Synthesis and spectroscopic and structural characterization of two novel photoactivatable Ca2+ compounds

Two novel photoactivatable Ca(2+) compounds were synthesized to achieve a fast concentration jump of calcium ions in solution; this is of paramount importance for investigating the physiological cellular response. The light-sensitive ligands 4-(2-nitrophenyl)-3,6-dioxaoctane dioic acid (H2L1) and 4-(4,5-dimethoxy-2-nitrophenyl)-3,6-dioxaoctane dioic acid (H2L2) were generated by multistep syntheses, and the corresponding calcium complexes, Ca1 and Ca2, were isolated and characterized. The solution equilibria of H2L1 and H2L2 with Ca2+ were investigated; for both ligands, the formation of a 1:2 Ca2+/ligand species is detected and the complete characterization is presented. The crystal structures of Ca1 and Ca2 were determined. In Ca1 the solid state assembly is attained by a polymeric association of [(CaL1(H2O))2(mu-OH2)] dimeric units. Each calcium ion coordinates four oxygen atoms of one ligand (two ethereal, one carboxylic, and one bridging carboxylic oxygen atom), one water molecule, one bridging water molecule, and a carboxylate group of the other ligand within the dimer. The octacoordination of the metal is completed by an interaction with the adjacent dimeric unit. The crystal structure of the complex Ca2 does not show a polymeric nature, but it is a centrosymmetric dimer. The coordination number of the metal ion is still 8:4 oxygen atoms of the ligand; 3 water molecules; 1 bridging carboxylate group. A preliminary study of the photochemical features of the complexes Ca1 and Ca2 is reported: photoexcitation by a nanosecond pulsed UV laser induces the cleavage of the ligand. This drastically reduces the affinity of the ligand toward Ca2+, which is then released in solution.     

A controlled supramolecular approach toward cation-specific chemosensors: alkaline earth metal ion-driven exciton signaling in squaraine tethered podands

Three different squaraine tethered bichromophoric podands 3a-c with one, two, and three oxygen atoms in the podand chain and an analogous monochromophore 4a were synthesized and characterized. Among these, the bichromophores 3a-c showed high selectivity toward alkaline earth metal cations, particularly to Mg(2+) and Ca(2+) ions, whereas they were optically silent toward alkali metal ions. From the absorption and emission changes as well as from the Job plots, it is established that Mg(2+) ions form 1:1 folded complexes with 3a and 3b whereas Ca(2+) ions prefer to form 1:2 sandwich dimers. However, 3c invariably forms weak 1:1 complexes with Mg(2+), Ca(2+), and Sr(2+) ions. The signal output in all of these cases was achieved by the formation of a sharp blue-shifted absorption and strong quenching of the emission of 3a-c. The signal transduction is achieved by the exciton interaction of the face-to-face stacked squaraine chromophores of the cation complex, which is a novel approach of specific cation sensing. The observed cation-induced changes in the optical properties are analogous to those of the "H" aggregates of squaraine dyes. Interestingly, a monochromophore 4a despite its binding, as evident from (1)H NMR studies, remained optically silent toward Mg(2+) and Ca(2+) ions. While the behavior of 4a toward Mg(2+) ion is understood, its optical silence toward Ca(2+) ion is rationalized to the preferential formation of a "Head-Tail-Tail-Head" arrangement in which exciton coupling is not possible. The present study is different from other known reports on chemosensors in the sense that cation-specific supramolecular host-guest complexation has been exploited for controlling chromophore interaction via cation-steered exciton coupling as the mode of signaling.     

Ruthenium complexes of easily accessible tridentate ligands based on the 2-aryl-4,6-bis(2-pyridyl)-s-triazine motif: absorption spectra, luminescence properties, and redox behavior

