Zwitterionic Mixed-Valence Species for the Design of Neutral Clocked Molecular Quantum-Dot Cellular Automata

Mixed-valence
compounds can be used for the design of molecular quantum-dot cellular
automata (QCA). Here, we investigate the QCA properties of a three-dot
“Y”-shaped functionalized zwitterionic neutral closo-carborane model 1-(3,5-{Cp­(dHpe)­Fe–CC−}2(C6H3))-10-Cp­(dHpe)­Fe–CC-closo-1-CB9H8 (1) (Cp
= cyclopentadienyl (η5-C5H5) and dHpe = 1,2-bis­(phosphino)­ethane (H2PCH2CH2PH2)) as a neutral clocked molecular half-cell.
DFT results clearly demonstrate that 1 can display simultaneously
the two most basic properties necessary for clocked QCA operation,
i.e., bistable switching behavior and clocked control. This is possible
due to the three stable states (two active and one null) of 1, corresponding to occupation of each of the three iron-ethynyl
groups by the positive charge. In addition, the proximal electronic
bias effects can be overcome by the zwitterionic nature of 1, which could be imposed by external counterions, rendering these
effects more predictable.