Properties of a Mixed-Valence (Fe^II)₂(Fe^III)₂ Square Cell for Utilization in the Quantum Cellular Automata Paradigm for Molecular Electronics

Abstract

The di-mixed-valence complex [{(eta(5)-C5H5)Fe(eta(5)-C5H4)}4(eta(4)-C4)Co(eta(5)-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(eta(5)-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 pi systems of the central linker and the ferrocene moieties most likely controls the rate of electron exchange between the dots.

Cyanide‐Bridged Molecular Squares – The Building Units of Prussian Blue

“…[28] Mixed-valence squares are considered to have potential applications in the quantum cellular automata approach to nanoelectronics. [29] Discrete mixed-valence compounds are classified by using the Robin-Day criteria to constitute three main groups of complexes. Class I corresponds to species that show no electronic coupling (localized valence electrons) between metal centers.…”

Radial tetra(ferrocenyl)- and tetra(cymantrenyl)cyclobutadienecobalt complexes: Synthesis and structures

“…At the same time, we can compare first oxidation potential for compounds 3 with that of cymatrene [9]. It is slightly shifted to the more anodic values for the compound 3 (see Table 2 couples might be detected in further experiments and were not observed in this studies due to previously reported problems such as absorption at the electrode surface [6].…”

“…the same Cb-ligand [6]. An introduction of eCO 2 Et group in complex 2 shifts the oxidation potentials to the higher anodic values.…”

“…Nowadays, the prospective CbCo complexes could be elaborated as building blocks for design and synthesis of new materials or supramolecular architectures: metallorganic dehydroannulenes [2], superphane and 'beltenes' molecules [3], novel ligands for catalysis [4], organometallic dendrimers and polymers [5], and materials for electronic devices [6]. Once the area has attracted considerable interest the need of straightforward synthetic approaches to develop such complicated systems arises.…”

Metal Dependence of Signal Transmission through MolecularQuantum-Dot Cellular Automata (QCA): A Theoretical Studyon Fe, Ru, and Os Mixed-Valence Complexes

“…For improvement in operation temperature and size of the devices, however, the idea of molecular quantum-dot cellular automata (molecular QCA) devices [5], in which a QCA cell constructed from small metallic dots is replaced by a single molecule, was proposed. Syntheses of tetranuclear complexes [6,7,8,9,10] and simplified dinuclear complexes [11,12], and single-molecule observation of the dinuclear complexes [13,14] have been investigated for the realization of molecular QCA devices. Also, theoretical simulations of QCA devices have been reported by many research groups [15,16,17,18,19,20,21].…”