Spectroscopic aspects for the Yb3+ coordination compound with a large energy gap between the ligand and Yb3+ excited states.

We present the experimental and theoretical results that made it possible to propose the energy transfer mechanism for a Yb complex with a large energy gap between the ligand and Yb excited states using a theoretical model and experimental data. Absorption and emission spectroscopy in the 300-4 K range is used for the study of the Yb3+ compound with N-phosphorylated sulfonamide (Na[YbL4]), which, despite the large energy gap, is characterized by high emission sensitization efficiency (ηsens = 40%) and relatively long Yb3+ emission lifetime (27 µs). The crystal structure of Na[YbL4], radiative lifetime (930 µs), refractive index (1.46), intrinsic (3.0%), and overall (1.3%) emission quantum yield were determined. To obtain the electronic properties of the Na[YbL4], a time-dependent density functional theory (TD-DFT) was performed. The intramolecular energy transfer (IET) rates from the excited states S1 and T1 to the Yb3+ ion as well as between the ligand and the ligand-to-metal charge transfer (LMCT) states were calculated. Once the intersystem crossing S1 â†’ T1 is not so effective due to a large energy gap between S1 and T1 (≈10000 cm-1), it has been shown that the LMCT state acts as an additional channel to feed the T1 state. Then, the T1 can transfer energy to the Yb3+ 2F5/2 energy level (WT), where WT is dominated by the exchange mechanism. Based on IET and a rate equation model, the overall emission quantum yield QLLn was simulated with and without the LMCT, this also confirmed that the pathway S1 â†’ LMCT â†’ T1 â†’ Yb3+ is more likely than the S1 â†’ T1 â†’ Yb3+ one.

New water-soluble isoxazole-linked 1,3,4-oxadiazole derivative with delocalized positive charge.

Herein we present a synthesis and characterization of a new and unique low-weight heterocyclic compound 5-amino-2-(5-amino-3-methyl-1,2-oxazol-4-yl)-3-methyl-2,3-dihydro-1,3,4-oxadiazol-2-ylium bromide with the unusual electron charge delocalization owing the local positive charge at the carbon atom of oxadiazole moiety. X-ray single crystal of C7H10N5O2·Br- showed the molecule crystalized in monoclinic, space group P21/c. Both five membered rings are planar and twisted forming the ring motif with the counter ion where H⋯Br interactions are one of the dominant. The presented compound is characterized by high ionization efficiency in ESI-MS mode and undergoes dissociation within oxadiazole moiety under ESI-MS/MS conditions even under low collision energies. The presented compound is an interesting example of heterocyclic stable carbocation which may serve as a new lead structure.

Luminescent properties of chameleon-like metal-organic framework between zinc(II) dichloride and two quinoline-N-oxide molecules.

Zinc compounds in the form of inorganic/organic hybrids containing both zinc halides and heterocyclic ligands show various interesting optical and physicochemical properties. Due to these properties, there is a potential for development of various innovative technologies and applications within the life sciences. In this study, experimental and theoretical results on the absorption and emission (steady state and time-resolved) properties of the hybrid ZnCl2(QO)2 complex formed between ZnCl2 and quinoline N-oxide, have been reported. Single crystal X-ray analysis revealed the tetragonal cell (Z = 4) with P41212 space group and a slight crystal distortion. Interestingly, experiments in aprotic solvents show that both absorption and emission spectra peak in the ultraviolet (UV) region suggesting a weak CT character of the emissive S1 state, confirmed by a middle Stokes shift values. The results of the nanosecond time-resolved emission spectroscopy suggest two different structures of the complex described by the two different lifetimes and variable amplitudes dependent on the polarity of the medium. In the solid state, a relatively strong, bright blue luminescence appears at 413 nm (τ = 2.26 ns). Theoretical calculations (DFT and TD DFT) confirm experimental studies and reveal the solvent-dependent chameleon properties of ZnCl2(QO)2 by two different structures in two solvents of a contrast polarity. In apolar cyclohexane (CHX, µ = 5.612 D), the planes of both lateral quinoline N-oxide (QO) rings show to be nearly parallel each to another, resembling the crystal structure, while in a strongly polar acetonitrile (AN, µ = 9.328 D) they are nearly perpendicular. Such parallel arrangement of quinoline rings of ZnCl2(QO)2 complex in weakly polar methylcyclohexane can hinder the process of Photoinduced Electron Transfer, resulting in a stronger emission and significant quantum yield in comparison to more polar media.

