Spin State Crossover, Vibrational, Computational, and Structural Studies of FeII 1-Isopropyl-1H-tetrazole Derivatives

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Mononuclear complexes of formula [Fe(iptz)6]X2 {X = BF4– (1), ClO4– (2); iptz = 1-isopropyl-1H-tetrazole} have been synthesized and characterized spectroscopically and structurally. These materials display a gradual and incomplete spin conversion around 95 K on cooling, as well as a reversible thermochromic effect. This magnetic behavior was satisfactorily simulated using the Sorai and Seki domain model (ΔH = 5.9 kJ mol–1, ΔS = 57 J mol–1 K–1 for 1, and ΔH = 5.4 kJ mol–1, ΔS = 63 J mol–1 K–1 for 2). Although spin crossover was observed earlier on a powdered sample of 1, we present the X-ray crystal structure and magnetic properties of the crystalline compound for the first time. The crystal structures of four new iron complexes are also provided: two polymorphs of [Fe(iptz)4(NCS)2] (3), and compounds [Fe(iptz)4Cl2] (4) and [Fe(iptz)2(H2O)2(CH3SO3)2] (5). Compound 3, which is the first FeII mononuclear thiocyanato complex with coordinated 1-R-1H-tetrazole ligands, is a high-spin complex. DFT computations enabled the estimation of the spin state energies for the trans and cis isomers of [Fe(iptz)4(NCS)2] as well as the [Fe(iptz)6]2+ cation. The stereoisomerism in 3 related to the mutual orientation of the ligand rings was also studied, along with π-acceptor properties of the iptz ligand, which are modified by the orientation of the coordinated ligand. The dependence between the Fe–N(CS) distance and the electronic energy of the tilt of the coordinated thiocyanato anion for trans-[FeL2(NCS)2] and trans-[FeL4(NCS)2] complexes is discussed, based on the comparison of X-ray data and DFT modelling for selected complexes.

Publication year:2018

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Authors:International

Authors from:Higher Education