Synthesis,characterization, and crystal structures of 2D cobalt(II) and nickel(II) coordination polymers containing flexible bis(benzimidazole) ligands

Three coordination polymers, namely {[Ni(L1)(nip)(H₂O)]·2H₂O} _n (1), [Co(L2)(tbip)] _n (2), and {[Co₂(L3)₂(bptc)]·3H₂O} _n (3) (L1 = 1,4-bis(5,6-dimethylbenzimidazole)butane, L2 = 1,4-bis(5,6-dimethylbenzimidazole)-2-butylene, L3 = 1,3-bis(5,6-dimethylbenzimidazole)propane, H₂nip = 5-nitro-isophthalic acid, H₂tbip = 5-tert-butyl-isophthalic acid, H₄bptc = biphenyl-3,3′,4,4′-tetracarboxylic acid), have been synthesized under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as by single-crystal X-ray diffraction analysis. Complexes 1 and 2 both feature a two-dimensional (4,4) layer with (4⁴ × 6²) topology. Complex 3 possesses a uninodal 4-connected 2D htb network. The fluorescence spectra and catalytic properties of the complexes for the degradation of methyl orange by sodium persulfate in a Fenton-like process are reported.     

Two new cadmium(II) coordination polymers with bis(benzimidazole) ligands

Two new cadmium(II) coordination polymers, {[Cd(L1)(tbta)]·H₂O} _n (1) and [Cd(L2)(tbta)] _n (2) (L1 = 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, H₂tbta = tetrabromoterephthalic acid and L2 = 1,4-bis(2-methylbenzimidazol-1-ylmethyl)benzene) are obtained under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction methods, IR spectroscopy, TGA and elemental analysis. The L1 and L2 ligands differ by subtle variation of substituents at semi-rigid bis(benzimidazole) bakcbones. Complex 1 features a 3D threefold interpenetrating dia array with a 4-connected 6⁶ topology. Complex 2 displays a 2D {4⁴.6²} sql/Shubnikov tetragonal plane network. Complexes 1 and 2 possess high thermal stabilities and promising fluorescence behavior in the solid state.     

Syntheses and crystal structures of two self-assembled dizinc(II) helicates with novel hydrazone linked polypyridyl ligands

The rationally designed polydentate ligands, L ¹ and L ² , based on the pyridinyl moiety and the hydrazone fragment have been synthesized to coordinate zinc(II) ions. We utilize pyridine as a rigid core connecting two bipyridines as ligand building blocks with a hydrozone linker for the L ¹ . The L ² has a reversed design in which a bipyridine was used as a hinging-available building block of the ligand core, connecting two pyridazine arms with a hydrazone linker. Two novel helical dizinc(II) complexes were obtained by the reaction of L ¹ and L ² with zinc(II) perchlorate in acetonitrile. The structures of both helicates were confirmed by X-ray diffractometry. Single-stranded helicate Zn ₂ L ¹ contains two zinc ions bridged by an oxygen atom. Except for the L ² ligand, no other bridging species were found between the two zinc ions in the double-stranded helicate Zn ₂ L ₂ ² . The self-assembling process of helicate Zn ₂ L ¹ in solution state was studied by UV–Vis spectrometric titration experiments. The stepwise formation constants imply a slightly positive cooperative behavior for the formation of helicates.     

Synthesis and characterization of copper(II) and nickel(II) coordination polymers containing 2,6-naphthalenedicarboxylate and bis(benzimidazole) ligands

Two coordination polymers, namely [Ni(L1)-(ndc)(H₂O)] _n (1) and [Cu(L2)_0.5(ndc)] _n (2) (L1 = 1,3-bis(2-methylbenzimidazol-1-ylmethyl)benzene, L2 = 1,4-bis(2-methylbenzimidazole)butane, H₂ndc = 2,6-naphthalenedicarboxylic acid) have been synthesized and characterized by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis. Complex 1 features a 2D 3-connected hcb network with 6³ topology, which is further extended into a 3D supramolecular framework by O–H···O hydrogen bonding interactions. Complex 2 possesses a 3D threefold interpenetrating (4,5)-connected xah topological network, and its Schläfli symbol is (4².6².8²)(4⁶.6⁴). Both complexes exhibit intense luminescence emissions in the solid state and promising catalytic activities for the degradation of Congo red azo dye in a Fenton-like process.     

