Enhanced relative stability of heterobimetallic Fe(II), Zn(II), and Mg(II) clusters supported by a µ-phenoxo bridge

Publication date: Available online 24 February 2020Source: Inorganica Chimica ActaAuthor(s): William D. Kerber, D. Sean Hartnett, Aiqiu Wang, Carson Hawkins Mafrice, Maxime A. SieglerAbstractEquilibrium populations of the dinucleating ligand H5(F-HXTA) (5-fluoro-2-hydroxy-1,3-xylene-α,α′-diamine-N,N,N′,N′-tetraacetic acid) in the presence of pairs of divalent metal ions were measured by 19F-NMR to assess the relative stability of the heterobimetallic complex [MaMbL]- (L = F-HXTA5-). Homobimetallic Fe(II), Zn(II) and Mg(II) complexes of F-HXTA having the general formula [M(H2O)6][M2(F-HXTA)(H2O)x]2 yH2O have been characterized by single crystal X-ray diffraction (x = 4, y = 14 for Fe(II) and Mg(II); x = 3, y = 10 for Zn(II)) and 1H and 19F-NMR data show the complex ions retain their structures in aqueous solution. Equilibrium constants for metal exchange between [Ma2L]- and [Mb2L]- to produce [MaMbL]- were measured to be Kex = 4.4 ± 0.3 for Fe(II)/Zn(II), 4.15 ± 0.07 for Mg(II)/Fe(II) and 5.59 ± 0.09 for Mg(II)/Zn(II). This trend of enhanced relative stability of the heterobimetallic state (Kex> 1) agrees with a previous report on the stability of Fe(II)/Mn(II) F-HXTA complexes. Density functional theory (DFT) and natural bond orbital (NBO) analysis were used to simulate metal exchange in the Zn(II)/Mg(II) system (Kcalc = 13) and revealed increased charge transfer between the bridging phenoxo ligand and metal ions in the lower symmetry environment of the heterobimet...
Source: Inorganica Chimica Acta - Category: Chemistry Source Type: research