The di-mixed-valence complex [{(η⁵-C₅H₅)Fe(η⁵-C₅H₄)}₄(η⁴-C₄)Co(η⁵-C₅H₅)]²⁺, 1 ²⁺, has been evaluated as a molecular four-dot cell for the quantum cellular automata paradigm for electronic devices. The cations 1 ¹⁺ and 1 ²⁺ are prepared in good yield by selective chemical oxidation of 1 ⁰ and are isolated as pure crystalline materials. The solid-state structures of 1 ⁰ and 1 ¹⁺ and the midrange- and near-IR spectra of 1 ⁰, 1 ¹⁺, 1 ²⁺, and 1 ³⁺ have been determined. Further, the variable-temperature EPR spectra of 1 ¹⁺ and 1 ²⁺, magnetic susceptibility of 1 ¹⁺ and 1 ²⁺, Mössbauer spectra of 1 ⁰, 1 ¹⁺, and 1 ²⁺, NMR spectra of 1 ⁰, and paramagnetic NMR spectra of 1 ¹⁺ and 1 ²⁺ have been measured. The X-ray structure determination reveals four ferrocene “dots” arranged in a square by C−C bonds to the corners of a cyclobutadiene linker. The four ferrocene units project from alternating sides of the cyclobutadiene ring and are twisted to minimize steric interactions both with the Co(η⁵-C₅H₅) fragment and with each other. In the solid state 1 ²⁺ is a valence-trapped Robin and Day class II compound on the 10^-¹² s infrared time scale, the fastest technique used herein, and unambiguous evidence for two Fe^II and two Fe^III sites is observed in both the infrared and Mössbauer spectra. Both EPR and magnetic susceptibility measurements show no measurable spin−spin interaction in the solid state. In solution, the NMR spectra show that free rotation around the C−C bonds connecting the ferrocene units to the cyclobutadiene ring becomes increasingly hindered with decreasing temperature, leading to spectra at the lowest temperature that are consistent with the solid-state structure. Localization of the charges in the cations, which is observed in the paramagnetic NMR spectra as a function of temperature, correlates with the fluxional behavior. Hence, the alignment between the π systems of the central linker and the ferrocene moieties most likely controls the rate of electron exchange between the dots.

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