Syntheses and crystal structures of dinuclear, trinuclear [2 × 1 + 1 × 1] and tetranuclear [2 × 1 + 1 × 2] copper(ii)–d10 complexes (d10 ⇒ ZnII, CdII, HgII and AgI) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine)

Abstract

Syntheses, characterization and crystal structures of heterotetranuclear [2 × 1 + 1 × 2] co-crystals [{Cu^IILZn^II(H₂O)₂}{Cu^IIL}₂](ClO₄)₂ (1) and [{Cu^IILCd^II(H₂O)₂(CH₃CN)}{Cu^IIL}₂](ClO₄)₂ (2), dinuclear compound [Cu^IILHg^II(CH₂COCH₃)](ClO₄) (3) and heterotrinuclear [2 × 1 + 1 × 1] co-crystal [{Cu^IILAg^I(H₂O)}{Cu^IIL}](ClO₄) (4) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine) (H₂L) are reported herein. Compounds 3 and 4 crystallize in the orthorhombic Pbca and monoclinic P2₁/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 Cu^IIHg^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 Cu^II₂Ag^I compound 4, one diphenoxo-bridged [Cu^IILAg^I(H₂O)]⁺ cation is co-crystallized with one mononuclear [Cu^IIL] moieties. On the other hand, the structures of the Cu^II₃M^II compounds 1 (M = Zn) and 2 (M = Cd) consist of one diphenoxo-bridged dinuclear Cu^IIM^II unit and two mononuclear [Cu^IIL] moiety; the composition of the dinuclear unit being [Cu^IILZn^II(H₂O)₂]²⁺ and [Cu^IILCd^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 O₃ 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 O₄ compartment of a [Cu^IIL] moiety resulting in the [2 × 1 + 1 × 1] (for 4) or [2 × 1 + 1 × 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 π–π stacking interactions which form dimers between pairs of adjacent molecules in the structure of 3 consisting of Cu^IIHg^II dimers, while one-dimensional stacks are formed in the Cu^II₃Zn^II (1), Cu^II₃Cd^II (2) and Cu^II₂Ag^I (4) complexes. The compositions of the title compounds are compared with the related systems derived from the same ligand. The [2 × 1 + 1 × 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 O₄ compartment of H₂L has also been highlighted in the present investigation.