Solid-state Luminescent Spectra Research Articles

Pressure-induced variations of MLCT and ligand-centered luminescence spectra in square-planar platinum(II) complexes

Solid-state luminescence spectra of five crystalline platinum(II) complexes at variable pressure and temperature are presented and compared. Maxima occur between 14000cm−1 and 15600cm−1 (approximately 700–640nm) at ambient temperature and pressure. Spectra can be broad bands, characteristic of MLCT transitions, or vibronically structured, characteristic of intraligand transitions. Both pressure and temperature variations can lead to distinctive changes in the luminescence spectra that differ between these two types of transitions. MLCT band maxima show shifts on the order of −20cm−1/kbar to lower energy; in contrast, ligand-centered luminescence bands do not show significant shifts between ambient pressure and 40kbar.

Tunable trimers: using temperature and pressure to control luminescent emission in gold(I) pyrazolate-based trimers.

A systematic investigation into the relationship between the solid-state luminescence and the intermolecular Au⋅⋅⋅Au interactions in a series of pyrazolate-based gold(I) trimers; tris(μ2-pyrazolato-N,N′)-tri-gold(I) (1), tris(μ2-3,4,5- trimethylpyrazolato-N,N′)-tri-gold(I) (2), tris(μ2-3-methyl-5-phenylpyrazolato-N,N′)-tri-gold(I) (3) and tris(μ2-3,5-diphenylpyrazolato-N,N′)-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer Au⋅⋅⋅Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au⋅⋅⋅Au contacts of between 0.04 and 0.08 Å. The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au⋅⋅⋅Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm−1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au⋅⋅⋅Au distance observed by diffraction.

Molecular and electronic structure of cyclic trinuclear gold(I) carbeniate complexes: insights for structure/luminescence/conductivity relationships.

An experimental and computational study of correlations between solid-state structure and optical/electronic properties of cyclotrimeric gold(I) carbeniates, [Au3(RN═COR')3] (R, R' = H, Me, (n)Bu, or (c)Pe), is reported. Synthesis and structural and photophysical characterization of novel complexes [Au3(MeN═CO(n)Bu)3], [Au3((n)BuN═COMe)3], [Au3((n)BuN═CO(n)Bu)3], and [Au3((c)PeN═COMe)3] are presented. Changes in R and R' lead to distinctive variations in solid-state stacking, luminescence spectra, and conductive properties. Solid-state emission and excitation spectra for each complex display a remarkable dependence on the solid-state packing of the cyclotrimers. The electronic structure of [Au3(RN═COR')3] was investigated via molecular and solid-state simulations. Calculations on [Au3(HN═COH)3] models indicate that the infinitely extended chain of eclipsed structures with equidistant Au--Au intertrimer aurophilic bonding can have lower band gaps, smaller Stokes shifts, and reduced reorganization energies (λ). The action of one cyclotrimer as a molecular nanowire is demonstrated via fabrication of an organic field effect transistor and shown to produce a p-type field effect. Hole transport for the same cyclotrimer-doped within a poly(9-vinylcarbazole) host-produced a colossal increase in current density from ∼1 to ∼1000 mA/cm(2). Computations and experiments thus delineate the complex relationships between solid-state morphologies, electronic structures, and optoelectronic properties of gold(I) carbeniates.

Hydrothermal Synthesis and Characterization of a Novel 1D Luminescent Zn(II) Framework With 1,4-di-(1,2,4-triazole-4-yl) Benzene

Using the benzene-based bis-triazole ligand 1,4-di-(1,2,4-triazole-4-yl)benzene(L) and corresponding zinc(II) salt, under hydrothermal conditions, a novel luminescent 1D Zn(II) coordination polymer, {[Zn(μ2-L)(H2O)4]SiF6·2H2O}n (1) has been isolated and characterized by single-crystal X-ray diffraction, FT-IR, and luminescent analysis. The crystal crystallizes in the Monoclinic C2/c space group, a = 12.997(5) Å, b = 19.376(4) Å, c = 8.080(6) Å, β = 109.379(18)°, Z = 4. These L ligands adopt the bi-dentate bridging coordination modes to link neighboring Zn(II) ions forming 1D chain structure. Solid state luminescent spectrum of 1 also has been investigated indicating the strong emission band centered at 370 nm. The result also represents a good example of the construction of these highly dimensional luminescent inorganic-organic hybrid frameworks.