Contribution of Energy Transfer from the Singlet State to the Sensitization of Eu3+ and Tb3+ Luminescence by Sulfonylamidophosphates.

A series of stable lanthanide complexes Na[Ln(L)4 ] (Ln=La3+ , Eu3+ , Gd3+ , Tb3+ , with L=dimethyl(4-methylphenylsulfonyl)amidophosphate and dimethyl-2-naphthylsulfonylamidophosphate) were synthesized. The compounds were characterized by single-crystal X-ray diffraction, IR, absorption, and emission spectroscopy at 293 and 77 K. In contrast to the usual and well-known dominant role of the ligand triplet state in intramolecular energy transfer processes in Ln complexes, in this particular new class of Ln compounds with sulphonylamidophosphate ligands, strong experimental and detailed theoretical evidence suggest a dominant role is played by the ligand first excited singlet state. The importance of the role played by the 7 F5 level in the case of the Tb3+ compound in this process is shown. The theoretical approach for the energy transfer rates was successfully applied to the rationalization of the experimental data. The higher-lying excited levels of Eu (5 DJ , 5 LJ , 5 GJ ) and Tb (5 DJ , 5 GJ , 5 LJ , 5 HJ , 5 FJ , 5 IJ ) were included in the calculations for the first time. Both the multipolar and exchange mechanisms were taken into account. The experimental intensity parameters (Ωλ ), emission lifetimes (τ), radiative (Arad ) and non-radiative (Anrad ) decay rates, and quantum yields (theoretical and experimental) were determined and are discussed in detail.

The Crystal Structure and Behavior of Fenamic Acid-Acridine Complex Under High Pressure.

The crystal structure of fenamic acid-acridine complex is determined by X-ray diffraction. The strong OHN hydrogen bond linking the complex components and other interactions responsible for packing of the molecules into a crystal are investigated within the Quantum Theory of Atom in Molecule theory. The crystal structure is compared with the structure optimized at B3LYP/6-311++G** level and with the theoretical structures optimized under systematically changed pressure. Analysis of the lattice constants, hydrogen bond lengths, and angles of the inter- and intramolecular hydrogen bond under compression is performed. The structural transformation observed at 5 GPa is connected with a change in the intermolecular OHN hydrogen bond. The proton shifts to acceptor and a new interaction in the crystal appears.

Transformation of barium-titanium chloro-alkoxide compound to BaTiO3 nanoparticles by BaCl2 elimination.

In this Article, we present how the molecular precursor of binary oxide material having an excess of alkali earth metal can be transformed to the highly phase pure BaTiO3 perovskite. Here, we synthesized and compared two barium-titanium complexes with and without chloride ligands to determine the influences of different ligands on the phase purity of binary oxide nanoparticles. We prepared two barium-titanium complexes, i.e., [Ba4Ti2(µ6-O)(OCH2CH2OCH3)10(HOCH2CH2OCH3)2(HOOCCPh3)4] (1) and [Ba4Ti2(µ6-O)(µ3,η2-OCH2CH2OCH3)8(µ-OCH2CH2OCH3)2(µ-HOCH2CH2OCH3)4Cl4] (2). The barium-titanium precursors were characterized using elemental analysis, infrared and nuclear magnetic resonance spectroscopies, and single-crystal X-ray structural analysis, and their thermal decomposition products were compared. The complex 1 decomposed at 800 °C to give a mixture of BaTiO3 and Ba2TiO4, whereas 2 gave a BaCl2/BaTiO3 mixture. Particles of submicrometer size (30-50 nm) were obtained after leaching of BaCl2 from the raw powder using deionized water. Preliminary studies of barium titanate doped with Eu(3+) sintered at 900 °C showed that the dominant luminescence band arose from the strong electric dipole transition, (5)D0-(7)F2.

Flux-Aided Synthesis of Lu2O3 and Lu2O3:Eu-Single Crystal Structure, Morphology Control and Radioluminescence Efficiency.

