Syntheses, crystal structures and spectroscopy of di/tri/tetranuclear discrete and co-crystalline copper(II)-Na^I/Zn^II/Cd ^II complexes derived from a compartmental ligand: Inconsistency in the shifting of the copper(II) d-d band

The work in this report presents the syntheses, characterization, crystal structures and electronic spectra of the six heteronuclear complexes [Cu ^IIL¹Na^I(μ-BF₄)₂Na ^IL¹Cu^II]·₂CH ₃COCH₃ (1), [Cu^IIL¹Na ^I(NO₃)(MeOH)] (2), [Cu^IIL¹Zn ^II(H₂O)2L¹Cu^II](ClO ₄)₂ (3), [Cu^II(MeOH)L¹Zn ^IICl₂] (4), [Cu^IIL¹Cd ^II(H₂O)(MeOH)₂](ClO₄)2 (5) and [Cu^IIL¹Cd^IICl2(MeOH)][Cu^II(MeOH) L¹Cd^IICl₂] (6), where H₂L ¹ is N,N′-ethylenebis(3-methoxysalicylaldimine). The crystal systems and space groups are as follows: 1 and 2, triclinic, P1̄; 3 and 6, monoclinic, P2₁/c; 4, orthorhombic, P2₁2₁2 ₁; 5, monoclinic, C2/c. While the N(imine)₂O(phenoxo) ₂ compartment accommodates the copper(II) center, the larger and open O(phenoxo)₂O(methoxy)₂ compartment interacts with the second metal ion. Compounds 2, 4 and 5 are diphenoxo-bridged dinuclear systems, compound 3 is a trinuclear system in which the two Cu^IIZn ^II pairs are monophenoxo-bridged, compound 1 is a tetranuclear system in which two diphenoxo-bridged Cu^IINa^I units are interlinked by two tetrafluoroborate moieties, and compound 6 is a [2×1+2×1] co-crystal of two dinuclear Cu^IICd^II units. The solid state electronic spectra of compounds 1-6 and also the mononuclear compound [Cu^IIL¹(H₂O)] have been recorded in the range 400-800 nm. While correlating the d-d band position with the structural parameters and a previously proposed correlation, some inconsistency has been found, indicating that this area should be explored further.