Oxocomplexes of Mo(vi) and W(vi) with 8-hydroxyquinoline-5-sulfonate in solution: structural studies and the effect of the metal ion on the photophysical behaviour

Abstract

Multinuclear ((1)H, (13)C, (95)Mo and (183)W) NMR spectroscopy, combined with DFT calculations, provides detailed information on the complexation between the Mo(VI) and W(VI) oxoions and 8-hydroxyquinoline-5-sulfonate (8-HQS) in aqueous solution. Over the concentration region studied, Mo(VI) and W(VI) oxoions form three homologous complexes with 8-HQS in water in the pH range 2-8. Two of these, detected at pH < 6, are mononuclear 1 : 2 (metal : ligand) isomers, with the metal centre (MO2(2+)) coordinated to two 8-HQS ligands. An additional complex, dominant at slightly higher pH values (5-8) for solutions with a 1 : 1 metal : ligand molar ratio, has a binuclear M2O5(2+) centre coordinated to two 8-HQS ligands. The two metal atoms are bridged by three oxygen atoms, two coming from 8-HQS, together with the M-O-M bridge of the bimetallic centre. We show that the long-range exchange corrected BOP functional with local response dispersion (LCBOPLRD), together with explicit solvent molecules, leads to geometries that readily converge to equilibrium structures having realistic bridging O8-HQS-M bonds. Previous attempts to calculate the structures of such binuclear complexes using DFT with the B3LYP functional have failed due to difficulties in treating the weak interaction in these bridged structures. We believe that the LCBOPLRD method may be of more general application in theoretical studies in related binuclear metal complexes. UV/visible absorption and luminescence spectra of all the complexes have also been recorded. The complex between Mo(vi) and 8-HQS is only weakly luminescent, in contrast to what has been observed with this ligand and many other metal ions. We suggest that this is due to the presence of low-lying ligand-to-metal charge transfer (LMCT) states close to the emitting ligand-based level which quench the emission. However, with W(VI), DFT calculations show that the LMCT states are now much higher in energy than the ligand based levels, leading to a marked increase in fluorescence.

Anisotropic Electrical Conductivity of a Single-Crystalline Oxo-Bridged Cr4IIIMo2VI Heterometallic Complex

“…The absorption spectrum of the O-CrMoHC crystals was similar to that of [Cr­(H 2 O) 6 ] 3+ rather than (NH 4 ) 2 MoO 4 , indicating that the electronic structure of the O-CrMoHC crystal was constructed via the modification of Cr 2 (OAc) 4 upon binding to MoO 4 2– . The spectral analysis infers the following conclusions: (i) O-CrMoHC has an octahedrally coordinated Cr­(III) metal center, (ii) O-CrMoHC contains a Mo­(VI) center, which does not generate any absorption band due to its empty d-orbitals, (iii) there are no intermetallic bonds observed between the octahedrally coordinated Cr­(III) centers despite the short average distance between Cr1···Cr1′ (2.950 Å), and (iv) the red-shifted absorption bands of O-CrMoHC with respect to [Cr­(H 2 O) 6 ] 3+ were caused by the stronger π-donating tendency of the OAc – and MoO 4 2– ligands compared to H 2 O. , Thus, the color of the single crystal of O-CrMoHC was blue-green due to the absorption of light at 603 nm in the red region of the visible-light spectrum, in contrast to a solution of [Cr­(H 2 O) 6 ] 3+ , which is violet. − , …”

“…ligands compared to H 2 O. 2,44 Thus, the color of the single crystal of O-CrMoHC was blue-green due to the absorption of light at 603 nm in the red region of the visible-light spectrum, in contrast to a solution of [Cr(H 2 O) 6 ] 3+ , which is violet. [30][31][32]42 The UV−vis absorption spectra suggest that during the formation of O-CrMoHC in the solvothermal process the quadruply bonded Cr(II) centers in Cr 2 (OAc) 4 appear to be oxidized to Cr(III), but the Mo(VI) center in MoO 4 2− retains its initial oxidation state.…”

Synthesis, Characterization and Evaluation of the Antibacterial and Antitumor Activity of HalogenatedSalen Copper (II) Complexes derived from Camphoric Acid

“…1 H NMR chemical shifts together with 13 C and metal ion NMR can provide valuable structural information, including the type of metal center and nature of ligand coordination present in the complexes. Broadening and/or coordination induced shifts of the 1 H and 13 C signals of the ligand in the presence of the metal ions, compared with those of the free ligand, can provide clear indications of metalligand binding sites, as illustrated in our previous studies of the complexation between various metal ions and relevant ligands, [33][34][35][36][37][38][39][40][41] including the paramagnetic copper (II) [38] and chromium (III) [37] ions.…”