Brian J. McCool

Supramolecular Complexation of Polynuclear Aqua Ions: A Crown Ether Adduct of aμ-Oxo-Bridged Iron(III) Aqua Dimer

Hydrolysis and polymerization of [Fe(OH(2))(6)](3+) in aqueous solution leads, in the early stages, to the oxo-bridged binuclear aqua ion [(H(2)O)(5)Fe(µ-O)Fe(OH(2))(5)](4+), which could be obtained in crystalline form through the use of [18]crown-6. The complex exhibits an almost linear Fe-O-Fe moiety and antiferromagnetic coupling that is consistent with current descriptions of exchange coupling in mono oxo-bridged binuclear Fe(III) complexes.

Excavatolides N–T, New Briaran Diterpenes from the Western Australian Gorgonian Briareum excavatum

A Western Australian sample of the gorgonian Briareum excavatum, collected at Rowley Shoals, afforded one known (10) and seven new briaran diterpenes (1), (3) and (5)–(9). Gross structures and relative stereochemistries were determined by spectroscopic methods and by comparison of spectral data with those of previously reported briarans. Support for a proposed conformation of the 10-membered ring (stabilized by hydrogen-bonding) to explain atypical 1H n.m.r. chemical shifts and coupling constants in (9) was obtained from energy minimization of the proposed structure by an ab initio density functional method.

On the nature of the host–guest interaction between cyclam and 4-tert-butylbenzoic acid—a system pre-assembled for metal complex formation

The host–guest interaction between cyclam and 4-tert-butylbenzoic acid has been investigated by NMR titration, X-ray diffraction, neutron diffraction and semi-empirical MO calculation; the product represents a system preassembled for metal-ion complexation.

Hydrogen-bonded Networks in Crown Ether Complexes of Hydrated Metal Ions

Abstract The hydrated metal nitrates (M(NO3)3.6H2O, M[dbnd]Co, Ni, Cu, Zn and Cd) have been crystallised from water in the presence of 18-crown-6 and their structures determined by X-ray crystallography. In the case of copper, a pseudo four-coordinate square planar complex resides in an extended six-coordinate octahedral array which is further bound in a single-stranded one-dimensional hydrogen bonded polymeric mode. For M[dbnd]Co,Ni,Zn and Cd isomorphous complexes are isolated where the octahedral [M(H2O)5(NO3)+ cation resides in a two-dimensional polymeric network through hydrogen bonds between the water ligands and either the crown ether oxygens or unbound nitrate ions or water molecules.

New macrocyclic ligands: XIV. synthesis and X-ray structures of potentially pentadentate ligands incorporating non-symmetrically arranged N4S-, N3OS-, N2O2S- and N2S2O-heteroatoms

The synthesis and characterization of new mixed-donor macrocyclic ligands incorporating nitrogen, sulfur and/or oxygen heteroatoms are described. The new 17- or 18-membered macrocyclic rings contain unsymmetrical arrangements of their heteroatoms in contrast to related, previously reported rings in which the donor sets are arranged symmetrically. The X-ray structures of the 17-membered rings incorporating N4O- and N4S-donor sets are presented.

Supramolekulare Komplexierung mehrkerniger Aquakomplexe: ein Kronenetheraddukt eines μ‐oxo‐verbrückten zweikernigen Eisen(III)‐Aquakomplexes

Hydrolyse und Polymerisation von [Fe(OH2)6]3+ in wasriger Losung fuhren in einem fruhen Stadium zum oxo-verbruckten, zweikernigen ionischen Aquakomplex [(H2O)5Fe(μ-O)Fe(OH2)5]4+, der durch Zusatz von [18]Krone-6 in kristalliner Form erhalten werden kann. Der Komplex enthalt einen nahezu linearen Fe-O-Fe-Kern und weist eine antiferromagnetische Kopplung auf, was mit den derzeitigen Beschreibungen der Austauschkopplung in zweikernigen FeIII-Komplexen mit einer Oxo-Brucke ubereinstimmt.

