LiM2(NCN)Br3 (M = Sr,Eu): Synthesis and Crystal Structures of Solid‐State Carbodiimides with Empty Tetrahedral Metal Entities

Two solid‐state carbodiimide compounds, LiM₂(NCN)Br₃ (M = Sr, Eu), with characteristic empty tetrahedral M₄ entities have been synthesized using a flux route, and their structures were determined by single‐crystal X‐ray diffraction. The new phases LiSr₂(NCN)Br₃ and LiEu₂(NCN)Br₃ are isotypical with the corresponding iodides and crystallize in the cubic system (( , Z = 16) but with smaller unit cells (a = 14.641(1) Å for LiSr₂(NCN)Br₃ and 14.572(1) Å for LiEu₂(NCN)Br₃). The extended structures comprise two interpenetrating three‐dimensional networks: the first one is built from isolated M₄ tetrahedra capped by NCN^2? anions on their triangular faces while the second is made from vertex‐sharing LiBr₆ octahedra. The linear NCN^2? anions exhibit the symmetrical carbodiimide shape and serve as linkers between the tetrahedral entities.     

Crystal structures of extended europium cyanamide-carbodiimide compounds derived from different reaction conditions: temperature-controlled syntheses of In(0.08)Eu4(NCN)3I3, Eu8I9(CN)(NCN)3, and In(0.28)Eu12(NCN)5I(14.91)

A different thermal treatment of identical reactants (EuI2, NaCN, NaN3, and InI) leads to the formation of the three title compounds. In(0.08)Eu4(NCN)3I3 is isotypic with the reported LiEu4(NCN)3I3, Eu8I9(CN)(NCN)3 represents the first mixed cyanide-cyanamide rare-earth compound, and In(0.28)Eu12(NCN)5I(14.91) is characterized by a sandwich-like stacking motif involving Eu4-NCN double layers stuffed by a layer of vertex-sharing InI6 octahedra. The redox behavior of In is the main factor that leads to alternative product formation as a function of the temperature.     

Refined crystal structure and idealized structure of mixed-valent Eu4F5(CN2)2: transition possible

The new europium fluoride carbodiimide Eu(4)F(5)(CN(2))(2) was synthesized by solid state reaction from mixtures of EuF(3) and Li(2)(CN(2)) at 700 °C. The crystal structure as refined by single crystal X-ray diffraction (P ?42(1)c, no. 114, a = 16.053(1) ?, c = 6.5150(6) ?, Z = 8) reveals three crystallographically distinct [N═C═N](2-) ions in the structure of mixed-valent Eu(4)F(5)(CN(2))(2). The presence of one Eu(3+) and three Eu(2+) per formula unit Eu(4)F(5)(CN(2))(2) is confirmed by magnetic measurements and (151)Eu-Mo?ssbauer spectroscopy. The arrangement of Eu ions and gravity centers of [NCN](2-) ions in the structure of Eu(4)F(5)(CN(2))(2) follow the motif formed by atoms in the CuAl(2)-type structure. A possible high-symmetry structure of Eu(4)F(5)(CN(2))(2) is discussed on the basis of a group-subgroup scheme.     

The rotation-vibration spectrum of gaseous carbodiimide (HNCNH)

In this communication we report for the first time the vapour-phase detection of carbodiimide. In the infrared spectrum of cyanamide vapour, three band systems of carbodiimide were measured and assigned to the NCN a-str mode, a combination mode (NCN s-str+NH a-bend) and the NH a-bending mode. The diode laser spectrum of a part of the NCN a-str band was obtained.     

XANES at Eu-L3 edge and valence of europium in SrB_4O_7: Eu and BaB_8O_(13): Eu

The luminescent materials SrB4O7: Eu and BaB8O13: Eu were synthesized, and the valence states of europium in the materials were measured by means of XANES at Eu-L3 edge. It is found that the Eu3 and Eu2 ions are all present in the materials, and more Eu3 ions can be reduced in SrB4O7: Eu than in BaB8O13:Eu. The excitation and emission spectra of Eu3 in SrB4O7: Eu and BaB8O13:Eu were determined.     

