Discrete Molecular Species Research Articles

To Be or Not to Be a (4,4) Net: Reactions of 4′-{4-(N,N-Diethylaminophenyl)}- and 4′-{4-(N,N-Diphenylaminophenyl)}-3,2′:6′,3″- and 4,2′:6′,4″-Terpyridines with Cobalt(II) Thiocyanate

The ligands 4′-{4-(N,N-diethylaminophenyl)}-3,2′:6′,3″-terpyridine (1) and 4′{4-(N,N-diphenylaminophenyl)}-3,2′:6′,3″-terpyridine (2) were prepared and characterized, including the single crystal structure of 2. Along with their 4,2′:6′,4″-terpyridine isomers, 3 and 4, ligands 1 and 2 were reacted with Co(NCS)2 under conditions of crystal growth by layering, using solvent mixtures of MeOH and CHCl3. The single crystal structures of [Co(NCS)2(1)]n·0.8nCHCl3, [Co(NCS)2(2)2(MeOH)2]·3CHCl3, [Co(NCS)2(3)]n·2nCHCl3, and [Co(NCS)2(4)]n were determined. The complexes with 1, 3, and 4 assemble into 2D (4,4) nets with the Co(II) centres as 4-connecting nodes, whereas [Co(NCS)2(2)2(MeOH)2] is a discrete molecular species, illustrating that MeOH can act as a non-innocent solvent. The effects on the structure of changing from the 3,2′:6′,3″-terpyridine (3,2′:6′,3″-tpy) to a 4,2′:6′,4″-tpy metal-binding unit, and of introducing R2N functionalities with different steric demands, are discussed. PXRD of bulk samples of all four products confirmed the single-crystal structures as representative of the bulk materials.

Energy Landscapes of Supramolecular Peptide-Drug Conjugates Directed by Linker Selection and Drug Topology.

Peptide-drug conjugates that self-assemble into supramolecular nanomaterials have promise for uses in drug delivery. These discrete molecular species offer high and precise drug loading, affording efficient carriers for various therapeutic agents. Their peptide modules, meanwhile, enable biological targeting and stimuli-responsive function while also ordering the assembled nanostructure. The often hydrophobic drug payload likewise acts as a directive for self-assembly in aqueous media. Though accessible synthetic methods have allowed for extensive exploration of the peptide design space, the specific contributions of the drug molecule and its linker to the resulting assembly have been less explored. Hydrophobic drugs frequently have planar domains, conjugated π-systems, and isolated polar groups, which in turn can lead to specific and directional self-interactions. These energies of interaction affect the free energy landscape of self-assembly and may impact the form and assembly process of the desired nanomaterial. Here, two model supramolecular peptide-drug conjugates (sPDCs) are explored, composed of the corticosteroid dexamethasone conjugated to a conserved peptide sequence via two different linker chemistries. The choice of linker, which alters the orientation, rotational freedom, and number of stereoisomers of the prodrug in the final sPDC, impacts the mechanism and energetic barrier of assembly as well as the nano/macroscale properties of the resultant supramolecular materials. Accordingly, this work demonstrates the nonzero energetic contributions of the drug and its linker to sPDC self-assembly, provides a quantitative exploration of the sPDC free energy landscape, and suggests design principles for the enhanced control of sPDC nanomaterials to inform future applications as therapeutic drug carriers.

Steric, Activation Method and Solvent Effects on the Structure of Paddlewheel Diruthenium Complexes

Conventional heating and solvothermal synthetic methods (with or without microwave activation) have been used to study the reaction of o-, m- and p-methoxybenzoic acid with [Ru2Cl(μ-O2CMe)4]. The tetrasubstituted series [Ru2Cl(µ-O2CC6H4-R)4], with R = o-OMe, m-OMe and p-OMe, has been prepared by the three procedures. Depending on the synthetic method and the experimental conditions, three compounds have been isolated (1a, 1b, 1c) with the o-methoxybenzoate ligand. However, with the m- and p-methoxybenzoate ligands, only the complexes 2 and 3 have been obtained, respectively. Compound 1a, with stoichiometry [Ru2Cl(µ-O2CC6H4-o-OMe)4]n, shows a polymeric structure with the chloride ions bridging the diruthenium units to form linear chains. Compounds 2 and 3, with the same stoichiometry, predictably form zig-zag chains in accordance with their insolubility and their magnetic measurements. Compound 1b, [Ru2Cl(µ-O2CC6H4-o-OMe)4(EtOH)], is a discrete molecular species with a chloride ion and one ethanol molecule occupying the axial positions of the dimetallic unit. Compound 1c is a cation-anion complex, [Ru2(µ-O2CC6H4-o-OMe)4(MeOH)2][Ru2Cl2(µ-O2CC6H4-o-OMe)4]. The cationic complex has two solvent molecules at the axial positions whereas the anionic complex has two chloride ligands at these positions. Complexes have been characterized by elemental analyses, mass spectrometry and IR and UV-vis-NIR spectroscopies. A magnetic study of complexes 1a, 1b, 2 and 3 have also been carried out. The crystal structure of compounds 1b and 1c have been solved by single X-ray crystal methods.

