Molecular engineering of an inverse hexacopper(II) coordination complex with a photoactive metallacyclophane centroligand as prototype of a magnetic photoswitch

Abstract

A primary goal of molecular spintronics is detecting the response of the spins from a single magnetic molecule to an external stimulus and, eventually, being able to implement logic quantum memory capabilities for information data storage and processing applications in quantum computation. Having this in mind, a novel hexanuclear oxamatocopper(II) complex of formula {[Cu2(naba)2][Cu(pmdien)]4}(ClO4)4·8H2O (2) [naba = N,N'-1,5-naphthalenebis(oxamate) and pmdien = N,N,N’,N”,N”-pentamethyldiethylenetriamine] has been prepared by the reaction of stoichiometric amounts of (nBu4N)4[Cu2(naba)2] · 4H2O (1) (nBu4N+ = tetra-n-butylammonium cation) and [Cu(pmdien)](ClO4)2 (1:4 molar ratio) in water. 2 exhibits a ladder-like “dimer-of-trinuclears” structure featuring a photoactive dicopper(II) naphthalenophane core acting as inverse coordination centre (centroligand) towards four peripheral [Cu(pmdien)]2+ groups through the outer amidate/carboxylate oxygen atoms of the oxamato fragments. 2 undergoes a unique magnetic photoswitching ON/OFF behaviour upon UV light irradiation because of an intramolecular (“pseudo-bimolecular”) photocycloaddition of the two facing naphthalene spacers through the more reactive carbon atoms at the 1,4 and 1’,4’ positions of the benzene rings to afford the putative [4 + 4] cycloaddition product c-2. Hence, the two oxamato-bridged S = 1/2 CuII3 linear units antiferromagnetically coupled within the CuII6 precursor (2, ON state) become magnetically uncoupled in the corresponding [4 + 4] photocycloaddition product (c-2, OFF state) [jeff = –2.13 (2) and 0 cm−1 (c-2); H = – jeffSA.SB with SA = SB = 1/2]. This new example of inverse coordination complex constitutes thus a potential candidate to molecular magnetic photoswitch in the “bottom-up” approach to nanometer-scale spintronic and quantum computing devices.