Formation of complex three- and one-dimensional interpenetrating networks within carbodiimide chemistry: NCN2(-)-coordinated rare-earth-metal tetrahedra and condensed alkali-metal iodide octahedra in two novel lithium europium carbodiimide iodides, LiEu2(NCN)I3 and LiEu4(NCN)3I3

Orange-red transparent single crystals of LiEu2(NCN)I3 and LiEu4(NCN)3I3 were synthesized from fluxes of europium iodide, sodium cyanide, sodium azide, and lithium iodide at elevated temperatures and structurally characterized by X-ray diffraction. While LiEu2(NCN)I3 crystallizes in the cubic system (Fdm, a = 15.1427(17) angstroms, V = 3472.2(7) angstroms3, Z = 16, R1 = 0.0322), LiEu4(NCN)3I3 adopts the hexagonal system (P6(3)/mmc, a = 10.6575(11) angstroms, c = 6.8232(10) angstroms, V = 671.16(14) angstroms3, Z = 2, R1 = 0.0246). Both extended structures are composed of complex frameworks built from europium tetrahedra coordinated by carbodiimide (symmetrical NCN2-) units on the one side and condensed iodine octahedra around lithium cations on the other. Within LiEu2(NCN)I3, vertex-sharing of the LiI6 subunits together with isolated europium tetrahedra results in two three-dimensional networks interpenetrating each other. Within LiEu4(NCN)3I3, face-sharing of the europium tetrahedra results in bitetrahedral units which further connect via two opposing vertexes into one-dimensional linkages. Likewise, the LiI6 octahedra share common faces to also yield one-dimensional linkages that fill the channels between the europium/carbodiimide substructure. The magnetic behavior of both compounds has been determined; the two phases follow Curie-Weiss laws with weak predominantly ferromagnetic exchange between the europium ions and atomic moments characterizing them as essentially divalent.     

Reactivity of "Eu(OiPr)2" with phenols: formation of linear Eu3, square pyramidal Eu5, cubic Eu8, and capped cubic Eu9 polymetallic europium complexes

The direct reaction of europium with 2-propanol and phenols has been investigated under a variety of conditions. The reaction of europium metal with 2,6-dimethylphenol and 2,6-diisopropylphenol in 2-propanol at reflux revealed that polymetallic europium complexes could be generated by this method. Hx[Eu8O6(OC6H3Me2-2,6)12(OiPr)8], 1, and H5[Eu5O5(OC6H3iPr2-2,6)6(NCCH3)8], 2, were isolated by recrystallization in the presence of hexanes and acetonitrile, respectively, and characterized by X-ray crystallography. Complex 1 has a cubic arrangement of europium ions with face-bridging mu 4-O donor atoms, edge-bridging mu-O(phenoxide/phenol) ligands, and terminal O(isopropoxide/2-propanol) ligands. Complex 2 is mixed valent and has a square pyramidal europium core with four Eu(II) ions at the basal positions and one Eu(III) ion at the apex. Since these reactions gave complicated mixtures of products from which 1 and 2 could only be obtained in low yields, direct reactions under less forcing reaction conditions were investigated. Europium reacts slowly at room temperature to form arene-soluble divalent [Eu(OiPr)2(THF)x]n, 3. Complex 3 reacts with 2,6-dimethylphenol to form the arene-insoluble complex (H[Eu(OC6H3Me2)2(OiPr)])n, 4. Recrystallization of 4 in the presence of THF results in the crystallographically characterizable divalent trimetallic complex [Eu(OC6H3Me2-2,6)2(THF)2]3, 5, which has an unusual linear metal geometry. In the presence of HOiPr at ambient conditions in the glovebox, crystals of 5 slowly convert to the mixed valent H10[Eu8O8(OC6H3Me2-2,6)10(OiPr)2(THF)6], 6, which was found to have a cubic arrangement of europium atoms similar to 1 by X-ray crystallography. Complex 4, upon heating under vacuum, followed by reaction with THF, forms the arene-soluble divalent complex H18([Eu9O8(OC6H3Me2-2,6)10(THF)7][Eu9O9(OC6H3Me2-2,6)10(THF)6]), 7, which contains two types of capped cubic arrangements of europium ions in the solid state.     

STRUCTURAL CHEMISTRY OF EIGHT-COORDINATE COMPLEXES OP MNTHANOID WITH BIDBNTATE LIGANDS IV.CRYSTAL STRUCTURES OF [C_4H_8OH] [Eu(S_2CNC_4H_8)_4]·xC_4H_8O(x=2,0)

<正> Compound [C4H3OH][Eu(S2CNC4H3)4].2C4H8O(I), Mr=953,80,monoclinic, P21/n,a = 11,332(3), b= 22,837(5), c= 15.671(2)A,β= 94.93(1)°, V= 4040.2 A3,Z= 4,Dc = 1.567 g/cm3. [C4H8OH][Bu(S2CNC4H8)4] (2),Mr=809.72, monoclinic,P 21/c,a= 12.184(2), b= 15.181(3), c= 18.334(3)A,β=98.57(1)°,V=3353,3 A3,Z = 4, Dc= 1.605 g/cm3. The Eu atom in the anions of 1 and 2 is coordinated by eight S atoms frow four S2CNC4H8 chelate groups in the form of a dodecahedron with approximate D2d symmetry.     