A family of tridendate ligands 1 a-e, based on the 2-aryl-4,6-di(2-pyridyl)-s-triazine motif, was prepared along with their hetero- and homoleptic Ru(II) complexes 2 a-e ([Ru(tpy)(1 a-e)](2+); tpy=2,2':6',2"-terpyridine) and 3 a-e ([(Ru(1 a-e)(2)](2+)), respectively. The ligands and their complexes were characterized by (1)H NMR spectroscopy, ES-MS, and elemental analysis. Single-crystal X-ray analysis of 2 a and 2 e demonstrated that the triazine core is nearly coplanar with the non-coordinating ring, with dihedral angles of 1.2 and 18.6 degrees, respectively. The redox behavior and electronic absorption and luminescence properties (both at room temperature in liquid acetonitrile and at 77 K in butyronitrile rigid matrix) were investigated. Each species undergoes one oxidation process centered on the metal ion, and several (three for 2 a-e and four for 3 a-e) reduction processes centered on the ligand orbitals. All compounds exhibit intense absorption bands in the UV region, assigned to spin-allowed ligand-centered (LC) transitions, and moderately intense spin-allowed metal-to-ligand charge-transfer (MLCT) absorption bands in the visible region. The compounds exhibit relatively intense emissions, originating from triplet MLCT levels, both at 77 K and at room temperature. The incorporation of triazine rings and the near planarity of the noncoordinating ring increase the luminescence lifetimes of the complexes by lowering the energy of the (3)MLCT state and creating a large energy gap to the dd state.     

以反丁烯二酰氯桥联的10,15,20-三（对-氯代苯基）卟啉二联体及其配合物的合成与性质研究

用5-（对-羟基苯基）-10,15,20-三（对-氯代苯基）卟啉为原料合成了以反丁烯二酰氯桥连的10,15,20-三（对-氯代苯基）卟啉二联体及其Zn,Cu,Co,Mn配合物,并用红外光谱、拉曼光谱、紫外光谱、质谱、核磁共振谱对其结构进行了表征.利用分子荧光光谱和表面光电压对其光学性质进行了研究.     

Formation and stability of mononuclear and dinuclear Eu(III) complexes and their catalytic reactivity toward cleavage of an RNA analog

The complex between Eu(III) and 1,7-diaza-4,10,13-trioxacyclopentadecane-N,N'-diacetic acid (L4) was characterized by pH potentiometric titration and 1H NMR spectroscopy. The conversion of the monomer to a dimeric complex is observed as the pH is increased from 7 to 10 in a reaction that releases one mol/HO- per dimer formed. The dimeric complex undergoes a further ionization with a pKa of 10.7. Kinetic parameters are reported for the cleavage of the simple phosphodiester 2-hydroxypropyl-4-nitrophenyl phosphate catalyzed by both the monomeric and the dimeric Eu(III) complexes. These data show that the monomer and dimer stabilize their bound reaction transition states with similar free energies of 7.1 and 7.6 kcal/mol, respectively. Clearly, a bridging hydroxide is not an optimal linker to promote cooperative catalysis between Eu(III) centers in macrocycles with multiple polyaminocarboxylate pendent groups.     

Formation of phosphino-substituted isocyanate by reaction of CO2 with group 2 complexes based on the (Me3Si)(i-Pr2P)NH ligand

The group 2 complexes [(Me(3)Si)(i-Pr(2)P)N](2)M(THF)(x) (M = Mg, x = 1; M = Ca/Sr, x = 2) as well as an unusual dimagnesium complex {[(Me(3)Si)(i-Pr(2)P)N](3)Mg}Mg(n-C(4)H(9)) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction. Each complex was shown to react with CO(2) under extremely mild conditions (15 min, 1 atm, room temperature) to give the isocyanate (i-Pr)(2)P-N═C═O. The independent syntheses of (i-Pr)(2)P-N═C═O and the carbodiimide dimer [(i-Pr)(2)PNCNP(i-Pr)(2)](2) are also reported.     

1H NMR studies of aerosol-OT reverse micelles with alkali and magnesium counterions: preparation and analysis of MAOTs

Simple procedures and characterization of a series of well-defined precursors are described for preparation of a unique microenvironment in nanoreactors, reverse micelles. The Na(+), K(+), Rb(+), Cs(+), and Mg(2+) surfactants were prepared using liquid-liquid ion exchange using chloride and nitrate salts. The surfactants were characterized using (1)H NMR spectroscopy and a variety of other techniques. (1)H NMR spectroscopy was found to be a sensitive probe for characterization of the size of the nanoreactor as well as its water content. (1)H NMR spectra can be used for detailed characterization of reactions in confined environments when counterion effects are likely to be important. (1)H NMR spectroscopy revealed two separate peaks corresponding to water in Mg(AOT)2 samples; one peak arises from water coordinated to the Mg(2+) ion while the other peak arises from bulk water. The two water signals arise directly from the slow exchange of the water coordinated to Mg(2+) in these microemulsions with water in the water pool, and provide an opportunity to study hydration of Mg(2+). This work thus extends the potential use of MAOT microemulsions for applications such as in green chemistry.     

