Electronic Structure Modulation in an Exceptionally Stable Non-Heme Nitrosyl Iron(II) Spin-Crossover Complex

The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF6)2 (bztpen=N‐benzyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethylenediamine) displays an S=1/2↔S=3/2 spin crossover (SCO) behavior (T1/2=370 K, ΔH=12.48 kJ mol−1, ΔS=33 J K−1 mol−1) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0↔S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120–420 K affording a detailed picture of how the electronic distribution of the t2g–eg orbitals modulates the structure of the {FeNO}7 bond, providing valuable magneto–structural and spectroscopic correlations and DFT analysis. ON–OFF switching of strong antiferromagnetic coupling and modulation of molecular and electronic structure are controlled through thermal spin crossover behavior in a non‐heme nitrosyl iron complex. This has been analyzed by using the thermal dependence of magnetic susceptibility, EPR, Mössbauer, UV/Vis, IR, and Raman spectroscopy, crystal structure (in the 120–420 K range), and DFT calculations (see figure).