Synthesis of an octanuclear Eu(III) cage from Eu(4)(2+): chloride anion encapsulation, luminescence, and reversible MeOH adsorption via a porous supramolecular architecture

The octanuclear complex [Eu8L4(1,4-BDC)2Cl8(MeOH)12].4Cl.2MeOH.18H2O (2) was obtained from the reaction of the tetranuclear Eu(III) species [Eu4L2Cl2(OH)4(H2O)4(MeOH)2].2Cl.7MeOH.2H2O (1) and 1,4-H2BDC (H2L = bis(5-bromo-3-methoxysalicylidene)ethylene-1,2-phenylenediamine, 1,4-H2BDC = 1,4-benzenedicarboxylic acid). Both 1 and 2 were structurally characterized by X-ray crystallography, and their luminescence properties were determined. The cagelike structure of 2 encapsulates two chloride anions via MeOH...Cl hydrogen bonding. In the solid state, 2 has an open three-dimensional network with extended channels and is capable of reversible MeOH adsorption.     

LiSr2(NCN)I3: the first empty tetrahedral strontium(II) entity coordinated by carbodiimide units but without strontium-strontium bonding

LiSr(2)(NCN)I(3), the first extended compound containing empty tetrahedral Sr(4) entities, is synthesized using a new flux route, and it exhibits two interpenetrating three-dimensional networks made up from Sr tetrahedra capped by NCN(2-) anions on their triangular faces and vertex-sharing LiI(6) octahedra.     

Origin of Thermal Degradation of Sr(2-x)Si(5)N(8):Eu(x) Phosphors in Air for Light-Emitting Diodes

The orange-red emitting phosphors based on M(2)Si(5)N(8):Eu (M = Sr, Ba) are widely utilized in white light-emitting diodes (WLEDs) because of their improvement of the color rendering index (CRI), which is brilliant for warm white light emission. Nitride-based phosphors are adopted in high-performance applications because of their excellent thermal and chemical stabilities. A series of nitridosilicate phosphor compounds, M(2-x)Si(5)N(8):Eu(x) (M = Sr, Ba), were prepared by solid-state reaction. The thermal degradation in air was only observed in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10, but it did not appear in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.02 and Ba analogue with x = 0.10. This is an unprecedented investigation to study this phenomenon in the stable nitrides. The crystal structural variation upon heating treatment of these compounds was carried out using the in situ XRD measurements. The valence of Eu ions in these compounds was determined by electron spectroscopy for chemical analysis (ESCA) and X-ray absorption near-edge structure (XANES) spectroscopy. The morphology of these materials was examined by transmission electron microscopy (TEM). Combining all results, it is concluded that the origin of the thermal degradation in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10 is due to the formation of an amorphous layer on the surface of the nitride phosphor grain during oxidative heating treatment, which results in the oxidation of Eu ions from divalent to trivalent. This study provides a new perspective for the impact of the degradation problem as a consequence of heating processes in luminescent materials.     

Synthesis and photoluminescence of Eu(III) complex compounds containing anions of perfluoro-3-methylbenzoic acid

Photoluminescent Eu(III) compounds with anions of the acid 3-CF₃C₆F₄COOH (LH) of composition Eu(L)₃·2H₂O and Eu(phen)(L)₃ were synthesized. The photoluminescence intensity of the complex Eu(phen)(L)₃ is higher than that of a similar Eu(III) complex containing anions of the acid 4-CF₃C₆F₄COOH as ligands.     

微过氧化物酶-8与Eu3+相互作用的机理

用紫外-可见(UV-Vis)吸收光谱和电化学方法研究Eu3+与微过氧化物酶-8(MP-8)相互作用的机理,发现Eu3+优先与MP-8中血红素基团的2个丙酸基的羧基氧发生强的配位作用,导致MP-8分子中血红素基团的非平面性、暴露程度和电化学可逆性的增加.过剩的Eu3+与MP-8分子中肽链上的含氧基团发生弱的相互作用,对血红素基团结构的影响较小.     

