Crystal Growth, Structure, and Optical Properties of LiGaGe2Se6.

Large single crystals of LiGaGe2Se6 were grown, and their structure and linear optical properties were studied. According to XRD results there is some disorder because of the Li ion fluctuation and their redistribution along two cationic sites. The shape of the fundamental absorption edge versus temperature was analyzed, and direct band gap values were estimated from the Tauc plots. Raman spectra were recorded and compared with results of ab initio calculations. The high quality of LiGaGe2Se6 crystals is confirmed by signals from free and self-trapped excitons. Photoluminescence in the 696 nm broad band and a set of bands in the 950 to 1100 nm range are related to self-trapped excitons and cation antisite defects, respectively. The luminescence intensity increases two orders as the crystal is cooled to 80 K. Four peaks are observed in the thermoluminescence curves with dominant ones at 218 and 410 K. Pyroelectric luminescence in the 100 to 180 K range confirms the noncentrosymmetric structure of this crystal.

Cd2+ complexation with P(CH2OH)3, OP(CH2OH)3, and (HOCH2)2PO2(-): coordination in solution and coordination polymers.

The coordination of Cd(2+) with P(CH(2)OH)(3) (THP) in methanol was followed by (31)P and (111)Cd NMR techniques. A cadmium-to-phosphine coordination ratio of 1:3 has been established, and effective kinetic parameters have been calculated. Air oxidation of THP in the presence of CdCl(2) at room temperature produces coordination polymer (3)(∞)[Cd(3)Cl(6)(OP(CH(2)OH)(3))(2)] (1). The same oxidation reaction at 70 °C gives another coordination polymer, (∞)[CdCl(2)(OP(CH(2)OH)(3))] (2). Complexes 1 and 2 are the first structurally characterized complexes featuring OP(CH(2)OH)(3) as a ligand that acts as a linker between Cd atoms. The addition of NaBPh(4) to the reaction mixture gives coordination polymer (∞)[Na(2)CdCl(2)(O(2)P(CH(2)OH)(2))(2)(H(2)O)(3)] (3) with (HOCH(2))(2)PO(2)(-) as the ligand. Coordination polymers 1-3 have been characterized by X-ray analysis, elemental analysis, and IR spectroscopy.

X-(Diiodoarsanyl)benzoic acid (X = 3 and 4).

The title compounds, 4-(diiodoarsanyl)benzoic acid, (I), and 3-(diiodoarsanyl)benzoic acid, (II), both [As(C(7)H(5)O(2))I(2)], which possess a -COOH coordinating group, form molecular crystal structures composed of hydrogen-bonded dimers, the packing differences of which are caused by the relative position of the diiodoarsanyl groups. The para isomer, with Z' = 1, crystallizes in a layered structure with shortened contacts of the As atoms to only the arene rings of adjacent molecules. In contrast, the meta isomer, with Z' = 3, forms separate rectangular blocks of three ribbons, each composed of dimeric molecular units positioned almost directly above each other and with the As atoms possessing only two As···I contacts to the I atoms of neighbouring molecules.

Tris(tetra-butyl-ammonium) hexa-kis-(tert-butane-thiol-ato-κS)hepta-µ(3)-chlorido-µ(3)-sulfido-hexa-molybdate dihydrate.

The octa-hedral cluster core of the anion in the structure of the title compound, (C(16)H(36)N)(3)[Mo(6)(C(4)H(9)S)(6)(µ(3)-Cl)(7)(µ(3)-S)]·2H(2)O, has -3 site symmetry. Two µ(3)-Cl atoms fully occupy positions in the cluster core, while the remaining six positions are statistically occupied by Cl and S atoms in a 1:5 ratio. The fully occupied Cl-atom positions are located on sites with 3 symmetry, and the N atom of tetra-butyl-ammonium cation is located on a site with 2 symmetry. The structure contains also two disordered solvent water mol-ecules, one of which is located on a threefold rotation axis and the other in a general position, both with an occupancy of 0.25. The water mol-ecules are localized in cavities formed by the tetra-butyl-ammonium cations and the tert-butane-thiol-ate groups. The metal clusters are stacked in a cubic close packing arrangement along [001].

