Coordination site-dependent cation binding and multi-responsible redox properties of Janus-head metalloligand, [Mo-V(1,2-mercaptophenolato)(3)]

The redox-active fac-[Mo-V(mp)(3)](-) (mp: o-mercaptophenolato) bearing asymmetric O- and S-cation binding sites can bind with several kinds of metal ions such as Na+, Mn-II, Fe-II, Co-II, Ni-II, and Cu-I. The fac-[Mo-V(mp)(3)](-) metalloligand coordinates to Na+ to form the contact ion pair {Na+(THF)(3)[fac-Mo-V(mp)(3)]} (1), while a separated ion pair, n-Bu4N[fac-Mo-V(mp)(3)] (2), is obtained by exchanging Na+ with n-Bu4N+. In the presence of asymmetric binding-sites, the metalloligand reacts with (MnCl2)-Cl-II center dot 4H(2)O, (FeCl2)-Cl-II center dot 4H(2)O, (CoCl2)-Cl-II center dot 6H(2)O, and (NiCl2)-Cl-II center dot 6H(2)O to afford UV-vis-NIR spectra, indicating binding of these guest metal cations. Especially, for the cases of the MnII and CoII products, trinuclear complexes, {M(H2O)(MeOH)-[ fac-Mo-V(mp)(3)](2)}center dot 1.5CH(2)Cl(2) (3.1.5CH(2)Cl(2) (M = Mn-II), 4.1.5CH(2)Cl(2) (M = Co-II)), are successfully isolated and structurally characterized where the M are selectively bound to the hard O-binding sites of the fac-[Mo-V(mp)(3)](-). On the other hand, a coordination polymer, {Cu-I(CH3CN)[mer-MoV(mp)(3)]}(n) (5), is obtained by the reaction of fac-[Mo-V(mp)(3)]-with [Cu-I(CH3CN)(4)]ClO4. In sharp contrast to the cases of 1, 3.1.5CH(2)Cl(2), and 4.1.5CH(2)Cl(2), the Cu-I in 5 are selectively bound to the soft S-binding sites, where each CuI is shared by two [MoV(mp) 3]-with bidentate or monodentate coordination modes. The second notable feature of 5 is found in the geometric change of the [MoV(mp) 3]-, where the original fac-form of 1 is isomerized to the mer-[Mo-V(mp)(3)](-) in 5, which was structurally and spectroscopically characterized for the first time. Such isomerization demonstrates the structural flexibility of the [Mo-V(mp)(3)](-). Spectroscopic studies strongly indicate that the association/dissociation between the guest metal ions and metalloligand can be modulated by solvent polarity. Furthermore, it was also found that such association/dissociation features are significantly influenced by coexisting anions such as ClO4- or B(C6F5)(4)(-). This suggests that coordination bonds between the guest metal ions and metalloligand are not too static, but are sufficiently moderate to be responsive to external environments. Moreover, electrochemical data of 1 and 3.1.5CH(2)Cl(2) demonstrated that guest metal ion binding led to enhance electron-accepting properties of the metalloligand. Our results illustrate the use of a redox-active chalcogenolato complex with a simple mononuclear structure as a multifunctional metalloligand that is responsive to chemical and electrochemical stimuli.