We report a detailed study of the magnetic and relaxation properties of a series of oxovanadium(Ⅳ)complexes comprising the aqua ion[VO(H_(2)O)_(5)]^(2+)and[VO(ox)_(2)]^(2-)(ox=oxalate),[VO(nta)]-(nta=nitrilotriacetat...We report a detailed study of the magnetic and relaxation properties of a series of oxovanadium(Ⅳ)complexes comprising the aqua ion[VO(H_(2)O)_(5)]^(2+)and[VO(ox)_(2)]^(2-)(ox=oxalate),[VO(nta)]-(nta=nitrilotriacetate),[VO(dtpa)]^(3-)(dtpa=diethylenetriaminepentaacetate)and[VO(acac)_(2)](acac=acetylacetonato)in solution.The complexes were characterized using continuous wave(X-band)and pulsed(Q-band)EPR measurements and ^(1)H nuclear magnetic relaxation dispersion(NMRD)studies in the 0.01-120 MHz ^(1)H Larmor frequency range.The ^(51)V A-tensor parameters obtained from the analysis of EPR spectra are in good agreement with those obtained using theoretical calculations at the DFT and coupled-cluster levels(DLPNO-CCSD),while g-tensors were obtained with CASSCF/NEVPT2 calculations.EPR measurements reveal significant differences in the electronic T_(1)^(e) and T_(m)^(e) relaxation times,with[VO(acac)_(2)]showing a markedly different behaviour due to the trans coordination geometry.The NMRD profiles measured at different temperatures have contributions from both the outer-and inner-sphere mechanisms,with the latter showing contributions from the dipolar and scalar mechanisms.The rotational correlation times(τ_(R))obtained from the fitting of NMRD and EPR data are in good mutual agreement.The scalar mechanism depends on the hyperfine coupling constants of the coordinated water molecule H_(a_(iso)),which were obtained from the fitting of the NMRD profiles and DFT calculations.Finally,the analysis of the data provided information on the exchange rate of coordinated water molecules,which display mean residence times of ~7-17μs at 298 K.展开更多
基金the financial support from the Ministero dell’Universitàe della Ricerca(PRIN 2017A2KEPL project)Ministerio de Ciencia e Innovación(PID2019-104626GB-I00)Xunta de Galicia(Grant ED431B 2020/52)for generous financial support.
文摘We report a detailed study of the magnetic and relaxation properties of a series of oxovanadium(Ⅳ)complexes comprising the aqua ion[VO(H_(2)O)_(5)]^(2+)and[VO(ox)_(2)]^(2-)(ox=oxalate),[VO(nta)]-(nta=nitrilotriacetate),[VO(dtpa)]^(3-)(dtpa=diethylenetriaminepentaacetate)and[VO(acac)_(2)](acac=acetylacetonato)in solution.The complexes were characterized using continuous wave(X-band)and pulsed(Q-band)EPR measurements and ^(1)H nuclear magnetic relaxation dispersion(NMRD)studies in the 0.01-120 MHz ^(1)H Larmor frequency range.The ^(51)V A-tensor parameters obtained from the analysis of EPR spectra are in good agreement with those obtained using theoretical calculations at the DFT and coupled-cluster levels(DLPNO-CCSD),while g-tensors were obtained with CASSCF/NEVPT2 calculations.EPR measurements reveal significant differences in the electronic T_(1)^(e) and T_(m)^(e) relaxation times,with[VO(acac)_(2)]showing a markedly different behaviour due to the trans coordination geometry.The NMRD profiles measured at different temperatures have contributions from both the outer-and inner-sphere mechanisms,with the latter showing contributions from the dipolar and scalar mechanisms.The rotational correlation times(τ_(R))obtained from the fitting of NMRD and EPR data are in good mutual agreement.The scalar mechanism depends on the hyperfine coupling constants of the coordinated water molecule H_(a_(iso)),which were obtained from the fitting of the NMRD profiles and DFT calculations.Finally,the analysis of the data provided information on the exchange rate of coordinated water molecules,which display mean residence times of ~7-17μs at 298 K.