Competitive cesium-133 NMR spectroscopic study of complexation of different metal ions with dibenzo-21-crown-7 in acetonitrile-dimethylsulfoxide and nitromethane-dimethylsulfoxide mixtures

(133)Cs NMR spectroscopy was used to determine the stoichiometry and stability of the Cs(+) ion complex with dibenzo-21-crown-7 (DB21C7) in acetonitrile-dimethylsulfoxide (96.5:3.5, w/w) and nitromethane-dimethylsulfoxide (96.5:3.5, w/w) mixtures. A competitive (133)Cs NMR technique was also employed to probe the complexation of Na(+), K(+), Rb(+), Ag(+), Tl(+), NH(4)(+), Mg(2+), Ba(2+), Hg(2+), Pb(2+) and UO(2)(2+) ions with DB21C7 in the same solvent systems. All the resulting 1:1 complexes in nitromethane-dimethylsulfoxide were more stable than those in acetonitrile-dimethylsulfoxide solution. In both solvent systems, the stability of the resulting complexes was found to vary in the order Rb(+)>K(+) approximately Ba(2+)>Tl(+)>Cs(+)>NH(4)(+) approximately Pb(2+)>Ag(+)>UO(2)(2+)>Hg(2+)>Mg(2+)>Na(+).     

Zirconium tetrachloride-formaldehyde sigma-complexes: A computational and spectroscopic investigation

We have carried out a combined theoretical-experimental study of the structures and energies of ZrCl(4)-aldehyde complexes using (13)C NMR spectroscopy and a DFT (B3LYP) computational approach. The computational investigation has demonstrated the existence of different types of complexes: a 1:1 complex (H(2)CO-ZrCl(4)), various 2:1 complexes ((H(2)CO)(2)-ZrCl(4)), and several dimeric species. The analysis of the energies involved in the formation of the various complexes has indicated that the dimeric species should correspond to the only adduct observed in the (13)C NMR spectra (carbonyl resonance at 226.96 ppm) when a 1:1 ZrCl(4)/aldehyde molar ratio is used, while the 2:1 complex should be responsible for the signal at 224.30 ppm that is recorded when this molar ratio is 1:2.     

Cation sensors containing a (bpy)Re(CO)3 group linked to an azacrown ether via an alkenyl or alkynyl spacer: synthesis, characterisation, and complexation with metal cations in solution

Two [(bpy)Re(CO)3L]+ complexes (bpy = 2,2'-bipyridine), where L contains an aza-15-crown-5 ether which is linked to Re via an alkenyl- or alkynyl-pyridine spacer, have been synthesised along with model complexes. Solutions of the complexes in acetonitrile have been studied by UV-Vis absorption spectroscopy, and by 1D and 2D 1H NMR spectroscopy. Strong UV-Vis bands, assigned to intraligand charge-transfer transitions localised at the L ligands, blue shift on protonation of the azacrown nitrogen atom or on complexation of alkali-metal (Li+, Na+ and K+) or alkaline-earth metal (Mg2+, Ca2+ and Ba2+) cations to the azacrown; the magnitude of the blue shift is dependent on the cation, with protonation giving the largest shift of ca. 100 nm. Cation binding constants in the range of log K= 1-4 depend strongly on the identity of the metal cation. Protonation or cation complexation causes downfield shifts in the 1H NMR resonances from most of the azacrown and L ligand protons, and their magnitudes correlate with those of the blue shifts in the UV-Vis bands; shifts in the azacrown 1H NMR resonances report on how the different metal cations interact with the macrocycle. UV-Vis and 1H NMR spectra of the free L ligands enable the effect of the Re centre to be assessed. Together, the data indicate that the alkene spacer gives a more responsive sensor than the alkyne spacer by providing stronger electronic communication across the L ligand.     