Co(II) and Ni(II) complexes with imidazole-containing ligands: Synthesis,structural characterization,and magnetic property

Hydrothermal reaction of Co(II) salt with 1,4-di(1-imidazolyl)benzene (L¹) and 4,4’-oxydiphthalic acid (H₄OA) yields a new complex [Co₃(HOA)₂(L¹)₄(H₂O)₄] (I). [Ni(L²)₂SO₄] · 0.5H₂O (II) can be obtained via the hydrothermal reaction of NiSO₄ · 6H₂O with 1,3-di(1H-imidazol-4-yl)benzene (L²). Complexes I and II have been characterized by single-crystal and powder X-ray diffraction (CIF files CCDC nos. 1019291 (I) and 1019292 (II)), IR, elemental, and thermogravimetric analyses. Complex I exhibits the uninodal six-connected 3D pcu framework structure of I with (4¹² · 6³) topology; Complex II consists of the uninodal four-connected 2D sql (4⁴ · 6²) networks. In addition, magnetic property of I was investigated.     

Zinc(II), nickel(II) and cadmium(II) coordination polymers based on the ligand oxamide <Emphasis Type="Italic">N,N</Emphasis>-bis(4-phthalic acid): synthesis,structural characterization and magnetic properties

Three coordination polymers based on the new ligand oxamide N,N-bis(4-phthalic acid), namely [Zn(L)_0.5-(2,2′-bpy)] _n (1), [Ni₂(2,2′-bpy)₄(µ ²-Ox)]L·3H₂O (2) and [Cd(L)(1,10-phen)] (3) [L = oxamide N,N-bis(4-phthalic acid)], (2,2′-bpy = 2,2′-bipyridine), (1,10-phen = 1,10-phenanthroline), have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction: compound 1 is one-dimensional ladder-like coordination polymer, compound 2 exhibits a three-dimensional structure resulting in extensive hydrogen bonds built with the help of lattice water molecules, compound 3 also exhibits a three-dimensional supramolecular structure. All compounds were also characterized by elemental analysis, IR spectra and thermogravimetric analysis; furthermore, the magnetic measurements for 2 reveal antiferromagnetic coupling between the nickel(II) ions.     

Synthesis,structures and characterization of two cobalt(II) coordination polymers with 2,5-dichloroterephthalic acid and flexible bis(benzimidazole) ligands

Two Co(II) coordination polymers (CPs), namely [Co(L1)(DCTP)]_n (1) and [Co(L2)(DCTP)]_n (2) [L1?=?1,4-bis(5,6-dimethylbenzimidazol-1-yl)butane, L2?=?1,5-bis(5,6-dimethylbenzimidazol-1-yl)pentane, H₂DCTP?=?2,5-dichloroterephthalic acid] were synthesized and characterized by single-crystal X-ray diffraction analysis, elemental analysis, powder X-ray diffraction (PXRD) and infrared spectroscopy. CP 1 has a 2D (4,4) corrugated sheet structure, which is further extended into a 2D double layer by C–H···O weak hydrogen bonding interactions, while CP 2 displays a 2D layer with hcb network, which is assembled into a 3D supramolecular framework through C–H···O hydrogen bonding. Both CPs exhibited promising photocatalytic activities for the degradation of methylene blue under UV irradiation. In addition, the thermal stabilities and the luminescence properties of both CPs have been investigated.     

Thermodynamics of interactions between lead(II) and cadmium(II) ions and azulene-based complexing polymer films

In order to understand the essential processes/interactions between the metal ions and modified electrodes which are based on complexing polymeric films, access to thermodynamic characteristics is compulsory. The paper enlarges the information concerning the sorption of metal ions within complexing polymer films, particularly based on azulene, which can be involved in metal detection sensors. Interactions between lead(II) or cadmium(II) ions and complexing polymer films have been studied using chemical preconcentration–anodic stripping method. The films have been obtained by controlled potential electrolysis in millimolar solutions of 4-azulen-1-yl-2,6-bis(2-thienyl)pyridine (L) in acetonitrile. PolyL films affinities towards these metal ions have been quantified at different temperatures by means of sorption isotherms. Parameters for sorption of lead(II) and cadmium(II) ions within polyL films have been calculated for Freundlich, Langmuir and Redlich–Peterson isotherms. The best fit was obtained when using Langmuir isotherm. The results evidence that lead ions are better sorbed than cadmium within polyL film. Thermodynamic parameters for the chemical sorption of lead(II) and cadmium(II) ions within polyL films have been calculated.     

