Relaxing amid Three: Slow Magnetization Relaxation in Three‐Coordinate Chromium(II) N‐Heterocyclic Carbene Complexes
Gabriela Handzlik, Irene Ligielli, Sakshi Nain, Rishu Khurana, Md. Ehesan Ali, Evangelos Papangelis, Charalampos Papapanagis, Corinne Bailly, Nikolaos Tsoureas, Marianna Danopoulou, Costas Bethanis, Pierre Braunstein, Dawid Pinkowicz, Jurek Krzystek, Panayotis Kyritsis, Andreas A. DanopoulosAbstract
Three‐coordinate, paramagnetic CrII complexes of type [Cr(amido)nBnm(NHC)], NHC = N, N’‐bis‐(2,4,6‐trimethylphenyl)‐imidazol‐2‐ylidene (IMes); N, N’‐bis‐(2,6‐di‐isopropylphenyl)‐imidazol(in)‐2‐ylidene, (S)IDiPP; N, N’‐bis‐(2,6‐di‐isopropylphenyl)‐imidazol‐4‐ylidene, (aIDiPP); amido = N(SiMe3)2, NH(DiPP); Bn = benzyl, n = 2, m = 0; n = 1, m = 1, were prepared by substitution or aminolysis and thermolysis methods from [Cr{N(SiMe3)2}2(THF)2] or [CrBn2((S)IDiPP)], respectively. Depending on the nature of the NHC and the amido ligands, different geometries at CrII (ranging from distorted trigonal planar, to extended Y‐, compressed Y‐, and distorted T‐shaped) and conformations, were observed. HFEPR spectroscopy was employed to accurately determine spin Hamiltonian parameters, consisting of zero‐field splitting (axial D and rhombic E components) and g‐values, of five S = 2 complexes exhibiting D and E/D in the range from −2.98 to −1.63 cm−1 and 0.026 − 0.069, respectively. AC magnetometry established slow magnetization relaxation in three complexes, operating by Raman or combined Raman‐Orbach processes. Ab initio calculations provided computed zfs values, in good agreement with those obtained by HFEPR. Magnetostructural comparisons are made within this three‐coordinate CrII family, as well as with previously studied two‐ or four‐ coordinate CrII complexes.