Synthesis of nitrogen mustards on cobalt(III).

Bis(bidentate) and bis(tridentate) Co(III) complexes of N-(2-hydroxyethyl)ethane-1,2-diamine (heen), 2-[(2-aminoethyl)amino]ethan-1-olate (heen-H), or N-(2-chloroethyl)ethane-1,2-diamine (ceen) ligands have been synthesised, and a range of reaction conditions established for their syntheses by different routes. They can all be ultimately derived from (OC-6-12')-[Co(heen)2(NO2)2]NO3 and provide access to the trans amine trans chloride nitrogen mustard complex, (OC-6-12')-[Co(ceen)2(Cl)2]Cl. Although complex isomeric mixtures were obtained from the reaction of (OC-6-12')-[Co(heen)2(NO2)2]NO3 under different reaction conditions, ultimately, the trans amine trans chlorido configuration around the Co(III) metal centre of the (OC-6-12')-[Co(ceen)2(Cl)2]Cl complex was favoured.

1,1'-Biisoquinolines-Neglected Ligands in the Heterocyclic Diimine Family That Provoke Stereochemical Reflections.

1,1'-Biisoquinolines are a class of bidentate nitrogen donor ligands in the heterocyclic diimine family. This review briefly discusses their properties and the key synthetic pathways available and then concentrates upon their coordination behaviour. The ligands are of interest as they exhibit the phenomenon of atropisomerism (hindered rotation about the C1-C1' bond). A notation for depicting the stereochemistry in coordination compounds containing multiple stereogenic centers is developed. The consequences of the chirality within the ligand on the coordination behaviour is discussed in detail.

The past, present, and future in the nomenclature and structure representation of inorganic compounds.

This review examines the origins and development of the compositional nomenclature and additive nomenclature that have been at the heart of formal descriptions of inorganic compounds since the times of Lavoisier and Werner, respectively. The rising importance of structural diagrams is noted, explained and correlated with a decreasing use of formal nomenclature. The future of structure representation is discussed, particularly in relation to cheminformatics and big data. International variations in nomenclature are discussed with reference to the recently published Brief Guide to the Nomenclature of Inorganic Chemistry and its translations, and implications of increasing internationalisation of chemistry for the integrity of regional languages are discussed.

Deliberate boxes and accidental wheels.

This report describes systems which combine the structural and reactive motifs of a dinucleating terpyridine-aminomethylpyridine ligand, L, with the coordination preferences and flexibilities of particular divalent metal ions to form a series of closely related box structures in a deliberate fashion. The ligand also produces unprecedented decanickel wheel complexes. Halogen to aromatic hydrogen interactions may be important in stabilising the decanickel wheel structures.

Heterodinuclear ruthenium(II)-cobalt(III) complexes as models for a new approach to selective cancer treatment.

Heterodinuclear ruthenium(II)-cobalt(III) complexes have been prepared as part of investigations into a new approach to selective cancer treatment. A cobalt(III) centre bearing amine ligands, which serve as models for cytotoxic nitrogen mustard ligands, is connected by a bridging ligand to a ruthenium(II)-polypyridyl moiety. Upon excitation of the ruthenium centre by visible light, electron transfer to the cobalt(III) centre results in reduction to cobalt(II) and consequent release of its ligands. We have synthesised several such structures and demonstrated their ability to release ligands upon excitation of the ruthenium centre by visible light.

Cobalt(III) complexes as functional ligands for metal (oxide) surfaces.

Co(III) polyamine complexes with either two or three labile coordination sites bind strongly to high surface area metal oxides such as goethite or aluminium trihydroxide, and have been shown to act as passivating agents for aluminium flake in aqueous media, in addition to providing a potential method for surface functionalisation.

High diastereoselectivity in borohydride reductions of coordinated imines.