Three cobalt(II) coordination polymers constructed from flexible bis(thiabendazole) and dicarboxylate linkers: crystal structures,fluorescence, and photocatalytic properties

Three Co(II) coordination polymers, namely, {Co(btbb)_0.5(ndc)(H₂O)}_n (1), {[Co(btbb)(bpdc)]·1.5H₂O}_n (2), and {[Co(btbp)₂(3-npa)]·2H₂O}_n (3) (btbb = 1,4-bis(thiabendazole)butane, btbp = 1,3-bis(thiabendazole)propane, H₂ndc = 2,6-naphthalenedicarboxylic acid, H₂bpdc = 4,4′-biphenyldicarboxylic acid and 3-H₂npa = 3-nitro phthalic acid) were synthesized under hydrothermal conditions. Their X-ray crystal structures show that complexes 1 and 2 both have 2D uninodal 3-connected hcb (honeycomb) structures. Complex 1 is further extended into a threefold interpenetrating 3D 4,4-connected mog (moganite) supramolecular architecture with the point symbol of {4.6⁴.8}₂{4².6².8²} by O–H···O hydrogen bonding interactions. Complex 2 shows a 3D supramolecular framework involving π···π stacking interactions. Complex 3 features a uninuclear structure, which is further assembled into an ordered 2D hydrogen-bonded-driven pattern with O–H···O and O–H···N hydrogen bonding interactions. The fluorescence spectra and photocatalytic properties of complexes 1–3 for degradation of methyl orange were investigated.     

Crystal structures and enhanced luminescence of Zn(II) and Cd(II) complexes containing conjugated organic ligands

By self-assembly of delocalized organic ligands (L¹ and L²) with Cd(SCN)₂, ZnI₂ and Zn(NCS)₂, three luminescent complexes ZnI₂(L¹)₂ (I), [Cd(L¹)₂(μ_1,3-SCN)₂] _n (II) and Zn(NCS)₂(L²)₂ (III) were obtained (L¹ = 2-{5,5-dimethyl-3-[2-(pyridine-4-yl)ethenyl]cyclohex-2-enylidene}propanedinitrile and L² = 2-{5,5-dimethyl-3-[2-(pyridine-3-yl)ethenyl]cyclohex-2-enylidene}propanedinitrile). The structures of the complexes were determined by single crystal X-ray diffraction analysis (CIF files CCDC nos. 1406116 (I), 1406115 (II), and 1400360 (III)). In complex I, Zn(II) is coordinated by two functional organic ligands and two I^– ions, to form a I₂N₂ distorted tetrahedral geometry. In 1D coordination polymer II, the Cd(II) centers show six-coordinated geometries, two organic ligands and four SCN^– ions involve in coordination with each Cd(II) center. The thiocyanate groups show μ_1,3-SCN bridging coordination modes and the adjacent Cd(II) ions are bridged by double μ_1,3-SCN ions to form an infinite chain. In complex III, Zn(II) is coordinated by two functional organic ligands and two NCS^– groups, to form a N₄ distorted tetrahedral geometry. Compared with the free ligands, the complexes show superior luminescent property with red-shift and enhancement of fluorescence intensity.     

