A calcium(II) coordination polymer showing two different bridging 2-carbamoyl-4-nitrobenzoate coordination modes

Aqueous reaction of CaCO₃ with 2-carbamoyl-4-nitrobenzoic acid (2-ca-4nbaH) results in the formation of a 1-D coordination polymer [Ca(H₂O)₂(2-ca-4nba)₂] (1), which crystallizes in the centrosymmetric triclinic space group P 1. The structure consists of a central Ca(II), two coordinated waters, a symmetrical bridging (µ₂-η ¹ : η ¹) 2-ca-4nba, and a tridentate bridging (µ₂-η ² : η ¹) 2-ca-4nba. The calcium in 1 is coordinated by two water molecules and five oxygens of four symmetry-related 2-ca-4nba, resulting in a distorted pentagonal bipyramidal {CaO₇} polyhedron. Pairs of {Ca(H₂O)₂} units are linked into a 1-D coordination polymer extending along the a-axis with the aid of pairs of bridging 2-ca-4nba ligands. In the infinite chain, alternating pairs of Ca(II) ions exhibit Ca ··· Ca separations of 4.124 and 4.855 Å.     

Two zinc(II) complexes based on indole-3-acetic acid: crystal structures,fluorescence sensors,and ion exchange with mercury(II)

Two new coordination complexes, [Zn(IA)₂(phen)] (1) and [Zn(IA)₂(4,4′-bipy)] _n ?·?C₂H₅OH (2) (IAH?=?indole-3-acetic acid, phen?=?1,10-phenanthroline, 4,4′-bipy?=?4,4′-bipyridine), have been prepared and characterized by single-crystal X-ray diffraction. Complex 1 is mononuclear and 2 presents a 1-D zigzag chain, in which 4,4′-bipy connects the Zn(II) ions. Both complexes show fluorescence emissions and exhibit fluorescence quenching when Hg²⁺ ions are present. ICP, EDS, and SEM experiments reveal that zinc in both complexes can be exchanged by toxic mercury ions.     

Synthesis,crystal structure and magnetic properties of a dinuclear manganese(III) tetradentate Schiff-base complex

A dinuclear manganese(III) tetradentate Schiff-base complex, [Mn₂(salophen)₂(4,4′-bipy)₃](BPh₄)₂ (1) (salophen = N,N′-o-phenylene-bis(salicylideneaminato)), has been synthesized and structurally characterized. Compound 1 crystallized in the triclinic, P 1 space group, a = 13.431(4), b = 13.791(4), c = 13.886(4) Å, α = 73.599(5)°, β = 80.410(6)°, γ = 71.241(5)°, V = 2328.3(12) ų. Complex 1 contains two Mn(salophen) moieties bridged by 4,4′-bipy to form a dinuclear unit, with two terminal 4,4′-bipy ligands. Variable temperature magnetic susceptibility (2–300 K) shows very weak ferromagnetic interactions between the Mn(III) ions.     

Synthesis and structural characterization of 2D Zn(II), Cd(II), and Co(II) coordination polymers containing 3-chloro-1,2-benzenedicarboxylate and positional isomers of triazole-bipyridine

Three compounds, [Zn₂L₂(4,4′-bpt)₂] _n (1), [Cd₂L₂(3,4′-bpt)(H₂O)₂] _n (2) and {[CoL(3,3′-bpt)(H₂O)]?H₂O} _n (3) (L?=?3-Cl-1,2-benzenedicarboxylate dianion, 4,4′-bpt?=?1H-3,5-bs(4-pyridyl)-1,2,4-itriazole, 3,4′-bpt?=?1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole and 3,3′-bpt?=?1H-3,5-bis(3-pyridyl)-1,2,4-triazole), based on three positionally isomeric triazole-bipyridine ligands, were synthesized. Structural analyses of 1–3 reveal diverse 2-D network structures, which are based on different [ML] _n (M?=?Zn, Cd, Co) chains. In the [ZnL] _n chains of 1, the carboxylic groups of L connect the adjacent Zn(II) centers with a monodentate bridging coordination mode (μ₂-η^{1 ?}/^? η¹ ). In 2, [CdL] _n is a double chain connected by the carboxylic groups of L with μ₃-η^{1 ?}/^? η²/η² and μ₃-η^{1 ?}/^? η^{1 ?}/^? η² bridges. The [CoL] _n chains of 3 are formed by the carboxylic groups of L with the μ₂-η^{1 ?}/^? η² coordination mode. The powder X-ray diffraction and the thermal stability of 1–3, the luminescent properties of 1 and 2, and the magnetic behavior of 3 have been briefly investigated.     

