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

Crystal structures of the complexes containing macrocyclic cations [M(cyclam)]2+ (M = Ni, Zn) and tetra-iodido-cadmate(2-) anion

The asymmetric units of the isostructural compounds (1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N)nickel(II) tetra-iodido-cadmate(II), [Ni(C10H24N4)][CdI4] (I), and tri-iodido-1κ3 I-μ-iodido-(1,4,8,11-tetra-aza-cyclo-tetra-decane-2κ4 N)cad-mium(II)zinc(II), [CdZnI4(C10H24N4)] (II) (C10H24N4 = 1,4,8,11-tetra-aza-cyclo-tetra-decane, cyclam, L), consist of the centrosymmetric macrocyclic cation [M(L)]2+ [M = NiII or ZnII] with the metal ion lying on a twofold screw axis, and the tetra-iodo-cadmate anion [CdI4]2- located on the mirror plane. In I, the anion acts as an uncoordinated counter-ion while in II it is bound to the ZnII atom via one of the iodide atoms, thus forming an electroneutral heterobimetallic complex [Zn(L)(CdI4)]. The NiII and ZnII ions are coordinated in a square-planar manner by the four secondary N atoms of the macrocyclic ligand L, which adopts the most energetically stable trans-III conformation. The [CdI4]2- anions in I and II are structurally very similar and represent slightly deformed tetra-hedrons with average Cd-I bond lengths and I-Cd-I angles of ca 2.79 Å and 109.6°, respectively. The supra-molecular organization of the complexes under consideration in the crystals is very similar and is determined by the hydrogen-bonding inter-actions between the secondary amino groups of the ligand L in the [M(L)]2+ cations and iodide atoms of the [CdI4]2- anion. In particular, the alternating cations and anions form chains running along the b-axis direction that are arranged into di-periodic sheets oriented parallel to the (101) and (01) planes. Because both kinds of sheets are built from the same cations and anions, this feature provides the three-dimensional coherence of the crystals of I and II.

Influence of the Reaction Sequence on the Complexation of an NS4-Macrocycle with CdII and CuI Salts Leading to the Formation of Supramolecular Isomers and an Endo/Exocyclic CuI Complex

In the construction of metallosupramolecules, the reaction sequence in a three-reactant system (one ligand plus two metal ions) could be one of the controlling factors influencing the outcome of the reaction. In this work, the formation of supramolecular isomers (1 and 2) and an endo/exocyclic Cu⁺ complex (4) of the NS₄-macrocycle (L) via different sequential metal addition protocols (routes I-III) is reported. In one-pot reactions of L with Cu(CH₃CN)₄PF₆ in the absence (route I) and presence (route II) of CdI₂, a cyclic dimer Cu^I complex, [Cu₂(L)₂](PF₆)₂ (1), and a one-dimensional coordination polymer, [Cu₂(L)₂]_n·n[CdI₄] (2), were obtained, respectively. Interestingly, the complex cations in 1 and 2 are supramolecular isomers formed via cyclization and polymerization upon complexation, respectively, probably due to different geometric and electronic complementarities, via the C-H···X^- hydrogen bonds, between L and the counterion. In the two-step reaction (route III), an endocyclic Cd²⁺ complex, [Cd(L)I₂] (3), obtained in the first step was utilized in the following reaction with Cu(CH₃CN)₄PF₆, giving rise to an endo/exocyclic tetranuclear Cu⁺ complex, [Cu₄(L)₂(CH₃CN)₆](PF₆)₄ (4), via Cd²⁺ → 2Cu⁺ substitution, which is not accessible by conventional procedures. Solution studies by comparative NMR and electrospray ionization mass spectroscopy also support metal substitution by showing the stronger binding affinity of Cu⁺ over Cd²⁺. These results demonstrate that the metal substitution protocol could be useful for reaching novel metallosupramolecules difficult to obtain by other methods.