Metal ion scrambling in hexanuclear M(6)(Et(2)NCO(2))(12) complexes (M = Co,Mg). Synthesis,solid state structure,and solution dynamics of heteronuclear Co(n)Mg(6-n)(Et(2)NCO(2))(12) complexes

Heteronuclear diethylcarbamato complexes of the form Co(n)()Mg(6)(-)(n)()(Et(2)NCO(2))(12) were prepared from the isostructural homonuclear precursors Mg(6)(Et(2)NCO(2))(12), 1, and Co(6)(Et(2)NCO(2))(12), 2, via a solvothermal methodology. Two materials were selected for single-crystal X-ray diffraction analysis: Co(1.6)Mg(4.4)(Et(2)NCO(2))(12) and Co(2.7)Mg(3.3)(Et(2)NCO(2))(12). Both compounds crystallize in the orthorhombic space group Ccca, as do 1 and 2. The molecular structure is best described as two trinuclear M(3) units cross-linked by diethylcarbamate ligands and twisted about one another, so that the complex has overall D(2) symmetry and is chiral. Each trinuclear unit consists of two terminal pentacoordinate metal ions and one central hexacoordinate metal ion. The X-ray diffraction data were unambiguous that the Co(2+) ions migrate exclusively to the pentacoordinate sites in the heteronuclear complexes, thus demonstrating that metal ion scrambling at the molecular level must occur. The composition of individual crystals can be continuously varied for Co(2+) mole fractions chi(Co) < 0.5, and the a and c unit cell distances are linearly related to chi(Co). This indicates that the compounds behave as solid solutions. There appears to be either a chemical or crystallographic phenomenon inherent in the synthetic methodology that prevents isolation of heteronuclear materials having chi(Co) > 0.5. Solution electronic spectroscopy and molecular weight measurements show that 2 can dissociate in chloroform and cyclohexane solution to give a dimeric complex 2'. This behavior contrasts with the stability of 1 in solution, as shown by NMR. The kinetic rate profile for formation of Co(n)Mg(6-n)(Et(2)NCO(2))(12) reveals saturation kinetics and is consistent with direct attack by 2' on 1 to give the heteronuclear complex via a higher nuclearity intermediate. This study illustrates a general method for the preparation of solids based on heteronuclear Werner-type complexes of the M(6)(Et(2)NCO(2))(12) structure type, and the mechanism by which such compounds can be formed from isostructural homonuclear precursors.     

Synthesis and characterization of novel Pd(II) complexes with chelating and non-chelating heterocyclic iminocarbene ligands

The imidazolium salts [3-R1-1-{2-Ar-imino)-2-R2-ethyl}imidazolium] chloride (C-N; Ar = 2,6-iPr2C6H3; R1/R2 = Me/Me (a), Me/Ph (b), Ph/Me (c), 2,4,6-Me3C6H2 (d), 2,6-iPr2C6H3 (e)) react with Ag(2)O to give Ag(I) iminocarbene complexes (C-N)AgCl (4a-e) in which the iminocarbene ligand is bonded to Ag via the imidazoline-2-ylidene carbon atom. The solid-state structures of 4b and 4d were determined by X-ray crystallography and revealed the presence of monomeric (carbene)AgCl units with Z and E configurations at the imine C=N bonds, respectively. Carbene transfer to Pd occurs when compounds 4b-e are treated with (COD)PdCl2 to yield bis(carbene) complexes (C-N)2PdCl2 (6b-e) containing two kappa1-C bonded iminocarbene moieties. NMR spectroscopic data indicated a trans coordination geometry at Pd. This conclusion was supported by an X-ray structure determination of 6b which clearly demonstrated the non-chelating nature of the iminocarbene ligand system. EXSY 1H NMR spectroscopy suggests that the non-chelating structures undergo E/Z isomerization at the imine C[double bond, length as m-dash]N double bonds in solution. The preparative results contrast our earlier report that the reaction between 4a and (COD)PdCl2 results in a chelating kappa2-C,N bonded iminocarbene complex (C-N)PdCl2. The coordination mode and dynamic behavior of the iminocarbene ligand systems have been found to be dramatically affected by changes in the substitution pattern of the ligand system. Sterically unencumbered systems (a) favor the formation of kappa2-C,N chelate structures containing one iminocarbene moiety per metal upon coordination at Pd(II); these complexes were demonstrated to engage in reversible, solvent-mediated chelate ring-opening reactions. Sterically encumbered systems (b-e) form non-chelating kappa1-C iminocarbene Pd(II) complexes containing two iminocarbene ligands per metal. Transannular repulsions across the chelate ring are believed to be the origin of these structural differences.     