Aggregation-Induced Emission-Active Gels: Fabrications, Functions, and Applications.

Chromophores that exhibit aggregation-induced emission (i.e., aggregation-induced emission luminogens [AIEgens]) emit intense fluorescence in their aggregated states, but show negligible emission as discrete molecular species in solution due to the changes in restriction and freedom of intramolecular motions. As solvent-swollen quasi-solids with both a compact phase and a free space, gels enable manipulation of intramolecular motions. Thus, AIE-active gels have attracted significant interest owing to their various distinctive properties and promising application potential. Herein, a comprehensive overview of AIE-active gels is provided. The fabrication strategies employed are detailed, and the applications of AIEgens are summarized. In addition, the gel functions arising from the AIE moieties are revealed, along with their structure-property relationships. Furthermore, the applications of AIE-active gels in diverse areas are illustrated. Finally, ongoing challenges and potential means to address them are discussed, along with future perspectives on AIE-active gels, with the overall aim of inspiring research on novel materials and ideas.

Lanthanide-Based Molecular Cluster-Aggregates: Optical Barcoding and White-Light Emission with Nanosized {Ln20 } Compounds.

Counterfeit goods represent a major problem to companies, governments, and customers, affecting the global economy. In order to protect the authenticity of products and documents, optical anti-counterfeit technologies have widely been employed via the use of discrete molecular species, extended metal-organic frameworks (MOFs), and nanoparticles. Herein, for the first time we demonstrate the potential use of molecular cluster-aggregates (MCA) as optical barcodes via composition and energy transfer control. The tuneable optical properties for the [Ln20 (chp)30 (CO3 )12 (NO3 )6 (H2 O)6 ], where chp- =deprotonated 6-chloro-2-pyridinol, allow the fine control of the emission colour output, resulting in high-security level optical labelling with a precise read-out. Moreover, a unique tri-doped composition of GdIII , TbIII , and EuIII led to MCAs with white-light emission. The presented methodology is a unique approach to probe the effect of composition control on the luminescent properties of nanosized molecular material.

Lanthanide‐Based Molecular Cluster‐Aggregates: Optical Barcoding and White‐Light Emission with Nanosized {Ln20} Compounds

AbstractCounterfeit goods represent a major problem to companies, governments, and customers, affecting the global economy. In order to protect the authenticity of products and documents, optical anti‐counterfeit technologies have widely been employed via the use of discrete molecular species, extended metal–organic frameworks (MOFs), and nanoparticles. Herein, for the first time we demonstrate the potential use of molecular cluster‐aggregates (MCA) as optical barcodes via composition and energy transfer control. The tuneable optical properties for the [Ln20(chp)30(CO3)12(NO3)6(H2O)6], where chp−=deprotonated 6‐chloro‐2‐pyridinol, allow the fine control of the emission colour output, resulting in high‐security level optical labelling with a precise read‐out. Moreover, a unique tri‐doped composition of GdIII, TbIII, and EuIII led to MCAs with white‐light emission. The presented methodology is a unique approach to probe the effect of composition control on the luminescent properties of nanosized molecular material.

Guest-Dependent Pressure-Induced Spin Crossover in FeII 4 [MIV (CN)8 ]2 (M=Mo, W) Cluster-Based Material Showing Persistent Solvent-Driven Structural Transformations.

