In the thematic review dedicated to polyoxometalate (POM) chemistry published in Chemical Reviews in 1998, no contribution was devoted to theory This is not surprising because computational modelling of molecular metal-oxide clusters was in its infancy at that time Nowadays, the situation has completely changed and modern computational methods have been successfully applied to study the structure, electronic properties, spectroscopy and reactivity of POM clusters Indeed, the progress achieved during the past decade has been spectacular and herein we critically review the most important papers to provide the reader with an almost complete perspective of the field

Structure, properties and reactivity of polyoxometalates: a theoretical perspective

Polyoxometalates containing noble metal ions, such as ruthenium, osmium, rhodium, palladium, platinum, silver and gold, are a structurally diverse class of compounds. They include both classical heteropolyanions (vanadates, molybdates, tungstates) in which noble metals are present as heteroatoms, as well as the recently discovered class of polyoxometalates with noble metal "addenda" atoms. The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.

Noble metals in polyoxometalates.

A critical assessment of the OPBE functional is made for its performance for the geometries and spin-states of iron complexes. In particular, we have examined its performance for the geometry of first-row transition-metal (di)halides (MnX2, FeX2, CoX2, NiX2, CuX, X=[F, Cl]), whose results were previously [J. Chem. Theory Comput. 2006, 2, 1282] found to be representative for a much larger and more diverse set of 32 metal complexes. For investigating the performance for spin ground-states of iron complexes, we examined a number of small iron complexes (Fe(II)Cl42−, Fe(III)Cl41−, Fe(II)Cl64−, Fe(III)Cl63−, Fe(II)CN64−, Fe(III)CN63−, Fe(VI)O42−, Fe(III)(NH3)63+), benchmark systems (Fe(II)(H2O)62+, Fe(II)(NH3)62+, Fe(II)(bpy)32+), and several challenging iron complexes such as the Fe(II)(phen)2(NCS)2 spin-crossover compound, the monopyridylmethylamine Fe(II)(amp)2Cl2 and dipyridylmethylamine Fe(II)(dpa)22+, and the bis complex of Fe(III)-1,4,7-triazacyclononane (Fe(III)(9aneN3)23+. In all these cases OPBE give...

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Accurate Spin-State Energies for Iron Complexes

The impact of early transition-metal oxygen-anion cluster (polyoxometalate or “POM”) geometric and electronic structural properties on POM-based catalysis is addressed. Three specific areas of general challenge in POM-based catalysis and catalytic materials are elaborated: (1) the role of ion pairing in catalyst stability, selectivity, and reactivity; (2) the presence of multiple reactive forms of the POMs and the interconvertability of these forms under turnover conditions; and (3) the impact of POM ground state and excited state electronic structure on turnover and selectivity.

Progress and challenges in polyoxometalate-based catalysis and catalytic materials chemistry

Polyoxometalates containing late transition and noble metal atoms

DFT calculations were driven for a set of differently charged polyoxoanions in the gas phase and in solution. We have calculated and analyzed their geometries and orbital energies to trace simple rules of behavior regarding the modeling of anions in isolated form. We discuss the quality of the results depending on the molecular charge, q, and the size of the cluster in terms of the number of metal centers, m. When the q/m ratio reaches a value of ∼0.8, DFT calculations for the isolated anion fail to describe the gap between the band of occupied oxo orbitals and the set of unoccupied orbitals delocalized among the metal atoms. In these cases the incorporation of the stabilizing external fields generated by the solvent through continuum models improves the geometries and orbital energies. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1542–1549, 2004

Are the solvent effects critical in the modeling of polyoxoanions

The electronic structure of group 6–8 transition metal (TM) nitrido derivatives [PW11O39{TMVIN}]4− is studied computationally and the potential reactivity of the polyoxoanions is discussed. The observed electrophilic reactivity for the RuVI nitrido derivative is rationalized from frontier molecular orbital analysis. When we move to the left or down in the periodic table (TM = Os, Tc, Re, Mo and W) the electrophilic character of the polyoxometalate decreases or the cluster should be better regarded as a nucleophile. The DFT analysis of the redox properties suggests that the still unknown high-valent MnVIN and FeVIN units could be stabilized by the porphyrin-like ligand [PW11O39]7− and their electronic structure indicates that these anions should have a high potential reactivity towards nucleophiles.

Influence of polyoxometalate ligands on the nature of high-valent transition metal nitrido species. A theoretical analysis of experimentally known and unprecedented compounds

Quantum chemistry calculations have been performed to unravel the electronic and electrochemical properties of a FeIII-sandwich polyoxometalate. Using a combination of methods, it is shown that in these clusters the first reduction occurs in the so-called external Fe, which is bonded to a water ligand. Calculations also show that the electron reductions are coupled with protonation processes, in full agreement with existing experimental results.

Density functional theory and ab initio study of electronic and electrochemistry properties of the tetranuclear sandwich complex [FeIII4(H2O)2(PW9O34)2]6-.

A valence bond analysis of the wave function of doubly reduced polyoxometales is presented, using the M6O19 Lindqvist structure as test case. By a unitary transformation of the delocalised valence orbitals to localised metal centred orbitals, the multiconfigurational wave function is mapped onto a valence bond function with three different types of configurations: the two electrons are on the same site, on neighbouring sites, or on next-nearest neighbour sites. The inspection of the relative weights of these configurations for triplet and singlet state shows that the triplet-coupled electrons are confined to a smaller volume, and hence have a higher energy than the singlet-coupled electrons. This is in line with the experimental observation that the doubly reduced polyoxometalates show non-mangetic behaviour.

Ab initio study of the singlet-triplet splitting in reduced polyoxometalates

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Density Functional Theory and ab initio Study of Electronic and Electrochemistry Properties of the Tetranuclear Sandwich Complex [FeIII4(H2O)2 (PW9O34)2]6-.

Susanna Romo

Papers

Are the solvent effects critical in the modeling of polyoxoanions

Influence of polyoxometalate ligands on the nature of high-valent transition metal nitrido species. A theoretical analysis of experimentally known and unprecedented compounds

Density functional theory and ab initio study of electronic and electrochemistry properties of the tetranuclear sandwich complex [FeIII4(H2O)2(PW9O34)2]6-.

Ab initio study of the singlet-triplet splitting in reduced polyoxometalates

Density Functional Theory and ab initio Study of Electronic and Electrochemistry Properties of the Tetranuclear Sandwich Complex [FeIII4(H2O)2 (PW9O34)2]6-.