Vanadyl as a Spectroscopic Probe of Tunable Ligand Donor Strength in Bimetallic Complexes

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 the assembly and study of a series of heterobimetallic complexes containing the vanadyl ion, [VO]2+, paired with monovalent cations (Cs+, Rb+, K+, Na+, and Li+) and a divalent 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 and electrochemical 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, isotropic hyperfine coupling constant for the vanadium center, and V(V)/V(IV) reduction potential 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.将次级金属离子(secondary metal ions)引入异双金属配合物(heterobimetallic complexes)，已成为理性调控化合物性质与反应活性的极具吸引力的策略，但针对其调控效应的溶液相直接光谱表征(spectroscopic interrogation)研究却未得到应有的重视。本文报道了一系列以氧钒离子(vanadyl ion，[VO]²+)为核心、分别与一价阳离子(Cs+、Rb+、K+、Na+及Li+)和二价阳离子(Ca²+)配位结合的异双金属配合物的合成与研究。这类配合物既可通过纯品形式分离得到，也可由常见的单金属氧钒基前驱体原位生成，借此可通过实验光谱学与电化学定量表征分析引入的阳离子对氧钒基团(vanadyl moiety)性质的影响。实验数据表明，该系列配合物中的V-O伸缩振动频率、钒中心的各向同性超精细耦合常数以及V(V)/V(IV)还原电位均呈现系统性偏移。这些偏移可通过基于阳离子Lewis酸性(Lewis acidity)参数化的电荷密度效应(charge density effects)进行解释，这提示氧钒离子在多金属物种(multimetallic species)中作为光谱探针具有广阔的应用潜力。