Syntheses, Structures, and Magnetic Properties of Mononuclear CuIIand Tetranuclear CuII₃MII(M = Cu, Co, or Mn) Compounds Derived fromN,N‘-Ethylenebis(3-ethoxysalicylaldimine): Cocrystallization Due to Potential Encapsulation of Water

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Abstract

Syntheses, structures, and magnetic properties of one mononuclear inclusion compound [CuIIL1 within (H2O)] (1) and three tetrametal systems of the composition [{CuIIL1}2{CuIIL1MII(H2O)3}]ClO4)2 (M = Cu (2), M = Co (3), M = Mn (4)) derived from the hexadentate Schiff base compartmental ligand N,N'-ethylenebis(3-ethoxysalicylaldimine) (H2L1) have been described. Compounds 1 and 2 crystallize in orthorhombic Pbcn and monoclinic P21/c systems, respectively, and the space group of the isomorphous compounds 3 and 4 is monoclinic C2/c. The water molecule in 1 is encapsulated in the vacant O4 compartment because of the hydrogen bonding interactions with the ether and phenolate oxygens, resulting in the formation of an inclusion product. The structures of 2-4 consist of the [CuIIL1MII(H2O)3]2+ cation and two mononuclear [CuIIL1] moieties. In the dinuclear [CuIIL1MII(H2O)3]2+ cation, the metal centers are doubly bridged by the two phenolate oxygens. The second metal center, MII (Cu in 2, Co in 3, and Mn in 4), in the [CuIIL1MII(H2O)3]2+ cation is pentacoordinated by the two phenoxo oxygens and three water molecules. Two of these three coordinated water molecules interact, similar to that in 1, with two mononuclear [CuIIL1] moieties, resulting in the formation of the tetrametal [{CuIIL1}2{CuIIL1MII(H2O)3}]2+ system that consists of the cocrystallized dinuclear (one) and mononuclear (two) moieties. Evidently, the cocrystallization observed in 2-4 is related to the tendency of a water molecule to be encapsulated in the vacant O4 compartment of the mononuclear [CuIIL1] species. In the case of 2, there are two independent [CuIIL1CuII(H2O)3]2+ units. The tau ((beta-alpha)/60, where beta and alpha are the largest and second largest bond angles, respectively) values in the pentacoordinated environment of the two copper(II) centers in 2 are 0.04 and 0.37, indicating almost ideal and appreciably distorted square pyramidal geometry, respectively. In contrast, the tau values (0.54 for 3 and 0.49 for 4) indicate that the coordination geometry around the cobalt(II) and manganese(II) centers in 3 and 4 is intermediate between square pyramidal and trigonal bipyramidal. The variable-temperature (2-300 K) magnetic susceptibilities of compounds 2-4 have been measured. The magnetic data have been analyzed in the model of one exchange-coupled dinuclear CuIIMII moiety and two noninteracting CuII centers. In all three cases, the metal ions in the dinuclear core are coupled by a weak antiferromagnetic interaction (J = -17.4 cm-1, -8 cm-1, and -14 cm-1 for 2, 3, and 4, respectively). The observation of a weak interaction has been explained in terms of the structural parameters and symmetry of the magnetic orbitals.

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