Electronic and bonding properties of mono-ruthenium-substituted Keggin-type polyoxometalates: a theoretical study of [{PW11O39}RuII/III(L)] n − (L = dimethyl sulfoxide (DMSO), water, pyridine, and ammonia) and [{GeW11O39}RuII(DMSO)3(H2O)]6−

Abstract

The electronic structure and bonding feature of a series of mono-ruthenium-substituted Keggin-type polyoxometalates (POMs) have been investigated by using density functional theory (DFT) calculation, natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). A comparison of the electronic properties of two known dimethyl sulfoxide (DMSO)-supported mono-ruthenium-substituted Keggin-type POMs shows that both complexes have the analogous frontier-molecular orbital feature. One of them possesses a relatively small HOMO–LUMO gap because of the high HOMO energy level. This difference comes from a high composition of POM ligand with antibonding feature in HOMO. In addition, three typical Keggin-type POM complexes [{PW11O39}RuII/III(L)]n− (L = H2O, C5H5N, NH3) have also been explored according to our computational studies. The NBO analysis shows that the RuII/III–L bond comes from donor–acceptor interactions between the end ligand and the ruthenium (II/III) centre. The EDA shows that the POM complex [{PW11O39}RuII(C5H5N)]5− has much stronger RuII–L bond than ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−. And the enhancement of the RuII–L bonding interaction in [{PW11O39}RuII(C5H5N)]5− is mainly due to the large orbital interaction energy ΔEorb. The ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5− and the aqua-ruthenium derivative [{PW11O39}RuII(H2O)]5− have an analogous magnitude of the total bond energy. This result supports a non-aqueous environment for synthesis of an ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−.