Spin-crossover (SCO) systems are the focus of intense research due to their intrinsic behaviour as molecular-level switches. A key parameter in the physical characterization of SCO systems, and key in its potential technological applications, is the transition temperature (T1/2). So far however, the lack of an accurate computational methodology that connects the electronic structure of SCO systems with the experimental trends was missing. In this communication, we present our results for the application of the meta-hybrid GGA functional TPSSh to the accurate calculation of T1/2 in SCO systems.[1,2] Our calculations provide with an electronic structure understanding of the changes in the physical properties in several families of SCO molecules. For instance, the family of tetracoordinated [PhB(MesIm)3Fe–N=PR3] molecules, an unusual coordination number displaying SCO, revealed that the interplay between the phosphine size and the changes in the T1/2 can be traced back to the changes in the electronic structure of the iron center.[3] A linear relationship between the phosphine cone angle and the shift in the T1/2 can be obtained and rationalized from the direct analysis of the underlying electronic structure in terms of the relevant molecular orbitals, results that match the experimental data.[4] Using the same methodology, we will also present the results for a series of dinuclear iron(II) compounds of general formula [FeL1(NCX)2]2L2 (X = S, Se or BH3), for which the stability of the different spin-states can be calculated, unrevealing the origin of the experimentally observed two-step transition for some of them.[5] Other examples where more subtle electronic effects are at play will be discussed, such as the functionalization of the bpp ligand (bpp = 1,3-bis(pyrazol-1′-yl)propane) in the [Fe(bpp)2]2+ system, which can be used to correlate the changes in the T1/2 via ligand functionalization with the corresponding Hammett parameters. Our methodology can provide with quantitative information about the ligand field effect on the d-based molecular orbitals and its implications on the fine-tuning of the T1/2, which can be of great help in the rational design on new SCO systems with tailored properties.

Computational modelling of the ligand tuning effect over the transition temperature in spin-crossover systems using density functional methods

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.