Eu(III) complexes as anion-responsive luminescent sensors and paramagnetic chemical exchange saturation transfer agents

The Eu(III) complex of (1S,4S,7S,10S)-1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (S-THP) is studied as a sensor for biologically relevant anions. Anion interactions produce changes in the luminescence emission spectrum of the Eu(III) complex, in the (1)H NMR spectrum, and correspondingly, in the PARACEST spectrum of the complex (PARACEST = paramagnetic chemical exchange saturation transfer). Direct excitation spectroscopy and luminescence lifetime studies of Eu(S-THP) give information about the speciation and nature of anion interactions including carbonate, acetate, lactate, citrate, phosphate, and methylphosphate at pH 7.2. Data is consistent with the formation of both innersphere and outersphere complexes of Eu(S-THP) with acetate, lactate, and carbonate. These anions have weak dissociation constants that range from 19 to 38 mM. Citrate binding to Eu(S-THP) is predominantly innersphere with a dissociation constant of 17 μM. Luminescence emission peak changes upon addition of anion to Eu(S-THP) show that there are two distinct binding events for phosphate and methylphosphate with dissociation constants of 0.3 mM and 3.0 mM for phosphate and 0.6 mM and 9.8 mM for methyl phosphate. Eu(THPC) contains an appended carbostyril derivative as an antenna to sensitize Eu(III) luminescence. Eu(THPC) binds phosphate and citrate with dissociation constants that are 10-fold less than that of the Eu(S-THP) parent, suggesting that functionalization through a pendent group disrupts the anion binding site. Eu(S-THP) functions as an anion responsive PARACEST agent through exchange of the alcohol protons with bulk water. The alcohol proton resonances of Eu(S-THP) shift downfield in the presence of acetate, lactate, citrate, and methylphosphate, giving rise to distinct PARACEST peaks. In contrast, phosphate binds to Eu(S-THP) to suppress the PARACEST alcohol OH peak and carbonate does not markedly change the alcohol peak at 5 mM Eu(S-THP), 15 mM carbonate at pH 6.5 or 7.2. This work shows that the Eu(S-THP) complex has unique selectivity toward binding of biologically relevant anions and that anion binding results in changes in both the luminescence and the PARACEST spectra of the complex.     

Structure and thermoelectric characterization of AxBa8-xAl14Si31 (A = Sr, Eu) single crystals

Single crystals of AxBa8-xAl14Si31 (A = Sr, Eu) were grown using a molten Al flux technique. Single-crystal X-ray diffraction confirms that AxBa8-xAl14Si31 (A = Sr, Eu) crystallize with the type I clathrate structure, and phase purity was determined with powder X-ray diffraction. Stoichiometry was determined to be Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31 by electron microprobe analysis. These AxBa8-xAl14Si31 phases can be described as framework-deficient clathrate type I structures with the general formula, AxBa8-xAlySi42-3y/4[]4-1/4y. DSC measurements indicate that these phases melt congruently at 1413 and 1415 K for Sr0.7Ba7.3Al14Si31 and Eu0.3Ba7.7Al14Si31, respectively. Temperature-dependent resistivity indicates metallic behavior, and the negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity of these phases remains low with Sr0.7Ba7.3Al14Si31 having the lowest values.     

Die Kristallstruktur von Cs5Eu(N3)8

Summary The crystal structure of pentacesium octaazidoeuropiate(III), Cs₅Eu(N₃)₈, was determined by single crystal X-ray diffraction: orthorhombic,a=16.811(4),b=16.860(5),c=16.964(3)Å, space group Pbca,Z=8, 2 310 observed reflections,R=0.048. Europium atoms are coordinated to eight azide groups, the coordination polyhedra have no azide groups in common. Four cesium atoms are surrounded by eight, one by seven azide groups. The azide groups are symmetric with mean N-N-distances of 1.17(1)Å.

     