Li2SO4 or (Li2SO4 + SiO2)-mixture fluxes were used to prepare a Lu2O3:Eu powder phosphor as well as an undoped Lu2O3 utilizing commercial lutetia and europia as starting reagents. SEM images showed that the fabricated powders were non-agglomerated and the particles sizes varied from single microns to tens of micrometers depending largely on the flux composition rather than the oxide(s)-to-flux ratio. In the presence of SiO2 in the flux, certain grains grew up to 300-400 µm. The lack of agglomeration and the large sizes of crystallites allowed making single crystal structural measurements and analysis on an undoped Lu2O3 obtained by means of the flux technique. The cubic structure with a = 10.393(2) Å, and Ia space group at 298 K was determined. The most efficient radioluminescence of Lu2O3:Eu powders reached 95%-105% of the commercial Gd2O2S:Eu.

Magnesium, zinc and aluminium complexes supported by tripodal diaminebis(aryloxido) ligands: synthesis, solid state and solution structure.

The reactions of the diaminebis(aryloxido) ligand precursors [Me2NCH2CH2N(CH2-4-R-C6H3OH)2] [R = C(CH3)2CH2C(CH3)3, H2L(1); R = CH3, H2L(2)] with Mg(n)Bu2, ZnEt2 and AlEt3 create complexes of general formula [M2(µ-L-κ(4)O,N,N,O)2] (M = Mg, 1a for L(1) and 1b for L(2); M = Zn, 2a for L(1) and 2b for L(2)) and [Al2(µ-L-κ(3)O,N,N,O)2Et2] (3 for L(1)) in good yields. Compounds 1a-3 were characterized by NMR spectroscopy and ESI-MS experiments. The definitive molecular structure of 1b·CH2Cl2, 2a·H2O, 2b·CH2Cl2 and 3 was provided by a single-crystal analysis and revealed their dimeric nature with an M2O2 planar core. The L(1) and L(2) ligands coordinate as the dianions in a tetradentate/bridging manner in 1b, 2a, 2b and in a tridentate/bridging mode in 3. The NMR spectra showed that the solid state of these compounds is essentially retained in solution.

Synthesis of functionalized materials using aryloxo-organometallic compounds toward spinel-like MM'2O4 (M = Ba2+, Sr2+; M' = In3+, Al3+) double oxides.

The predesigned single-source precursors [Ba{(µ-ddbfo)(2)InMe(2)}(2)] (1), [Me(2)In(µ-ddbfo)](2) (2), [Sr{(µ-ddbfo)(2)AlMe(2)}(2)] (4), and [Me(2)Al(µ-ddbfo)](2) (5) (ddbfoH = 2,3-dihydro-2,2-dimethylbenzofuran-7-ol) for spinel-like double oxides and group 13 oxide materials were prepared via the direct reaction of the homoleptic aryloxide [M(ddbfoH)(4)](ddbfo)(2)·ddbfoH (M = Ba(2+), Sr(2+) (3)) and InMe(3) or AlMe(3) in toluene. In all of the reactions, there was an organometallic-driven abstraction of the OH protons from the 7-benzofuranols in the Ba(2+) and Sr(2+) cation sphere. All compounds were characterized by elemental analysis, (1)H NMR, and FT-IR spectroscopy. In addition, the molecular structures of 1, 2, and 3 were determined by single-crystal X-ray diffraction. The oxide products derived from the compounds mentioned above were studied using elemental analysis, Raman spectroscopy, X-ray powder diffraction, and scanning and transmission electron microscopy equipped with an energy-dispersive spectrometer. Moreover, their specific surface area and mesopore size distribution were evaluated using nitrogen porosimetry. Preliminary investigations of the Eu-doped SrAl(2)O(4) and In(2)O(3) phosphors revealed that the oxides obtained could be considered as matrices for lanthanide ions.

Triple C-H bond activation of a nickel-bound methyl group: synthesis and X-ray structure of a carbide cluster (NiCp)6(µ6-C).

