Spin-crossover transition metal complexes as candidates to single-molecule devices.

Abstract

Recently, spin-crossover complexes have been especially appealing due to their electron transport ability amongst other useful properties. By switching its spin state this conductance can be modified, even cancelled. Thus, SCO complexes can be used in new electronic and spintronic devices, such as memories, nanoparticle electronics and single-molecule devices by changing their spin state by many external stimuli, such as temperature, pressure or light, which are truly easy controllable parameters. This work focuses on mononuclear coordination complexes taking into consideration different metallic centres (FeII, CoII, CrII, MnIII and MnII) to gather information about their conducting ability. The study has been performed using Density Functional Theory (DFT) methods with six different exchange-correlation functionals (B3LYP, B2PLYP, TPSSh, OPBE, M06 and ωB97x) in order to compare their accuracy in the estimation of the energy difference between high- and low-spin states. Hence, a universal functional for any metallic complex can be defined, as until now only FeII systems have been exhaustively studied in the spin transition field. Results obtained show that for the thirteen compounds studied, the functional that has best performed is the hybrid TPSSh. One of the FeII compounds studied, [Fe(amp)2Cl2], has been found to be the best candidate to become a single-molecule device, generating a β-polarised current when a differential of potential is applied. Otherwise, the other compounds researched showed a mediocre conducting ability. Therefore, further research is required in order to obtain more potential candidates to become single-molecule devices.