Inert Transition Metal Ion Complexes in Organic Synthesis: Protection and Activation.

Single-crystal X-ray diffraction studies for a variety of metal ion complexes of functionalised sarcophagines (sarcophagine=sar=3,6,10,13,16,19-hexa-azabicyclo[6.6.6]icosane) have further confirmed not only that the form of the metal ion/sar unit is unique for each metal, albeit with a sensitivity of the conformation to the associated counter anions, but also that for any given metal and ligand substituent, the dimensions (bond lengths and angles) of the complex and the substituent at the secondary nitrogen centres do not differ significantly from those of the isolated components.

Hydrogen Bonding Directed Self-Assembly of a Binuclear Ag(I) Metallacycle into a 1D Supramolecular Polymer.

An Ag(I) metallacycle obtained unexpectedly during the preparation of Pd(II) complexes of the bifunctional ligand 5-([2,2'-bipyridin]-5-yl)pyrimidine-2-amine () has been characterized using X-ray structure determination as a binuclear, metallacyclic species [Ag](SbF), where both the bipyridine and pyrimidine-N donors of are involved in coordination to the metal. The full coordination environment of the Ag(I) defines a case of highly irregular 4-coordination. In the crystal, the Ag-metallacycles assemble into one-dimensional supramolecular metalladynamers linked together by hydrogen-bonding interactions.

Dynamer and Metallodynamer Interconversion: An Alternative View to Metal Ion Complexation.

A bifunctional molecule containing both a bidentate binding site for metal ions and an aminopyrimidine H-bond donor-acceptor site has been synthesized, and its properties, in its free and coordinated forms, have been established in solution and in the solid state by analytical and spectroscopic methods as well as by X-ray structure determinations. Structural characterization has shown that it forms a one-dimensional H-bonded polymeric assembly in the solid state, while spectroscopic measurements indicate that it also aggregates in solution. The reaction of a simple Fe(II) salt with this assembly results in the emergence of two geometrical isomers of the complex: [FeL](BF4)·9HO- (meridional, ) and [FeL](SiF)(BF)·12HO- (facial, ).

Intermolecular Interaction Tuning of Spin-Crossover Iron(III) Complexes with Aromatic Counteranions.

Iron(III) spin-crossover (SCO) complexes [Fe(qsal)]BS·MeOH·HO (1), [Fe(qsal)](NS)·MeOH (2), [Fe(qnal)](NS) (3), and [Fe(qnal)]PS·MeOH·CHCl (4) (Hqsal, N-(8-quinolinyl)salicylaldimine; Hqnal, N-(8-quinolinyl)-2-hydroxy-1-naphthaldimine; BS, benzenesulfonate; NS, 1-naphthalenesulfonate; PS, 1-pyrenesulfonate) have been synthesized and characterized by X-ray structure determinations and temperature-dependent magnetic susceptibility measurements. The aromatic counteranions BS, NS, and PS can be used for the tuning of intermolecular coupling through a variety of weak interactions. All of the complexes show temperature-dependent SCO behavior.

Quaterpyridines as Scaffolds for Functional Metallosupramolecular Materials.

Quaterpyridine (qtpy) ligands have found significant applications as N-heterocyclic scaffolds in self-assembly processes, in particular the formation of various metallosupramolecular architectures, limited, however, by difficulties in their synthesis. Recent progress in the preparative organic and organometallic chemistry of polypyridines has resulted in the elimination of the most serious drawbacks concerning qtpy synthesis, consequently giving rise to a renewed interest in this class of compounds. Herein, we endeavor to define the essential aspects of quaterpyridine chemistry and provide the reader with a perspective on the ways in which this field has begun to flourish.

Isothermal titration calorimetry study of a bistable supramolecular system: reversible complexation of cryptand[2.2.2] with potassium ions.

Isothermal titration calorimetry (ITC) is used to investigate the thermodynamics of the complexation of potassium ions by 1,10-diaza-4,7,13,16,21,24-hexaoxabicyclo[8.8.8]hexacosane (cryptand[2.

Theoretical and structural analysis of long C-C bonds in the adducts of polycyanoethylene and anthracene derivatives and their connection to the reversibility of Diels-Alder reactions.

X-ray structure determinations on four Diels-Alder adducts derived from the reactions of cyano- and ester-substituted alkenes with anthracene and 9,10-dimethylanthracene have shown the bonds formed in the adduction to be particularly long. Their lengths range from 1.58 to 1.

Supramolecular interactions of terpyridine-derived cores of metallomesogen precursors.

