Snapshot and crystallographic observations of kinetic and thermodynamic products for NO 2 S 2 macrocyclic complexes

Abstract

Direct observation and structural characterization of a kinetic product and a thermodynamic product for complexes with an NO 2 S 2 macrocycle (L) are reported. L reacts with copper(I) iodide to give a mononuclear complex [Cu(L)] 2 (Cu 2 I 4)·2CH 2 Cl 2 (1), featuring three separate units. When cadmium(II) iodide was reacted with L, an anion-coordinated complex [Cd(L)I] 2 (Cd 2 I 6)·4CH 3 CN (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 [Cd 2 (L) 2 I 2 ](Cd 2 I 6) (3) with a brick-type crystal shape as the thermodynamic product. The dissolution-recrystallization process resulted in the elimination of the lattice solvent molecules (acetonitrile) in 2 and the contraction of two neighboring macrocyclic complex units [Cd(L)I] +, forming the pseudo-dimer 3 via 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).