Transition metal binding properties of the redox-active 1,4,7,10,13,16-hexa(ferrocenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane and its electrochemical behaviour in a non-aqueous solvent

Solution studies to elucidate the coordination behaviour and the electrochemical response of the ferrocene-functionalized polyazamacrocycle 1,4,7,10,13,16-hexa(ferrocenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane (L¹) by potentiometric methods and electrochemical techniques have been carried out. Potentiometric methods in the presence of Cd²⁺, Hg²⁺, Pb²⁺ and Zn²⁺ were carried out in 1,4-dioxane/water (70:30 v/v, 25°C, 0.1 mol dm⁻³ KNO₃). Electrochemical studies were carried out in acetonitrile/dichloromethane (50:50 v/v, 25°C, 0.1 mol dm⁻³ TBAClO₄) in the presence of transition metal ions and anions.     

Composition and electrochemical properties of LiCu xMn 2- xO 4 and LiCu 0.5- yAl yMn 1.5O 4

In order to gain a better understanding of the parameters affecting the capacity and performance of spinel electrode materials, the chemical composition and cation distribution of three members of the LiCu_xMn_2–xO₄ and LiCu_0.5–yAl_yMn_1.5O₄ series have been studied by chemical analysis, X-ray diffraction and X-ray absorption spectroscopy. The synthesis used stoichiometric and lithium-excess precursors. The results evidence that lithium is always incorporated in lower contents than expected from the nominal stoichiometry, owing to the occurrence of significant amounts of copper in the tetrahedral sites of the structure. Manganese displays an oxidation state below 4+ in all these solids, while the lithium-excess synthesis leads to a slightly higher average oxidation state. The electrochemical results evidence the lack of improvement in capacity by using lithium-excess synthesis, while a significant increase in capacity is obtained by aluminium doping, reaching values of 100 mAh/g.     

Electrochemical Sensing of Mercury over Cadmium and Lead Cations by the Redox-Active Polyazacycloalkane Ligand 1,1″: 1′,1′′′-Bis[ethane-1,2-diylbis(iminomethylene)]bis[ferrocene]

The coordination behaviour of the redox-active polyazacycloalkane L¹ against the toxic heavy-metal ions Cd²⁺, Pb²⁺, and Hg²⁺ was studied in THF/H₂O 70 : 30 (containing 0.1 mol⋅dm⁻³ of (Bu₄N)ClO₄). The crystal and molecular structure of the cadmium complex [Cd(L¹)(NO₃)₂] ( 1 ) was determined by X-ray single-crystal analysis. The cadmium ion is in a 4+2 surrounding with the ligand L¹ acting as tetradentate and the apical positions occupied by the O-atoms of the nitrate anions. An electrochemical study reveals that L¹ shows a selective electrochemical response against Hg²⁺ over Cd²⁺ and Pb²⁺.     

ATP Sensing with Anthryl‐Functionalized Open‐Chain Polyaza‐alkanes

The anthryl‐functionalized open‐chain polyaza‐alkanes L ¹ , L ² , and L ³ have been synthesized, and their activity as fluorescent chemosensors has been studied in MeCN/H₂O 70 : 30 (v/v) and H₂O at 25° against the anions bromide, phosphate, sulfate, ATP, ADP, and GMP. The crystal structure of L ³ has been solved by single‐crystal X‐ray‐diffraction techniques. The emission intensity of L ¹ and L ² is selectively quenched in the presence of ATP at acidic pH in MeCN/H₂O 70 : 30 (v/v). In H₂O, the emission intensity of L ¹ and L ² is enhanced at neutral pH in the presence of ADP and ATP. The sensing behavior is discussed in terms of H‐bonding or electrostatic anion‐cation interactions. Receptor L ³ does not show any significant change in fluorescence emission upon addition of anions. Protonation constants of the three ligands and stability constants of L ² with phosphate and sulfate were determined by potentiometric titration in MeCN/H₂O. The stability constants obtained are compared with those obtained for the interaction of these anions with related open‐chain polyamines.     