Hydrothermal synthesis,characterization and properties of a d10 metal coordination polymer with a layered structure based on carboxyphosphinate ligand, 4,4′-bipyridine and four-coordinated zinc ion

Abstract

Hydrothermal reaction of Zn(NO₃)₂ · 6?H₂O with 2-carboxyethyl(phenyl)phosphinate (H₂L) and 4,4'-bipyridine (4,4′-bipy) led to a novel zinc(II) carboxyphosphinate [ZnL(4,4′-bipy)_0.5]_n (1). The zinc ion is tetrahedrally coordinated by two phosphinate oxygen atoms, one carboxylate oxygen atom, and one nitrogen atom of 4,4′-bipy ligand. The L^2- ligand and zinc ion can be seen as three- and four-connected nodes, respectively. Compound 1 shows a layered network with (3,4)-connected topology. It exhibits a broad blue fluorescent emission band at 459?nm, which can be attributed to 4,4′-bipy intraligand emission as well as to H₂L emission. It is a diamagnetic system between 300?K and 11?K.     

Synthesis and characterization of Pb(II) compounds constructed from N-tosyl-L-glutamic acid

{[Pb(tsgluo)]?·?H₂O} _n (1), [Pb₂(tsgluo)₂(phen)₂] (2), and [Pb₂(tsgluo)₂(bipy)₂] (3) (H₂tsgluo?=?N-p-tolylsulfonyl-L-glutamate, phen?=?1,10-phenanthroline, bipy?=?2,2′-pyridine) have been synthesized in the absence or presence of phen or 2,2′-bipy and structurally characterized by elemental analysis, IR, and X-ray crystallography. Single-crystal X-ray analyses reveal that tsgluo exhibits two coordination modes to link lead ions. Complex 1 gives a 2-D layer structure while 2 and 3 exhibit monomolecular structures; 3 is further connected into a double-chain structure by hydrogen bonds. Phen and 2,2′-bipy are very important for the crystal structure. Fluorescence of the compounds is also discussed.     

Acetato and formato copper(II) paddle-wheel complexes with nitrogen ligands

Compounds Cu(AcO)₂(pydz) (1), Cu(HCOO)₂(pymd)_1/2 (2), Cu(AcO)₂(pymd)_1/2 (3), and Cu(AcO)₂(4,4′-bipy)_1/2 (4) were obtained by reactions of Cu(AcO)₂?H₂O and Cu(HCOO)₂ ? 4H₂O with pyridazine, pyrimidine, or 4,4′-bipyridine. In all the studied structures, the paddle-wheel units [Cu₂[µ-RCOO)₄] are present. Coppers show a square pyramidal coordination determined by four oxygens in the equatorial positions and a nitrogen in the axial position. Compound 1 consists of centrosymmetric dimeric molecules. Compounds 2 and 3 instead consist of zig-zag chains of [Cu₂[µ-RCOO)₄] units linked by bridging pyrimidine molecules. The chains run in the (1 0 1) and (1 1 ?2) directions in 2 and 3, respectively. By crystallization of a solution of 4 in chloroform, Cu(AcO)₂(4,4′-bipy)_1/2 ? 1/2CHCl₃ (5) was obtained. It consists of monodimensional chains of [Cu₂(µ-CH₃COO)₄] units linked by bridging 4,4′-bipy molecules. The chains, of two different types, run parallel to the b-axis in the crystal. Two chlorines of each CHCl₃ molecule are close to two oxygens of two parallel chains. The packing can be described as sheets parallel to the (1 0 ?1) plane. Magnetic properties and electron paramagnetic resonance spectra have been studied.     

