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

Syntheses, structures, and magnetic properties of one mononuclear inclusion compound [Cu^IIL¹⊂(H₂O)] (<b>1</b>) and three tetrametal systems of the composition [{Cu^IIL¹}₂{Cu^IIL¹M^II(H₂O)₃}](ClO₄)₂<b></b>(M = Cu (<b>2</b>), M = Co (<b>3</b>), M = Mn (<b>4</b>)) derived from the hexadentate Schiff base compartmental ligand <i>N</i>,<i>N</i>‘-ethylenebis(3-ethoxysalicylaldimine) (H₂L¹) have been described. Compounds <b>1</b> and <b>2</b> crystallize in orthorhombic <i>Pbcn</i> and monoclinic <i>P</i>2₁/<i>c</i> systems, respectively, and the space group of the isomorphous compounds <b>3</b> and <b>4</b> is monoclinic <i>C</i>2/<i>c</i>. The water molecule in <b>1</b> 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 <b>2</b>−<b>4 </b>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 <b>2</b>, Co in <b>3</b>, and Mn in <b>4</b>), 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 <b>1</b>, 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 <b>2</b>−<b>4</b> 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 <b>2</b>, 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 <b>2</b> are 0.04 and 0.37, indicating almost ideal and appreciably distorted square pyramidal geometry, respectively. In contrast, the τ values (0.54 for <b>3</b> and 0.49 for <b>4</b>) indicate that the coordination geometry around the cobalt(II) and manganese(II) centers in <b>3</b> and <b>4</b> is intermediate between square pyramidal and trigonal bipyramidal. The variable-temperature (2−300 K) magnetic susceptibilities of compounds <b>2</b>−<b>4</b> 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 (<i>J</i> = −17.4 cm^-1, −8 cm^-1, and −14 cm^-1 for <b>2</b>, <b>3</b>, and <b>4</b>, respectively). The observation of a weak interaction has been explained in terms of the structural parameters and symmetry of the magnetic orbitals.