Hexacarbonyl-2κ(3) C,3κ(3) C-di-µ3-sulfido-tetra-kis-(tetra-hydro-furan-1κO)calcium-diiron(II)(Fe-Fe).

Reaction between [Fe2(µ-S2)(CO)6] and [Ca(thf)4(dpp-BIAN)] [dpp-BIAN = 1,2-bis-(2,6-diisopropyl-phenyl-imino)-acenaphthene and thf = tetra-hydro-furan] proceeds as a redox process via a two-electron reduction of [Fe2(µ-S2)(CO)6] and a two-electron oxidation of (dpp-BIAN)(2-), resulting in the formation of the title heterometallic trinuclear cluster, [CaFe2(µ3-S)2(C4H8O)4(CO)6], and neutral dpp-BIAN. In the cluster, the Ca(II) atom is connected to two S atoms of an Fe2S2 core [Ca-S = 2.7463 (8) and 2.7523 (8) Å]. No Fe-Ca bonds are formed [Fe⋯Ca = 3.6708 (6) and 3.5802 (6) Å]. There are five close C-H⋯O-C contacts in the crystal structure.

N-Hydroxy-N-oxide photoinduced tautomerization and excitation wavelength dependent luminescence of ESIPT-capable zinc(II) complexes with a rationally designed 1-hydroxy-2,4-di(pyridin-2-yl)-1H-imidazole ESIPT-ligand.

The ability of 1-hydroxy-1H-imidazoles to undergo proton transfer processes and to exist in N-hydroxy and N-oxide tautomeric forms can be used in coordination chemistry for the design of ESIPT-capable complexes. A series of ESIPT-capable zinc(II) complexes [Zn(HL)Hal2] (Hal = Cl, Br, I) with a rationally designed ESIPT-ligand 1-hydroxy-5-methyl-2,4-di(pyridin-2-yl)-1H-imidazole (HL) featuring spatially separated metal binding and ESIPT sites have been synthesized and characterized. Crystals of these compounds consist of a mixture of two isomers of [Zn(HL)Hal2]. Only a major isomer has a short intramolecular hydrogen bond O-H⋯N as a pre-requisite for ESIPT. In the solid state, the complexes [Zn(HL)Hal2] demonstrate temperature- and excitation wavelength dependent fluorescence in the cyan region due to the interplay of two intraligand fluorescence channels with excited state lifetimes spanning from 0.2 to 4.3 ns. The coordination of HL by Zn2+ ions results in an increase in the photoluminescence efficiency, and the photoluminescence quantum yields (PLQYs) of the complexes reach 12% at λex = 300 nm and 27% at λex = 400 nm in comparison with the PLQY of free HL of ca. 2%. Quantum chemical calculations indicate that N-hydroxy-N-oxide phototautomerization is both thermodynamically and kinetically favourable in the S1 state for [Zn(HL)Hal2]. The proton transfer induces considerable geometrical reorganizations and therefore results in large Stokes shifts of ca. 230 nm. In contrast, auxiliary ESIPT-incapable complexes [ZnL2][Zn(OAc)2]2·2H2O and [ZnL2][ZnCl2]2·4H2O with the deprotonated ligand exhibit excitation wavelength independent emission in the violet region with the Stokes shift reduced to ca. 130 nm.

Tuning ESIPT-coupled luminescence by expanding π-conjugation of a proton acceptor moiety in ESIPT-capable zinc(II) complexes with 1-hydroxy-1H-imidazole-based ligands.