Discrete molecular species that can perform certain functions in response to multiple external stimuli constitute a special class of multifunctional molecular materials called smart molecules. Herein, cyanido-bridged coordination clusters {[FeII (2-pyrpy)2 ]4 [MIV (CN)8 ]2 }⋅4 MeOH⋅6 H2 O (M=Mo (1 solv), M=W (2 solv) and 2-pyrpy=2-(1-pyrazolyl)pyridine are presented, which show persistent solvent driven single-crystal-to-single-crystal transformations upon sorption/desorption of water and methanol molecules. Three full desolvation-resolvation cycles with the concomitant change of the host molecules do not damage the single crystals. More importantly, the Fe4 M2 molecules constitute a unique example where the presence of the guests directly affects the pressure-induced thermal spin crossover (SCO) phenomenon occurring at the FeII centres. The hydrated phases show a partial SCO with approximately two out-of-four FeII centres undergoing a gradual thermal SCO at 1 GPa, while in the anhydrous form the pressure-induced SCO effect is almost quenched with only 15 % of the FeII centres undergoing high-spin to low-spin transition at 1 GPa.

Spatial Coordination of Cooperativity in Silica-Supported Cu/TEMPO/Imidazole Catalytic Triad

Multifunctional catalysts obtained by the covalent immobilization of discrete molecular species on porous supports represent a unique approach to emulate some of the design principle and performances of enzymes. However, it is decisive in such systems to control the stoichiometry, spatial distribution, and proximity between the grafted catalytic centers to satisfy the chemical and geometrical requirements for cooperativity. Here, we present strategies to optimize the activity of a catalytic triad on mesoporous silica particles in the representative aerobic oxidation of benzyl alcohol and show that, in contrast with the more-traditional mixed-monolayer approach, activity can be amplified by tuning the spatial distribution of the co-catalysts to maximize the probability of full synergistic pairings.

Ligand-Based Phase Control in Porous Molecular Assemblies.

Functionalization of isophthalic acid ligands with linear alkoxide groups from ethoxy through pentoxy is shown to have a pronounced effect on both the synthesis of porous paddlewheel-based molecular assemblies and their resulting surface areas and gas adsorption properties. Shorter chain length is compatible with either tetragonal or hexagonal two-dimensional materials, with the hexagonal phase favored with longer chain length. Precise tuning of reaction conditions affords discrete molecular species that are soluble in a variety of organic solvents. The isolated porous molecules display BET surface areas ranging from 125 m2/g to 545 m2/g. The pentoxide-based molecular assembly shows considerable promise for the separation of hydrocarbons with average isosteric heats of adsorption of -48 and -31 kJ/mol for ethylene and ethane, respectively.

Pre-aggregation kinetics and intermediates of \u03b1-synuclein monitored by the ESIPT probe 7MFE

The defining feature of the extensive family of amyloid diseases is the formation of networks of entangled elongated protein fibrils and amorphous aggregates exhibiting crossed β-sheet secondary structure. The time course of amyloid conversion has been studied extensively in vitro with the proteins involved in the neurodegenerative pathology of Parkinson’s disease (α-synuclein), Alzheimer’s disease (Tau) and Huntington’s disease (Huntingtin). Although much is known about the thermodynamics and kinetics of the transition from a soluble, intrinsically disordered monomer to the fibrillar end state, the putative oligomeric intermediates, currently considered to be the major initiators of cellular toxicity, are as yet poorly defined. We have detected and characterized amyloid precursors by monitoring AS aggregation with ESIPT (excited state intramolecular protein transfer) probes, one of which, 7MFE [7-(3-maleimido-N-propanamide)-2-(4-diethyaminophenyl)-3-hydroxychromone], is introduced here and compared with a related compound, 6MFC, used previously. A series of 140 spectra for sparsely labeled AS was acquired during the course of aggregation, and resolved into the relative contributions (spectra, intensities) of discrete molecular species including the monomeric, fibrillar, and ensemble of intermediate forms. Based on these findings, a kinetic scheme was devised to simulate progress curves as a function of key parameters. An essential feature of the model, one not previously invoked in schemes of amyloid aggregation, is the catalysis of molecular fuzziness by discrete colloidal nanoparticles arising spontaneously via monomer condensation upon exposure of AS to ≥ 37 °C.

Pressure-Induced Polymerization of LiN(CN)2.

The high-pressure behavior of lithium dicyanamide (LiN(CN)2) was studied with in situ Raman and infrared (IR) spectroscopies, and synchrotron angle-dispersive powder X-ray diffraction (PXRD) in a diamond anvil cell (DAC) to 22 GPa. The fundamental vibrational modes associated with molecular units were assigned using a combination of experimental data and density functional perturbation theory. Some low-frequency modes were observed for the first time. On the basis of spectroscopic and diffraction data, we suggest a polymorphic phase transformation at ∼8 GPa, wherein dicyanamide ions remain as discrete molecular species. Above ca. 18 GPa, dicyanamide units polymerize, forming a largely disordered network, and the extent of polymerization may be increased by annealing at elevated temperature. The polymerized product consists of tricyanomelaminate-like groups containing sp2-hybidized carbon-nitrogen bonds and exhibits a visible absorption edge near 540 nm. The product is recoverable to ambient conditions but is not stable in air/moisture.

