Fac and mer isomers of Ru(II) tris(pyrazolyl-pyridine) complexes as models for the vertices of coordination cages: structural characterisation and hydrogen-bonding characteristics

We have prepared a series of mononuclear fac and mer isomers of Ru(II) complexes containing chelating pyrazolyl-pyridine ligands, to examine their differing ability to act as hydrogen-bond donors in MeCN. This was prompted by our earlier observation that octanuclear cube-like coordination cages that contain these types of metal vertex can bind guests such as isoquinoline-N-oxide (K = 2100 M−1 in MeCN), with a significant contribution to binding being a hydrogen-bonding interaction between the electron-rich atom of the guest and a hydrogen-bond donor site on the internal surface of the cage formed by a convergent set of CH2 protons close to a 2+ metal centre. Starting with [Ru(LH)3]2+ [LH = 3-(2-pyridyl)-1H-pyrazole] the geometric isomers were separated by virtue of the fact that the fac isomer forms a Cu(I) adduct which the mer isomer does not. Alkylation of the pyrazolyl NH group with methyl iodide or benzyl bromide afforded [Ru(LMe)3]2+ and [Ru(Lbz)3]2+ respectively, each as their fac and mer isomers; all were structurally characterised. In the fac isomers the convergent group of pendant –CH2R or –CH3 protons defines a hydrogen-bond donor pocket; in the mer isomer these protons do not converge and any hydrogen-bonding involving these protons is expected to be weaker. For both [Ru(LMe)3]2+ and [Ru(Lbz)3]2+, NMR titrations with isoquinoline-N-oxide in MeCN revealed weak 1 : 1 binding (K ≈ 1 M−1) between the guest and the fac isomer of the complex that was absent with the mer isomer, confirming a difference in the hydrogen-bond donor capabilities of these complexes associated with their differing geometries. The weak binding compared to the cage however occurs because of competition from the anions, which are free to form ion-pairs with the mononuclear complex cations in a way that does not happen in the cage complexes. We conclude that (i) the presence of fac tris-chelate sites in the cage to act as hydrogen-bond donors, and (ii) exclusion of counter-ions from the central cavity leaving these hydrogen-bonding sites free to interact with guests, are both important design criteria for future coordination cage hosts

Chromo- and Fluorogenic Organometallic Sensors

Compounds that change their absorption and/or emission properties in the presence of a target ion or molecule have been studied for many years as the basis for optical sensing. Within this group of compounds, a variety of organometallic complexes have been proposed for the detection of a wide range of analytes such as cations (including H+), anions, gases (e.g. O 2, SO2, organic vapours), small organic molecules, and large biomolecules (e.g. proteins, DNA). This chapter focuses on work reported within the last few years in the area of organometallic sensors. Some of the most extensively studied systems incorporate metal moieties with intense long-lived metal-to-ligand charge transfer (MLCT) excited states as the reporter or indicator unit, such as fac-tricarbonyl Re(I) complexes, cyclometallated Ir(III) species, and diimine Ru(II) or Os(II) derivatives. Other commonly used organometallic sensors are based on Pt-alkynyls and ferrocene fragments. To these reporters, an appropriate recognition or analyte-binding unit is usually attached so that a detectable modification on the colour and/or the emission of the complex occurs upon binding of the analyte. Examples of recognition sites include macrocycles for the binding of cations, H-bonding units selective to specific anions, and DNA intercalating fragments. A different approach is used for the detection of some gases or vapours, where the sensor's response is associated with changes in the crystal packing of the complex on absorption of the gas, or to direct coordination of the analyte to the metal centre

Optically active imidazoles derived from enantiomerically pure trans-1,2-diaminocyclohexane