The emission of ESIPT-fluorophores is known to be sensitive to various external and internal stimuli and can be fine-tuned through substitution in the proton-donating and proton-accepting groups. The incorporation of metal ions in the molecules of ESIPT fluorophores without their deprotonation is an emerging area of research in coordination chemistry which provides chemists with a new factor affecting the ESIPT reaction and ESIPT-coupled luminescence. In this paper we present 1-hydroxy-5-methyl-4-(pyridin-2-yl)-2-(quinolin-2-yl)-1H-imidazole (HLq) as a new ESIPT-capable ligand. Due to the spatial separation of metal binding and ESIPT sites this ligand can coordinate metal ions without being deprotonated. The reactions of ZnHal2 with HLq afford ESIPT-capable [Zn(HLq)Hal2] (Hal = Cl, Br, I) complexes. In the solid state HLq and [Zn(HLq)Hal2] luminesce in the orange region (λmax = 600-650 nm). The coordination of HLq by Zn2+ ions leads to the increase in the photoluminescence quantum yield due to the chelation-enhanced fluorescence effect. The ESIPT process is barrierless in the S1 state, leading to the only possible fluorescence channel in the tautomeric form (T), S1T → S0T. The emission of [Zn(HLq)Hal2] in the solid state is blue-shifted as compared with HLq due to the stabilization of the ground state and destabilization of the excited state. In CH2Cl2 solutions, the compounds demonstrate dual emission in the UV (λmax = 358 nm) and green (λmax = 530 nm) regions. This dual emission is associated with two radiative deactivation channels in the normal (N) and tautomeric (T) forms, S1N → S0N and S1T → S0T, originating from two minima on the excited state potential energy surfaces. High energy barriers for the GSIPT process allow the trapping of molecules in the minimum of the tautomeric form, S0T, resulting in the possibility of the S0T → S1T photoexcitation and extraordinarily small Stokes shifts in the solid state. Finally, the π-system of quinolin-2-yl group facilitates the delocalization of the positive charge in the proton-accepting part of the molecule and promotes the ESIPT reaction.

A 1-Hydroxy-1H-imidazole ESIPT Emitter Demonstrating anti-Kasha Fluorescence and Direct Excitation of a Tautomeric Form.

The ability of 1-hydroxy-1H-imidazoles to exist in the form of two prototropic tautomers, the N-hydroxy and the N-oxide forms, can be utilized in the design of new types of ESIPT-fluorophores (ESIPT=excited state intramolecular proton transfer). Here we report the first example of 1-hydroxy-1H-imidazole-based ESIPT-fluorophores, 1-hydroxy-5-methyl-2,4-di(pyridin-2-yl)-1H-imidazole (HL), featuring a short intramolecular hydrogen bond O-H⋅⋅⋅N (O⋅⋅⋅N 2.56 Å) as a pre-requisite for ESIPT. The emission of HL originates from the anti-Kasha S2 →S0 fluorescence in the N-oxide form as a result of a large S2 -S1 energy gap slowing down the S2 →S1 internal conversion. Due to an energy barrier between the N-hydroxy and N-oxide forms in the ground state, the HL molecules can be trapped and photoexcited in the N-oxide form leading to the Stokes shift of ca. 60 nm which is the smallest among known ESIPT-fluorophores.

LiBaAlF6 and the crystal chemistry of LiAIIBIIIF6 phases.

Lithium barium hexafluoroaluminate (LBAF), LiBaAlF(6), is a new member of the large family of compounds of formula LiA(II)B(III)F(6). These materials display a variety of structures depending on the sizes of the A and B cations. LiBaAlF(6), which is isomorphous with LiBaCoF(6), belongs to the monoclinic P2(1)/c subset and has a three-dimensional network structure consisting of distorted LiF(4)(3-) tetrahedra corner-sharing with AlF(6)(3-) octahedra and BaF(12) polyhedra. All of the atoms reside on general positions. An analysis of the ionic radii of the A cations versus formula volumes for the known members of the family yields a structure map that reasonably segregates the compounds by space group. The data obtained are thus suitable for predicting new isomorphic crystal structures.