Borohydride reduction of the imine groups in a pyruvate-derived cobalt(III) complex, (OC-6-33')-[Co(Aim(2)trien)](2)[ZnCl(4)], occurs with high diastereoselectivity. The major diastereoisomeric product, (OC-6-33'-ARSSR,CSRRS)-[Co(A(2)trien)]Cl has been isolated and crystallographically characterised. The results from base-induced isomerisation of the major isomer allow us to conclude that most of the remaining material from the reduction reactions (consisting of minor diastereoisomers) differs from the major isomer only in the relative configuration of the coordinated amines. Therefore the initial borohydride attack on the imine groups must have occurred predominantly on the same face of each imine as that which produces the major isomer. The diastereoselectivity of the reaction can be rationalised by proposing hydrogen bonding interactions between the incoming hydride reagent and other donor groups in the complex.

Buffer-regulated biocorrosion of pure magnesium.

Magnesium (Mg) alloys are being actively investigated as potential load-bearing orthopaedic implant materials due to their biodegradability in vivo. With Mg biomaterials at an early stage in their development, the screening of alloy compositions for their biodegradation rate, and hence biocompatibility, is reliant on cost-effective in vitro methods. The use of a buffer to control pH during in vitro biodegradation is recognised as critically important as this seeks to mimic pH control as it occurs naturally in vivo. The two different types of in vitro buffer system available are based on either (i) zwitterionic organic compounds or (ii) carbonate buffers within a partial-CO(2) atmosphere. This study investigated the influence of the buffering system itself on the in vitro corrosion of Mg. It was found that the less realistic zwitterion-based buffer did not form the same corrosion layers as the carbonate buffer, and was potentially affecting the behaviour of the hydrated oxide layer that forms on Mg in all aqueous environments. Consequently it was recommended that Mg in vitro experiments use the more biorealistic carbonate buffering system when possible.

Photoinduced ligand release in a ruthenium(II)-cobalt(III) heterodinuclear system.

Two Ru(II)-Co(III) heterodinuclear complexes have been synthesised as model complexes for photoactivated cytotoxins. Photoinduced ligand release has been demonstrated and the rate shown to depend on dioxygen concentration. Emission lifetimes and quantum yields are reported. These results validate the concept and justify further work to synthesise systems containing cytotoxic ligands.

Coordination chemistry of a terpyridine-tris(pyrazolyl) ditopic ligand.

A new ditopic ligand, 4'-(4-(2,2,2-tris(1H-pyrazol-1-ido)ethoxymethyl)phenyl)-2,2':6',2''-terpyridine (pzt), has been prepared and its coordination chemistry studied. Metal ions with a preference for octahedral geometry form ML(2) complexes that are readily isolated and characterised, with the metal ion being bound to the terpyridine sites of both ligands. Other metal ions bind to the terpyridine site of just one ligand. In the case of silver(i), a dinuclear M(2)L(2) complex has been isolated in which each silver ion is coordinated to the terpyridine site of one ligand and to a single pyrazolyl donor group from the second ligand. Evidence for binding of metal ions to the tris(pyrazolyl) binding site was obtained by electrospray mass spectrometry and NMR techniques. The free ligand and three metal complexes, including the disilver complex, have been characterised by X-ray crystallographic techniques.

Preparation and photochemistry of cobalt(III) amino and amino acidato complexes containing tripodal polypyridine ligands.

The photochemical reactivities of cobalt(III)-diamine and cobalt(III)-amino acid compounds have been compared using complexes that also contain polypyridyl ligands. Metallacyclic complexes result from UV-induced photodecarboxylation reactions of the amino acid complexes. UV-irradiation of closely related complexes with amine donors replacing the carboxylate donors does not lead to the production of the same metallacyclic products. The reported UV-induced fragmentation of amine donors and subsequent metallacycle formation appears not to be a general reaction. Nine cobalt(III) complexes of polypyridyl ligands have been structurally characterised, including four that also contain amino acid ligands and one that contains a three-membered metallacyclic ring.