Two sensitizers of Tb(III) constructed from alkaline earth metals and semi-rigid tripodal ligand

Three alkaline earth (AE) coordination polymers, namely, [Mg(H2BCPBA)2(H2O)4]n (1), [Sr(HBCPBA)(H2O)2]n (2), [Ba(H2BCPBA)2]n (3), (H3BCPBA=3,5-bi(4-carboxy-phenolxy)-ben-zoic acid) have been synthesized in mixed solvents under hydrothermal conditions. The single crystal analysis show 1 is mononuclear compound, which forms 3D supramolecular framework through H-bonding and π–π interaction. In compound 2, dinuclear Sr(II) subunits were connected by the tripod linkers to afford the 3D metal–organic framework. Compound 3 displays 3D structure and each Ba(II) center in the framework acts as a 4,8-connected binode to give a unique network with a Schläfli symbol of {44.62}2{48.618.82}. The solid-state luminescent spectra of complexes 1–3 reveals that all of them have different degree of redshift compared with free ligand. The experiments of sensitization to Eu(III) and Tb(III) are performed on these three compounds. The results show that 2 and 3 can sensitize Tb(III) ion to exhibit its characteristic green emission.

CuII complexes with co-planar [CuII(N–N)(HIMC−)], their anti-cancer activities, ΔG, ΔE and solid luminescence

[Cu(II)(phen)(HIMC(-))(H2O)]·[Cu(II)(phen)(HIMC(-))(NO3(-))]·NO3(-)·H2O (1) and [Cu(II)(2,2'-bipy)(HIMC(-))]·NO3(-)·xH2O (2) (phen = 1,10-phenanthroline, 2,2'-bipy = 2,2'-bipyridine, HIMC(-) = 1H-imidazole-4-carboxylate acid anion) have been synthesized at 180 °C, of which the HIMC(-) is produced by an in situ decarboxylation from H3IDC (1H-imidazole-4,5-dicarboxylic acid) in a one-pot hydrothermal reaction. The anticancer activity experiments in vitro show that 1 exhibited excellent activities against A549, Bel-7402 and HCT-8 cancer cells and is even better than the clinical anticancer drug 5-Fu (5-fluorouracil), while 2 shows little response toward the cancer cells. The single crystal X-ray diffraction indicated that complex 1 possess a co-planar [Cu(II)(N-N)(HIMC(-))] coordination geometry. The IR, elemental analysis and solid-state luminescent spectra of complexes 1 and 2 indicated that the composition of these two complexes are similar, whereas the 2,2'-bipy in complex 2 replaced phen in complex 1. The calculation by the Gaussian 03 program illustrated that the decrease in the energy gaps between π*-π from the free to the coordinated ligand for 2,2'-bipy and phen (ΔE) are 5.3 eV to 4.0 eV and 4.8 eV to 4.5 eV separately, and the relative changes of the Gibbs free energies (ΔG) for complex 1 and 2 decomposing into free Cu(2+) and ligands are about 0 kcal mol(-1) and 7 kcal mol(-1) respectively, which revealed that it is more stable when 2,2'-bipy is coordinated with Cu(II) than phen, and 1 is easier to disassociate into free Cu(2+) than 2. By relating the ΔE, ΔG, luminescent qualities and anticancer toxicities of the complexes with their composition, it can be concluded that both Cu(II) and their coordinated ligands are responsible for the inhibition against cancer cells.

Hydrothermal Synthesis and Characterization of a Novel 3D Chiral Inorganic-Organic Hybrid Cadmium(II) Framework With Achiral 1,4-Naphthalenedicarboxylic Acid Ligand