Macrocyclic Eu3+ chelates show selective luminescence responses to anions

A series of lanthanide-containing macrocycles, Eu2-Eu5, exhibited unique luminescent responses in the presence of strong hydrogen-bond-accepting anions (F-, CH3COO-, and H2PO4-) in dimethyl sulfoxide. The macrocycles examined herein were designed to include a lanthanide chelate, aromatic spacers that function as antennae, thiourea groups as anion-binding units, and an alkyl or aryl linker between the thioureas that tailors the size and rigidity of the macrocycle. The anion-induced change in the emission intensity (lambda(exc) = 272 nm; lambda(em) = 614 nm) varied across the series of macrocycles and was dependent on the basicity of the anion. The largest luminescence response was observed in Eu(2), whereby the emission increased 77% upon the addition of 8 equiv of fluoride. A change in luminescence was not observed when exciting Eu3+ directly (lambda(exc) = 395 nm) over the course of anion titration experiments with all of the anions studied. These macrocycles contain only slight variations in structure, and insights into the mechanism of the anion interaction have been gained through monitoring of anion titrations via luminescence, absorbance, and luminescence lifetime measurements. In addition, model compounds (2-5) lacking the Eu3+ moiety were synthesized to study the binding pockets of Eu2-Eu5 using absorbance and 1H NMR spectroscopy. These studies indicate that the anions interact with the thiourea moiety of Eu2-Eu5, and the luminescent response is controlled by changes in the morphology of the macrocycle binding pocket.     

Novel yellow-emitting Sr8MgLn(PO4)7:Eu2+ (Ln=Y, La) phosphors for applications in white LEDs with excellent color rendering index

Eu(2+)-activated Sr(8)MgY(PO(4))(7) and Sr(8)MgLa(PO(4))(7) yellow-emitting phosphors were successfully synthesized by solid-state reactions for applications in excellent color rendering index white light-emitting diodes (LEDs). The excitation and reflectance spectra of these phosphors show broad band excitation and absorption in the 250-450 nm near-ultraviolet region, which is ascribed to the 4f(7) → 4f(6)5d(1) transitions of Eu(2+). Therefore, these phosphors meet the application requirements for near-UV LED chips. Upon excitation at 400 nm, the Sr(8)MgY(PO(4))(7):Eu(2+) and Sr(8)MgLa(PO(4))(7):Eu(2+) phosphors exhibit strong yellow emissions centered at 518, 610, and 611 nm with better thermal stability than (Ba,Sr)(2)SiO(4) (570 nm) commodity phosphors. The composition-optimized concentrations of Eu(2+) in Sr(8)MgLa(PO(4))(7):Eu(2+) and Sr(8)MgY(PO(4))(7):Eu(2+) phosphors were determined to be 0.01 and 0.03 mol, respectively. A warm white-light near-UV LED was fabricated using a near-UV 400 nm chip pumped by a phosphor blend of blue-emitting BaMgAl(10)O(17):Eu(2+) and yellow-emitting Sr(8)MgY(PO(4))(7):0.01Eu(2+) or Sr(8)MgLa(PO(4))(7):0.03Eu(2+), driven by a 350 mA current. The Sr(8)MgY(PO(4))(7):0.01Eu(2+) and Sr(8)MgLa(PO(4))(7):0.03Eu(2+) containing LEDs produced a white light with Commission International de I'Eclairage (CIE) chromaticity coordinates of (0.348, 0.357) and (0.365, 0.328), warm correlated color temperatures of 4705 and 4100 K, and excellent color rendering indices of 95.375 and 91.75, respectively.     

Spectroelectrochemical studies of [Mo(dtc)_4][Eu(dtc)_4] and [Mo(dtc)_4][Er(dtc)_4]

Redox and spectroscopic properties of the eight-coordination complexes of molybdenum and the rare-earth elements Eu or Er with N,N-diethyldithiocarbamate (dtc) were characterised by cyclic voltamrnetry and UV-visible absorption spectra.The complex cation [Mo(dtc)4]+ is more stable than the complex anions [Eu(dtc)4]-and [Er(dtc)4]-in redox processes,and possesses good redox reversibility.The electron transfer number,formal standard electrode potential in the redox process for the complex cation and its diffusion coefficients were obtained by in aitu spectroelectro-chemistry.     

Anion-Dependent Outstanding Luminescence Enhancement of Eu(D-facam)3 Upon Coexistence With the Tetramethylammonium Cation

The effect of a series of tetramethylammonium salts with different counter anions on the photophysical properties of a chiral Eu(III) complex (Eu(D-facam)₃) was investigated. Anion-dependent luminescence of the Eu(III) complex was observed, and particularly in the presence of acetate ions, an outstanding luminescence enhancement (>300 times) and induced circularly polarized luminescence (g_lum=−0.63) were obtained. The energy transfer process was then evaluated using key photophysical parameters, and it was found that the sensitisation efficiency of the Eu(III) complex significantly increased in the presence of tetramethylammonium acetate (TMAOAc). The interactions between Eu(D-facam)₃ and TMAOAc were confirmed by luminescence analysis, circular dichroism spectroscopy, Fourier transform infrared spectroscopy and mass spectral measurements.