Synthesis and structure of a paramagnetic Mo3S4 incomplete cuboidal cluster with seven cluster skeletal electrons.

The electron precise incomplete cuboidal complex [Mo(3)S(4)(dppe)(3)Br(3)]Br (1a) with 6 cluster skeletal electrons (CSE) and its halogen-mixed analogue [Mo(3)S(4)(dppe)(3)(Br,Cl)(3)](Br,Cl) (1b) can be smoothly reduced to the paramagnetic [Mo(3)S(4)(dppe)(3)X(3)] clusters (2a, X = Br; 2b, X = Cl/Br) with 7 CSE by treatment with liquid Ga.

Iron(III) dihydrogenphosphate(I).

The structure of rhombohedral (R3) iron(III) tris[dihydrogenphosphate(I)] or iron(III) hypophosphite, Fe(H2PO2)3, has been determined by single-crystal X-ray diffraction. The structure consists of [001] chains of Fe3+ cations in octahedral sites with -3 symmetry bridged by bidentate hypophosphite anions.

Zr(IV)-monosubstituted Keggin-type dimeric polyoxometalates: synthesis, characterization, catalysis of H2O2-based oxidations, and theoretical study.

The previously unknown Zr(IV)-monosubstituted Keggin-type polyoxometalates (Zr-POMs), (n-Bu4N)7H[{PW11O39Zr(mu-OH)}2] (1), (n-Bu4N)8[{PW11O39Zr(mu-OH)}2] (2), and (n-Bu4N)9[{PW11O39Zr}2(mu-OH)(mu-O)] (3) differing in their protonation state, have been prepared starting from heteropolyacid H5PW11ZrO40.14H2O. The compounds were characterized by elemental analysis, potentiometric titration, X-ray single-crystal structure, and IR, Raman, and 31P and 183W NMR spectroscopy. The single-crystal X-ray analysis of 2 reveals that two Keggin structural units [PW11O39Zr]3- are linked through two hydroxo bridges Zr-(OH)-Zr with Zr(IV) in 7-fold coordination. The IR spectra of 1 and 2 show a characteristic band at 772 cm(-1), which moves to 767 cm(-1) for 3, reflecting deprotonation of the Zr-(OH)-Zr bond. Potentiometric titration with methanolic Bu4NOH indicates that 1-3 contain 2, 1, and 0 acid protons, respectively. (83W NMR reveals Cs symmetry of 2 and 3 in dry MeCN, while for 1, it discovers nonequivalence of its two subunits and their distortion resulting from localization of the acidic proton on one of the Zr-O-W bridging O atoms. The (31)P NMR spectra of 2 and 3 differ insignificantly in dry MeCN, showing only signals at delta -12.46 and -12.44 ppm, respectively, while the spectrum of 1 displays two resonances at delta -12.3 (narrow) and -13.2 (broad) ppm, indicating slow proton exchange on the (31)P NMR time scale. The theoretical calculations carried out at the density functional theory level on the dimeric species 1-3 propose that protonation at the Zr-O-Zr bridging site is more favorable than protonation at Zr-O-W sites. Calculations also revealed that the doubly bridged hydroxo structure is thermodynamically more stable than the singly bridged oxo structure, in marked contrast with analogous Ti- and Nb-monosubstituted polyoxometalates. The interaction of 1-3 with H(2)O and H(2)O(2) in MeCN has been studied by both (31)P and (183)W NMR. The stability of the [PW(11)O(39)ZrOH](4-) structural unit toward at least 100-fold excess of H2O2 in MeCN was confirmed by both NMR and Raman spectroscopy. The interaction of 1 and 2 with H2O in MeCN produces most likely monomeric species (n-Bu4N)3+n[PW11O39Zr(OH)(n(H2O)(3-n)] (n = 0 and 1) showing a broad 31P NMR signal at delta -13.2 ppm, while interaction with H2O2 leads to the formation of an unstable peroxo species (delta -12.3 ppm), which reacts rapidly with cyclohexene, producing 2-cyclohexen-1-one and trans-cyclohexane-1,2-diol. Both 1 and 2 show a pronounced catalytic activity in H2O2 decomposition and H2O2-based oxidation of organic substrates, including cyclohexene, alpha-pinene, and 2,3,6-trimethylphenol. The oxidation products are consistent with those of a homolytic oxidation mechanism. On the contrary, 3 containing no acid protons reacts with neither H2O nor H2O2 and shows negligible catalytic activity. The Zr-monosubstituted polyoxometalates can be used as tractable homogeneous probes of Zr single-site heterogeneous catalysts in studying mechanisms of H2O2-based oxidations.

