Andrew C. Warden

Binding of inorganic oxoanions to macrocyclic ligands: interactions of sulfate and dithionate with protonated forms of [18]aneN6

Three sulfate-macrocycle adducts [H6L(HSO4)4(SO4)]·H2O (1), [H6L(SO4)3] n (2) and [H6L(HSO4)2Cl4]·2H2O (3) n (where L = n [18]aneN6) were crystallized from solutions containing the macrocycle and the appropriate inorganic acids, and [H4L(S2O6)2]·2H2O (4) from an aqueous solution of the macrocycle and sodium dithionate. All four structures show that the polyammonium groups on the protonated macrocycle participate in ‘co-ordination’ or supramolecular interactions with one or more oxygen atoms from the polyoxoanions (i.e., SO42−, HSO4− or S2O62−). In 3, the protonated macrocyclic cavity holds the two chloride anions in preference to the oxoanions. The sulfate anions show remarkable versatility in their interactions with the macrocycle. Of particular note is a unique η-5 N–H⋯O cluster involving the sole sulfate anion in 1, but there are many common features throughout the structures, such as the inclusion of one anion on either side of the macrocycle and the participation of all ammonium protons in H-bonding interactions.

Anion binding to azamacrocycles: synthesis and X-ray crystal structures of halide adducts of [12]aneN4 and [18]aneN6

An investigation into the halide binding properties of two polyazamacrocycles [12]aneN4 n (L1) and [18]aneN6 n (L2) has resulted in the determination of the molecular structure of five compounds [H4L1(Br)4]·2H2O (1), [H2L1(I3)2]·2I2·2CH3CN (2), [H6L2(Cl)6]·4H2O (3), [H4L2(Br)4]·2H2O (4) and [H4L2(I)2(I3)2] n (5). [18]aneN6 n (L2) was generally found to bind two anions within the macrocyclic cavity. In the adducts formed by [12]aneN4 n (1 and 2), the anions and solvent of crystallization do not sit within the [12]aneN4 cavity, instead preferring to occupy positions exterior to the macrocycle. Left- and right-handed helices are formed by the I3− and I2 moieties in 2 that house acetonitrile solvent molecules in the centre of the spiral. In most cases, chloride and bromide adopt trigonal pyramidal co-ordination motifs with various degrees of distortion from a regular geometry. The ring size, conformational flexibility and level of protonation were found to influence the halide binding characteristics of the macrocycles.

The synthesis, structure and properties of copper(II) complexes of asymmetrically functionalized derivatives of 1,4,7-triazacyclononane

Reaction of 1-propylamino-4-acetato-1,4,7-triazacyclononane (L1), 1-benzyl-4-acetato-1,4,7-triazacyclononane (L2) and 1-benzyl-4-propylamino-1,4,7-triazacyclononane (L3) with a copper(II) salt gave Na2[CuL1](ClO4)3(1a), [CuL2]Cl (2) and [Cu2L32](ClO4)4.5H2O (3), respectively. [CuL4]ClO4 (4) was formed by reacting 1-formyl-4-ethylacetato-1,4,7-triazacyclononane with cupric chloride in aqueous solution. The X-ray crystal structures of the complexes reveal that the ligands generate distorted square pyramidal or square planar coordination environments about the Cu(II) centre, but in three complexes (1b, 3 and 4) weak interactions to an oxygen atom from a perchlorate anion and, in the case of 4, also to an amide nitrogen leading to tetragonally elongated octahedral Cu(II) geometries. In 4, the formyl group is found to reduce the coordinating ability of the macrocyclic nitrogen to which it is attached, as evidenced by the weak CuN interaction. The formation of five-membered chelate rings on coordination of the ligands further contributes to the distortion from the ideal geometries. The crystal lattices contain a number of novel supramolecular features. 1a contains a negatively charged sodium perchlorate chain of composition [Na2(ClO4)3]x(x-), with a complex series of Na-O-Na bridges flanked by [CuL1]+ units, while 3 contains highly complex hydrogen bonded sheets approximately 20 A thick that stack through van der Waals interactions. One-dimensional chains comprised of copper complexes are found in 2 and 4, and are held together by hydrogen bonds in 2 and acetate bridges between the copper cations in 4. The solution EPR spectra indicate that the copper(II) centres exist in isolated distorted square pyramidal (possibly square planar for 4) environments, while in the solid state there is evidence for the existence of weak exchange and dipole-dipole coupling for some complexes.