Valence tautomeric dinuclear adducts of Co(ii) diketonates with redox-active diquinones for the design of spin qubits: computational modeling

Abstract

The possibility of employing the mechanism of intramolecular electron transfer between metal and ligand centers in the valence tautomeric complexes formed as electrically neutral 2 : 1 adducts of Co(II) diketonates and redox-active tetradentate di-o-quinones, for quantum information processing, has been computationally studied using the DFT B3LYP*/6-311++G(d,p) method. It has been shown that by the proper choice of a linker group bridging the quinone rings and substituents in the diketonate fragments, complexes with the properties required in 2-qubit quantum gates (sufficiently narrow energy gaps between the spin states and weakly coupled paramagnetic centers) can be designed, in order to realize the mechanism of thermally driven migration of paramagnetic centers between the o-quinone fragments and metal atoms. These are exemplified by the adduct of bis-(hexafluoroacetylacetonate)Co(ii) with a diquinone containing dimethylene linker. Valence tautomerism is considered as a new, promising mechanistic paradigm for the molecular design of 2-qubit molecular systems.

Rational design of potential spin qubits manipulated by the valence tautomerism mechanism: quantum-chemical modeling of the trinuclear transition metal complexes with bischelate linkers

“…To sum up, the DFT B3LYP*/6-311++G(d,p) calculations performed on a broad series of electrically neutral adducts of Co II diketonates with the functionalized redox-active di-o-quinones 2 (M = Co, Ni, Cu, Zn; X = O, NR 0 ; R = H, CH 3 , CF 3 ; R 0 = H, CH 3 , Ph) and model compounds 3-6 allowed uncovering of two groups of complexes 2 (M = Cu and Co; X = O; R = CF 3 ) that may potentially have the properties of molecular spin qubits, magnetic characteristics of which can be additionally tuned through the occurrence of low-energy barrier VT rearrangements. The results of the calculations extend the approach 17,18,52 to the application of the mechanism of valence tautomerism for the design of molecular 2-qubit quantum gates to trinuclear metal complexes with transition metal containing linker groups. ), relative energies (DE) and relative enthalpies at 298 K (DH 298 ) (all energy values are given in kcal mol À1 ) and exchange spin coupling constants (J b , given in cm À1 ) of the adducts 2 (M = HS Co II ; X = O; R = CH 3 , CF 3 ) calculated by the DFT B3LYP*/ Tables S5 and S7).…”

“…In the development of these studies, we have assumed and computationally justified [16][17][18] that the dinuclear complexes designed on the basis of redox-active (non-innocent 19 ) ligands capable of undergoing thermally or photochemically initiated reversible intramolecular rearrangements caused by electron transfer between the metal and ligand centers (valence tautomerism VT [20][21][22][23][24][25] can acquire useful properties of controllable switching of their spin states allowing additional manipulation by spin qubits. The involvement in the spin exchange processes of paramagnetic centers located on the organic moieties is an important distinction of the dinuclear complexes with redox-active ligands from the weakly coupled metal complexes in which spin densities are concentrated at the metal ions.…”

Electric Field Control of the Valence‐Tautomeric Transformation in Cobalt Complexes

“…The experimental findings concerning the valence‐tautomeric transformation in the six‐coordinate complex trans ‐[Co(tbdiox) 2 (4‐papy) 2 ] (tbdiox = redox‐active 3,5‐di‐ tert ‐butyl‐ o ‐dioxolene, 4‐papy = 4‐phenylazopyridine) were also confirmed and supported by DFT studies . The computational design of transition‐metal complexes that have magnetic properties controlled by valence‐tautomeric mechanism has also been discussed previously …”

“…[23] The computational design of transition-metal complexes that have magnetic properties controlled by valence-tautomeric mechanism has also been discussed previously. [39][40][41][42] The modeling of the valence-tautomeric interconversion in the quasiclassical approximation performed in ref. [43] was aimed at elucidating the role played by intra-and intermolecular interactions in the magnetic properties of isolated complexes and crystals undergoing valence-tautomeric transformation.…”

The Cluster Fe<sub>2</sub>Si<sub>18</sub> as the New Quantum Bit System

“…The search of the two-state systems represents intriguing story in the modern investigations of a quantum computer systems. We mention here the point-like NV defect state in diamond [4] [5] and molecular-like pair of defect spin states (V Si -V C ) in carbide [6] and the search of the two-level states in biophysical molecular structures [7] [8]. The singlet state of Fe 2 Si 18 cluster would have a special interest in this connection.…”