|dc.description.abstract||The understanding of the structural features within molecular compounds that facilitate their intermolecular assembly by hydrogen bonding, either with themselves or with complementary species, is important for the construction of functional co-crystallised systems and the development of rational methods for their synthesis. These multi-component solids have potential applications in a variety of fields including pharmaceuticals, catalysis, and materials. While there has been plenty of study into purely organic co-crystals, those containing transition metal complexes are much less common. In particular, complex co-crystals with triple hydrogen bonding synthons are especially rare, with less 30 structures reported in the Cambridge Crystallographic Database (November 2018). This thesis introduces the background topics including supramolecular chemistry and intramolecular interactions as well as a summary of the potential hydrogen bonding tectons reported in the literature, before presenting the synthesis and characterisation of a series of transition metal complexes which are potential hydrogen bonding tectons containing primarily ADA or DAD type hydrogen bonding motifs. Finally the methods undertaken in an a attempt to co-crystallise the presented complexes with each other as well as complementary organic molecules are presented along with the results of these co-crystallisations, which include two co-crystal structures of DAD containing platinum(II) complexes with complementary ADA containing organic molecules, as well as a novel co-crystal structure containing a cationic, DDD containing, platinum(II) complex hydrogen bonded to an anionic, AAA containing, barbitone moiety.
Chapter 1 introduces the field of supramolecular chemistry, describing some of the major subfields with notable examples from each, as well as the field of crystal engineering, which is closely linked with supramolecular chemistry. A key part of understanding both fields is the variety of intermolecular interactions which occur between molecules, and these interactions as well as their relative strengths and how they occur is described, with particular focus given to hydrogen bonding interactions, as well as extended hydrogen bonding motifs, due to their key role in the work conducted. Hirshfeld surface analysis is introduced as a method for the analysis of intermolecular interactions in X-ray crystal structures. Transition metal chemistry is introduced with a focus on multimetallic transition metal catalysts, both synthetic and biological, and some of the various synthetic methods which have been reported for the synthesis of heterometallic species. Following this, a summary of the variety of triple hydrogen bond motif containing ligands and their transition metal complexes is presented, showing the variety of potential tectons which exist in the literature. The chapter ends with a brief outline of the proposed ligands and complexes which were planned for this project along with the reasoning behind the choices made with consideration to crystal engineering and co-crystallisation studies.
Chapter 2 describes the synthesis and characterisation of a series of 2-phenylpyridine palladium(II) and platinum(II) complexes of substituted 1,5-diarylbiguanides, as well bis-2,2’-bipyridine ruthenium(II) and bis-2-phenylpyridine iridium(III) complexes of 2,4-diamino-1,3,5-triazine substituted 2-pyridyl-1,2,3-triazole ligands. X-ray crystal structures for four palladium(II) complexes, two ruthenium(II) complexes, and one of the platinum(II) complexes were also obtained and are reported along with Hirshfeld surface analysis of each structure. All of these complexes (excluding some of the palladium(II) complexes) potentially contain ADA type hydrogen bonding motifs, which are either incorporated proximal to the chelate ring, in the case of the diarylbiguanides, or more isolated from the metal ion, as in the case of the pyridyl-triazole complexes. The diarylbiguanides complexes suffered from both poor solubility (particularly in the case of the palladium(II) complexes), as well as obfuscation of the potential ADA surface due to conformational position of the aryl rings.
Chapter 3 describes the synthesis and characterisation of the bis-2,2’-bipyridine ruthenium(II) and bis-2-phenylpyridine iridium(III) complexes of orotic acid, the copper(II), zinc(II), bis-2,2’-bipyridine ruthenium(II) , and 2-phenylpyridine iridium(III) complexes of 2-pyridylmethylenehydantoin, as well as the bis(diphenylphosphino)ethane platinum(II) complex of biuret. X-ray crystal structures of both the ruthenium(II) complexes, one of iridium(III) complexes, as well as of the copper(II) and platinum(II) complexes were obtained and are reported along with the Hirshfeld surface analysis of each structure.
Chapter 4 introduces the small collection of literature ADA:DAD hydrogen bond containing co-crystals which also contain at least one metal complex component. All of these structures were found to have non-planar geometries between the two hydrogen bonded moieties and a method for calculating the individual geometry components (θ1, θ2, τ) which describe the deviation from co-planar in three dimensions was developed. The methods utilised for co-crystallisations are described followed by the co-crystallisation combinations using the complexes reported in chapters 2 and 3, with the complementary organic molecules, 4-dimethylaminonaphthalimide, barbitone, phthalimide, and 6-phenyl-2,4-diamino-1,3,5-triazine. From these crystal jars three complex-organic co-crystals were obtained; [(Pt(ppy)(tBubigu)):dmaNaph]·0.3CHCl3, [(Pt(ppy)2(diOMebigu)):dmaNaph], and [(Pt(ppy)(biguH)):(barb-H)]·CHCl3. The X-ray crystal structures, Hirshfeld analysis, and hydrogen bonding geometry of each structure is reported and discussed. The sum of the attempted complex-complex co-crystallisations along with the results of these attempts was then described. No complex-complex co-crystals were obtained from these co-crystallisation attempts and the likely reasons of this are discussed along with the suggestion of future methods, particularly the use of ligands with multiple hydrogen bonding motifs which favour the formation of larger or polymeric supramolecular structures, which should improve the chances of obtaining complex-complex co-crystals.||