Snapshot and crystallographic observations of kinetic and thermodynamic products for NO₂S₂ macrocyclic complexes

Direct observation and structural characterization of a kinetic product and a thermodynamic product for complexes with an NO₂S₂ macrocycle (L) are reported. L reacts with copper(I) iodide to give a mononuclear complex [Cu(L)]₂(Cu₂I₄)·2CH₂Cl₂ (1), featuring three separate units. When cadmium(II) iodide was reacted with L, an anion-coordinated complex [Cd(L)I]₂(Cd₂I₆)·4CH₃CN (2) with a needle-type crystal shape was formed as the kinetic product. Interestingly, when the needle-type kinetic product was left undisturbed in the mother solution it gradually transformed to the pseudo-dimer complex [Cd₂(L)₂I₂](Cd₂I₆) (3) with a brick-type crystal shape as the thermodynamic product. The dissolution-recrystallization process resulted in the elimination of the lattice solvent molecules (aceto-nitrile) in 2 and the contraction of two neighboring macrocyclic complex units [Cd(L)I]⁺, forming the pseudo-dimer 3via an intermolecular Cd⋯I interaction between two monomers. For the entire process from kinetic to thermodynamic products, it was possible to obtain sequential photographic snapshots, single-crystal X-ray structures and powder X-ray diffraction patterns. For the copper(I) and cadmium(II) complexes, competitive NMR results agree with the solid-state data that show copper(I) has a higher affinity for L than does cadmium(II).