Syntheses and crystal structures of dinuclear, trinuclear [2x1+1x1] and tetranuclear [2x1+1x2] copper(II)-d(10) complexes (d(10)double right arrow Zn-II, Cd-II, Hg-II and Ag-I) derived from N,N '-ethylenebis(3-ethoxysalicylaldimine)

Syntheses, characterization and crystal structures of heterotetranuclear [2 x 1 + 1 x 2] co-crystals [{(CuLZnII)-L-II(H2O)(2)}{(CuL)-L-II}(2)](ClO4)(2) (1) and [{(CuLCdII)-L-II(H2O)(2)(CH3CN)}{(CuL)-L-II}(2)](ClO4)(2) (2), dinuclear compound [(CuLHgII)-L-II(CH2COCH3)](ClO4) (3) and heterotrinuclear [2 x 1 + 1 x 1] co-crystal [{(CuLAgI)-L-II (H2O)}{(CuL)-L-II}](ClO4) (4) derived from N,N'-ethylenebis(3-ethoxysalicylaldimine) (H2L) are reported herein. Compounds 3 and 4 crystallize in the orthorhombic Pbca and monoclinic P2(1)/c systems, respectively, while the space group of compounds 1 and 2 is monoclinic C2/c. The structure of 3 consists of a monophenoxo-bridged (CuHgII)-Hg-II dinuclear core in which the mercury(II) centre is dicoordinated by the bridging phenoxo oxygen atom and the CH2 carbon atom of the mono-deprotonated acetone anion. The coordination environment of Hg-II in this compound is almost linear. In the (Cu2AgI)-Ag-II compound 4, one diphenoxo-bridged [(CuLAgI)-L-II(H2O)](+) cation is co-crystallized with one mononuclear [(CuL)-L-II] moieties. On the other hand, the structures of the (Cu3MII)-M-II compounds 1 (M = Zn) and 2 (M = Cd) consist of one diphenoxo-bridged dinuclear (CuMII)-M-II unit and two mononuclear [(CuL)-L-II] moiety; the composition of the dinuclear unit being [(CuLZnII)-L-II(H2O)(2)](2)(+) and [(CuLCdII)-L-II(H2O)(2)(CH3CN)](2)(+) for 1 and 2, respectively. The Ag-I (in 4), Zn-II (in 1) and Cd-II (in 2) ions in the diphenoxo-bridged dinuclear cores are tri-, tetra-and heptacoordinated, respectively. The metal ions are coordinated to two bridging phenoxo oxygen atoms, with the silver(I) and zinc(II) centres being additionally coordinated to one and two water molecules, respectively. While in the case of cadmium(II), the additional five coordination positions are occupied by two ethoxy oxygen atoms, two water oxygen atoms and one acetonitrile nitrogen atom. The coordination environment of silver(I) in 4 is pyramidal with a scalene O-3 triangle as the base, whereas those of zinc(II) and cadmium(II) in 1 and 2 are distorted tetrahedral and distorted pentagonal bipyramidal, respectively. The coordinated water molecule in 4 and each of the two coordinated water molecules in 1 and 2 are encapsulated into the O-4 compartment of a [(CuL)-L-II] moiety resulting in the [2 x 1 + 1 x 1] (for 4) or [2 x 1 + 1 x 2] (for 1 and 2) cocrystallization and self-assemblies. Clearly, the encapsulation of the coordinated water molecule(s) is the governing force for the formation of dinuclear-mononuclear co-crystals in 1, 2 and 4. In addition all four compounds 1-4 have pi-pi stacking interactions which form dimers between pairs of adjacent molecules in the structure of 3 consisting of (CuHgII)-Hg-II dimers, while one-dimensional stacks are formed in the (Cu3ZnII)-Zn-II (1), (Cu3CdII)-Cd-II (2) and (Cu2AgI)-Ag-II (4) complexes. The compsitions of the title compounds are compared with the related systems derived from the same ligand. The [2 x 1 + 1 x 1] co-crystal, 4, is a new type of system in terms of the number of components. Again, in spite of the tri-, tetra-and hepta-coordinated nature of the second metal ion in the dinuclear cores, co-crystallization in 1, 2 and 4, respectively, are new observations. The accommodation/coordination of varieties of metal ions by the O-4 compartment of H2L has also been highlighted in the present investigation.