Two alkali metal chlorites, LiClO2 and KClO2.

The structures of tetragonal (P4(2)/ncm) lithium chlorite, LiClO2, and orthorhombic (Cmcm) potassium chlorite, KClO2, have been determined by single-crystal X-ray analyses. In LiClO2, the Li atom is at a site of -4 symmetry, while in KClO2, the K atom is at a site with 2/m symmetry. In both compounds, the unique Cl and O atoms are at sites with mm and m symmetry, respectively. The structure of LiClO2 consists of layers of Li+ cations coordinated by ClO2- anions. In contrast, the structure of KClO2 contains pseudo-layers of K+ and ClO2- ions containing four short K-O distances. The Li+ and K+ cations are surrounded by four and eight chlorite O atoms in tetrahedral and distorted cubic coordination environments, respectively.

Barium chlorite hydrate, Ba(ClO2)2.3.5H2O.

The structure of barium chlorite hydrate, Ba(ClO2)2.3.5H2O, has been determined by single-crystal X-ray analysis at 150 K. The structure is monoclinic, space group C2/c, with Z = 8. It contains layers of Ba2+ cations coordinated by ClO2- anions and water molecules. There are also solvate water molecules involved only in hydrogen bonding of the layers. Three solvate water O atoms are on sites of twofold symmetry, while all other atoms are in general positions. The full coordination environment of the Ba2+ cation consists of ten O atoms belonging to six chlorites and three water molecules, forming a bicapped square antiprism.

The bivalent metal hypophosphites Sr(H2PO2)2, Pb(H2PO2)2 and Ba(H2PO2)2.

The structures of isomorphous monoclinic strontium and lead bis(dihydrogenphosphate), Sr(H2PO2)2 and Pb(H2PO2)2, and orthorhombic barium bis(dihydrogenphosphate), Ba(H2PO2)2, consist of layers of hypophosphite anions and metal cations exhibiting square antiprismatic coordination by O atoms. The Sr and Pb atoms are located on sites with point symmetry 2, and the Ba atoms are on sites with point symmetry 222. Within the layers, each anion bridges four metal cations.

Synthesis and crystal structure of unprecedented oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes.

Two new polynuclear oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes are obtained upon treatment of Ga(3+)(aq) with pyridine: the supramolecular compound of macrocyclic cavitand cucurbit[6]uril with gallium complex containing 32 metal atoms [Ga(32)(mu(4)-O)(12)(mu(3)-O)(8)(mu(2)-O)(7)(mu(2)-OH)(39)(H(2)O)(20)](PyH subsetC(36)H(36)N(24)O(12))(3)(NO(3))(6).53H(2)O (1) and the tridecanuclear complex [Ga(13)(mu(3)-OH)(6)(mu(2)-OH)(18)(H(2)O)(24)](NO(3))(15).12H(2)O (2). It follows that two modes of nucleation exist when Ga(3+)(aq) is hydrolyzed: one around the tetrahedral GaO(4) units (complex 1) and the other around the octahedral GaO(6) units (complex 2). This is the first time that polynuclear oxo/hydroxo-bridged aqua complexes of Ga(III) have been isolated without the use of other ligands to control or block olygomerization.