Copper(II) complexes of tetradentate N2S2 donor sets: Synthesis,crystal structure characterization and reactivity

Two mononuclear and one dinuclear copper(II) complexes, containing neutral tetradentate NSSN type ligands, of formulation [Cu^II(L¹)Cl]ClO₄ (1), [Cu^II(L²)Cl]ClO₄ (2) and [Cu^II₂(L³)₂Cl₂](ClO₄)₂ (3) were synthesized and isolated in pure form [where L¹ = 1,2-bis(2-pyridylmethylthio)ethane, L² = 1,3-bis(2-pyridylmethylthio)propane and L³ = 1,4-bis(2-pyridylmethylthio)butane]. All these green colored copper(II) complexes were characterized by physicochemical and spectroscopic methods. The dinuclear copper(II) complex 3 changed to a colorless dinuclear copper(I) species of formula [Cu^I₂(L³)₂](ClO₄)₂,0.5H₂O (4) in dimethylformamide even in the presence of air at ambient temperature, while complexes 1 and 2 showed no change under similar conditions. The solid-state structures of complexes 1, 2 and 4 were established by X-ray crystallography. The geometry about the copper in complexes 1 and 2 is trigonal bipyramidal whereas the coordination environment about the copper(I) in dinuclear complex 4 is distorted tetrahedral.     

Structural diversity in Cu(II), Cd(II) and Hg(II) coordination complexes with the rigid N,N′-bis(2/3-aryl)-1,4-benzenedicarboxamide ligand

The syntheses and structures of a series of metal complexes, namely Cu₂Cl₄(L¹)(DMSO)₂·2DMSO (L¹ = N,N′-bis(2-pyridinyl)-1,4-benzenedicarboxamide), 1; {[Cu(L²)_1.5(DMF)₂][ClO₄]₂·3DMF}_∞ (L² = N,N′-bis(3-pyridinyl)-1,4-benzenedicarboxamide), 2; {[Cd(NO₃)₂(L³)]·2DMF}_∞ (L³ = N,N′-bis-(2-pyrimidinyl)-1,4-benzenedicarboxamide), 3; {[HgBr₂(L³)]·H₂O}_∞, 4, and {[Na(L³)₂][Hg₂X₅]·2DMF}_∞ (X = Br, 5; I, 6) are reported. All the complexes have been characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. Complex 1 is dinuclear and the molecules are interlinked through S?S interactions. In 2, the Cu(II) ions are linked through the L² ligands to form 1-D ladder-like chains with 60-membered metallocycles, whereas complexes 3 and 4 form 1-D zigzag chains. In complexes 5 and 6, the Na(I) ions are linked by the L³ ligands to form 2-D layer structures in which the [Hg₂X₅]⁻ anions are in the cavities. The L² ligand acts only as a bridging ligand, while L¹ and L³ show both chelating and bridging bonding modes. The L¹ ligand in 1 adopts a trans-anti conformation and the L² ligand in 2 adopts both the cis-syn and trans-anti conformations, whereas the L³ ligands in 3–6 adopt the trans conformation.     

Synthesis and structural properties of thiapyridinophane and its complex with Ni(II) and Ag(I)

The 2,11-dithia[3.3](3,5)pyrdinophane (L¹) has been synthesized by a new method and characterized by ¹H NMR, which is used to form coordination complexes C₁₄H₁₄N₄O₆S₂Ni (I) by addition of Ni²⁺ cation and C₁₄H₁₄N₃O₃S₂Ag (II) by addition of Ag⁺ cation. 2,11,20-Trithia[3.3.3](3,5)pyridinophane (L²) and 2,11,20,29-tetrathia[3.3.3.3](3,5)pyridinophane (L³) have also been synthesized as by-products. Single-crystal X-ray analysis reveals that the conformation of the L¹ is syn(boat-chair), complexes I and II also adopt syn(boat-chair) (CIF files CCDC nos. 1400332 (I) and 700724 (II)). While in I, Ni(II) is coordinated with L¹ with two nitrogen and four oxygen atoms, in II, Ag(^I) is coordinated with L¹ by two nitrogen and two sulfur atoms came from four ligands. In complexes I and II, the formation of three-dimensional structure depends on π???π stacking and hydrogen bonds.     

