Manganese (III) Compounds Derived from R-Salicylaldoxime and 9-Anthracenecarboxylate Ligands: A Study of Their Synthesis and Structural, Magnetic, and Luminescent Properties

Abstract

The reaction of Mn(II) salts in the air with different R-salicylaldehyde oximes and the sodium or cesium salts of 9-anthracenecarboxylato (9-AC) allows for the isolation of new six polynuclear compounds: [Mn3NaO(salox)3(9-AC)2(EtOH)3H2O]n·2EtOH (1), [Mn3NaO(3-Me-salox)3(9-AC)2(EtOH)3H2O]n·EtOH (2), [Mn6O2(salox)6(9-AC)2(EtOH)2(H2O)2]·3EtOH (3), [Mn3O(3-Me-salox)3(9-AC)(EtOH)3(H2O)]·1.8EtOH·3H2O (4), [Mn6O2(Me-salox)6(9-AC)2(EtOH)4(H2O)2]·0.5H2O (5), and [Mn6O2(Et-salox)6(9-AC)2(EtOH)4(H2O)2]·3EtOH (6). H2salox is a salicylaldehyde oxime, H2(3-Me-salox) is a 3-methyl-salicylaldehyde oxime, H2Me-salox is a 1-(2-hydroxyphenyl)ethan-1-one oxime and a H2-Et-salox is 1-(2-hydroxyphenyl)propan-1-one oxime. Structurally, compounds 1 and 2 consist of chains of trinuclear {MnIII3(μ3-O)(salox)3}+ units connected by Na+ ions. Compounds 3, 5, and 6 are hexanuclear units formed by two parallel trinuclear units {MnIII3(μ3-O)(salox)3}+ or {MnIII3(μ3-O)(Me-salox)3}+ planes related through an inversion center. Compound 4 consists of two isolated [Mn3O(3-Me-salox)3(9-AC)(EtOH)3(H2O)] trinuclear molecules in the unit cell showing crystallographic differences. Magnetic studies reveal a set of antiferromagnetic interactions in compounds 1 and 2 and a combination of antiferromagnetic and ferromagnetic interactions in compounds 3, 5, and 6. In all cases, the magneto-structural correlation between the intramolecular MnIII-N-O-MnIII torsion angle and the magnetic exchange within these units have been confirmed. For compounds 5 and 6, ac magnetic measurements reveal the slow relaxation of magnetization with moderate energy barriers of 19.9 cm−1 and 31.1 cm−1, respectively. Absorbance and fluorescence measurements in solution show the transitions of the 9-anthracenecarboxylate chromophore for all the compounds.