Using the achiral 1,4-naphthalenedicarboxylic acid (H2L) ligand and corresponding cadmium(II) salts, under hydrothermal conditions, a novel 3D chiral inorganic-organic hybrid complex with the formula [Cd(μ6-L)(DMF)]n has been isolated and characterized by single-crystal X-ray diffraction, FT-IR, TGA, and luminescent analysis. The crystal crystallizes in the chiral space group P212121, a = 6.7180(10) Å, b = 13.507(2) Å, c = 15.229(2) Å, Z = 4, the flack parameter is near zero (–0.02(4)). Two kinds of 1D infinite right-handed Cd-O-Cd helical chains can be observed, which are further interlinked into 1D infinite Cd-O-Cd linkage in a unique arrangement way. Solid-state luminescent spectrum of 1 also has been investigated indicating the strong emission band centered at 494 nm upon excitation at 370 nm. The result also represents a good example of the construction of those chiral inorganic-organic hybrid frameworks containing infinite M-O-M linkage using the achiral precursor. Supplementary materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

ChemInform Abstract: Models for Intrinsic and Extrinsic Fracto‐mechanoluminescence of Solids

AbstractReview: 162 refs.

Synthesis, structures of four coordination compounds constructed from o-methacrylamidobenzoic acid and their relationship between structure and solid state luminescence

Four new coordination compounds, namely, Zn( o -MAABA) 2 (Phen) ( 1 ), [Cd( o -MAABA) 2 · 2H 2 O] 2 ( 2 ), {[Pb 2 Cl 2 ( o -MAABA) 2 (Phen) 4 ]} · 2H 2 O ( 3 · 2H 2 O ), [Pb(NO 3 )( o -MAABA)(Phen)] n ( 4 ), where o -MAABA = o -methacrylamidobenzoic acid and phen=1, 10-phenanthroline, have been synthesized. All compounds were fully confirmed by FT-IR, elemental analysis and TGA analysis. Their structures were determined by single crystal X-ray diffraction, in which compound 1 shows a mononuclear structure, compounds 2 and 3 have binuclear structures and compound 4 shows an infinite chain. In 2 and 4 , the adjacent chains are extended into a 3D supramolecular architecture via π–π interactions. Solid-state room temperature luminescence spectra revealed that emission bands of compound 1 were located at 524 nm ( λ ex =352 nm) and compound 4 at 479 and 584 nm ( λ ex =390 nm) assigned to the excimer formation. The emission at 454 nm ( λ ex =340 nm) of compound 2 was mainly ascribed to the Ligand–Metal Charge Transfer (LMCT). Four coordination compounds constructed by o -methacrylamidobenzoic, phenanthroline and metal ions are reported. The photoluminescent properties is studied, which is affected by the molecular stacking and LMCT.

A study of zinc(II) coordination polymers with identical meso-helix based on 1,4-bis(2-methyl-imidazol-1-yl)butane

On the basis of 1,4-bis(2-methyl-imidazol-1-yl)butane (bib), four new coordination polymers (CPs), namely, {[Zn(bib)(male)]2·2H2O}n(1), {[Zn(bib)(suc)]·H2O}n(2), {[Zn(bib)(fum)]·CH3OH}n(3), {[Zn(bib)(bpdc)]·2H2O}n(4) (H2mal=maleic acid, H2suc=succinic acid, H2fum=fumaric acid, bpdc2-−=2,2’2′-bipyridine-3,3’3′-dicarboxylate) have been synthesized by the reaction of zinc(II) salts and bib with four different aliphatic/aromatic binary acids under the same conditions, respectively. These coordination polymers are structurally characterized by elemental analysis, IR, single-crystal X-ray crystallography and TG analysis. All of them host a same meso-helical chain constructed by metal centers and bib ligands. 1 and 2 feature similar 2-D wave-like topology containing a meso-helical chain; 3 is a 3-D diamond-like structure, comprising two different meso-helical chains, and shows 4-fold interpenetrated framework with {6^6} topology; 4 is a 3-D diamond-like structure, containing a meso-helical chain, and displays 3-fold interpenetrated net with {6^6} topology. In addition, the phase purities of bulk samples were further identified by X-ray powder diffraction analysis. Solid state luminescent spectra have been investigated at room temperature, and the luminescent lifetime of 3 was monitored at room temperature.