On the short C–C bond lengths in macrocyclic ligand systems incorporating ether donors: a comparative neutron and X-ray diffraction study of an O2N3 donor macrocycle: 6,7,8,9,10,11,12,13,19,20-decahydro-5H-dibenzo[e,p][1,4,8,11,14]dioxatriazacycloheptadecine

The neutron diffraction structure of a 17-membered macrocyclic ligand incorporating an O2N3-donor set has been determined in order to investigate whether the C–C bond in the –OCH2CH2O– atom string remains short as found in the corresponding X-ray structure of this compound; the evidence suggests that the short bond found by X-ray diffraction in this as well as in many other polyether compounds is largely an artefact with the ‘real’ component of the shortening being quite minor.

Interaction of related open-chain and macrocyclic ligands incorporating oxygen- and nitrogen-donor atoms with COII, NiII, CuII, ZnII, and CdII. X-Ray structures of a seven-co-ordinate zinc(II) complex as well as seven- and eight-co-ordinate cadmium(II) derivatives

The interaction of CoII, NiII, CuII, ZnII, and CdII with an O2N3-donor open-chain ligand has been investigated and the properties of the resulting 1 : 1 complexes compared with those of two related macrocyclic derivatives. The log K values have been determined in 95% methanol (I= 0.1 mol dm–3, NEt4ClO4). X-Ray structures of the cadmium complexes of the open-chain ligand (L1) and the cyclic derivative (L3) are presented. The open-chain ligand complex is seven-co-ordinate with an approximate pentagonal-bipyramidal co-ordination geometry: nitrate ions occupy axial sites with the O2N3-donor set of the organic ligand co-ordinating equatorially. The complex of the macrocycle (L3)(O2N4-donor set) is eight-co-ordinate with the six macrocyclic donor atoms showing only a small deviation from planar co-ordination while the backbone of the macrocycle is not flat but adopts a puckered arrangement. A nitrate ion occupies one ‘axial’ co-ordination site while the second site is occupied by a water in half of the molecules and a methanol in the remaining half. Solution studies indicate that this latter cadmium complex is substantially more stable than its zinc analogue, an observation which may reflect the better accommodation of the larger cadmium ion by this (18-membered ring) macrocycle relative to ZnII. Molecular-mechanics calculations provide no evidence of any mismatch between the macrocyclic cavity and the cadmium ion. The X-ray structure of the zinc complex of the related O2N3-donor macrocycle (L2) has also been determined; ZnII is seven-co-ordinate with the macrocycle binding to this ion via its five donor groups in an approximately pentagonal-planar fashion. The axial sites are occupied by a nitrate ion and a water molecule, respectively.

Self-assembly directed by NH···O hydrogenbonding: a neutron study of a trilayered supramolecular array formedbetween 1,2-diaminoethane and benzoic acid

The supramolecular array formed by co-crystallisation of 1,2-diaminoethane and benzoic acid is investigated by neutron diffraction; the system self-assembles into an unusual layered structure composed of two-dimensional hydrogen-bonded networks sandwiched between layers of edge-to-face stacked aromatic systems; the number of hydrogen-bond donors and acceptors is balanced in the structure.

Macrocyclic ligand ring size effects. Part 1. Complexation of tetra-aza ligands containing fused dibenzo substituents with ZnII and CdII: a solution stability, X-ray crystal structure, and molecular mechanics study

The interaction of ZnII and CdII with an extensive series of dibenzo-substituted macrocyclic and open-chain tetra-amines has been investigated. All ligands form 1 : 1 (metal : ligand) complexes in solution with these metal ions; the thermodynamic stabilities of the complexes in 95% methanol (I= 0.1 mol dm–3, NEt4ClO4) have been determined. Along one series of 14- to 16-membered macrocyclic systems a dislocation in the stability pattern occurs for ZnII at the 16-membered ring complex while, for CdII, the dislocation corresponded to the 15-membered ring species. As a consequence there is an enhanced stability difference (ZnII > CdII) between the complexes of this latter ring. The observed discrimination shown by the 15-membered ring is largely maintained when bulky alkyl substituents are appended to carbons adjacent to two of the secondary amine donors; however, the absolute magnitudes of the respective stabilities are decreased because of steric effects. In an extension of this study it has been found that open-chain analogues show no unusual discrimination between ZnII and CdII. Other macrocyclic and open-chain ligands containing only anilino nitrogen donors have been shown to form only very weak complexes with ZnII and CdII. The X-ray structures and molecular mechanics investigation of two free ligands and three metal complexes are reported.