Self-assembly in inorganic chemistry

The study of self assembly processes influences almost all facets of modern inorganic chemistry as it encompasses elements from across the periodic table and traverses all spatial domains. By definition, self-assembly entails the spontaneous and reversible association of molecules or ions to form larger, more complex (supra)-molecular entities according to the basic information contained in the molecules themselves.¹ The utilisation of self assembly in inorganic chemistry therefore impacts upon cutting edge research that ranges from surface supramolecular assembly, through discrete coordination complexes and multinuclear assemblies; to the organization in the solid-state via crystal engineering. These studies provide a better understanding of the underlying principles that lead to the formation of higher complexity and function, that underpin current research efforts in coordination, bio-inorganic, materials, medicinal, catalytic chemistry and nano-technology.

In this themed issue of Dalton Transactions we have tried to provide an overview of self-assembly in inorganic chemistry, from fundamental chemistry to more applied aspects, and to blend together contributions from new and established researchers. The theme is vast in its breadth and immense in its depth and this is reflected by the number of contributions to this themed issue which is in excess of 50 papers! However, a single issue of Dalton Transactions cannot provide a comprehensive treatment of this topic, but we hope the selection of papers here might serve as a primer to those new to the area so that they might learn of its importance and come to appreciate the far reaching implications of its study. Indeed, it might also serve as useful refresher to those more familiar with the concept but perhaps not so up-to-date with the latest developments in the area.

A very topical perspective giving an overview of metal-ion directed self-assembly in the formation of supramolecular sensors for ions, molecules and bio-molecules is given by Jim Thomas (DOI:10.1039/C1DT10876J), and continuing in the theme of luminescent self-assembled complexes are contributions by Faulkner (DOI:10.1039/C1DT11103E) featuring Eu ions, Credi with Ru/CdTe nano-crystals (DOI:10.1039/C1DT11054C), and Yam and co-workers (DOI:10.1039/C1DT10741K) who report interesting thermo-responsive luminescent metallo-supramolecular Pt(II) complexes that emit with near-infrared (NIR) emission upon heating. De Cola and colleagues (DOI:10.1039/C1DT11251A) similarly report upon aggregation induced colour changes for phosphorescent Ir(III) complex-anionic surfactants. Further lanthanide examples are provided by Lincheneau et al. (DOI:10.1039/C1DT11225B) who present a rather interesting lanthanide directed self-assembly synthesis and photophysical evaluation of chiral Eu(III) luminescent “half-helicates”.

Numerous papers detail the self-assembly formation of archetypal metallo-supramolecular edifices including helicates, polygons, grids, metallo-macrocycles and cages. Lindoy and co-workers (DOI:10.1039/C1DT10820D) report upon Ni(II) and Fe(II) triple helicates assembled from expanded quaterpyridine ligands, Archer et al. (DOI:10.1039/C1DT11381J) detail fascinating solvation affects upon the spin crossover behaviour in a dinuclear Fe(II) triple helicate complex, and Halcrow and co-workers (DOI:10.1039/C1DT10620A) reveal dramatic solvent induced affects on the spin-state of an Fe(II) spin crossover complex across a range of solvents. Albrecht and co-workers (DOI:10.1039/C1DT10775E) report upon self-assembled hetero-dinuclear La(III)/Ga(III) helicates, and Ward and co-authors (DOI:10.1039/C1DT10781J) detail the structures, host–guest chemistry and mechanism of stepwise self-assembly of M₄L₆ tetrahedral cage complexes. Schalley et al. (DOI:10.1039/C1DT10621J) present a study that investigates the effects of subtle differences in ligand constitution and conformation in metallo-supramolecular self-assembled polygons. Crowley's paper (DOI:10.1039/C1DT10551E) details the synthesis, structural modification and stability of self-assembled Pd(II) “click” cages. In the contribution by Lehn et al. (DOI:10.1039/C1DT11226K) the mechanisms and kinetic control over the structural and metallo-selectivity in the assembly of [2 × 2] grid-type metallo-supramolecular species are reported and the design, synthesis and sensing study of coordination-driven self-assembly of 2D-metallamacrocycles using a shape-selective Pt(II)₂-organometallic 90° acceptor are provided by Mukherjee and co-workers (DOI:10.1039/C1DT10790A).

Recent studies have turned toward investigating the role that anions play in self-assembly processes and reported here are several papers that detail aspects of this phenomenon. In two contributions Beer and co-workers (DOI:10.1039/C1DT10186B) reveal chloride anion triggered motion in a bis-imidazolium rotaxane and clipping and stoppering anion templated synthesis of a [2]rotaxane host system (DOI:10.1039/C1DT10887E). Pleiger et al. (DOI:10.1039/C1DT10808E) demonstrate anion-driven conformation control and enhanced sulfate binding utilising aryl linked salicylaldoxime dicopper helicates; Das and co-authors (DOI:10.1039/C1DT11195G) reveal encapsulation of the phosphate anion within a rigidified π-stacked dimeric capsular assembly of a tripodal receptor; whereas Gale and colleagues (DOI:10.1039/C1DT10213C) report a synergistic approach to anion antiport across 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles.