Synthesis and structure of a series of new d(1)-Aryl imido-vanadium(IV) complexes stabilized by n-donor ligands

A family of new coordination vanadium(IV) compounds supported by a terminal or bridged aryl imido ligand are reported. Reaction of V(NMe(2))(4) with anilines ArNH(2), where Ar = 2,6-i-Pr(2)-C(6)H(3), 2,6-Me(2)-C(6)H(3), Ph, 2,6-Cl(2)-C(6)H(3), and C(6)F(5), afforded the diamagnetic imido-bridged complexes [V(NAr)(NMe(2))(2)](2) (1a-e). Chlorination of 1a-e with trimethylchlorosilane afforded complexes 2a-e formulated as [V(=NAr)Cl(2)(NHMe(2))(x)()](n)(). One-pot reaction of V(NMe(2))(4) with ArNH(2) in the presence of an excess of trimethylchlorosilane gave the five-coordinate compound [V(=NAr)Cl(2)(NHMe(2))(2)] (3a-e). Reaction of 3a-e with pyridine, bipyridine (bipy), or N,N,N',N'-tetramethylethylenediamine (tmeda) gave respectively the six-coordinate tris- or bis(pyridine) adducts [V(=NAr)Cl(2)(Py)(3)] (4a-e) or [V(=NAr)Cl(2)(Py)(2)(NHMe(2))] (5a), bipyridine complexes [V(=NAr)Cl(2)(bipy)(NHMe(2))] (5a-e) and [V(=NAr)Cl(2)(bipy)(Py)] (9a), and tmeda adduct [V(=NAr)Cl(2)(tmeda)(NHMe(2))] (10a). Moreover, five-coordinate complexes free of NHMe(2) ligands, such as [V(=NAr)Cl(2)(Py)(2)] (5a), [V(=NAr)Cl(2)(bipy)] (8a), and [V(=NAr)Cl(2)(tmeda)] (11a), were directly prepared starting from precursors 2a-e. All compounds were totally characterized by spectroscopic methods (IR, (1)H NMR for diamagnetic complexes, and EPR for paramagnetic complexes), elemental analysis, magnetism, and single-crystal X-ray diffraction studies for 1b, 3a, 3d, 4b, 4d, 7c, 10a, and 11a.     

Stabilization of ketone and aldehyde enols by formation of hydrogen bonds to phosphazene enolates and their aldol products

Solution properties of enolates generated using the phosphazene (Schwesinger) base P4-tBu were investigated by NMR spectroscopy. With a full equivalent of base the benzyl ketones 1a and 1b, the acetophenone 2, the arylacetaldehyde 1c, and the methyl arylacetate 1d formed the expected "naked" (P4H+) enolates 3 and 7. However, at a half-equivalent of base the ketones 1a and 1b as well as the aldehyde 1c formed solutions of stable hydrogen-bonded dimeric (enol-enolate) structures (4). The acetophenone 2, on the other hand, forms only traces of the H-bonded dimer 8 during deprotonation of 2. The thermodynamic product was the isomeric self-aldol condensation product 12. The mechanism of this condensation was elucidated by low temperature rapid-injection (RI) NMR spectroscopy. Solutions of 8 stable enough for NMR characterization could be transiently generated by semiprotonation of the enolate 7 with HCl.OEt2 at -130 degrees C using RINMR. The ester enolate 1d gave no trace of 4d even on a time scale as short as a few seconds at -130 degrees C either during the semideprotonation of 1d, or during semiprotonation of the enolate 3d. Long-lived solutions of the enols derived from 1a, 1b, 1c, and 2 (but not 1d) could be produced by full protonation of the phosphazene enolates with HCl.OEt2 at low temperature.     

