Leonard F. Lindoy

Triangles and tetrahedra: metal directed self-assembly of metallo-supramolecular structures incorporating bis-β-diketonato ligands

The interaction of six aryl-linked bis-beta-diketones, including a new naphthylene linked species, with copper(II), iron(III) and, in one instance gallium(III), has been investigated with the aim of obtaining metallo-supramolecular assemblies exhibiting different geometries. New examples of two assembly types incorporating the above bis-beta-diketones (L) were generated. The first type is represented by a range of molecular triangles of formula [Cu(3)(L-H(2))(3)](solvent)(n) while the second is given by a corresponding selection of less-common neutral molecular tetrahedra of formula [Fe(4)(L-H(2))(6)](solvent)(n) as well as [Ga(4)(L-H(2))(6)].8.5THF.0.5H(2)O; an example of each type has been characterised by X-ray crystallography. A magnetochemical investigation of [Fe(4)(-H(2))(6)].6THF is reported. The susceptibility is Curie like and consistent with very weak coupling occurring between the iron(III) d(5)(high spin) centres. The X-ray structures of two trinuclear copper(II) as well as a tetranuclear iron(III) and a tetranuclear gallium(III) assembly confirm their discrete triangular and tetrahedral geometries, respectively. The structure of the gallium(III) species is closely related to that of the corresponding iron(III) species. The tetrahedral structures provide rare examples of such assemblies encapsulating guest solvent molecules--in each case tetrahydrofuran is incorporated in the central cavity.

A new FeII quaterpyridyl M4L6 tetrahedron exhibiting selective anion binding

A rigid linear bis-bidentate quaterpyridine undergoes metal directed self-assembly with iron(ii) salts yielding M(4)L(6) host-guest complexes; selective anion binding for PF(6)(-) over BF(4)(-) is observed.

Hierarchical Self-Assembly of a Chiral Metal–Organic Framework Displaying Pronounced Porosity†

[Extract] Significant recent attention has been devoted to the development of useful self-assembled hybrid materials.[1] This is particularly the case for metal–organic frameworks (MOFs), which display properties such as regularity, porosity, robustness, and high surface area that lead to potential applications in areas such as catalysis, gas separation, and storage.[2, 3] Our research groups and others have been developing new methods for the synthesis of both discrete and extended metal–organic materials, with particular interest in the controlled generation of increased structural complexity.[4] Herein we report a hierarchical self-assembly strategy which has been used to synthesize a new metal–organic framework. This strategy differs from the commonly employed molecular building block (MBB) and secondary building unit (SBU) approaches, where single metal ions or small inorganic clusters (polyhedra) are linked by bridging (often carboxylate) ligands in a one-pot reaction.[5] In these approaches, substantial pore volume is achieved principally through the enthalpically favorable formation of an open framework overcoming the entropic penalties associated with the entrapment of solvent guest molecules. Kinetic control over the formation of the framework is achieved largely through the trial-and-error optimization of synthetic conditions to prevent formation of unwanted kinetic intermediates.[6]

Self-assembled Metallo-supramolecular Systems Incorporating β-Diketone Motifs as Structural Elements

Publisher Summary This chapter discusses the synthesis and properties of metal-containing molecular architectures incorporating β-diketonate motifs. The chapter focuses on the systems in which the use of designed metal-ion-directed assembly is employed for constructing new supramolecular entities. The simplest β-diketone ligand is 2,4-pentanedione (acetylacetone, acacH). β-diketones such as acacH show a tendency to form neutral complexes—with the geometry adopted normally reflecting the preferred geometry of the metal ion involved. In the case of cobalt(II), tetrahedral complexes can also result if a bulky β-diketonate ion is used. The ability to form higher coordinate species can be tuned through variation of the terminal R groups on the β-diketone. Reflecting the available relative orientations of the β-diketonate groups in each ligand type, a range of both dinuclear (rectangular) and trinuclear (triangular) “platform-like” products are isolated and characterized. In the lanthanum-containing complex, the lanthanum(III) ion is eleven coordinate being bound by the six “internal” oxygens from the β-diketonate groups, the three pyridyl nitrogens, a tetrahydrofuran group, and a water molecule.

Comparative molecular mechanics study of the low-spin nickel(II) complexes of an extended series of tetraaza macrocycles

Molecular mechanics calculations of metal complex structures are often not straight forward because of uncertainties concerning the appropriate force-field parameters for structural elements involving the metal. A systematic study aimed at extending the Allinger MM2 force field for use with N 4 -macrocyclic complexes of low-spin Ni(II) is reported. The application of the extended force field to the re-examination of the configurational isomers of [Ni(cyclam)] 2+ and their N,N,N,N-tetramethylated derivatives is reported

Unprecedented encapsulation of a [FeIIICl4]− anion in a cationic [FeII4L6]8+ tetrahedral cage derived from 5,5′′′-dimethyl-2,2′:5′,5′′:2′′,2′′′-quaterpyridine

A unique example of incorporation of a tetrahalometalate anion in a small supramolecular cage is described in which a tetrahedral cage of type [Fe4L6]8+ selectively encapsulates a [FeIIICl4]− anion over a [FeIICl4]2− anion in its central cavity to yield a discrete, mixed oxidation state, Fe(II)/Fe(III) supramolecular assembly. This unusual outcome has been achieved using two alternative synthetic strategies.

The Transition Metal ION Chemistry of Linked Macrocyclic Ligands

Publisher Summary This chapter discusses the transition metal ion chemistry of linked macrocyclic ligands. Linked macrocyclic systems are capable of simultaneously binding two or more metal ions, thus yielding the prospect of generating unusual electronic, catalytic, and/or redox properties (associated with the proximity of the metal centers). Heterometallic complexes are also a possibility and if rigid spacers are employed then the distance between metal centers can be tuned. Steric interaction between the methyl substituents surrounding the double bond linkage joining the rings results in this link being quite strained. As a consequence, the respective double bonds in the dimer are almost completely localized. The visible spectra of each of the new (dinuclear) complexes confirmed the presence of a square planar coordination environment for the Ni (II) ions. A small yield of the linked cyclam derivative was identified as a minor product in the Ni(II) template synthesis of cyclam.

Heavy metal ion chemistry of linked macrocyclic systems incorporating oxygen and/or sulfur in their donor sets

Abstract The heavy metal chemistry of linked macrocyclic ligand systems incorporating all oxygen, all sulfur, oxygen and nitrogen, oxygen and sulfur; nitrogen and sulfur as well as oxygen, nitrogen and sulfur in their donor sets is reviewed.

Twisted Cucurbit[n]urils

Two new twisted cucurbiturils, cucurbit[13]uril (tQ[13]) and cucurbit[15]uril (tQ[15]), have been synthesized and separated, and their structures have been confirmed by NMR spectroscopy and MALDI-TOF mass spectrometry together with the X-ray structures of two new complexes, {Dy(H2O)4Cd(H2O)4tQ[13]}·2.5[CdCl4]·65H2O and {Cd0.5(H2O)2tQ[15]}·[CdCl4]·47H2O. tQ[15] is the largest cucurbit[n]uril (Q[n]) in the Q[n] family reported to date. The X-ray diffraction studies of both complexes indicated that these large tQ[n]s effectively exhibit two different cavities-a central cavity and two side cavities. Preliminary host-guest behavior by each of the new systems was investigated by NMR studies.

Transition and post-transition metal systems incorporating linked synthetic macrocycles as structural elements

The transition and post-transition metal chemistry of linked macrocyclic ligand systems incorporating all nitrogen as well as mixed-donor sets is reviewed.