Synthesis,characterization and crystal structure of a chiral polymeric Cu(II) complex bridged by tartrate

A chiral metal-organic coordination polymer, [Cu(Tar)(2,2′-bipy) · 5H₂O] (1) (Tar = L-tartrate dianion, 2,2′-bipy = 2,2′-bipyridine), has been synthesized by hydrothermal reaction of Cu(OAc)₂, Na₂T (H₂T = 2,3-O-isopropylidene-L-tartaric acid) and 2,2′-bipyridine, and characterized by IR, UV–vis spectra, elemental analyses, TG-DTA, and single crystal X-ray diffraction. In the hydrothermal reaction, the protection group isopropylidene for tartaric acid was hydrolyzed. The crystal structure of the coordination polymer 1 shows that each tartrate chelates two Cu(II) ions at opposite ends using one carboxylate oxygen and one hydroxyl oxygen and each Cu(II) ion is chelated by two halves of tartrate dianions, forming coordination polymer chains. Distorted octahedral geometry around copper is completed by a chelating 2,2′-bipyridine molecule. The 2,2′-bipyridine groups in two of parallel 1-D chains are interwoven, constituting ladder-shaped double chains. Strong offset π–π stacking interactions with a face-to-face distance of 3.33 Å for pyridine rings are observed. All the lattice water molecules hydrogen-bond to each other or to the carbonyl oxygen of tartrate, forming a 3-D supramolecular structure.     

Synthesis and crystal structures of 3D supramolecular compounds: [ M (4,4′-bipy)2(H2O)4] · (4,4′-bipy)2 · (3,5-daba)2 · 8H2O ( M =Zn,Mn)

Two new supramolecular compounds [M(4,4′-bipy)₂ (H₂O)₄] ·?(4,4′-bipy)₂ ·?(3,5-daba)₂ ·?8H₂O (M=Zn(1) or Mn(2), 4,4′-bipy =?4,4′-bipyridine, 3,5-daba =?3,5-diaminobenzoic acid anion) were synthesized and characterized by elemental analysis and X-ray crystal diffraction. In [M(4,4′-bipy)₂(H₂O)₄]²⁺, the M(II) is coordinated by two nitrogen atoms from two 4,4′-bipy molecules and four oxygen atoms from four waters to form an octahedral configuration. There exist uncoordinated 4,4′-bipy molecules, 3,5-diaminobenzolate counterions and water guests in the compounds. The 3D structures of the title supramolecular compounds are constructed by rich hydrogen bonds among [M(4,4′-bipy)₂(H₂O)₄]²⁺, uncoordinated 4,4′-bipy molecules, water molecules and 3,5-daba, containing a diverting hexa-member water ring.     

Syntheses and characterization of η 5-pentamethylcyclopentadienyl rhodium(III) and iridium(III) complexes containing polypyridyls

Reaction of [(η ⁵-C₅Me₅)M(μ-Cl)Cl]₂ {M?=?Rh (1), Ir (2)} and [(η ⁵-C₅Me₅)MCl₂(DBT)] (DBT?=?dibenzothiophene) {M?=?Rh (3), Ir (4)} with polypyridyl ligands 2,3-bis(2-pyridyl)pyrazine (bpp), 2,3-bis(2-pyridyl)quinoxaline (bpq), 1,3,5-tris(2-pyridyl)-2,4,6-triazine (tptz), 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 4′-pyridyl-2,2′:6′,2′′-terpyridine (py-terpy) results in the formation of mononuclear cationic complexes, [(η ⁵-C₅Me₅)MCl(poly-py)]⁺ (poly-py?=?polypyridyl ligand). The complexes were isolated as hexafluorophosphate salts and characterized by IR and NMR spectroscopy.     

Construction of Zn(II)-ferrocenyl carboxylate coordination complexes via changing adjuvant ligands

Five Zn(II)-ferrocenyl carboxylate complexes, {[Zn(OOCClH₃C₆Fc)(η ²OOCClH₃C₆Fc)(dpa)]?·?(H₂O)} (1), [Zn(η ²-OOCClH₃C₆Fc)₂(2,2′-dip)]?·?(H₂O)_0.25} (2), {[Zn(η-OOCClH₃C₆Fc)₂(bix)]₂?·?(THF)} (3), [Zn(η-OOCClH₃C₆Fc)₂?·?(Hfcz)] _n (4) and {[Zn(η-OOCClH₃C₆Fc)₂(H₂L₁)]?·?(DMF)₂} _n (5) [dpa?=?2,2′-dipyridylamine, 2,2′-dip?=?2,2′-bipyridine, bix?=?1,4-bis(imidazol-1-ylmethyl)benzene, Hfcz?=?α-(2,4-difluorophenyl)-α-(1H-1,2,4-triazol-l-ylmethyl)-1H-1,2,4-triazole-l-ethanol, H₂L₁?=?N,N′-bis(pyridin-4-yl)pyridine-2,6-dicarboxamide, Fc?=?ferrocene, FcC₆H₃ClCOONa?=?sodium 2-chloro-4-ferrocenylbenzoic], have been synthesized and characterized. Single-crystal X-ray analysis reveals that 1 and 2 are mononuclear structures, 3 is a dimer, and 4 and 5 are 1-D structures. The five complexes exhibit some differences in their conformations, which can be attributed to the influence of adjuvant ligands. Notably, various π–π interactions as well as CH/π interactions are discovered in 1–5, and they have significant contributions to self-assembly. The electrochemical properties of 1–5 indicate that half-wave potentials shift to positive potential compared with that of 2-chloro-4-ferrocenylbenzoic acid.     