A new hexanuclear cyclopentadienylnickel carbide cluster (NiCp)(6)(µ(6)-C) (1) was obtained through the thermolysis of the alkene complex [NiCp(CH(3))(η(2)-CH(2)═CHC(4)H(9))] (4). The X-ray molecular structure of 1 (monoclinic; P2(1)/c; Ni-C(carbide) = 1.767(4)-2.109(4) Å) reveals a highly deformed octahedral arrangement of nickel atoms with two octahedron edges opened (Ni-Ni bonding distances = 2.410(1)-2.623(1) Å, Ni···Ni nonbonding distances = 3.107(2) and 3.108(2) Å). Cluster 1 is the first example of a homoleptic, cyclopentadienylnickel carbide cluster. Moreover, (13)C-labeling studies proved that the carbido ligand in cluster 1 originated from the Ni-bound methyl group. This transformation requires a triple C-H bond activation in the methyl group, which has not been observed so far for late transition metal compounds.

The impact of solvent polarity on intramolecular proton and electron transfer in 2-alkylamino-4-nitro-5-methyl pyridine N-oxides.

The crystal structure of 2-butylamino-4-nitro-5-methyl pyridine N-oxide (2B5M) and solution studies of both 2B5M and 2-methylamino-4-nitro-5-methyl pyridine (2M5M) N-oxide are presented. Steady-state absorption and emission measurements were employed for both molecules while a picosecond fluorescence up-conversion technique was used to follow the dynamic behavior of the 2M5M system. The experimental methods were complemented by DFT and TD DFT B3LYP/6-31G(d,p) calculations involving ground and excited-state optimization which in the case of the smaller 2M5M molecule were extended to the CAM-B3LYP/6-31G(d,p) method. The solvent effect is incorporated by applying the polarizable continuum (PCM) model. The data reveal that the 2B5M molecule crystallizes in the monoclinic space group P2(1)/c and its crystal lattice is composed of monomers with intramolecular N-H···O [2.572(3) Å] hydrogen bonds, connected into a polymer network by weak intermolecular C-H…O [3.2-3.4 Å]-type interactions. Quantum-chemical calculations show that the aminoalkyl substitutent in aminoalkyl-pyridine N-oxides is a specific determinant of the CT nature of the lowest-lying excited electronic ππ* state, distinguishing them from other nitroaromatic compounds. The results of both picosecond fluorescence up-conversion experiments in different solvents and quantum-chemical calculations suggest that in nonpolar media the ESIPT process in 2M5M is favored, while in polar acetonitrile, the N* → PT* transition demands barrier-crossing and thus unfavorable thermodynamic conditions do not allow the ESIPT to occur. The signals of picosecond fluorescence up-conversion of 2M5M are solvent- and emission-wavelength dependent. The three time components found in a weakly polar isooctane-dioxane mixture have been attributed to solvation dynamics (∼500 fs), and to relaxation of N* and PT* forms while in acetonitrile, a very rapid fluorescence decay with a time constant (2.3-4.0 ps) indicative of the presence of the normal (N*) form was observed. Much shorter fluorescence lifetimes in alcohols (a few picoseconds) and in D(2)O (less than 200 fs) than in aprotic solvents suggest that in protic media, the solvent molecules participate in the ESIPT, bridging between the methylamine group and the N-oxide group of 2M5M.

Vanadate complexes bearing an imidazolidine-bridged bis(aryloxido) ligand: synthesis and solid state and solution structure.

A new imidazolidine-bridged bis(aryloxido) ligand precursor (H(2)L) [H(2)L = 2,2'-(imidazolidine-1,3-diylbis(methylene))bis(4-(1,1,3,3-tetramethylbutyl-2-yl)phenol)] was prepared in a relatively high yield (∼60%) via a single-step Mannich condensation of 4-(1,1,3,3-tetramethylbutyl)phenol, ethylenediamine and paraformaldehyde at 2:1:3 molar ratio and characterized by chemical and physical techniques including X-ray crystallography. Reactions of H(2)L with [VO(OEt)(3)] at 1:1 and 1:2 molar ratios in toluene afforded [V(L-κ(3)O,N,N,O)(O)(OEt)] (1) and [V(2)(µ-L-κ(4)O,N,N,O)(µ-OEt)(2)(O)(2)(OEt)(2)] (2), respectively. Alcoholysis of 1 with EtOH enables elimination of one molecule of H(2)L and the formation of 2. Compounds 1 and 2 were characterized by IR and NMR spectroscopy as well as ES-MS experiments. The definitive molecular structure of 2 was provided by a single-crystal analysis and revealed its dinuclear nature, featuring two octahedral vanadium centres bridged by both OEt groups and the L ligand. The (51)V, (1)H and (13)C NMR spectra as well as ES-MS showed that 2 does not stay intact in solution and undergoes dissociation to give 1 and [VO(OEt)(3)].