An extremely topical area of contemporary research involves the self-assembly of metal based coordination polymers and several papers focus on this area within the themed issue. Boskovic et al. (DOI:10.1039/C1DT10866B) detail the generation of a novel polyoxometalate-based 3D framework; Hardie and co-workers (DOI:10.1039/C1DT10662G) report new coordination polymers with extended arm cyclotriguaiacyclene ligands; Abrahams and colleagues (DOI:10.1039/C1DT10962F) present the synthesis, structure and host–guest properties of a new type of robust microporous coordination polymer with a 2D square grid structure; and Schröder et al. (DOI:10.1039/C1DT10901D) describe the variation in structure and H₂ adsorption by increasing nuclearity of secondary building units in porous Co(II) metal–organic frameworks. In related crystal engineering work, Aakeröy and co-workers (DOI:10.1039/C1DT10911A) pose an interesting question when examining the structural landscape in a series of Cu(II)-acac complexes: Halogen bonding or close packing?

Several papers detail studies dedicated to the self-assembly and characterisation of multi-metallic cluster species. Dalgarno and colleagues (DOI:10.1039/C1DT10821B) report interesting self-assembly properties of p-tert-butylcalix[8]arene in combination with sodium and manganese ions; Junk and co-workers (DOI:10.1039/C1DT10580A) present a systematic study of the formation of the lanthanoid cubane cluster motif that is mediated by the steric modification of diketonate ligands; and Konno et al. (DOI:10.1039/C1DT10778J) describe the self-assembly of mixed-metal clusters with D-penicillaminato and their organization into extended supramolecular structures.

Prominent within the papers detailing the self-assembly of cluster species is the study of the magnetic properties which are particularly interesting. Doyle and co-workers (DOI:10.1039/C1DT11004G) report the facile synthesis, structure and magnetic analysis of a synthetically persistent, self assembled polyoxovanadate species; Winpenny et al. (DOI:10.1039/C1DT10855G) reveal antiferromagnetic behaviour within the core structures of octa- and hexa-metallic Fe(III) phosphonate cage complexes; Batten and co-workers (DOI:10.1039/C1DT11369K) report the self-assembly, structure and magnetism within Mn, Fe and Co complexes featuring a hexanitrile ligand; and Murray et al. (DOI:10.1039/C1DT10739A) present the magnetic properties of decanuclear [Na₂Mn(II)₄Mn(III)₄] complexes that display large spin ground states and probable SMM behaviour; whereas Murrie and colleagues (DOI:10.1039/C1DT10910C) describe the cubic assembly of a geometrically frustrated {Fe₁₂} spin cluster.

Traditionally, the synthesis of complexes of acyclic, macrocyclic and cryptand ligands has been at the heart of studies of self-assembly in inorganic chemistry. Champness et al. (DOI:10.1039/C1DT10815H) show that copper(I) iodide aggregation in the solid state is inhibited via macrocyclic encapsulation; McKee and co-workers (DOI:10.1039/C1DT11341K) identify, through an ESI-MS study, a double template effect in [4 + 4] Schiff base macrocycle formation; Brooker and colleagues (DOI:10.1039/C1DT10730E) detail complexes of an N₄-Schiff-base macrocycle; Blackman et al. (DOI:10.1039/C1DT10627A) reveal the factors influencing mononuclear versus multinuclear coordination in a series of potentially hexadentate acyclic N₆ ligands; and Ogden and co-workers (DOI:10.1039/C1DT10441A) provide further insight into the coordination of 2,5-dicarbothioamidopyrrole ligands. Love et al. (DOI:10.1039/C1DT10861A) report palladium cluster complexes of wide-span diimine and diamine ligands; and Johnson and co-workers (DOI:10.1039/C1DT10817D) present the design, synthesis and characterization of self-assembled As₂L₃ and Sb₂L₃ cryptands.

We invite you to delve further into these contributions and those of others within this special themed issue. We have really enjoyed helping to gather these articles together and we thank each author for their excellent contribution. We also thank the Dalton Transactions Editorial team for their professionalism and timeliness in handling the multitude of manuscripts, and we trust that you, the reader, will enjoy reading them.

References

1. Supramolecular Chemistry, 2nd edition, pp 592–594, J. W. Steed and J. L. Atwood, 2009, John Wiley & Sons, Ltd ISBN: 978-0-470-51233-3.

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