Spin Crossover in cis Manganese(III) Quinolylsalicylaldiminates

• Published in: European journal of inorganic chemistry Vol. 2015; no. 15; pp. 2534 - 2542
• Main Authors: Sirirak, Jitnapa, Harding, David J., Harding, Phimphaka, Murray, Keith S., Moubaraki, Boujemaa, Liu, Lujia, Telfer, Shane G.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.05.2015; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Cationic; Cations; Chemistry; Chemistry, Inorganic & Nuclear; Crossovers; DFT calculations; Diffraction; Ligands; Magnetic permeability; Manganese; Mathematical analysis; Physical Sciences; Redox activity; Schiff base ligands; Schiff bases; Science & Technology; Spin crossover; TRANSITION; ELECTROCHEMISTRY; PROFILE; SERIES; Redox activity; LIGANDS; PHENOXYL RADICAL COMPLEXES; Spin crossover; STATE; Schiff base ligands; DFT calculations; Manganese
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201500196

Two new MnII/III redox pairs, [Mn(qsal‐Cl)2]0/+ 10/+ and [Mn(qsal‐Br)2]0/+ 20/+ have been synthesized employing the tridentate Schiff base ligands, 5‐X–N‐(8‐quinolyl)salicylaldimine (Hqsal‐X, X = Cl and Br). The neutral MnII complexes 1 and 2 were prepared from MnCl2 and Hqsal‐Cl and Hqsal‐Br while oxidation of 1 or 2 with AgOTf yields the cationic MnIII complexes, [Mn(qsal‐Cl)2]OTf, 1+, and [Mn(qsal‐Br)2]OTf, 2+. 1 and 2 have been characterized by single‐crystal X‐ray diffraction as CH2Cl2 solvates. The Mn centres adopt a strongly distorted octahedral geometry with cis O donors due to the pair of meridionally bound qsal‐X ligands. Electrochemical studies indicate two reversible one‐electron redox processes, Mn2+/3+ and Mn3+/4+. Spectroscopic studies show the LMCT bands move to lower wavelengths by ca. 30 nm while the νC=N stretches are little changed in the cationic complexes. Variable temperature magnetic susceptibility measurements indicate that 1+ and 2+ undergo gradual half spin crossover, despite having cis O donors. DFT calculations reveal a small HS–LS gap in the MnIII systems consistent with spin crossover and provide insight into the ligand design necessary for spin crossover in cis‐N4O2 MnIII compounds. We report the redox pairs [Mn(qsal‐X)2]0/+ in which the MnIII cations exhibit spin crossover despite the cis O donors.