Lithium complexes supported by tripodal diaminebis(aryloxido) ligands: synthesis and structure.

The diaminebis(aryloxido) ligand precursors H(2)L(1) and H(2)L(2) [H(2)L(1) = Me(2)NCH(2)CH(2)N(CH(2)-4-CMe(2)CH(2)CMe(3)-C(6)H(3)OH)(2); H(2)L(2) = Me(2)NCH(2)CH(2)N(CH(2)-4-Me-C(6)H(3)OH)(2)] were synthesized by a straightforward single-step Mannich condensation. Their reactions with 2 molar equivalents of MeLi in thf afforded [Li(4)(µ-L-κ(4)O,N,N,O)(2)(thf)(2)] (1a, L(1); 1b, L(2)) and unexpectedly small amounts (∼9%) of [Li(6)(µ-L-κ(4)O,N,N,O)(2)(µ(3)-Cl)(2)(thf)(4)]·thf (2a·thf; L(1); 2b·thf, L(2)). Stoichiometric reactions of LiCl, MeLi and ligand precursors H(2)L led to the formation of 2a and 2b in high yield (∼80%). All compounds were characterized by chemical and physical techniques including X-ray crystallography for H(2)L(1), H(2)L(2), 1b, 2a and 2b.

Design of a magnesium-pridinolum complex for polylactide-drug conjugates formation.

Polylactide conjugates of the muscle contraction agent Pridinolum (PriOH = 1,1-diphenyl-3-(1-piperidinyl)-1-propanol) were prepared directly by ring-opening polymerization of L-lactide (L-LA) mediated by the pridinolum magnesium complex [Mg(µ,η(2)-OPri)(η(1)-OPri)](2). The ancillary O,N - bifunctional drug as a ligand stabilizes the magnesium species and initiates L-LA polymerization affording a polymer chain terminated by covalently attached drug molecules to the PLLA through ester linkers to form PriO-PLLA conjugate. Up to 80% of the pridinolum can be released from the conjugate by treatment with deuterated hydrochloric acid DCl at pH = 1.5 for 10 h at 37 °C.

On the nature of Ni···Ni interaction in a model dimeric Ni complex.

A new dinuclear complex (NiC(5)H(4)SiMe(2)CHCH(2))(2) (2) was prepared by reacting nickelocene derivative [(C(5)H(4)SiMe(2)CH=CH(2))(2)Ni] (1) with methyllithium (MeLi). Good quality crystals were subjected to a high-resolution X-ray measurement. Subsequent multipole refinement yielded accurate description of electron density distribution. Detailed inspection of experimental electron density in Ni···Ni contact revealed that the nickel atoms are bonded and significant deformation of the metal valence shell is related to different populations of the d-orbitals. The existence of the Ni···Ni bond path explains the lack of unpaired electrons in the complex due to a possible exchange channel.

Chemoselective alcoholysis of lactide mediated by a magnesium catalyst: an efficient route to alkyl lactyllactate.

Alkyl-(S,S)-O-lactyllactate was prepared by chemoselective alcoholysis of lactide LA mediated by a magnesium catalyst. When ROH reacted with LA it yielded the ring-opened product R-(S,S)-O-lactyllactate exclusively, which remained intact as long as LA was present in the reaction mixture. Consumption of LA caused the reaction to proceed further giving R-(S)-lactate.

Titanocene as a precursor for a cyclopentadienyl-free titanium(III)-manganese(II) cluster: a new approach for nano-size materials.

A simple and unique route to access the heterometallic cluster [Mn4Ti4(micro-Cl)2(micro3,eta2-L)2(micro,eta2-L)10Cl6] (1) with two Mn2Ti2 butterfly core motifs is reported. This method comprises elimination of the Cp ring from Cp2TiCl2 as CpH in the presence of metallic Mn in 2-methoxoethanol (LH) as a proton source. Complex 1 belongs to a group of magnetic clusters, which consists of two weakly interacting M4 subunits.