Ferrocene-cyclam: a redox-active macrocycle for the complexation of transition metal ions and a study on the influence of the relative permittivity on the coulombic interaction between metal cations

The reaction of 1,1'-ferrocene-bis(methylenepyridinium) salt with 1,4,8,11-tetraazacyclotetradecane-5,12-dione, followed by LiAlH4 reduction results in the formation of FcCyclam. Metal complexes of FcCyclam with M2+ = Co2+, Ni2+, Cu2+, and Zn2+ were synthesized from FcCyclam and the respective metal triflates. The complexation of Cu2+ and FcCyclam in CH3CN is preceeded by a rapid electron transfer, followed by a slower complex formation reaction and a reverse electron transfer. The protonation constants of FcCyclam and the stability constants for the Cu2+ complex of FcCyclam (logK = 9.26(4) for the formation of the [Cu(FcCyclam)]2+ complex) were determined in 1,4-dioxane/water 70:30 v/v, 0.1 moldm(-3), KNO3, 25 degrees C. By using FcCyclam one can selectively sense the presence of Cu2+ ions in the presence of Ni2+, Zn2+, Cd2+, Hg2+, and Pb2+ with a very large deltaE approximately 200 mV, depending on pH. The X-ray crystal structures of FcCyclam and of complexes with Co2+, Ni2+, Cu2+, and Zn2+ were determined and Fe-M2+ distances obtained: Fe-Co2+ 395.9, Fe-Ni2+ 385.4, Fe-Cu2+ 377.7, and Fe-Zn2+ 369.0 pm. The redox potential of FcCyclam is influenced in a characteristic manner by the complexation of M2+. A linear correlation of 1/r approximately/= deltaE [r = distance Fe-M2+ from crystal data, deltaE=-E1/2([M(FcCyclam)]2+) - E1/2(FcCyclam)] was found; this is indicative of a mainly Coulomb type interaction between the two metal centers. The nature of the Fe...M2+ interaction was also investigated by determining deltaE in several solvents (mixtures) of different dielectric constants epsilon. The expected relation of deltaE approximately/= 1/epsilon was only found at very high values of epsilon. At epsilon < 40 increased ion-pairing appears to reduce the effective positive charge at M2+ leading to progessively smaller values of deltaE with lowered epsilon. The dependence of deltaE and epsilon can be calculated semiquantitatively by combining the Fuoss ion-pairing theory with the Coulomb model.     

Chromogenic silica nanoparticles for the colorimetric sensing of long-chain carboxylates

Silica nanoparticles functionalized with chromogenic spirobenzopyran and thiourea subunits show selective colour changes in the presence of certain long-chain carboxylates.     

Fluorescent chemosensors containing a Ru(tpy)2 2+ core and open-chain polyazaalkanes

4-[4-(Bromomethyl)phenyl]-2,2:6,2-terpyridine reacts with triethylenetetraamine or tetraethylenepentaamine in CH₂Cl₂ to yield the ligands L¹ and L², respectively. Reaction of L¹ and L² with Ru(mtpy)Cl₃ (mtpy = 4-methyl-2,2:6,2-terpyridine) in MeOH yielded, after column chromatography and precipitation with [NH₄][PF₆], the compounds [Ru(L¹)(mtpy)][PF₆]₂ and [Ru(L²)(mtpy)][PF₆]₂. These metallo-receptors contain triethylenetetraamine or tetraethylenepentaamine recognition sites and [Ru(tpy)₂]²⁺ cores as fluorescent signalling subunits. The fluorescent behaviour of [Ru(L¹)(mtpy)]²⁺ and [Ru(L²)(mtpy)]²⁺ in the presence of metal ions and anions has been studied in MeCN:H₂O (70:30 v/v) as a function of the pH.     

1,15-Diferrocenyl-2,5,8,11,14-pentaazapentadecane,an Open-Chain Redox-Active Ferrocene-Functionalized Polyazaalkane Ligand for Anions

The interaction of the ferrocene-functionalized open-chain polyazaalkane 1,15-diferrocenyl-2,5,8,11,14-pentaazapentadecane (L¹) with the sulfate, phosphate, and ATP anions has been studied by potentiometric methods in THF/H₂O 70 : 30 (v/v) (containing 0.1M (Bu₄N)ClO₄ at 25°). Additionally, the electrochemical response of L¹ in the presence of H⁺, HSO^-₄, H₂PO^-₄, Br⁻, and Cl⁻ in a non-aqueous solvent such as MeCN has been studied. A remarkable cathodic shift of the ferrocene oxidation potential was induced for phosphate (198 mV) and sulfate (145 mV) showing an EC mechanistic response. Competitive electrochemical studies showed that L¹ is able to electrochemically and selectively recognize HSO^-₄ vs. H₂PO^-₄ in a mixture of both anions in MeCN.