanned by the two relevant configuration coordinates in [Fe(terpy) 2 ] 2+ were computed both at the DFT and CASPT2 levels. These 2D surfaces indicate that the singlet-triplet and triplet-quintet states are separated along different coordinates, i.e. different vibration modes. Our results confirm that in contrast to the case of complexes with mono-and bidentate ligands, the singlet-quintet transitions in [Fe(terpy) 2 ] 2+ cannot be described using a single configuration coordinate.
Progress in Electronic Structure Calculations on Spin-Crossover Complexes
European Journal of Inorganic Chemistry, 2013
Keywords: Ab initio calculations / Computational chemistry / Density functional calculations / Quantum chemistry / Spin crossover Spin-crossover (SCO) complexes are an ongoing challenge to quantum chemistry due to their delicate balance of electronic and entropic contributions to the adiabatic enthalpy difference between the high-spin and the low-spin state. This challenge has fuelled the improvement of existing quantum chemical methods and the development of new ones and will go on to do so. The progress in electronic structure calculations on SCO complexes in the last years has made quantum chemical methods valuable tools that may aid the design of new SCO compounds with desired features. Post-Hartree-Fock ab initio methods are able to calculate the adiabatic energy difference between the high-spin and the low-spin state with satisfactory accuracy but are currently limited to model systems or smaller molecular SCO complexes.
Methods for Molecular Modeling of Metal Complexes with Open D-Shell
With use of cumulants of two-electron density matrices semiempirical and DFT methods are analyzed from a point of view of their suitability to describe qualitative features of electronic correlation important for molecular modeling of electronic structure of the transition metal complexes (TMC). It is shown that traditional semiempirical methods relying upon the Hartree-Fock-Roothaan form of the trial wave function suffer from a structural deficiency not allowing them to distinguish the energies of the atomic multiplets of the TMCs' d-shells. The same applies to the DFT methodology. On the other hand, the effective Hamiltonian of the crystal field (EHCF) previously proposed by the authors is shown to be suitable for further parameterization. It has been applied for calculations of geometries in a series of polyatomic spin-active TMCs and has shown remarkable precision and an overall consistency. This allowed to solve in a sequential manner two long standing problems: extending molecular mechanics to transition metals and developing semiempirical quantum mechanical (QM) methods for transition metals.
The Journal of Chemical Physics, 2005
Previous work testing density functionals for use in calculating high-spin-low-spin energy differences, ⌬E HL , for iron͑II͒ spin-crossover transitions has tended to conclude that only properly reparametrized hybrid functionals can predict ⌬E HL since it seems to depend critically on a correct description of the electron pairing energy governed by the exchange term. Exceptions to this rule are the previous three papers ͑I, II, and III in the present series of papers͒ where it was found that modern generalized gradient approximations ͑GGAs͒ and meta-GGAs could do as well as hybrid functionals, if not better, for this type of problem. In the present paper, we extend these previous studies to five more molecules which are too large to treat with high-quality ab initio calculations, namely, the series ͓Fe͑L͒͑'NHS 4 ' ͔͒, where NHS 4 = 2.2Ј-bis͑2-mercaptophenylthio͒diethylamine dianion, and L =NH 3 , N 2 H 4 , PMe 3 , CO, and NO + . Since we know of no reliable experimental estimate of ⌬E HL , we content ourselves with a comparison against the experimentally determined ground-state spin symmetry including, in so far as possible, finite-temperature effects. Together with the results of Papers I, II, and III, this paper provides a test of a large number of functionals against the high-spin/low-spin properties of a diverse set of Fe͑II͒ compounds, making it possible to draw some particulary interesting conclusions. Trends among different classes of functionals are discussed and it is pointed out that there is at least one functional, namely, the OLYP generalized gradient approximation, which is able to give a reasonably good description of the delicate spin energetics of Fe͑II͒ coordination compounds without resorting to hybrid functionals which require the relatively more expensive calculation of a Hartree-Fock-type exchange term. Downloaded 07 Dec 2010 to 195.221.206.203. Redistribution subject to AIP license or copyright; see http://jcp.aip.org/about/rights\_and\_permissions 234321-2 Ganzenmüller et al. J. Chem. Phys. 122, 234321 ͑2005͒ Downloaded 07 Dec 2010 to 195.221.206.203. Redistribution subject to AIP license or copyright; see http://jcp.aip.org/about/rights\_and\_permissions 234321-10 Ganzenmüller et al.