Biomimetic oxidation of catechol employing complexes formed in situ with heterocyclic ligands and different copper(II) salts

In the present work, catecholase activity is presented. The complexes were prepared by condensation of the organic ligand pyrazolyl L ₁ –L ₄ and copper(II) ion in situ. The pyrazolyl compounds L ₁ –L ₄ used in this study are: L ₁ is (3,5-dimethyl-pyrazol-1-ylmethyl)-(4-methyl-pyridin-2-yl)-pyrazol-1-ylmethyl-amine; L ₂ is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-pyrazol-1-ylmethyl-amino]-phenyl}-ethanone; L ₃ is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-phenyl}-ethanone, and L ₄ is 2-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-6-methyl-pyrimidin-4-ol, and copper ions salts Cu(II) are (Cu(CH₃COO)₂, CuCl₂, Cu(NO₃)₂ and CuSO₄). In order to determine factors influencing the catecholase activity of these complexes, the effect of ligand nature, ligand concentration, nature of solvent and nature of counter anion has been studied. The best activity of catechol oxidation is given by the combination formed by one equivalent of ligand L ₂ and one equivalent of Cu(CH₃COO)₂ in methanol solvent which is equal to 9.09 µmol L^?1 min^?1. The Michaelis–Menten model is applied for the best combination, to obtain the kinetic parameters, and we proposed the mechanism for oxidation reaction of catecholase.     

Synthesis and crystal structure of zinc(II) and manganese(II) complexes of 2-(diphenylacetyl)indandione-1,3

Zinc(II) and manganese(II) complexes of 2-(diphenylacetyl)indandione-1,3 (HL) were synthesized. Crystals of [M(DMSO)₂L₂] · CHCl₃, where M= Zn^(II) (I) and Mn^(II) (II), obtained from chloroform plus dimethyl sulfoxide (DMSO) mixture were found to be isostructural based on the similarity of their unit cell parameters and unit cell volumes. The crystals are triclinic, Z = 2, space group P \(\bar 1\); a = 10.422(1) Å, b = 11.929(1) Å, c = 20.429(1) Å, α = 73.616(1)°, β = 85.095(1)°, γ = 77.586(1)° for complex I; a = 10.436(1) Å, b = 12.297(1) Å, c = 19.924(2) Å, α = 78.138(2)°, β = 87.625(2)°, γ = 82.048(2)° for complex II. X-ray structural analysis of complex I was carried out. For complex II, the structure was not refined because all of its atoms are each disordered over three to five positions. The two DMSO molecules in complex I coordinate the central metal atoms in the monodentate mode via their donor oxygen atoms to occupy an axial position and an equatorial position in an octahedral polyhedron. The other four positions are occupied by the four oxygen atoms of the two deprotonated ligands L^? coordinated in the bidentate-cyclic mode. The outer sphere of complex I contains the solvating chloroform molecule.     

Syntheses and luminescence of four supramolecular coordination complexes with flexible ligand

Four d ¹⁰-based complexes with chemical formulae {[Zn(L¹)₂(H₂O)₂(4,4′-Bipy)₂] (I), {[Zn₂(L¹)₄(Mi)] · 4H₂O} (II), {[Zn(L¹)₂(Phen)] · H₂O} (III) {[Cd(L¹)₂(Phen)] · 2H₂O} (IV) (HL¹ = p-hydroxy phenylacetic acid, 4,4′-Bipy = 4,4′-bipyridine, Phen = 1,10-phenanthroline, Mi = 1,4-bis(imidazol-1-yl)butane) have been synthesized and structurally characterized by single crystal X-ray diffraction (CIF files CCDC nos. 1047119 (I), 1047120 (II), 1047121 (III), 1047122 (IV)). The significant effect of assistant ligands and metal ions on assembly of I?IV has been demonstrated, which leads to the formation of distinct crystalline products. Complexes I?IV show various coordination motifs with different existing forms and coordination modes of the organic ligands. Furthermore, extend supramolecular networks are connected by secondary interactions such as hydrogen-bonding and aromatic stacking. The thermal stability and luminescent properties of the compounds were discussed in detail.     