Solvothermal synthesis, crystal structures and properties of two new magnesium coordination polymers of (l)-malic acid

Abstract Two new three dimensional magnesium coordination polymers of formula, [Mg 4 (HL-MA) 2 (HCO 2 ) 2 (OH) 2 ]∙(EtOH)∙2(H 2 O) ( 1 ), and [Mg(HL-MA)(H 2 O)] ( 2 ), (H 3 L-MA = l -malic acid) have been solvothermally synthesized in order to study the coordination properties of (L)-malic acid and the structural features of the resulting coordination polymers (CPs). The structures of the newly synthesized CPs have been determined by single-crystal X-ray diffraction analysis and further characterized by various analytical and spectroscopic techniques. The single crystal structure analysis showed that the complexes, 1 and 2 form three-dimensional frameworks. Topological analysis revealed that the 1 can be described as a new 4-nodal net with Schlafli symbol of {4 3 .6 2 .8}{4 3 }{4 7 .6 3 }{4 7 .6 5 .8 2 .10} and 2 can be described as a ‘ sra ’ net. The ligand acted as a bi-anionic hepta-dentate and bi-anionic penta-dentate in 1 and 2 respectively. Moreover, the solid-state luminescent spectra of the two Mg(II) complexes indicated that the two complexes emitted their own characteristic sensitized luminescence.

Hydrothermal Synthesis and Characterization of a Novel Inorganic Organic Hybrid Complex of Pb(II) With 5-methyl-pyrazine-2-carboxylic Acid

Under hydrothermal conditions, using 5-methyl-pyrazine-2-carboxylic acid (HL) and lead(II) bromide, a new 2D lead(II) framework [Pb(L)(μ2-Br)(H2O)]n (1) can be isolated, in which infinite Pb-O-Pb and Pb-Br-Pb helical chains can be observed. The crystal crystallizes in the monoclinic system, space group P2(1)/c, a = 7.5493(10), b = 6.6775(9), c = 19.335(3) Å, β = 92.884(2)°, and Z = 1. The X-ray analysis shows that strong O-H···N and weak O-H···Br hydrogen bonds further extending 1 into a 3D supramolecular packing architecture. Solid state luminescent spectrum of 1 also has been investigated indicating strong emission bands centered at 453 nm.

Models for intrinsic and extrinsic elastico and plastico-mechanoluminescence of solids

A large number of solids exhibit extrinsic elastico–mechanoluminescence (ML) and extrinsic plastico ML, only a few solids exhibit intrinsic elastico ML and intrinsic plastico ML. Whereas the elastico ML and plastico ML of a large number of solids are caused by the electron trapping and electron bombardment mechanisms, the elastico ML and plastico ML of only a few solids are caused by the chemiluminescence and other mechanisms. The elastico ML of rare earth doped strontium aluminate, rare earth doped strontium silicates and certain other crystals is so intense that it can be seen in day light with naked eye. For a long time, the detection of luminescence of metals was considered to be impossible; however, now-a-days, it has been found that the intrinsic ML in certain metals can be produced by their plastic deformation at fast rate. In an ultraviolet-irradiated CdS single crystal immersed in liquid nitrogen, the intrinsic elastico ML resembling edge emission can be produced simply by tapping it along its c-axis. Of the order of a 1000 flashes may be obtained from a well-stimulated crystal by tapping more or less uniformly over the whole surface. After the stimulation is exhausted, the crystal can be re-activated by a brief ultraviolet illumination, and the process of obtaining multiple flashes by tapping can be repeated. The spectra of the plastico ML of certain non-irradiated alkali halide crystals resemble the plastico ML spectra of the corresponding X- or γ-irradiated crystals. Such result can be understood on the basis of the formation of F-centres and hole centres during the intersection of the forest of immobile and mobile dislocations. Depending on the prevailing conditions, either the continuous plastico ML or pulsed plastico ML is observed in II–VI semiconductors and in certain non-irradiated alkali halide crystals. Whereas the spectra of elastico ML resemble the solid state luminescence spectra, depending on the solids the spectra of plastico ML consist of either only the solid state luminescence spectra or the combination of solid state luminescence spectra and discharge spectra of the adsorbed molecules of surrounding gases. Till now the elastico ML and plastico ML have been studied only in a limited number of solids, and therefore, they need further investigation. The study of the elastico ML and plastico ML of rubbers and polymers may be very interesting. The understanding of the mechanisms of intrinsic and extrinsic elastico ML and plastico ML may be useful in preparing suitable elastico and plastico mechanoluminescent materials and it may be helpful in designing the devices based on elastico ML and plastico ML. Theorists need the models or mechanisms of the phenomena to propose and develop their theories and experimentalists also need the models and mechanisms of the phenomena for improving their materials and devices. In this regard, the present study may also be useful and important.