Use of Hirshfeld surfaces calculated from crystal structure determinations on various transition metal ion complexes of three terpyridine ligands carrying trimethoxyphenyl substituents has enabled an assessment of the contribution made by the ligand components to the interactions determining the lattice structures, interactions expected also to be present in metallomesogens derived from similar ligands. The form of the link joining the trimethoxyphenyl substituent to the 4' position of 2,2';6',2''-terpyridine is of some importance. In the case of the Co(II) complexes of two of the ligands, their spin-crossover characteristics can be rationalised in terms of the different interactions seen in their lattices.

Spin crossover in Co(II) metallorods--replacing aliphatic tails by aromatic.

Terpyridine ligands with ter- and quater-phenyl substituents at the 4' position provide bis(ligand)Co(II) complexes showing very different magnetic properties to those of their analogues with long-chain aliphatic substituents, with no evidence of "re-entrant" behavior involving multiple high- and low-spin species. Structure determinations of [Co(tptpy)2](BF4)2·CH3OH and [Co(qptpy)2](BPh4)2·3.5dmf·2H2O (dmf = N,N-dimethylformamide) show the metal ion centres in both to be relatively distant and that the "terpyridine embrace" observed to be partially retained in their analogues is completely lost.

Synthesis, structure and luminescence properties of Cu(II), Zn(II) and Cd(II) complexes with 4'-terphenylterpyridine.

The complexes [M(tptpy)(2)](ClO(4))(2) (M = Zn(II) (1), Cd(II) (2), and Cu(II) (3)); tptpy = 4'-[1,1':4',1'']terphenyl-4''-yl-[2,2':6',2'']terpyridine = 4'-terphenylterpyridine) have been synthesized, structurally characterized by X-ray crystallography and subjected to preliminary luminescence studies. In the crystalline state, all the metal ions have an N(6) coordination sphere of distorted octahedral geometry and the structures of the Zn(II) and Cd(II) complexes are isomorphous but differ from that of the Cu(II) complex, which also differs from the other two in that it is non-emissive. The structure determinations show that aromatic-aromatic interactions involving both the terpyridine heads and the terphenyl tails are important factors influencing the crystalline array.

Giant core-shell nanospherical clusters composed of 32 Co or 32 Ni atoms held by 6 p-tert-butylthiacalix[4]arene units.

Using combinations of p-tert-butylthiacalix[4]arene (TCA) and [M(DMSO)(6)(BF(4))(2)] salts (M = Co(II) or Ni(II)), two almost isostructural core-shell-type thermally stable giant nanoclusters, composed of 32 metal centers, 6 deprotonated calix units binding the metal centers by both their O and S atoms, 24 μ-oxo or μ-hydroxo bridging groups, and 6 MeOH molecules, have been prepared under mild and reproducible conditions. For both giant clusters, the oxidation state II [M(II)(32)O(16)(OH)(8)(CH(3)OH)(6)TCA(6) (M = Co or Ni)] for the metal center was demonstrated by X-ray photoelectron and electronic absorption spectroscopies.

Cluster control in oligouranyl complexes of p-t-butylcalix[8]arene.

Formation of uranyl ion complexes of p-t-butylcalix[8]arene by reaction of the calixarene with [UO(2)(dmso)(5)](2+) in the presence of various bases leads to the crystallisation of solids with interestingly different stoichiometry, involving both di- and tri-uranate oligomers bound to the calixarene in anionic species. In all, the calixarene hexa-anion is present in a virtually identical conformation, suggesting that conformational preferences of the ligand must be a major factor controlling the form of the bound oxo-metal complex. Hydrogen bonding to the anions does not appear to be prominent even in the presence of protonated amines and this may explain the formation of some remarkable cation/solvent/simple anion clusters found within the lattices.

Long tailed cage amines: Synthesis, metal complexation, and structure.

The generation of amphiphiles derived from macrobicyclic hexamines of the "sarcophagine" class can be prepared through efficient and selective reactions involving the reductive alkylation, using long-chain aldehydes, of amino-functionalised sarcophagines when bound to Cu(ii) or Mg(ii). The Mg(ii) pathway is particularly convenient for the ultimate isolation of the free ligands, which can then be used to form metalloamphiphiles with a variety of metal ions. Structural studies have been made of one of the free (protonated) ligands and some of their complexes.

Structural and electrochemical studies of Co(III) cage amine complexes with pendent thienylmethylamino groups.

Various 2- and 3-thienylmethylamino-substituted cobalt(III) cage amine complexes, prepared with the objective of obtaining cage-functionalized polythienyls, have been found to be resistant to oxidative polymerization by both electrochemical and chemical procedures. X-ray structure determinations indicate that there is negligible perturbation of the physical dimensions of the thiophene moieties by the cage substituents and thus that the resistance to polymerization must be associated with the high positive charge carried by these substituents.

Functionalised azetidines as ligands: species derived by selective alkylation at substituent-nitrogen.

