Syntheses, Structures, and Magnetic Properties of Mononuclear Cu^II and Tetranuclear Cu^II₃M^II (M = Cu, Co, or Mn) Compounds Derived from N,N‘-Ethylenebis(3-ethoxysalicylaldimine):  Cocrystallization Due to Potential Encapsulation of Water

Syntheses, structures, and magnetic properties of one mononuclear inclusion compound [Cu^IIL¹⊂(H₂O)] (1) and three tetrametal systems of the composition [{Cu^IIL¹}₂{Cu^IIL¹M^II(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 [Cu^IIL¹M^II(H₂O)₃]²⁺ cation and two mononuclear [Cu^IIL¹] moieties. In the dinuclear [Cu^IIL¹M^II(H₂O)₃]²⁺ cation, the metal centers are doubly bridged by the two phenolate oxygens. The second metal center, M^II (Cu in 2, Co in 3, and Mn in 4), in the [Cu^IIL¹M^II(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 [Cu^IIL¹] moieties, resulting in the formation of the tetrametal [{Cu^IIL¹}₂{Cu^IIL¹M^II(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 [Cu^IIL¹] species. In the case of 2, there are two independent [Cu^IIL¹Cu^II(H₂O)₃]²⁺ units. The τ ((β − α)/60, where β and α 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 τ 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 Cu^IIM^II moiety and two noninteracting Cu^II 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.