New members of the polynuclear manganese family: MnMn single-molecule magnets and MnMn antiferromagnetic complexes. Synthesis and magnetostructural correlations

• Published in: Dalton transactions : an international journal of inorganic chemistry 2020-10, Vol.49 (4), p.1397-13985
• Main Authors: Reis Conceição, Nuno, Nesterova, Oksana V, Rajnák, Cyril, Bo a, Roman, Pombeiro, Armando J. L, Guedes da Silva, M. Fátima C, Nesterov, Dmytro S
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d0dt02652b

The synthesis, crystal structures and magnetic properties are reported for three novel mixed-valence tetranuclear [Mn II 2 Mn III 2 (HBuDea) 2 (BuDea) 2 (EBA) 4 ] ( 1 ), [Mn II 2 Mn III 2 (HBuDea) 2 (BuDea) 2 (DMBA) 4 ] ( 2 ) and undecanuclear [Mn II 3 Mn III 8 O 4 (OH) 2 (BuDea) 6 (DMBA) 8 ] ( 3 ) clusters, where H 2 BuDea is N -butyldiethanolamine, HEBA is 2-ethylbutyric acid and HDMBA is 2,2-dimethylbutyric acid. The compounds have been prepared through self-assembly reactions of manganese( ii ) chloride with H 2 BuDea and respective carboxylic acid in methanol solution in air, affording 1 with HEBA, and 2 or 3 with HDMBA, depending on the experimental conditions. The single crystal X-ray analysis reveals that 1 and 2 have similar centrosymmetric structures based on the {M 4 (μ 3 -O) 2 (μ-O) 4 } core, while 3 discloses the unprecedented {M 11 (μ-O) 4 (μ 3 -O) 12 } one. The Mn 4 complexes display single-molecule magnet (SMM) behavior with a S = 9 spin ground state and a high energy barrier U eff / k B of up to 51 K. The magnetic properties of 2 are successfully modeled with J Mn III -Mn III / hc = 25.7 cm −1 and two J Mn III -Mn II / hc constants of 3.1 and −0.93 cm −1 (data correspond to the = − J 1 · 2 formalism). The Mn 11 cluster exhibits a paramagnetic behavior with dominant antiferromagnetic coupling. A possible influence of intermolecular effects and of different peripheries of the magnetic cores designed by using 2-ethylbutyrate (in 1 ) or 2,2-dimethylbutyrate (in 2 ) on the magnetic properties of 1 and 2 is discussed. The experimental magnetostructural correlations for the {Mn II 2 Mn III 2 (μ 3 -O) 2 (μ-O) 4 } cores, supported by broken symmetry DFT calculations, disclose the X-Mn III Mn III angle and Mn III -O distance (where Mn III -X and Mn III -O are axial Jahn-Teller bonds) as the structural factors having the strongest influence on J Mn III -Mn III exchange coupling. It is shown that two J Mn III -Mn II constants are necessary for the correct description of magnetic exchange couplings in the {Mn II 2 Mn III 2 (μ 3 -O) 2 (μ-O) 4 } tetranuclear unit. Three novel Mn 4 and Mn 11 complexes were synthesized and characterized. Tetranuclear complexes behave as single-molecule magnets with a high energy barrier.