Incorporation of secondary metal ions into heterobimetallic complexes has emerged as an attractive strategy for rational tuning of compounds’ properties and reactivity, but direct solution-phase spectroscopic interrogation of tuning effects has received less attention than it deserves. Here, we report assembly and study of a series of heterobimetallic complexes containing the vanadyl ion, [VO]2+, paired with mono-valent cations (Cs+, Rb+, K+, Na+, and Li+) or a di-valent cation (Ca2+). These complexes, which can be isolated in pure form or generated in situ from a common monometallic vanadyl-containing precursor, enable experimental spectroscopic quantification of the influence of the incorporated cations on the properties of the vanadyl moiety. The data reveal systematic shifts in the V–O stretching frequency and isotropic hyperfine coupling constant for the vanadium center in the complexes. These shifts can be interpreted as charge density effects parametrized through the Lewis acidities of the cations, suggesting broad potential for the vanadyl ion to serve as a spectroscopic probe in multimetallic species.

Compounds containing multiple metals attract significant interest due to the useful redox and reactivity properties of such species. Here, the electrochemical properties of a family of macrocyclic complexes that feature a zinc(II) center paired with a second redox-inactive metal cation in heterobimetallic (Na+, Ca2+, Nd3+, Y3+) motifs or a homobimetallic (Zn2+) motif have been investigated. The new complexes were prepared via a divergent strategy, isolated, and structurally characterized by single-crystal X-ray diffraction (XRD) analysis. XRD results show that the structure of the complexes is modulated by the identity of the incorporated secondary metal ions. Cyclic voltammetry data reveal that ligand-centered reduction is promoted in the bimetallic complexes and that the paired metal ions synergistically influence the redox properties of the complexes. Similar to prior work from our group and others, the bimetallic complexes containing stronger Lewis acids undergo more significant reduction potential shifts; contrasting with prior work on complexes containing redox-active metals, however, the zinc(II) complexes studied here display faster electron transfer (as judged by lower reorganization energies, λ) when incorporating di- or tri-valent Lewis acids in contrast to monovalent (and more weakly acidic) sodium. The quantified trends in these data offer insights that help distinguish metal- versus ligand-centered reduction of bimetallic complexes.<br>

Compounds containing multiple metals attract significant interest due to the useful redox and reactivity properties of such species. Here, the electrochemical properties of a family of macrocyclic complexes that feature a zinc(II) center paired with a second redox-inactive metal cation in heterobimetallic (Na+, Ca2+, Nd3+, Y3+) motifs or a homobimetallic (Zn2+) motif have been investigated. The new complexes were prepared via a divergent strategy, isolated, and structurally characterized by single-crystal X-ray diffraction (XRD) analysis. XRD results show that the structure of the complexes is modulated by the identity of the incorporated secondary metal ions. Cyclic voltammetry data reveal that ligand-centered reduction is promoted in the bimetallic complexes and that the paired metal ions synergistically influence the redox properties of the complexes. Similar to prior work from our group and others, the bimetallic complexes containing stronger Lewis acids undergo more significant reduction potential shifts; contrasting with prior work on complexes containing redox-active metals, however, the zinc(II) complexes studied here display faster electron transfer (as judged by lower reorganization energies, λ) when incorporating di- or tri-valent Lewis acids in contrast to monovalent (and more weakly acidic) sodium. The quantified trends in these data offer insights that help distinguish metal- versus ligand-centered reduction of bimetallic complexes.<br>