Supramolecular polymer assembly in aqueous solution arising from cyclodextrin host-guest complexation.

The employment of cyclodextrin host–guest complexation to construct supramolecular assemblies with an emphasis on polymer networks is reviewed. The main driving force for this supramolecular assembly is host–guest complexation between cyclodextrin hosts and guest groups either of which may be discrete molecular species or substituents on a polymer backbone. The effects of such complexation on properties at the molecular and macroscopic levels are discussed. It is shown that cyclodextrin complexation may be used to design functional polymer materials with tailorable properties, especially for photo-, pH-, thermo- and redox-responsiveness and self-healing.

Spin Crossover, Polymorphism and Porosity to Liquid Solvent in Heteroleptic Iron(III) {Quinolylsalicylaldimine/Thiosemicarbazone-Salicylaldimine} Complexes.

Heteroleptic iron(III) complexes of formula [Fe(qsal)(thsa)]⋅solvent have been synthesized: [Fe(qsal)(thsa)]⋅0.4 BuOH (1), [Fe(qsal)(thsa)]⋅0.5 MeCN (2) and [Fe(qsal)(thsa)]⋅0.5 THF, (3). The latter two show partial solvent loss at room temperature to yield [Fe(qsal)(thsa)]⋅0.1 MeCN (2') and [Fe(qsal)(thsa)]⋅0.1 THF (3'), respectively. This family maintains a structural integrity which is analogous over different degrees of solvation, a rare occurrence in discrete molecular species. Uniquely, removal of MeCN from compound 2 leads to retention of crystallinity yielding the isostructural, fully desolvated compound [Fe(qsal)(thsa)] (2'') and a new high spin polymorph, 4. To the best of our knowledge, this is the first compound that forms polymorphs through a desolvation process. The desolvated mixture, 2'' and 4, is porous and can reabsorb MeCN and give rise to 2' again. This illustrates the reversible single-crystal-to-single-crystal transformation of two polymorphs back to a purely original phase, 2''+4↔2'. The structural, magnetic and Mőssbauer features of the various samples are described in terms of spin crossover.

Fine-Tuning Nickel Phenoxyimine Olefin Polymerization Catalysts: Performance Boosting by Alkali Cations

To gain a better understanding of the influence of cationic additives on coordination-insertion polymerization and to leverage this knowledge in the construction of enhanced olefin polymerization catalysts, we have synthesized a new family of nickel phenoxyimine-polyethylene glycol complexes (NiL0, NiL2-NiL4) that form discrete molecular species with alkali metal ions (M(+) = Li(+), Na(+), K(+)). Metal binding titration studies and structural characterization by X-ray crystallography provide evidence for the self-assembly of both 1:1 and 2:1 NiL:M(+) species in solution, except for NiL4/Na(+) which form only the 1:1 complex. It was found that upon treatment with a phosphine scavenger, these NiL complexes are active catalysts for ethylene polymerization. We demonstrate that the addition of M(+) to NiL can result in up to a 20-fold increase in catalytic efficiency as well as enhancement in polymer molecular weight and branching frequency compared to the use of NiL without coadditives. To the best of our knowledge, this work provides the first systematic study of the effect of secondary metal ions on metal-catalyzed polymerization processes and offers a new general design strategy for developing the next generation of high performance olefin polymerization catalysts.

Structural studies of (prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine hetero-scorpionate copper complexes.

