More surprising differences between two closely similar compartmental ligand families and another dinuclear synthon to stabilize dinuclear–mononuclear cocrystals

Abstract

This paper presents syntheses, characterization, crystal structures and magnetic properties of two diphenoxo-bridged heterodinuclear Cu^IIMn^II/Cu^IIFe^II compounds [Cu^IIL¹Mn^II(H₂O)₃](ClO₄)₂ (1) and [Cu^IIL¹Fe^II(H₂O)₃](ClO₄)₂ (2) and two tetranuclear Cu^II₃Mn^II/Cu^II₃Fe^II compounds [{Cu^IIL²Mn^II(H₂O)(MeOH)₂}(Cu^IIL²)₂](ClO₄)₂·MeOH (3) and [{Cu^IIL²Fe^II(H₂O)(MeOH)₂}(Cu^IIL²)₂](ClO₄)₂·MeOH (4) derived from two 3-methoxysalicylaldehyde-diamine Schiff base compartmental ligands H₂L¹ and H₂L², in which the diamine counterpart comes from 1,3-diaminopropane and o-phenylenediamine, respectively. The two compounds 1 and 2 crystallize in the same space group (monoclinic P2₁/n) with practically identical unit cell parameters and are isomorphous. Similarly, the two compounds 3 and 4 crystallize in the same space group (monoclinic P2₁/c) with practically identical unit cell parameters and are isomorphous. The tetranuclear [{Cu^IIL²M^II(H₂O)(MeOH)₂}(Cu^IIL²)₂]²⁺ dication in 3 (M = Mn) and 4 (M = Fe) is a self-assembly of one diphenoxo-bridged dinuclear [Cu^IIL²M^II(H₂O)(MeOH)₂]²⁺ dication and two mononuclear [Cu^IIL²] units. One mononuclear unit is self-assembled with the dinuclear unit by four bifurcated water⋯phenoxo/methoxy (O–H⋯O) hydrogen bonds and three π⋯π stacking interactions, while the second mononuclear unit is interlinked with the dinuclear unit by one methanol⋯phenoxo (O–H⋯O) hydrogen bond only. Clearly, compounds 3 and 4 are [2 × 1 + 1 × 2] cocrystals of one dinuclear and two mononuclear units. Variable-temperature magnetic susceptibility measurements of all the four compounds have been carried out, revealing moderate antiferromagnetic interaction between the copper(II) and manganese(II)/iron(II) in the dinuclear cores with J values (H = −2JS₁S₂) −29.1, −36.9, −15.9 and −20.2 cm⁻¹, respectively. The magnetic properties are in line with those of previous related examples. Unique features in the structures of 1–4 have been discussed.