Investigation of SCO property–structural relationships in a family of mononuclear Fe(ii) complexes

• Published in: Inorganic chemistry frontiers 2019-08, Vol.6 (8), p.2194-2199
• Main Authors: Xiu-Qin Chen, You-De, Cai, Yi-Shan, Ye, Ming-Liang, Tong, Bao, Xin
• Format: Article
• Language: English
• Subjects: Coordination; Crossovers; Crystallography; Ethane; Field strength; Inorganic chemistry; Ligands; Quinoline
• ISSN: 2052-1545; 2052-1553
• DOI: 10.1039/c9qi00577c

Six new mononuclear Fe(ii) complexes of the [FeL(NCE)2] family have been synthesized: L = N,N‘-dimethyl-N,N‘-bis-(quinoline-2-ylmethyl)ethane-1,2-diamine (2MeLquinoline), E = S (1), Se (2), BH3 (3) and L = N,N‘-dibenzyl-bis-(pyridin-2-ylmethyl) ethane-1,2-diamine (DibenzylL), E = S (4a and 4b), Se (5), and BH3 (6). Introduction of quinolyl groups in 1–3 results in elongated Fe–N(quinolyl) distances and severe distortion of the coordination environment. The quinolyl and benzyl groups in the tetradentate ligand hamper a dense crystal packing and only weak van der Waals interactions were found for all these complexes. 1, 2, 3, 4b and 5 are all stabilized in a high spin (HS) state over all temperatures. 4a, a polymorph of 4b, undergoes a spin crossover (SCO) around 81 K. 6 is also SCO-active and the conversion curve is centred at 183 K. A comparison of 23 analogous [FeL(NCE)2] complexes reported so far shows that both the ligand field strength of the NCE− co-ligands and the Fe–N≡C(E) angle play a determinant role in T1/2. The replacement of the tetradentate ligand (confined to those of the same type as 2MeLquinoline and 2MeLquinoline) does not affect the first coordination sphere notably, except in the case of a highly steric ligand 2MeLquinoline, and hence has a slight effect on the temperature of SCO.