Models for intrinsic and extrinsic fracto-mechanoluminescence of solids

A large number of noncentric and centric organic and inorganic crystals exhibit intrinsic and extrinsic fracto-mechanoluminescence (ML) due to the electron bombardment and electron-trapping mechanisms, and only a few crystals show ML due to the chemically induced fracto-ML and other possible mechanisms. The charged surfaces produced during fracture of solids owing to piezoelectrification, defective-phase piezoelectrification, movement of charged dislocations, baro-diffusion of defects near the crack-tip, and many other processes may cause production of very high electric field near the charged surfaces. In the case of non-photoluminescent and non-cathodoluminescent materials, the high energy electrons may be emitted from the charged surfaces and the electron bombardment (EB) mechanism may excite the molecules of surrounding gases and subsequently the gas discharge ML may be produced. In photoluminescent and cathodoluminescent solids, the electron bombardment may cause cathodoluminescence. In certain photoluminescent crystals, the light of gas discharge may excite photoluminescence. In many solids, the free electrons produced at fracture may be captured in the traps and consequently the electron-trapping (ET) mechanism may give rise to the light emission. Few solids may exhibit chemiluminescence because of the chemical reactions at the newly created surfaces. Some solids may exhibit black body radiations because of the high temperature produced near the tip of the moving cracks. Infrared radiation may also be emitted during the fracture of certain crystals. In certain solids, the gas discharge fracto-ML and the photoluminescence excited by the gas discharge disappear when the solids are fractured inside liquids; however, in certain solids the solid state fracto-ML appears even inside the liquids if they are not based on the processes involving gas discharge. Overall, depending on the prevailing conditions the ML spectra consist of either the gas discharge spectra or solid state luminescence spectra or the combination of the both. The fracto-ML of SrAl2O4:Eu, europium tetrakis (dibenzoyl methide) triethyl ammonium, ditriphenylphosphine oxide manganese bromide, freshly grown impure saccharin, etc. is so intense that it can be seen in day light with naked eye. The understanding of the mechanism of fracto-ML may be useful in preparing suitable fracto-mechanoluminescent materials and it may be helpful in designing the fracto-ML based devices such as fracture sensor, impact sensor, damage sensor, safety management monitoring system, fuse system for army warheads, etc.

Hydrothermal syntheses and crystal structures of PbII coordination polymers based on a N,O-donor ligand

Abstract In this article, four new lead(II) coordination polymers based on a N,O-donor ligand 2′-(1 H-1,3,7,8-tetraaza-cyclopenta[l]phenanthren-2-yl)biphenyl-2-carboxylic acid (HL) have been hydrothermally synthesized, namely, [PbL2]·2H2O (1), [PbL2]·2H2O·CH3CH2OH (2), [Pb5L2(m-BDC)4]·3H2O (3) and [Pb2L2(p-BDC)] (4), where m-BDC = 1,3-benzenedicarboxylate and p-BDC = 1,4-benzenedicarboxylate. Compound 1 shows a 2D bilayer structure, which is further extended into a 3D supramolecular structure through π–π stacking interactions. Compound 2 shows a 3D supramolecular structure based on a zero-dimensional molecule by π–π stacking interactions of neighboring molecules. Compound 3 shows a 2D layer structure. Compound 4 displays a 1D chain-like structure, which is then stacked by π–π interactions to result in a 2D supramolecular structure. Solid-state luminescent spectra of four lead(II) complexes indicate intense fluorescent emissions.

Construction of (CuX)2n Cluster-Containing (X = Br, I; n = 1, 2) Coordination Polymers Assembled by Dithioethers ArS(CH2)mSAr (Ar = Ph, p-Tol; m = 3, 5): Effect of the Spacer Length, Aryl Group, and Metal-to-Ligand Ratio on the Dimensionality, Cluster Nuclearity, and the Luminescence Properties of the Metal–Organic Frameworks

