Endocyclic and Endo–Exocyclic Silver(I) Complexes of Thiaoxaaza Macrocycles: Crystallographic and NMR Studies

A comparative investigation of the coordination behaviour of a 19-membered NO2S2-macrocycle (L1) and a 20-membered NO2S3-macrocycle (L2) is reported. On silver(i) complexation, L1 yields a discrete endocyclic mononuclear complex, whereas L2 affords a one-dimensional coordination polymer in which the endo-coordinated macrocyclic complex units are linked by silver(i) ions outside the cavity via endo–exo-coordination. The larger ring cavity along with the flexible nature of L2 may induce the weaker endocyclic complexation and contribute to exocyclic coordination as well. In NMR titration studies for the corresponding complex system, however, no evidence of exocyclic coordination was observed. Instead, L1 and L2 form a stable endocyclic 1 : 1 silver(i) nitrate complex, with a higher affinity for the former ligand.

Cooperative anion recognition in copper(II) and zinc(II) complexes with a ditopic tripodal ligand containing a urea group

The ability of Cu(II) and Zn(II) complexes of the ditopic receptor H2L [1-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenyl)-3-(3-nitrophenyl)urea] for anion recognition is reported. In the presence of weakly coordinating anions such as ClO4(-), the urea group binds to the metal ion (Cu(II) or Zn(II)) through one of its nitrogen atoms. The study of the interaction of the metal complexes with a variety of anions in DMSO shows that SO4(2-) and Cl(-) bind to the complexes through a cooperative binding involving simultaneous coordination to the metal ion and different hydrogen-bonding interactions with the urea moiety, depending on the shape and size of the anion. On the contrary, single crystal X-ray diffraction studies show that anions such as NO3(-) and PhCO2(-) form 1:2 complexes (metal/anion) where one of the anions coordinates to the metal center and the second one is involved in hydrogen-bonding interaction with the urea group, which is projected away from the metal ion. Spectrophotometric titrations performed for the Cu(II) complex indicate that this system is able to bind a wide range of anions with an affinity sequence: MeCO2(-) ∼ Cl(-) (log K11 > 7) > NO2(-) > H2PO4(-) ∼ Br(-) > HSO4(-) > NO3(-) (log K11 < 2). In contrast to this, the free ligand gives much weaker interactions with these anions. In the presence of basic anions such as MeCO2(-) or F(-), competitive processes associated with the deprotonation of the coordinated N-H group of the urea moiety take place. Thus, N-coordination of the urea unit to the metal ion increases the acidity of one of its N-H groups. DFT calculations performed in DMSO solution are in agreement with both an anion-hydrogen bonding interaction and an anion-metal ion coordination collaborating in the stabilization of the metal salt complexes with tetrahedral anions.

Zwitterionic dicopper helicates: anion encapsulation and binding studies

The synthesis and spectroscopic studies of a dicopper(II) double helicate capable of binding anions is described. X-Ray crystallographic analysis of three anion variations of the complex have shown that the helicate is capable of accommodating anions with an approximate volume of 0.09 nm(3) and smaller. ESI-MS revealed that the supramolecular complexes retain the 2 : 2 ligand : metal cluster in solution. Spectrometric analysis has shown the complex is capable of binding anions in a 1 : 1 ratio of helicate to anion, in the order SO(4)(2-) > HPO(4)(2-) > ClO(4)(-) approximately BF(4)(-) approximately NO(3)(-). We demonstrate that coordination to the metal centre, H-bonding and electrostatic interactions all play a role in encapsulating the anions.

Anion Selectivity in Zwitterionic Amide-Functionalised Metal Salt Extractants

Amide-functionalised salen ligands capable of extracting metal salts have been synthesised and characterised. Single-crystal X-ray structure determinations of complexes of NiSO4, [Ni(L)(SO4)], confirm that the ionophores are in a zwitterionic form with Ni(II) bound in the deprotonated salen moiety and the SO4(2-) ion associated with protonated pendant N'-amidopiperazine groups. Treatment of [Ni(L)(SO4)] with base removes the protons from the pendant amido-amine group resulting in loss of the SO4(2-) ion and formation of metal-only complexes of type [Ni(L-2H)], which have been characterized by single-crystal X-ray diffraction. Three of the ligands with solubilities suitable for solvent extraction studies show loading and stripping pH-profiles that are suitable for the recovery of CuSO4 or CuCl2 from industrial leach solutions. The copper-only complexes, [Cu(L-2H)], are selective for Cl- over SO4(2-) in both solvent extraction and bulk liquid membrane transport experiments and were found to bind Cl- in two steps via the formation of a 1:1:1 [Cu(L-H)Cl] assembly, followed by a 1:1:2 [Cu(L)Cl2] assembly as the pH of the aqueous phase is lowered. The anion transport selectivity was evaluated for a number of other mono-charged anions and interestingly the ligands were found to display a preference for the Br- ion. To probe the influence of the Hofmeister bias on the selectivity of anion complexation, single-phase potentiometric titration experiments were employed to investigate the binding of SO4(2-) and Cl- by one of the copper only complexes, [Cu(L-2H)] in 95 %/5 % MeOH/water. Under these conditions selectivity was reversed (SO4(2-)>Cl-) confirming that the Hofmeister bias, which reflects the relative hydration energies of the anions, dominates the selectivity of anion extraction from aqueous media into CHCl3.

Two complexes of copper(ii) salts with 5-amino-3-(pyrid-2-yl)-1H-pyrazole, the prototype for a new class of ditopic ligand

The title ligand ('L') in crystalline [CuBrL(2)]Br.CH(3)OH and [Cu(OH(2))L(2)]SO(4).H(2)O.CH(3)OH chelates to both the copper(II) cations and the charge-balancing anions.

Dimetallo[3.3]para- and metacyclophanes by self-assembly of pyridylmethyl armed-monoazatrithia- and monoazadithiaoxa-12-crown-4 ethers with Ag+ ions

New pyridylmethyl armed-monoazadithiaoxa- and monoazatrithia-12-crown-4 have been prepared. The structures of the Ag+ complexes of the new ligands were investigated by X-ray crystallography, 1H NMR titrations, and FAB-MS measurements. In all cases, the Ag+ complexes form dimetallo[3.3]para- or metacyclophane structures depending on the position of the N atom of the pyridine rings.

Order of the coordinating ability of polyatomic monoanions established from their interaction with a disilver(i) metallacyclophane skeleton

An ordered sequence of the coordinating ability of a series of polyatomic monoanions has been established on the basis of structural parameters derived from their interaction with a disilver(I) metallacyclophane skeleton in isostructural complexes.

Macrocyclic ligand design. Structure–function relationships involving the interaction of pyridinyl-containing, oxygen–nitrogen donor macrocycles with selected transition and post transition metal ions on progressive N-benzylation of their secondary amines

Structure-function relationships underlying the interaction of progressively N-benzylated N(4)O(2)-donor macrocycles with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) have been probed using a range of techniques that include X-ray diffraction, DFT computations, solvent extraction, potentiometric stability constant determinations and competitive membrane transport experiments. Collectively, the results indicate that N-benzylation of the secondary amine donor groups of the parent macrocyclic ring results in an enhanced tendency towards selectivity for silver(I) relative to the other six metals investigated. The observed behaviour serves as additional exemplification of the previously proposed concept of selective 'detuning' as a mechanism for metal ion discrimination.