Investigation of group 12 metal complexes with a tridentate SNS ligand by X-ray crystallography and 1H NMR spectroscopy

Two series of zinc triad complexes containing the ligand 2,6-bis(methylthiomethyl)pyridine (L1) were synthesized and characterized by X-ray crystallography and solution-state 1H NMR spectroscopy. The distorted meridional octahedral M(L1)2(ClO4)2 series includes the first structurally characterized Zn(II) and Cd(II) complexes with N2(SR2)4 coordination spheres. Coordination of HgCl2 and ZnCl2 with 1 equiv of ligand afforded mononuclear, five-coordinate species Hg(L1)Cl2 and Zn(L1)Cl2, respectively, with distorted square-pyramidal and trigonal-bipyramidal geometries. With CdCl2, the dimeric [Cd(L1)Cl(mu-Cl)]2 complex was obtained. The distorted octahedral coordination geometry of each Cd(II) center in this complex is formed by one tridentate ligand, two bridging chloride ions, and one terminal chloride ion. NMR spectra indicate that the intermolecular ligand-exchange rate of [M(L1)2](2+) decreased in the order Cd(II) > Zn(II) > Hg(II). Slow intermolecular ligand-exchange conditions on the chemical-shift time scale were found for 1:2 metal-to-ligand complexes of L(1) with Hg(II) and Zn(II) but not Cd(II). Slow intermolecular ligand-exchange conditions in acetonitrile-d(3) solutions permitting detection of (3-5)J(199Hg1H) were found for 1:1 and 1:2 Hg(ClO4)2/L1 complexes, but not for the related Cd(ClO4)2) complexes. The magnitudes of J(199Hg1H) for equivalent protons were smaller in [Hg(L1)2](2+) than in [Hg(L1)(NCCH3)x](2+). The relative intermolecular ligand-exchange rates of the zinc triad complexes investigated here suggest that the toxicity of Hg(II) is accentuated by the relative difficulty of displacing it from the coordination sites encountered.     

A comparative study of pi-arene-bridged lanthanum arylamide and aryloxide dimers. Solution behavior, exchange mechanisms, and X-ray crystal structures of La2(NH-2,6-iPr2C6H3)6, La(NH-2,6-iPr2C6H3)3(THF)3, and La(NH-2,6-iPr2C6H3)3(py)2

Reaction of 3 equiv of 2,6-diisopropylaniline with La[N(SiMe(3))(2)](3) produces the dimeric species La(2)(NHAr)(6) (1). X-ray crystallography reveals a centrosymmetric structure, where the dimeric unit is bridged by intermolecular eta(6)-arene interactions of a unique arylamide ligand attached to an adjacent metal center. Exposure of 1 to THF results in formation of the monomeric tris-THF adduct La(NHAr)(3)(THF)(3) (2), which was shown by X-ray crystallography to maintain a fac-octahedral structure in the solid state. (1)H NMR spectroscopy illustrates that the binding of THF to 1 to form 2 is reversible and removal of THF under vacuum regenerates dimeric 1. Addition of pyridine to 1 yields the monomeric bis-pyridine adduct La(NHAr)(3)(py)(2) (3), which exhibits a distorted trigonal-bipyramidal La metal center. Solution (1)H NMR, IR, and Raman spectroscopy indicate that the pi-arene-bridged dimeric structure of 1 is maintained in solution. Variable-temperature (1)H NMR spectroscopic investigations of 1 are consistent with a monomer-dimer equilibrium at elevated temperature. In contrast, variable-temperature (1)H NMR spectroscopic investigations of the aryloxide analogue La(2)(OAr)(6) (4) show that the bridging and terminal aryloxide groups exchange by a mechanism in which the dimeric nature of the compound is retained. Density functional theory (DFT) calculations were carried out on model compounds La(2)(OC(6)H(5))(6), La(2)(NHC(6)H(5))(6), and (C(6)H(5)R)La(XC(6)H(5))(3), where X = O or NH and R = H, OH, or NH(2). The formation of eta(6)-arene interactions is energetically favored over monomeric LaX(3) (X = OPh or NHPh) with the aryloxide pi-arene interaction being stronger than the arylamide pi-arene interaction. Calculation of vibrational frequencies reveals the origin of the observed IR spectral behavior of both La(2)(OC(6)H(5))(6) and La(2)(NHC(6)H(5))(6), with the higher energy nu(C=C) stretch due to terminal ligands and the lower energy stretch associated with the bridging ligands.     