Reaction of CuI with bis(phenylthio)propane in a 1:1 ratio yields the two-dimensional coordination polymer [{Cu(μ(2)-I)(2)Cu}{μ-PhS(CH(2))(3)SPh}(2)](n) (1). The 2D-sheet structure of 1 is built up by dimeric Cu(2)I(2) units, which are connected via four bridging 1,3-bis(phenylthio)propane ligands. In contrast, treatment of 2 equiv of CuI with 1,3-bis(phenylthio)propane in MeCN solution affords in a self-assembly reaction the strongly luminescent metal-organic 2D-coordination polymer [Cu(4)I(4){μ-PhS(CH(2))(3)Ph}(2)](n) (2), in which cubane-like Cu(4)(μ(3)-I)(4) cluster units are linked by the dithioether ligands. The crystallographically characterized one-dimensional (1D) compound [{Cu(μ(2)-Br)(2)Cu}{μ-PhS(CH(2))(3)SPh}(2)](n) (3) is obtained using CuBr. The outcome of the reaction of PhS(CH(2))(5)SPh with CuI also depends of the metal-to-ligand ratio employed. Mixing CuI and the dithioether in a 2:1 ratio results in formation of [Cu(4)I(4){μ-PhS(CH(2))(5)Ph}(2)](n) (4) in which cubane-like Cu(4)(μ(3)-I)(4) clusters are linked by the bridging dithioether ligand giving rise to a 1D necklace structure. A ribbon-like 1D-polymer with composition [{Cu(μ(2)-I)(2)Cu}{μ-PhS(CH(2))(5)SPh}(2)](n) (5), incorporating rhomboid Cu(2)I(2) units, is produced upon treatment of CuI with 1,5-bis(phenylthio)pentane in a 1:1 ratio. Reaction of CuBr with PhS(CH(2))(5)SPh produces the isomorphous 1D-compound [{Cu(μ(2)-Br)(2)Cu}{μ-PhS(CH(2))(5)SPh}(2)](n) (6). Strongly luminescent [Cu(4)I(4){μ-p-TolS(CH(2))(5)STol-p}(2)](n) (7) is obtained after mixing 1,5-bis(p-tolylthio)pentane with CuI in a 1:2 ratio, and the 2D-polymer [{Cu(μ(2)-I)(2)Cu}(2){μ-p-TolS(CH(2))(5)STol-p}(2)](n) (8) results from reaction in a 1:1 metal-to-ligand ratio. Under the same reaction conditions, 1D-polymeric [{Cu(μ(2)-Br)(2)Cu}{μ-p-TolS(CH(2))(5)STol-p}(2)](n) (9) is formed using CuBr. This study reveals that the structure of the self-assembly process between CuX and ArS(CH(2))(m)SAr ligands is hard to predict. The solid-state luminescence spectra at 298 and 77 K of 2 and 4 exhibit very strong emissions around 535 and 560 nm, respectively, whereas those for 1 and 5 display weaker ones at about 450 nm. The emission lifetimes are longer for the longer wavelength emissions (>1.0 μs arising from the cubane species) and shorter for the shorter wavelength ones (<1.4 μs arising from the rhomboid units). The Br-containing species are found to be weakly fluorescent.

Thermal and Fluorescence Properties of New Nanostructured Hg(ll) -2,2′-Bipyridine Derivative Complexes

Two new nano-structured Hg(II) supramo- lecular complexes, (Hg(5,5 0 -di-t-but-bpy)(l-Br)Br)2(Hg(5, 5 0 -di-t-but-bpy)Br2)(1) and (Hg(5,5 0 -di-t-but-bpy)I2 )( 2) were synthesized by the sonochemical method. The struc- tures of 1 and 2 were characterized by elemental analysis, IR, 1 H-NMR, and 13 C-NMR spectroscopy and single crystal X-ray diffraction. Their thermal stabilities were studied by thermogravimetric and differential thermal analyses. Solid-state luminescent spectra of 1 and 2 indi- cate a fluorescent broad emission band between 304 and 404 nm with excitation at 284 nm. These nanostruc- tured coordination polymers were characterized by scan- ning electron microscopy, elemental analysis, and IR spectroscopy.