Hexaaquacobalt(II) bis(hypophosphite) and hexaaquacobalt(II)/nickel(II) bis(hypophosphite).

The title compounds, hexaaquacobalt(II) bis(hypophosphite), [Co(H(2)O)(6)](H(2)PO(2))(2), and hexaaquacobalt(II)/nickel(II) bis(hypophosphite), [Co(0.5)Ni(0.5)(H(2)O)(6)](H(2)PO(2))(2), are shown to adopt the same structure as hexaaquamagnesium(II) bis(hypophosphite). The packing of the Co(Ni) and P atoms is the same as in the structure of CaF(2). The Co(II)(Ni(II)) atoms have a pseudo-face-centred cubic cell, with a = b approximately 10.3 A, and the P atoms occupy the tetrahedral cavities. The central metal cation has a slightly distorted octahedral coordination sphere. The geometry of the hypophosphite anion in the structure is very close to ideal, with point symmetry mm2. Each O atom of the hypophosphite anion is hydrogen bonded to three water molecules from different cation complexes, and each H atom of the hypophosphite anion is surrounded by three water molecules from further different cation complexes.

The alkali hypophosphites KH2PO2, RbH2PO2 and CsH2PO2.

The structures of the hypophosphites KH(2)PO(2) (potassium hypophosphite), RbH(2)PO(2) (rubidium hypophosphite) and CsH(2)PO(2) (caesium hypophosphite) have been determined by single-crystal X-ray diffraction. The structures consist of layers of alkali cations and hypophosphite anions, with the latter bridging four cations within the same layer. The Rb and Cs hypophosphites are isomorphous.

Hexaaquanickel(II) bis(hypophosphite).

The structure of hexaaquanickel(II) bis(hypophosphite), [Ni(H(2)O)(6)](H(2)PO(2))(2), has been determined. The crystals are prismatic. The packing of the Ni and P atoms (not the entire hypophosphite anions) is the same as in the structures of [Co(H(2)O)(6)](H(2)PO(2))(2) and [Co(0.5)Ni(0.5)(H(2)O)(6)](H(2)PO(2))(2). The Ni(II) cations have a pseudo-face-centered cubic cell, with cell parameter a approximately= 10.216 A and tetrahedral cavities occupied by P atoms. The Ni(II) cation has crystallographically imposed twofold symmetry and has an octahedral coordination sphere consisting of six water O atoms, two of which also lie on the twofold axis. The planes of oppositely coordinated water molecules are in a cross conformation. The geometry of the hypophosphite anion is close to point symmetry mm2. The hypophosphite anions are hydrogen bonded to the coordinated water molecules.

Copper(II) hypophosphite: the alpha- and beta-forms at 270 and 100 K, and the gamma-form at 270 K.

Copper(II) hypophosphite has been shown to exist as several polymorphs. The crystal structures of monoclinic alpha-, orthorhombic beta- and orthorhombic gamma-Cu(H(2)PO(2))(2) have been determined at different temperatures. The geometry of the hypophosphite anion in all three polymorphs is very close to the idealized one, with point symmetry mm2. Despite having different space groups, the structures of the alpha- and beta-polymorphs are very similar. The polymeric layers formed by the Cu atoms and the hypophosphite ions, which are identical in the alpha- and beta-polymorphs, stack in the third dimension in different ways. Each hypophosphite anion is coordinated to three Cu atoms. On cooling, a minimum amount of contraction was observed in the direction normal to the layers. The structure of the polymeric layers in the gamma-polymorph is quite different. There are two symmetry-independent hypophosphite anions; the first is coordinated to two Cu atoms, while the second is coordinated to four Cu atoms. In all three polymorphs, the Cu atoms are coordinated by six O atoms of six hypophosphite anions, forming tetragonal bipyramids; in the alpha- and beta-polymorphs, there are four short and two long Cu-O distances, while in the gamma-polymorph, there are four long and two short Cu-O distances.