Magnetostructural Relationships For Fe(III) Spin Crossover Complexes

Abstract

Structural data for fifteen complexes of Fe(III) of a general formula [FeL 5 X], with pentadentate Schiff-base ligands L 5 and unidentate coligands X − , were subjected to a statistical analysis. The multivariate methods such as Pearson correlation, cluster analysis and principal component analysis split the data into two clusters depending upon the low-spin and/or high-spin state of the complex at the temperature of the X-ray experiment. Some of these complexes exhibit a thermally induced spin crossover. The numerical analysis of the magnetic susceptibility and magnetization data for an enlarged set of Fe(III) spin crossover systems yields the enthalpy ΔH and entropy ΔS of the transition along with the transition temperature T 1/2 and the solid state cooperativeness. The thermodynamic data show a mutual relationship manifesting itself by linear ΔS vs ΔH and T 1/2 vs ΔH correlations.

Above Room Temperature Spin Transition in Thermally Stable Mononuclear Fe(III) Complexes

“…To this end, the thermodynamic parameters are Δ H = 8.73 kJ mol –1 and Δ S = 21.27 J K –1 mol –1 at T c = 410 K (when x L = x H = 0.5). These data span the higher edge of those typical for the Fe­(III) containing SCO systems …”

“…These data span the higher edge of those typical for the Fe(III) containing SCO systems. 30 The value of the enthalpy change is not too far from the experimental DSC determination (Figure S8 in the Supporting Information); however, the predicted transition temperature is by far higher than experimentally found T c = 360 K. We only can say that this discrepancy is due to the approximate character of the applied Ising-like model of the SCO. The magnetic data for the complex 2 are essentially analogous to 1 (Figure 9c).…”

Thieno[3,2-c]Pyridine Complex of Ni(II) with Unusual Magnetic Properties

“…Most probably a phase transition applies. The present structural and magnetic data can be utilized in enrichment of the magnetostructural D-correlations and also more advanced statistical methods can be applied for them (TITIŠ et al, 2010;AUGUSTÍN et al, 2015).…”

Structural, Magnetic, and Electrochemical Characterization of Iron(III) and Cobalt Complexes with Penta‐N3O2‐dentate Ligands

“…[16][17][18][19][20] One example is the series of [M III (L R1,R2 )X] complexes (M: Co or Fe; L: N,N'-bis(2'-hydroxybenzylidene)-1,6diamino-3-azahexane; X: pseudo halide or organic molecule) which was studied extensively in the past (Figure 1). [21][22][23][24][25][26][27] The Co(III) complexes are in low spin (LS) states, [27] whereas some Fe(III) complexes showed temperature induced reversible conversions between LS and high spin (HS) states, called spin crossover (SCO). [21][22][23][24][25][26]28,29] The spin state and SCO properties of these iron(III) complexes can be changed by introducing substituents to the Schiff base ligand and by exchanging the monodentate ligand.…”

“…[21][22][23][24][25][26][27] The Co(III) complexes are in low spin (LS) states, [27] whereas some Fe(III) complexes showed temperature induced reversible conversions between LS and high spin (HS) states, called spin crossover (SCO). [21][22][23][24][25][26]28,29] The spin state and SCO properties of these iron(III) complexes can be changed by introducing substituents to the Schiff base ligand and by exchanging the monodentate ligand. Especially the complexes [Fe III (L H,Cl )X], [22] [Fe III (L H,Br )X] [24] and [Fe III (L Cl,Cl )X] [29] (X=N 3 , NCS, NCSe) should be mentioned, which show a temperature induced SCO, whereas the compounds [Fe III (L Br,Br )X] [29] are only in the HS state.…”