Abstract
The molecular nanocluster [Ni36–xPd5+x(CO)46]6– (x = 0.41) (16–) was obtained from the reaction of [NMe3(CH2Ph)]2[Ni6(CO)12] with 0.8 molar equivalent of [Pd(CH3CN)4][BF4]2 in tetrahydrofuran (thf). In contrast, [Ni37–xPd7+x(CO)48]6– (x = 0.69) (26–) and [HNi37–xPd7+x(CO)48]5– (x = 0.53) (35–) were obtained from the reactions of [NBu4]2[Ni6(CO)12] with 0.9–1.0 molar equivalent of [Pd(CH3CN)4][BF4]2 in thf. After workup, 35– was extracted in acetone, whereas 26– was soluble in CH3CN. The total structures of 16–, 26–, and 35– were determined with atomic precision by single-crystal X-ray diffraction. Their metal cores adopted cubic close packed structures and displayed both substitutional and compositional disorder, in light of the fact that some positions could be occupied by either Ni or Pd. The redox behavior of these new Ni–Pd molecular alloy nanoclusters was investigated by cyclic voltammetry and in situ infrared spectroelectrochemistry. All three compounds 16–, 26–, and 35– displayed several reversible redox processes and behaved as electron sinks and molecular nanocapacitors. Moreover, to gain insight into the factors that affect the current–potential profiles, cyclic voltammograms were recorded at both Pt and glassy carbon working electrodes and electrochemical impedance spectroscopy experiments performed for the first time on molecular carbonyl nanoclusters.
Highlights
Very often, high-nuclearity metal carbonyl clusters (HNMCCs) display extended redox activity affording reversible electron cascades.[1−5] In this sense, they are multivalent and display electron-sink behavior; that is, they are able to accept and release electrons reversibly in sequence at well-defined potentials
High-nuclearity metal carbonyl clusters (HNMCCs) display extended redox activity affording reversible electron cascades.[1−5] In this sense, they are multivalent and display electron-sink behavior; that is, they are able to accept and release electrons reversibly in sequence at well-defined potentials. This behavior is somehow related to the fact that the metallic core of the cluster undergoes a transition from an insulator to a semiconductor and, eventually, conductor regime as its size increases. As this metal core is shielded by an insulator layer of carbon monoxide, multivalent HNMCCs may be viewed as molecular nanocapacitors.[1,2]
To gain insight into the factors that affect the current−potential profiles, the cyclic voltammograms were recorded at both Pt and glassy carbon (GC) working electrodes and electrochemical impedance spectroscopy (EIS) experiments performed for the first time on molecular carbonyl nanoclusters
Summary
High-nuclearity metal carbonyl clusters (HNMCCs) display extended redox activity affording reversible electron cascades.[1−5] In this sense, they are multivalent and display electron-sink behavior; that is, they are able to accept and release electrons reversibly in sequence at well-defined potentials This behavior is somehow related to the fact that the metallic core of the cluster undergoes a transition from an insulator to a semiconductor and, eventually, conductor regime as its size (nuclearity) increases. Via proper selection of the cyclic potential range, it is possible to observe a completely reversible shift of the νCO bands of the complexes toward higher or lower wavenumbers as a consequence of an oxidation or a reduction, respectively, according to the scan direction This applies to both terminal (νtCO) and bridging (νbCO) carbonyl groups. To gain insight into the factors that affect the current−potential profiles, the cyclic voltammograms were recorded at both Pt and glassy carbon (GC) working electrodes and electrochemical impedance spectroscopy (EIS) experiments performed for the first time on molecular carbonyl nanoclusters
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