A Simple Approach for Predicting the Spin State of Homoleptic Fe(II) Tris-diimine Complexes

Abstract

We propose a simple method for predicting the spin state of homoleptic complexes of the Fe(II) d ion with chelating diimine ligands. The approach is based on the analysis of a single metric parameter within a free (noncoordinated) ligand: the interatomic separation between the N-donor metal-binding sites. An extensive analysis of existing complexes allows the determination of critical N···N distances that dictate the regions of stability for the high-spin and low-spin complexes, as well as the intermediate range in which the magnetic bistability (spin crossover) can be observed. The prediction has been tested on several complexes that demonstrate the validity of our method.

Pybox-Iron(II) Spin-Crossover Complexes with Substituent Effects from the 4-Position of the Pyridine Ring (Pybox = 2,6-Bis(oxazolin-2-yl)pyridine)

“…The HS states are known to favor distorted coordination geometry in general [34][35][36][37][38][39], which is related to long Fe-N distances and also accommodation of steric congestion during transition. From the N-Fe-N bond angles summarized in Table 3, we can calculate the Σ value [37] for estimation of distortion degree (Table 4), according to Equation (2).…”

“…The φ (N py -Fe-N py angle) and θ (dihedral angle between two pybox systems) values are measures of the angular Jahn-Teller distortion, as Halcrow et al proposed to describe the criterion of SCO [Fe(X-1-bpp) 2 ] 2+ and related compounds [14]. Very recently, a new empirical rule has been proposed based on the interatomic N-N distance in the chelatable diimine structure [36]. Since there is no structural data of the free ligands, the distances were calculated with the density functional theory on the b3lyp/6-311+G(2d,p) level in Gaussian 03 [41].…”

Deciphering the Influence of Meridional versus Facial Isomers in Spin Crossover Complexes

“…Since both the spectrophotometric series (which controls Δ oct ) and the nephelauxetic series (which controls P through the Racah parameters B and C ) depend on the strength and on the nature of the metal‐ligand interactions, it is not so surprising that, for [FeN 6 ] units, the coordination sphere of which is systematically made up of six heterocyclic nitrogen donor, some simple metric parameters were found to be valuable reporters for predicting the emergence of either pure low‐spin state ( ), pure high‐spin state ( ) or spin state equilibria ( ≈ RT , Eq. ) …”

Investigation of the Spin Crossover Properties of Three Dinulear Fe(II) Triple Helicates by Variation of the Steric Nature of the Ligand Type

“…Homoleptic tris-diimine moieties have been extensively explored as ligand donors in SCO complexes [26], with the 2,4-imidazole-imine functional groups commonly displaying SCO behaviour in Fe(II) complexes of this manner [24,27]. Imidazole-imine groups create N-H hydrogen-bond donor sites towards the exterior of the chemical structure, providing an increased potential for the organisation of the induvial subunits into a larger network within the crystal structure, leading to magnetic cooperativity between molecular subunits [25].…”