Nathan L. Kilah

Enhancement of anion recognition exhibited by a halogen-bonding rotaxane host system

We report the first use of solution-phase halogen bonding to control and facilitate the assembly of an interlocked structure through the bromide anion-templated formation of a rotaxane based upon an iodotriazolium axle. The incorporation of a halogen atom into the rotaxane host cavity dramatically improves the anion-recognition capabilities of the interlocked receptor, giving unusual iodide selectivity in a competitive aqueous medium.

Halogen bond anion templated assembly of an imidazolium pseudorotaxane

Halogen bonding has been exploited in the assembly of an interpenetrated molecular system. The strength of chloride-anion-templated pseudorotaxane formation with a 2-bromo-functionalized imidazolium threading component and an isophthalamide macrocycle (see picture) is significantly enhanced compared to hydrogen-bonded pseudorotaxane analogues. (Figure Presented).

Reversible Luminescence Switching of a Redox-Active Ferrocene–Europium Dyad

The copper-catalyzed cycloaddition reaction between a propargyl-appended europium complex and azidomethylferrocene yields a d-f dyad whose photophysical properties can be reversibly switched by varying the oxidation state of the ferrocene chromophore.

Sixty years young: The diverse biological activities of metal polypyridyl complexes pioneered by Francis P. Dwyer

Sixty years ago, the Australian chemist Francis P. Dwyer pioneered the use of ruthenium polypyridyl complexes as biologically active compounds. These chemically inert and configurationally stable complexes revealed an astonishing range of interesting biological activities, such as the inhibition of the enzyme acetylcholinesterase, anti-cancer activity in vivo, and bacteriostatic/bacteriocidal action. This review commemorates the sixtieth anniversary of Dwyer and co-workers’ landmark 1952 publication, summarises their broader achievements in biological inorganic chemistry, and discusses the contribution of this work to the development of modern biological and medicinal inorganic chemistry.

Lanthanide appended rotaxanes respond to changing chloride concentration

Lanthanide appended rotaxanes have been prepared by the CuAAC ‘click’ reaction between an azide appended rotaxane and lanthanide complexes of propargyl DO3A. The resulting complexes are luminescent, and exhibit chloride responsive luminescence behavior consistent with the existence of two independent halide binding pockets, one in the rotaxane cavity and one on the ninth (axial) coordination site of the lanthanide. Strong halide binding to europium gives rise to changes in the relative intensity of the hypersensitive ΔJ = 2 transition compared to the rest of the europium emission spectrum, combined with quenching of the overall intensity of emission as a consequence of non-radiative quenching by the bound halide. The weaker interaction with the rotaxane pocket mediates a subsequent recovery of intensity of the europium centered luminescence despite the considerable separation between the lanthanide and the rotaxane binding pocket.

The luminescence of Sm2+ in alkaline earth borophosphates

The temperature-dependent luminescence of Sm2+ ions in MBPO5 (M = Ca2+, Sr2+, Ba2+) was studied. At low temperature, Sm2+ in this series shows 4f(6) --> 4f(6) luminescence with only a single emission line observed for the D-5(0) --> F-7(0) transition, revealing that only one crystallographic cationic site is available for Sm2+ in all the hosts. With increasing temperature, the emission intensity of the D-5(0) --> F-7(0) transition increases whereas that of the D-5(0) --> 7F(1) transitions decreases. The D-5(1) --> F-7(0) transitions of Sm2+ were observed in BaBPO5 and its intensity increases with increasing temperature. At 450 K, a broad band of the 4f(5)5d --> 4f(6) luminescent transition of Sm2+ in SrBPO5 and BaBPO5 with maximum at similar to600 ran appears due to the thermal population. The lifetime of the D-5(0) --> F-7(0) transition Sm2+ was recorded at different temperatures, showing a single exponential decay for in SrBPO5 and BaBPO5,but a nonsingle-exponential decay in CaBPO5

Luminescence properties of Sm2+-activated barium chloroborates

The luminescence properties of Sm2+-activated stoichiometric and non-stoichiometric Ba2B5O9Cl were investigated from 16 to 450 K. In stoichiometric Ba2B5O9Cl, the emission spectra of Sm2+ are composed of 4f6-4f6 transitions over the 16-450K temperature range studied. Luminescence was observed from Sm2+ in four inequivalent cationic sites at 16K andtwo inequivalent sites at room temperature. In the non-stoichiometric compound, the emission is characterized by 4f6-4f6 transitions at low temperature and 4f->5d1-4f6 transitions at high temperature. The Sm2+ doped into the Ca2+ and Sr 2+ analogues in the M2B5O9Cl series shows the broadband 4f->5d1-4f6 luminescence in both the stoichiometric and non-stoichiometric compounds due to the increased ligand field caused by the smaller ionic radii of the metal ions.

Tertiary arsine-stabilised arsenium salts: syntheses and comparisons with phosphine analogues

The first tertiary arsine-stabilised arsenium salts, [(L)AsMePh]OTf (L = Ph3As, Me2PhAs, [2-(MeOCH2)C6H4]Ph2As, [2-(MeOCH2)C6H4]Me2As), have been prepared by chloride abstraction from chloromethylphenylarsine with trimethylsilyl triflate in the presence of the arsine. The complexes have been characterised by crystallography and 1H NMR spectroscopy. The chiral cations in the complexes have structures based on the trigonal pyramid in which the arsine is coordinated orthogonally to the prochiral, six-electron MePhAs+ ion that forms the base of the pyramid. The NMR data for the complexes in dichloromethane-d2 are consistent with rapid exchange of the arsine on the arsenium ion, even at 183 K. The corresponding phosphine-stabilised complexes are considerably more stable than their arsine counterparts in dichloromethane-d2 with the free energy of activation DeltaG = ca. 60 kJ mol(-1) being calculated for phosphine exchange in [(Me2PhP)AsMePh]OTf at 281 K; for [(Me2[2-(MeOCH2)C6H4]P)AsMePh]OTf in the same solvent, DeltaG = ca. 70 kJ mol(-1) at 323 K.

Chloride-Anion-Templated Synthesis of a Strapped-Porphyrin-Containing Catenane Host System

The synthesis, structure and anion-recognition properties of a new strapped-porphyrin-containing [2]catenane anion host system are described. The assembly of the catenane is directed by discrete chloride anion templation acting in synergy with secondary aromatic donor–acceptor and coordinative pyridine–zinc interactions. The [2]catenane incorporates a three-dimensional, hydrogen-bond-donating anion-binding pocket; solid-state structural analysis of the catenane⋅chloride complex reveals that the chloride anion is encapsulated within the catenane’s interlocked binding cavity through six convergent CH⋅⋅⋅⋅Cl and NH⋅⋅⋅Cl hydrogen-bonding interactions and solution-phase 1H NMR titration experiments demonstrate that this complementary hydrogen-bonding arrangement facilitates the selective recognition of chloride over larger halide anions in DMSO solution.

Pyridine and Pyridinium-Based Anion Receptors

Abstract Pyridine and pyridinium heterocycles play an important role in anion receptor chemistry. Hydrogen bond arrays are frequently preorganized by the presence of the pyridine nitrogen lone pair of electrons, whilst the positively charged pyridinium group is capable of interacting with anions via a number of polarized noncovalent interactions. This review describes the development of pyridine and pyridinium-based anion receptors, separated into topologically distinct acyclic, macrocyclic, macrobicyclic and interlocked host systems.