Two three-dimensional cadmium supramolecular architectures containing extensive hydrogen-bonding networks based on CdSO4 and bis-imidazole ligands

In this study, two novel three-dimensional (3D) supramolecular networks, [Cd(BIM)2(SO4)(H2O)]·(C2H5OH) (H2O)2 (1) and [Cd(2-mBIM)(SO4)(H2O)3]·H2O (2) [BIM=bis(imidazol-1-yl)-methane, 2-mBIM=bis(2-methylimidazol-1-yl)methane], were synthesized by the reactions of CdSO4 with BIM or 2-mBIM ligand via solvent diffusion methods. The networks were then characterized by elemental analyses, IR, TGA, and X-ray diffraction. Both compounds 1 and 2 have a 3D hydrogen-bonding network with an infinite one-dimensional (1D) double chain structure and an infinite 1D helix channel, respectively. These results suggest that the subtle change in the ligand structure may have a strong influence on the resulting architectures of the metal–organic frameworks. The solid-state luminescent spectra of compounds 1 and 2 indicate weak fluorescent emissions at ca. 338 and 389nm, respectively.

Synthesis and structural characterization of several new coordination polymers of 2-(1H-imidazol-1-yl) acetic acid

The combination of the polydentate ligand 2-(1H-imidazol-1-yl) acetic acid (Hima) with metal ions (Pb2+, Li+, Zn2+, Cd2+, Fe2+ and Co2+) leads to seven different coordination polymers: [Pb3(imaH)2Cl6]n (1, layer), [Pb(ima)2(NO3)2]n (2, chain), [Li2H(ima)2(H2O)2Cl]n (3, chain), [Zn(imaH)(ima)Cl]n (4, chain), [Cd(imaH)Cl2]n (5, chain), and [M(ima)2]n (6, M=Fe; 7, M=Co; layer). All compounds were characterized by FT-IR, elemental analysis and TG analysis, and their structures were determined by single crystal X-ray diffraction. According to the structural analysis, compound 1 shows a [Pb3Cl6] layer; compounds 2–4 show an infinite chain, but they were connected with imaH or ima bridges, respectively; compound 5 also has an infinite chain constructed of double chloride bridges; and compounds 6 and 7 exhibit layers without chloride ions involved. In these compounds, the ligand adopts two kinds of forms (anion, ima or zwitterion, imaH) and shows diverse modes of coordination. More interestingly, chloride as the second anion participated in the structural architecture based on its different affinities with metal ions. Solid-state room temperature luminescence spectra revealed that emission bands of compound 1 were located at 455nm, compound 4 at 425nm, and compound 5 at 550nm (λex=390nm), which is mainly assigned to the Ligand–Metal Charge Transfer (LMCT).

Fracto-mechanoluminescence and mechanics of fracture of solids

The present paper explores the correlation between fracto-mechanoluminescence and fracture of solids and thereby provides a clear understanding of the physics of fracto-mechanoluminescence. When a fluorescent or non-photoluminescent crystal is fractured impulsively by dropping a load on it, then initially the mechanoluminescence (ML) intensity increases linearly with time, attains a maximum value Im at a particular time tm and later on it decreases exponentially with time. However, when a phosphorescent crystal is fractured impulsively by dropping a load on it, then initially the ML intensity increases linearly with time, attains a maximum value Im at a particular time tm and later on it decreases initially at a fast rate and then at a slow rate. For low impact velocity the value of tm is constant, however, for higher impact velocity tm decreases logarithmally with the increasing impact velocity. Whereas the peak ML intensity Im increases linearly with the impact velocity, the total ML intensity IT, initially increases linearly with the impact velocity and then it tends to attain a saturation value for higher values of the impact velocity. The value of tm increases logarithmally with the thickness of crystals, Im increases linearly with the area of cross-section of crystals and IT increases linearly with the volume of crystals. Generally, the ML of non-irradiated crystals decreases with increasing temperature of crystals. Depending on the prevailing conditions the ML spectra consist of either gas discharge spectra or solid state luminescence spectra or combination of the both. On the basis of the rate of generation of cracks and the rate of creation of new surface area of crystals, expressions are derived for the ML intensity and they are found to explain satisfactorily the temporal, spectral, thermal, crystal-size, impact velocity, surface area, and other characteristics of ML. The present investigation may be useful in designing of damage sensors, fracture sensors, ML-based safety management monitoring system, fuse-system for army warheads, milling machine, etc. The present study may be helpful in understanding the processes involved in earthquakes, earthquake lights and mine-failure as they basically involve fracture of solids.