Weak Exchange Interactions in Multispin Systems: EPR Studies of Metalloporphyrins Decorated with {Cr7Ni} Rings.

Both metalloporphyrins and heterometallic {Cr7Ni} rings are of significant research interest due to their proposed roles in quantum information processing devices. In this study, we present a series of complexes in which [Cr7NiF3(Etglu)(O2CtBu)15] (N-EtgluH5 = N-ethyl-d-glucamine) heterometallic rings are coordinated to metalloporphyrin linkers: the symmetric [M(TPyP)] for M = Cu2+, VO2+, and H2TPyP = 5,10,15,20-tetra(4-pyridyl)porphyrin; and the asymmetric [{VO}(TrPPyP)] for H2(TrPPyP) = 5,10,15-(triphenyl)-20-(4-pyridyl)porphyrin. The magnetic interactions present in these complexes are unraveled using the continuous wave (CW) electron paramagnetic resonance (EPR) technique. The nature of the coupling between the {Cr7Ni} rings and the central metalloporphyrin is assessed by numerical simulations of CW EPR spectra and determined to be on the order of 0.01 cm-1, larger than the dipolar ones and suitable for individual spin addressability in multiqubit architectures.

Two- and Three-Spin Hybrid Inorganic-Organic [2]Rotaxanes Containing Metallated Salen Groups.

Mono- and bis-salen functionalised [2]rotaxanes have been synthesised from the esterification of [2]rotaxanes containing phenol-terminated threads (salen = N,N'-bis(salicylidene)ethylenediamine). The [2]rotaxanes have general formula [RH][Cr7NiF8(O2CtBu)16], where [RH]+ is a thread with a central secondary ammonium site that templates a [Cr7NiF8(O2CtBu)16]- ring. The threads are terminated at one or both ends by carboxylic acid functionalised salen groups. The {M(salen)} groups can be free-base [M = (H+)2] or metallated [M = Cu2+, Ni2+, (VO)2+]. The [2]rotaxanes have been characterised by single crystal XRD and solid- and solution-state EPR spectroscopy. Where two paramagnetic M ions are involved [M = Cu2+ and/or (VO)2+] the [2]rotaxanes contain three electron spin S = ½ centres, since the {Cr7Ni} ring has an S = ½ ground state which is well isolated at low temperatures. These three-spin [2]rotaxanes have been characterised in solution by pulsed dipolar EPR spectroscopies (DEER, also known as PELDOR, and RIDME). The M···M and M···{Cr7Ni} interactions measured are consistent with dipolar interactions and also with the distances from single crystal XRD.