Three 2D mixed-ligand Co(II) coordination polymers containing flexible bis(benzimidazole) ligands with different spacers

Three new Co(II) coordination polymers, [Co(L1)(bpdc)] _n (1), [Co(L2)(ndc)(H₂O)·2H₂O] _n (2) and [Co(L3)(ndc)(H₂O)·H₂O] _n (3) (L1 = 1,2-bis(5,6-dimethylbenzimidazole)ethane, L2 = 1,3-bis(5,6-dimethylbenzimidazole)propane, L3 = 1,4-bis(5,6-dimethylbenzimidazole)butane, H₂bpdc = 4,4′-biphenyldicarboxylic acid, H₂ndc = 2,6-naphthalenedicarboxylic acid) have been synthesized under hydrothermal conditions and structurally characterized by X-ray crystallography. All three complexes feature (4,4) networks that extend into 3D supramolecular frameworks via hydrogen bonding interactions. The luminescence properties and catalytic activities of these complexes with respect to the degradation of methyl orange in a Fenton-like process have been investigated.     

Supramolecular assembly of three Ag(I) coordination polymers derived from flexible N-containing ligands and polycarboxylates: synthesis,structures, and catalytic properties

Three Ag(I) coordination polymers [Ag(L1)]·(H₃bptc)·H₂O (1), [Ag₂(L2)(oba)]·H₂O (2), and [Ag₂(L2)₂]·(H₂bptc) (3) [L1 = 1,4-bis(3,5-dimethylpyrazole)butane, L2 = 1,4-bis(2-methylbenzimidazole)butane, H₄bptc = 3,3′,4,4′-biphenyltetracarboxylic acid, H₂oba = 4,4′-oxybis(benzoic acid)] constructed from N-containing ligands with different flexibilities and organic carboxylates as co-ligands have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis. All three complexes display 1D chain structures, which are further extended into 2D supramolecular networks via non-classical C–H···O hydrogen bonding interactions. The fluorescence and catalytic properties of the complexes 1–3 have been investigated in detail. Complexes 2 and 3 reveal promising catalytic activities for the degradation of methyl orange in a Fenton-like process.     

Syntheses,characterization, and crystal structures of two dinuclear nickel(II) and copper(II) complexes with Schiff bases

The phenolic azide bridged dinuclear nickel(II) complex, [Ni₂(L¹)₂(N₃)(H₂O)(μ_1,1-N₃)] · EtOH (I), and the thiocyanate bridged dinuclear copper(II) complex, [Cu₂(L²)₂(μ_1,1-NCS)₂] (II), where L¹ and L² are the deprotonated forms of 2-mothoxy-6-[(2-piperidin-1-ylethylimino)methyl]phenol and 2,4-dichloro-6-[(2-methylaminoethylimino)methyl]phenol, respectively, were synthesized and characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. The crystal of I is orthorhombic: space group Pbca, a = 12.172(1), b = 20.953(1), c = 29.779(2) Å, V = 7594.8(9) ų, Z = 8. The crystal of II is monoclinic: space group P2₁/n, a = 8.7615(11), b = 19.672(2), c = 16.568(2) Å, β = 99.449(2)°, V = 2816.9(6) ų, Z = 4. The Ni atoms in I are in octahedral coordinations, and the Cu atoms in II are in square-pyramidal coordinations.     

Three coordination polymers constructed from succinic acid and 1,4-bis(1H-imidazol-4-yl)benzene: synthesis,crystal structures,and properties

Three coordination polymers involving transition metals, namely [Co(suc)(1,4-bib)(H₂O)₂]_n (1), [Mn(suc)(1,4-bib)(H₂O)₂]_n (2), [Cd(suc)(1,4-bib)]_n (3) (H₂suc?=?succinic acid, 1,4-bib?=?1,4-bis(1H-imidazol-4-yl)benzene), have been synthesized under solvothermal conditions. All three compounds were characterized by single-crystal X-ray diffraction, elemental analysis, FTIR, UV–Vis spectroscopy, powder X-ray diffraction and thermogravimetric analyses. Compounds 1 and 2 show 2D metal–organic layers with the point symbol of {4⁴·6²}. The 3D framework of compound 3 displays a 4-connected dia net with the point symbol of {6⁶} topology. Magnetic susceptibility studies of compound 1 indicate weak antiferromagnetic coupling between the Co(II) centers. The adsorption experiment results show that compound 3 exhibits rapid and selective separation of congo red over methylene blue and rhodamine B.