Supramolecular stores of acetic acid--an alternative for metal-organic frameworks.

A series of new complexes: [M(quin-2-c)(2)(H(2)O)(2)]x 4CH(3)COOH (M=Mn(2+), Co(2+) or Ni(2+), quin-2-c is quinoline-2-carboxylate ion) have been synthesized and characterized by X-ray single crystal study. The crystals of the complexes reveal very interesting 1D structures comprising acetic acid molecules. The processes of re- and desolvation of acetic acid by the manganese complex in mild conditions have been studied. The de- and resolvated materials were characterized by elemental analysis, IR spectroscopy and XRD study. The results show that binding of acetic acid is reversible and stoichiometric.

Cyclopentadienyl/alkoxo ligand exchange in group 4 metallocenes: a convenient route to heterometallic species.

A simple and efficient strategy for the synthesis of nonorganometallic heterometallic clusters from cheap organometallic precursors is reported. This unique synthetic method involves elimination of the cyclopentadienyl ring from Cp(2)MCl(2) (M = Ti, Zr, Hf) as CpH in the presence of M'L(2) or M'L'(2) (M' = Ca, Sr, Mn; CH(3)OCH(2)CH(2)OH = LH or (CH(3))(2)NCH(2)CH(2)OH = L'H) in an alcohol as a source of protons. In the reactions presented, a series of compounds, [Ca(4)Ti(2)(mu(6)-O)(mu(3),eta(2)-L)(8)(eta-L)(2)Cl(4)] (1), [Sr(4)Hf(2)(mu(6)-O)(mu(3),eta(2)-L)(8)(eta-L)(2)(eta-LH)(4)Cl(4)] (2), [Ca(4)Zr(2)(mu(6)-O)(mu-Cl)(4)(mu,eta(2)-L)(8)Cl(2)] (3), [Sr(4)Ti(2)(mu(6)-O)(mu(3),eta(2)-L)(8)(eta-L)(2)(eta-LH)(2)Cl(4)] (4), [Ca(4)Zr(2)Cp(2)(mu(4)-Cl)(mu-Cl)(3)(mu(3),eta(2)-L)(4)(mu,eta(2)-L)(4)Cl(2)] (5), [CaTiCl(2)(mu,eta(2)-L')(3)(eta-L'H)(3)][L'] (6), [Ca(2)Ti(mu,eta(2)-L')(6)Cl(2)] (7), [Mn(4)Ti(4)(mu-Cl)(2)(mu(3),eta(2)-L)(2)(mu,eta(2)-L)(10)Cl(6)] (8), and [Mn(10)Zr(10)(mu(4)-O)(10)(mu(3)-O)(4)(mu(3),eta(2)-L)(2)(mu,eta(2)-L)(16)(mu,eta-L)(4)(eta-L)(2)Cl(8)] (9), were obtained in good yield. All of the complexes were characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray structural analysis. Complex 8 belongs to a group of magnetic clusters that consists of Mn(4) subunits held together by two mu-Cl bridges. Compounds 6 and 7 underwent thermal decomposition, yielding an alternative source for some heterometallic oxides, which were analyzed by X-ray powder diffraction.

Nickelacyclic-cobaltocene vs. nickelacyclic-nickelocene. Synthesis, X-ray structures, electron transfer activity, EPR spectroscopy, and theoretical calculations.

Reactions of 9-nickelafluorenyllithium with cobalt and nickel pentamethylcyclopentadienyl-acetylacetonates resulted in the formation of the novel nickelacyclic-cobaltocene 2 and nickelacyclic-nickelocene 3, respectively, in which the central metal atom is bonded to the nickelafluorenyl ring. On the basis of their redox propensity, compounds 2 and 3 were oxidized to the corresponding monocations [2](+) and [3](+). The crystal and molecular structures of both the redox couples were determined by single-crystal X-ray analysis. In spite of their structural similarity, they display a rather different electron transfer ability. To throw light on such an aspect, the pertinent redox couples have been examined by EPR spectroscopy and the nature of the frontier orbitals involved in the redox activity of the neutral precursors has been supported by extended Huckel theoretical calculations.