Synthesis and characterization of novel dinuclear copper(I) complexes. Dimerization of [CuL(PPh3)2] (L = methyl 3-hydroxy-3-(p-R-phenyl)-2-propenedithioate)

We report the synthesis of new copper(I) complexes 6a-e from methyl 3-hydroxy-3-(p-R-phenyl)-2-propenedithioate ligands. These complexes were characterized by IR and 1H, 13C, and 31P NMR spectroscopy. The expected O,S-coordination mode was confirmed by the X-ray diffraction studies of 6b and 6e. The unexpected dimerization of 6b-e leads to the formation of four novel dinuclear copper(I) compounds (7b-e). The dinuclear complex structure was fully established by the X-ray diffraction analysis of 7a, in which the presence of a Cu-Cu interaction was observed.     

Terphenyl-phenanthroline conjugate as a Zn(2+) sensor: H(2)PO(4)(-) induced tuning of emission wavelength

A new terphenyl-based macrocycle 5 incorporating phenanthroline as a fluorophore has been designed, synthesized and examined for its recognition ability toward various cations (Pb(2+), Hg(2+), Ba(2+), Cd(2+), Ag(+), Zn(2+), Cu(2+), Ni(2+), Co(2+), K(+), Mg(2+), Na(+) and Li(+)) by UV-vis, fluorescence and NMR spectroscopy. The receptor 5 showed highly selective 'Off-On' fluorescence signaling behavior for Zn(2+) ions in THF. Interestingly, the addition of H(2)PO(4)(-) ions to the [5-Zn] complex regulates the binding site for additional Zn(2+) ions and hence leads to a blue-shifted emission band.     

Synthesis, structures, and olefin polymerization capability of vanadium(4+) imido compounds with fac-N3 donor ligands

One-pot reactions of V(NMe2)4 with a range of primary alkyl- and arylamines RNH2 and Me3SiCl afforded the corresponding five-coordinate vanadium(4+) imido compounds V(NR)Cl2(NHMe2)2 [R = 2,6-C6H3(i)Pr2 (1a, previously reported), 2-C6H4(t)Bu (1b), 2-C6H4CF3 (1c), (t)Bu (1d), Ad (Ad = adamantyl, 1e)]. The crystal structures of 1b (two diamorphic forms) and 1c featured N-H...Cl hydrogen-bonded chains. Reaction of 1a-e with the neutral face-capping, N3 donor ligands TACN (TACN = 1,4,7-trimethyltriazacyclononane) or TPM [TPM = tris(3,5-dimethylpyrazolyl)methane] gave the corresponding six-coordinate complexes V(NR)(TACN)Cl2 (2a-e) and V(NR)(TPM)Cl2 (3a-e). The X-ray structures of 2b, 2c, 2d, 3b, 3c, and 3e were determined. When activated with methylaluminoxane, certain of the complexes V(NR)(TPM)Cl2 (3) formed moderately active ethylene polymerization catalysts, whereas none of the compounds V(NR)(TACN)Cl2 (2) were active.     

Photoprocesses in <Emphasis Type="Italic">N</Emphasis>-ammonioalkyl derivatives of azacrown-containing styryl dyes and their complexes with metal perchlorates

Photophysical processes and photochemical reactions in the N-ammonioalkyl derivatives of the azacrown-containing styryl dyes and their complexes with lead and barium perchlorates in MeCN and CH₂Cl₂ were studied by ¹Н NMR spectroscopy, absorption spectroscopy, luminescence spectroscopy, laser kinetic spectroscopy, and quantum chemistry. Molecules of the styryl dyes and their complexes are able to undergo normal (fast) and delayed fluorescence and trans–cis-photoisomerization. The molecules in the triplet state participate in degradation processes of the electron excitation energy.