A new exploration of some monoprotected derivatives of trans-1,2-diaminocyclohexane as a platform for the synthesis of enantiomerically pure imidazole derivatives is described. The primary amino group (-NH2), present in the mono-imine derivative of salicylic aldehyde (hemi-salen derivative) 5 was used for sequential reactions with formaldehyde and a corresponding α-(hydroxyimino)ketone. (S)-(–)-1-Phenylethylamine was also used as starting material for the preparation of new imidazole N-oxides 7c and 10a-c, bearing a chiral N-(1-phenylethyl)carboxamido function at C(4). Imidazole N-oxides 10a-b possessing a Me or i-Pr group at N(1), respectively, follow the known sulfur-transfer pathway affording the corresponding imidazole-2-thiones 13a-b. However, in the case of imidazole N-oxide 10c with the bulky adamantan-1-yl substituent at N(1), the attempted ‘sulfur-transfer reaction’ led to the deoxygenated imidazole derivative 14. Finally, the same reaction with 7c, bearing the electron-withdrawing N-(1-phenylethyl)carboxamide residue at C(4) of the imidazole ring, yielded a mixture of deoxygenated imidazole 16 and imidazole-2-thione 15c

Metal-directed self-assembly of terphenyl based dithiocarbamate ligands

The synthesis of dithiocarbamate ligands based on an m-terphenyl scaffold is reported. These ligands self-assemble with zinc(II), nickel(II) and copper(II) ions to afford neutral, dinuclear metallomacrocycles in varied yields. The assemblies have been characterised by a range of techniques, including 1H NMR,13C NMR and UV-vis spectroscopy, elemental analysis, mass spectrometry and cyclic voltammetry. Intramolecular coordination of bipyridyl guests has been investigated with the zinc(II) containing macrocycles. NMR spectroscopy and FAB mass spectrometry demonstrate the formation of 1 : 1 inclusion complexes with 4,4′-bipyridyl

Approaches towards the enantioselective recognition of anionic guest species using chiral receptors based on rhenium(I) and ruthenium(II) with amide bipyridine ligands

The syntheses of chiral anion receptors based on rhenium(I) and ruthenium(II) with amide bipyridine ligands are reported. The rhenium(I) hosts were prepared in moderate to high yields by co-ordinating chiral bipyridine ligands to a Re(CO)3Br centre. The ruthenium(II) receptors were synthesised via the chiral building blocks Λ- and Δ-[Ru(bpy)2-(py)2]2+ or by chromatographic resolution on a SP Sephadex C-25 cation exchanger. Chiral purity was determined by 1H NMR and circular dichroism spectroscopy and lanthanide shift experiments. 1H NMR titration studies showed that these receptors bind chiral carboxylate anions in DMSO-d6, although significant chiral discrimination was not observed

Anion selectivity properties of ruthenium(II) tris(5,5 '-diamide-2,2 '-bipyridine) receptors dictated by solvent and amide substituent

The ratio of the dichloromethane-methanol solvent mixture medium and nature of the receptor amide substituent critically dictates chloride vs. nitrate selectivity properties of new ruthenium(II) tris(5,5′-diamide-2,2′-bipyridine) receptors

Crystal Structure And Hirshfeld Surface Analysis Of (E)-4-{[2-(4-Hy­Droxy­Benzo­Yl)Hydrazin-1-Yl­Idene]Meth­Yl}Pyridin-1-Ium Nitrate

The title aroyl hydrazone Schiff base salt, consists of one mol­ecular cation in the keto tautomeric form, adopting an E configuration with respect to the azomethine bond, and one nitrate anion., The asymmetric unit of the title aroyl hydrazone Schiff base salt, C13H12N3O2 +·N O3 −, consists of one mol­ecular cation in the keto tautomeric form, adopting an E configuration with respect to the azomethine bond, and one nitrate anion. The two units are linked via an N—H⋯O hydrogen bond. The mol­ecule overall is non-planar, with the pyridinium and benzene rings being inclined to each other by 4.21 (4)°. In the crystal, cations and anions are linked via inter­molecular O—H⋯O and bifurcated N—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (101). These networks are further linked by C—H⋯O hydrogen bonds, forming slabs parallel to (101). The slabs are linked by offset π–π inter­actions, involving the benzene and pyridinium rings of adjacent slabs [inter­centroid distance = 3.610 (2) Å], forming a three-dimensional structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯O/O⋯H (45.1%), H⋯H (19.3%), H⋯C/C⋯H (14.5%), H⋯N/N⋯H (7.9%) and C⋯C (6.0%) inter­actions.PubMedScopu