The structures of five compounds consisting of (prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine complexed with copper in both the Cu(I) and Cu(II) oxidation states are presented, namely chlorido{(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(I) 0.18-hydrate, [CuCl(C15H17N3)]·0.18H2O, (1), catena-poly[[copper(I)-μ2-(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(5)N,N',N'':C(2),C(3)] perchlorate acetonitrile monosolvate], {[Cu(C15H17N3)]ClO4·CH3CN}n, (2), dichlorido{(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(II) dichloromethane monosolvate, [CuCl2(C15H17N3)]·CH2Cl2, (3), chlorido{(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(II) perchlorate, [CuCl(C15H17N3)]ClO4, (4), and di-μ-chlorido-bis({(prop-2-en-1-yl)bis[(pyridin-2-yl)methylidene]amine-κ(3)N,N',N''}copper(II)) bis(tetraphenylborate), [Cu2Cl2(C15H17N3)2][(C6H5)4B]2, (5). Systematic variation of the anion from a coordinating chloride to a noncoordinating perchlorate for two Cu(I) complexes results in either a discrete molecular species, as in (1), or a one-dimensional chain structure, as in (2). In complex (1), there are two crystallographically independent molecules in the asymmetric unit. Complex (2) consists of the Cu(I) atom coordinated by the amine and pyridyl N atoms of one ligand and by the vinyl moiety of another unit related by the crystallographic screw axis, yielding a one-dimensional chain parallel to the crystallographic b axis. Three complexes with Cu(II) show that varying the anion composition from two chlorides, to a chloride and a perchlorate to a chloride and a tetraphenylborate results in discrete molecular species, as in (3) and (4), or a bridged bis-μ-chlorido complex, as in (5). Complex (3) shows two strongly bound Cl atoms, while complex (4) has one strongly bound Cl atom and a weaker coordination by one perchlorate O atom. The large noncoordinating tetraphenylborate anion in complex (5) results in the core-bridged Cu2Cl2 moiety.

Structure, Stability, and Electronic Interactions of Polyoxometalates on Functionalized Graphene Sheets

Polyoxometalates (H(3)PMo(12)O(40), H(3)PW(12)O(40), H(4)PMo(11)VO(40)) supported on oxygen- and alkyl-functionalized graphene sheets were investigated. Discrete molecular species were directly observed by electron microscopy at loadings below 20 wt.%. The interaction between the polyoxometalates and the graphene surface was found to significantly impact their vibrational spectra and a linear correlation between the frequency of the M-O(c)-M vibration and the dispersion was evidenced by FTIR. While bulk-like electronic properties were observed for small aggregates (2-5 nm), UV-vis spectroscopy and cyclic voltammetry revealed changes in the electronic structure of isolated molecular species as a result of their interaction with graphene. Because of the ability to disperse alkyl-functionalized graphene in a variety of polar and nonpolar solvents, the materials synthesized in this work provide an opportunity to disperse polyoxometalates in media in which they would not dissolve if unsupported.

Noble Metals in Polyoxometalates

Polyoxometalates containing noble metal ions, such as ruthenium, osmium, rhodium, palladium, platinum, silver and gold, are a structurally diverse class of compounds. They include both classical heteropolyanions (vanadates, molybdates, tungstates) in which noble metals are present as heteroatoms, as well as the recently discovered class of polyoxometalates with noble metal "addenda" atoms. The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.

Stabilising pentavalent actinides—visible–near infrared and X-ray absorption spectroscopic studies of the utility of the [(Np3W4O15)(H2O)3(MW9O33)3]18−(M = Sb, Bi) structural type

We report the interaction between B-type tri-lacunary heteropolyoxotungstate anions and actinyl(V) cations in aqueous solution, yielding a greater understanding of the stability of the O≡An≡O(1+) linear dioxo actinide moiety. Previously we reported that B-α-[BiW(9)O(33)](9-) and B-α-[SbW(9)O(33)](9-) will react with NpO(2)(1+) to yield [(Np(3)W(4)O(15))(H(2)O)(3)(MW(9)O(33))(3)](18-) (M = Bi, or Sb). Single crystal structural characterisation of salts of these complexes revealed a core in which three Np(V) atoms interact with a central W(VI) atom through bridging oxo groups. These bridging oxygen atoms come from one of the two axial oxygens in O≡Np≡O(1+) and represent a highly unusual interaction for a discrete molecular species. In this study visible/near infra-red spectroscopy indicates that [(Np(3)W(4)O(15))(H(2)O)(3)(BiW(9)O(33))(3)](18-) could be readily stabilized in solution at near neutral pH for several months, with (NH(4))(14)Na(4)[(Np(3)W(4)O(15))(H(2)O)(39)BiW(9)O(33))(3)]·62H(2)O crystallising from solution in high yield. At lower pH and [BiW(9)O(33)](9-) : NpO(2)(1+) ratios additional Np(V) species could be observed in solution. Stabilization of [(Np(3)W(4)O(15))(H(2)O)(3)(SbW(9)O(33))(3)](18-) in solution proved more challenging, with several distinctive Np(V) near infra-red transitions observed in solution. Slow complexation kinetics and reduction to Np(IV) was also observed. High [SbW(9)O(33)](9-) : NpO(2)(1+) molar ratios and careful control of solution pH was required to prepare solutions in which [(Np(3)W(4)O(15))(H(2)O)(3)(SbW(9)O(33))(3)](18-) was the only neptunium containing species. In stark contrast to the NpO(2)(1+) chemistry, [BiW(9)O(33)](9-) readily oxidizes PuO(2)(1+) to PuO(2)(2+) yielding further evidence of the decreased stability of Pu(V)vs. Np(V). Np L(II)-edge XAFS measurement revealed very good agreement with single crystal diffraction data for the Np structural environment for [(Np(3)W(4)O(15))(H(2)O)(3)(MW(9)O(33))(3)](18-) (M = Bi, or Sb) in the solid state. There was also good agreement between coordination shells for [(Np(3)W(4)O(15))(H(2)O)(3)(BiW(9)O(33))(3)](18-) in the solid state and in solution, yielding further confirmation of the high stability of this particular cluster.