Selective functionalisation of the tridentate ligand 1-(2-aminoethyl)-3-methyl-3-(2-pyridyl)azetidine at its terminal amino-nitrogen atom can be readily achieved by both reductive alkylation and simple alkylation reactions to give tri-, quadri-, quinque- and sexi-dentate derivatives. Simple alkylation by 2-picolinyl chloride provides the only example of a second reaction pathway where the azetidine ring of the reactant has undergone activation towards ring opening. Structural characterisation of the Cu(II) complexes of these ligands has revealed several remarkable aspects of their solid-state coordination chemistry, including the formation of infinite helical aggregates through pi-stacking and tetramerisation through carboxylate bridging, as well as further examples of the crystallisation of mixed species found to be rather common with complexes of the parent ligand.

Wormlike micelles from a cage amine metallosurfactant.

We have shown that copper and cobalt metallosurfactants derived from Cu(II) and Co(III) complexes of a macrobicyclic hexamine ("cage") can form wormlike micelles in aqueous solution that may coexist with or easily interconvert with vesicle structures. The cylindrical micelle structures are unusual for triple-chain surfactants with a single headgroup and are not easily accounted for using geometrical packing arguments. The solution behavior has been characterized by cryo-TEM and SAXS measurements.

Polyhapto-aromatic interactions in lead(II) coordination.

In its crystalline form, the Pb(II) complex of 1,3-diphenylpropane-1,3-dionate (dibenzoylmethanide, DBM(-)) can be regarded as containing polymeric chains of centrosymmetric, dimeric Pb(2)(DBM)(4) units linked through hexahapto interactions of the Pb atoms with phenyl groups from adjacent units. Each Pb atom also appears to be involved in intraunit dihapto-aromatic interactions, thus attaining a total hapticity of thirteen. Comparison with the analogous Sn(II) compound indicates that the unusually high coordination number may reflect the capacity of Pb(II) to act as both a Lewis acid and a Lewis base.

Stereochemistry in functionalized macrocycle complexes: control of hydroxyl substituent orientation.

Use of a hydroxyl-functionalized open chain tetramine in a template reaction based on its Cu(II) complex leads, after reduction, to a new tetraaza macrocycle with both amino and hydroxyl substituents. The macrocycle is formed predominantly as its trans (anti) isomer, though the cis form is detectable and both have been structurally characterized in the form of their metal complexes. Although both the Cu(II) and the Co(III) complexes of the tetramine precursor ligand have the hydroxyl group in an axial position of a chair six-membered chelate ring, the trans macrocycle forms Co(III) complexes with this substituent in both equatorial and axial positions.

Functionalized macrocycles from functionalized tetra-amines: pendent-arm macrocycles derived from dichloropivalic acid.

Reaction between ethane-1,2-diamine and 3,3'-dichloropivalic acid results in different, isomeric tetra-amine derivatives, one a tetraamino carboxylic acid and the other a carboxamidotriamino alcohol, depending upon reaction conditions. Intended conversion of the Cu(II) complex of the former to a cyclam-like macrocycle through reaction with nitroethane and formaldehyde results in isolation of derivatives of both the former and the latter. This can be rationalized by assuming the intermediacy of an azetidinone, a species similar to that seen in simpler reactions of dichloropivalates.

Factors influencing solvent adduct formation by calixarenes in the solid state.

Structural studies of seven very differently functionalised derivatives of calix[4]arene have been used to provide an analysis of the numerous factors which may influence solvent adduct formation by calixarenes. Evidence is presented that even where a solvent guest is included within the calixarene cavity, interactions solely within the cavity cannot be seen as the sole influences upon the guest position and orientation.

Alkali metal ion complexes of functionalised calixarenes--competition between pendent arm and anion bonding to sodium.

Determination of the crystal structure of the acetonitrile inclusate of the complex formed between sodium trifluoromethanesulfonate (triflate, CF3SO3-) and the narrow-rim functionalised calix[4]arene, 5,11,17,23-tetra-tert-butyl-25,27-di(phenylmethoxy)-26,28-di(2'-methoxyethoxy)calix[4]arene, has shown, somewhat unexpectedly, that the diether pendent arms do not chelate the sodium cation, although coordination of all four phenolic oxygen atoms does draw the calixarene into a nearly symmetrical cone form, consistent with conclusions drawn earlier from solution 1H NMR data. Crystals of C64H80O6.NaO3S.

Koilands from thiophiles: mercury(II) clusters from thiacalixarenes.

Tetra- and hexa-nuclear mercury(II) complexes have been obtained from tetrathiacalix[4]arene and tetramercaptotetrathiacalix[4]arene, respectively, and structurally characterised in the solid state; the complexes provide new digonal and trigonal receptors of the koiland type.