Highly accurate estimates of the high-spin/low-spin energy difference ΔE HL el in the high-spin complexes [Fe(NCH) 6 ] 2+ and [Co(NCH) 6 ] 2+ have been obtained from the results of CCSD(T) calculations extrapolated to the complete basis set limit. These estimates are shown to be strongly influenced by scalar relativistic effects. They have been used to assess the performances of the CASPT2 method and 30 density functionals of the GGA, meta-GGA, global hybrid, RSH, and double-hybrid types. For the CASPT2 method, the results of the assessment support the proposal [Kepenekian, M.; Robert, V.; Le Guennic, B. J. Chem. Phys. 2009, 131, 114702] that the ionization potential−electron affinity (IPEA) shift defining the zeroth-order Hamiltonian be raised from its standard value of 0.25 au to 0.50−0.70 au for the determination of ΔE HL el in Fe(II) complexes with a [FeN 6 ] core. At the DFT level, some of the assessed functionals proved to perform within chemical accuracy (±350 cm −1 ) for the spin-state energetics of [Fe(NCH) 6 ] 2+ , others for that of [Co(NCH) 6 ] 2+ , but none of them simultaneously for both complexes. As demonstrated through a reparametrization of the CAM-PBE0 range-separated hybrid, which led to a functional that performs within chemical accuracy for the spin-state energetics of both complexes, performing density functionals of broad applicability may be devised by including in their training sets highly accurate data like those reported here for [Fe(NCH) 6 ] 2+ and [Co(NCH) 6 ] 2+ .
ACS omega, 2017
The relative ease of Mossbauer spectroscopy and of density functional theory (DFT) calculations encourages the use of Mossbauer parameters as a validation method for calculations, and the use of calculations as a double check on crystallographic structures. A number of studies have proposed correlations between the computationally determined electron density at the iron nucleus and the observed isomer shift, but deviations from these correlations in low-valent iron βdiketiminate complexes encouraged us to determine a new correlation for these compounds. The use of B3LYP/def2-TZVP in the ORCA platform provides an excellent balance of accuracy and speed. We provide here not only this new correlation and a clear guide to its use but also a systematic analysis of the limitations of this approach. We also highlight the impact of crystallographic inaccuracies, DFT model truncation, and spin states, with intent to assist experimentalists to use Mossbauer spectroscopy and calculations together.
Mössbauer and electronic spectral studies of iron(III) complexes of oximes
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2003
The hydroxo-bridge complexes of the type [Fe 2 (ligand Ã/H) 4 (OH) 2 ] with bidentate nitrogen Á/oxygen donor ligands, viz. 2-hydroxynaphthaldehydeoxime [hnoH 2 ], 2-hydroxyacetphenoneoxime [haoH 2 ], salicylaldooxime [SalH 2 ], 2hydroxypropiophenoneoxime [hnoH 2 ] have been prepared. All the complexes have been characterized by elemental analysis, magnetic moments, electronic and Mö ssbauer spectral studies. Mö ssbauer parameters of the complexes clearly suggest high spin configuration of Fe(III) showing lower magnetic moment to that of the spin only value, i.e. 5.92 BM. It may be due to the antiferromagnetic interaction between Fe(III) centers. #
Importance of the Basis Set for the Spin-State Energetics of Iron Complexes
Journal of Physical Chemistry A, 2008
We have performed a systematic investigation of the influence of the basis set on relative spin-state energies for a number of iron compounds. In principle, with an infinitely large basis set, both Slater-type orbital (STO) and Gaussian-type orbital (GTO) series should converge to the same final answer, which is indeed what we observe for both vertical and relaxed spin-state splittings. However, we see throughout the paper that the STO basis sets give consistent and rapidly converging results, while the convergence with respect to the basis set size is much slower for the GTO basis sets. For example, the large GTO basis sets that give good results for the vertical spin-state splittings of compounds 1-3 (6-311+G**, Ahlrichs VTZ2D2P), fail for the relaxed spin-state splittings of compound 4. Very demanding GTO basis sets like Dunning's correlation consistent (cc-pVTZ, cc-pVQZ) basis sets are needed to achieve good results for these relaxed spin-states. The use of popular (Pople-type) GTO, 2 Effective Core Potentials Basis-set (ECPB) or mixed ECPB(Fe):GTO(rest) basis sets is shown to lead to substantial deviations (2-10 kcal/mol, 14-24 kcal/mol for 3-21G), in particular for the high spin-states that are typically placed at too low energy. Moreover, the use of an effective core potential in the ECPB basis sets results in spin-state splittings that are systematically different from the STO-GTO results. Keywords Density functional theory-spin state energies-iron compounds-Slater-type orbitals-Gaussian-type orbitals-Effective Core Potentials. the OPBE functional. Moreover, also for NMR chemical shifts does OPBE seem to perform significantly better than other DFT functionals, and in many cases even surpasses MP2. 12,13,27 Despite these promising successes of OPBE, other recent papers 20,22,28,29 criticized the OPBE functional, and questioned its reliability for the spin-state splittings. However, several of these papers used Gaussian-type orbitals (GTOs) 30 or Effective Core Potentials Basis-sets (ECPBs), 30 while the abovementioned successes of OPBE were mainly shown in studies that use (the a priori better) Slatertype orbital (STO) 30,31 basis sets. Moreover, by comparing two ECPBs with an all-electron GTO basis set, Kamachi and Yoshizawa 32 showed that spin-state splittings of iron complexes may easily change by 8 kcal/mol, i.e. of the same order of magnitude as the spin-state splittings themselves. Therefore, the Computational details The calculations using the unrestricted formalism have been performed with four computational chemistry programs: ADF 37,38 (version 2006.01), Gaussian03 39 (revision B.02), NWChem 40 (version 5.0) and ORCA 41 (version 2.5.20).