Synthesis, crystal structure and photophysical properties of lanthanide coordination polymers of 4-[4-(9H-carbazol-9-yl)butoxy]benzoate: the effect of bidentate nitrogen donors on luminescence

A new aromatic carboxylate ligand, 4-[4-(9H-carbazol-9-yl)butoxy]benzoic acid (HL), has been synthesized by the replacement of the hydroxyl hydrogen of 4-hydroxy benzoic acid with a 9-butyl-9H-carbazole moiety. The anion derived from HL has been used for the support of a series of lanthanide coordination compounds [Ln = Eu (1), Gd (2) and Tb (3)]. The new lanthanide complexes have been characterized by a variety of spectroscopic techniques. Complex 3 was structurally authenticated by single-crystal X-ray diffraction and found to exist as a solvent-free 1D coordination polymer with the formula [Tb(L)(3)](n). The structural data reveal that the terbium atoms in compound 3 reside in an octahedral ligand environment that is somewhat unusual for a lanthanide. It is interesting to note that each carboxylate group exhibits only a bridging-bidentate mode, with a complete lack of more complex connectivities that are commonly observed for extended lanthanide-containing solid-state structures. Examination of the packing diagram for revealed the existence of two-dimensional molecular arrays held together by means of CH-π interactions. Aromatic carboxylates of the lanthanides are known to exhibit highly efficient luminescence, thus offering the promise of applicability as optical devices. However, due to difficulties that arise on account of their polymeric nature, their practical application is somewhat limited. Accordingly, synthetic routes to discrete molecular species are highly desirable. For this purpose, a series of ternary lanthanide complexes was designed, synthesized and characterized, namely [Eu(L)(3)(phen)] (4), [Eu(L)(3)(tmphen)] (5), [Tb(L)(3)(phen)] (6) and [Tb(L)(3)(tmphen)] (7) (phen = 1,10-phenanthroline and tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline). The photophysical properties of the foregoing complexes in the solid state at room temperature have been investigated. The quantum yields of the ternary complexes 4 (9.65%), 5 (21.00%), 6 (14.07%) and 7 (32.42%), were found to be significantly enhanced in the presence of bidentate nitrogen donors when compared with those of the corresponding binary compounds 1 (0.11%) and 3 (1.45%). Presumably this is due to effective energy transfer from the ancillary ligands.

Measurement of radon and xenon binding to a cryptophane molecular host

Xenon and radon have many similar properties, a difference being that all 35 isotopes of radon ((195)Rn-(229)Rn) are radioactive. Radon is a pervasive indoor air pollutant believed to cause significant incidence of lung cancer in many geographic regions, yet radon affinity for a discrete molecular species has never been determined. By comparison, the chemistry of xenon has been widely studied and applied in science and technology. Here, both noble gases were found to bind with exceptional affinity to tris-(triazole ethylamine) cryptophane, a previously unsynthesized water-soluble organic host molecule. The cryptophane-xenon association constant, K(a)=42,000 ± 2,000 M(-1) at 293 K, was determined by isothermal titration calorimetry. This value represents the highest measured xenon affinity for a host molecule. The partitioning of radon between air and aqueous cryptophane solutions of varying concentration was determined radiometrically to give the cryptophane-radon association constant K(a)=49,000 ± 12,000 M(-1) at 293 K.