Synthesis and Structural Characterization of Dinuclear Manganese(III) Complexes with Cyclam-Based Macrocyclic Ligands Having Schiff-Base Pendant Arms as Chelating Agents

Abstract

Reaction of a series of dodecadentate ligands (H4L), 1,4,8,11-tetrakis(salicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane and its substituted derivatives, with manganese(II) salts afforded ten dinuclear manganese(III) complexes, [Mn2X2L] (X = O2CCH3, O2CC6H5, and N3), which were characterized by analyzing infrared and electronic spectra and determining the temperature dependence of magnetic susceptibilities (4.5–300 K). Single-crystal X-ray crystallography of [Mn2(O2CCH3)2(tbsaec)]·2CHCl3 (3·2CHCl3) (H4tbsaec = 1,4,8,11-tetrakis(5-bromosalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane), [Mn2(O2CC6H5)2(tbsaec)] (4), [Mn2(O2CC6H5)2(tcsaec)] (6) (H4tcsaec = 1,4,8,11-tetrakis(5-chlorosalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane), [Mn2(N3)2(tnaec)]·2CHCl3 (7·2CHCl3) (H4tnaec = 1,4,8,11-tetrakis(2-hydroxy-1-naphthylmethylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane), [Mn2(O2CCH3)2(tmsaec)] (8) (H4tmsaec = 1,4,8,11-tetrakis(3-methoxysalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane) showed that each manganese(III) ion is chelated by two Schiff-base pendant arms outside the central tetraazacyclotetradecane ring, forming an axially compressed octahedron (for 3, 4, 6, and 8) or trigonal bipyramid (for 7) with an intramolecular Mn–Mn distance of 9.676(4)–10.096(2) Å. In accordance with the crystal structures, the magnetic interaction between the two manganese ions was very weak with a rather significant zero-field splitting of the manganese(III) ions.

Synthesis, Crystal Structures, and Magnetic Properties of Mixed-Valent Tetranuclear Complexes with Y-Shaped MnII2MnIII2 Core

“…The LMCT (Ligand-to-Metal Charge Transfer) bands may be responsible for the high-intensity absorptions in the UV region. In particular, the absorption band at the near-UV region (434sh nm for 3; 442sh for 4) can be assumed as a characteristic LMCT band of phenolato-oxygen to manganese(III) as found in some Schiff-base manganese(III) complexes [24,35]. Furthermore, d-d bands due to six-or five-coordinated manganese(III) ions appeared and hid behind the strong near-UV bands in the visible and NIR regions until around 1000 nm [35].…”

“…Many kinds of tetranuclear Mn II 2 Mn III 2 complexes have appeared in the literature, and butterfly-shaped tetranuclear Mn II 2 Mn III 2 complexes have remarkable magnetic properties with ferromagnetic couplings and SMM behavior [13][14][15]. Based on this background, we have focused on the synthesis of manganese complexes with multidentate organic ligands [16][17][18][19][20][21][22][23][24][25][26][27][28]. We and other researchers have studied coordination compounds based on a multidentate Schiff-base, 1,3-bis(salicylideneamino)-2-propanol, as a dinucleating ligand to make mononuclear, dinuclear, tetranuclear, and polynuclear manganese complexes [16, [29][30][31][32].…”

Synthesis, Crystal Structure, and Properties of Copper(II) Complexes with 1,4,7-Tris(2-Aminoethyl)-1,4,7-Triazacyclononane

“…The taec ligand forms unique dinuclear metal complexes, where the two metal ions are bound by the four pendant groups outside the cyclam ring. Substitution of the 2-aminoethyl pendant groups by other groups such as salicylideneaminoethyl groups also afforded similar dinuclear metal complexes [17][18][19][20]. Concerning these cyclam-based ligands with four pendant groups, the corresponding tacn-based hexadentate ligands with three pendant groups are of interest [21][22][23].…”