Four Co(II)/Zn(II) coordination polymers with a multidentate ligand: syntheses,structures, thermal,and photoluminescent properties

Two pairs of isostructural transition metal coordination polymers, {[Co(L)(H₂O)]_n} (1) and {[Zn(L)(H₂O)]_n} (3), {[Co(L)(4,4′-bipy)(H₂O)]·H₂O}_n (2) and {[Zn(L)(4,4′-bipy)(H₂O)]·H₂O}_n (4) (H₂L = N-pyrazinesulfonyl-glycine acid and 4,4′-bipy = 4,4′-bipyridine), have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental and thermogravimetric analyses. The structures show that 1 and 3 display 2-D polymeric grid frameworks with a 3-connected (4, 8²) topology. 2 and 4 also exhibit a 2-D polymeric grid structure, but are constructed by a 4-connected (4, 4) topology. The adjacent 2-D polymeric grid frameworks for 1–4 are further linked by hydrogen bonding O–H?O interactions to form 3-D supramolecular interweaved orderly networks. The fluorescent properties of 3 and 4 were investigated in the solid state.     

Synthesis,characterization and antimicrobial activity of zinc(II) ibuprofen complexes with nitrogen-based ligands

Metal carboxylate complexes possess different carboxylate coordination modes, e.g. monodentate, bidentate, and bridging bidentate. Five Zn(II) complexes were prepared and characterized in order to examine their coordination modes in addition to their biological activity. The syntheses were started by preparation of [Zn(ibup)₂(H₂O)₂] (1). Then, different nitrogen-donor ligands reacted with 1 to produce [Zn(ibup)₂(2-ampy)₂] (2), [Zn(ibup)(2-ammethylpy)] (3), [Zn(ibup)(2,2′-bipy)] (4), and [Zn₂(ibup)₄(2-methylampy)₂] (5) (ibup = ibuprofen, 2-ampy = 2-aminopyridine, 2-ammethylpy = 2-aminomethylpyridine, 2,2′-bipy = 2,2′-bipyridine, 2-methylampy = 2-(methylamino)pyridine). IR, ¹H NMR, ¹³C{¹H}-NMR and UV–vis spectroscopies were used for characterization. The crystal structures of 2 and 5 were determined by single-crystal X-ray diffraction. Investigation of in vitro antibacterial activities for the complexes against Gram-positive (Micrococcus luteus, Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis) bacteria were done using agar well-diffusion method. Complex 1 showed antibacterial activity against Gram-positive bacteria. Complexes 2 and 3 did not exhibit antibacterial activity. Complex 4 showed antibacterial activity and was chosen for further studies to determine the inhibition zone diameter for different concentrations and to set the minimum inhibitory concentration. The antibacterial activity against most of the bacteria was minimized as a result of the complexation of zinc ibuprofen with 2,2′-bipy in 4.     

A series of new oxo-vanadium(IV) complexes with octahedral coordinated vanadium centers

A series of new oxo-vanadium(IV) complexes, [VOCl0.69(OH)0.31 (2,2′-bipy)2]Cl·2H2O (1, 2,2′-bipy?=?2,2′-bipyridine) [(VO)₂Cl₄(4,4'-bipy)₃ (H₂O)₂] (2, 4,4'-bipy?=?4,4'-bipyridine), [VO(ida)(H₂O)]_n (3, H₂ida?=?iminodiacetic acid), and [(VO)₂(oa)₄]_n·4n(H₃O)·n(H₂O) (4, H₂oa?=?oxalic acid), have been synthesized and structurally characterized. 1 contains a [VOCl_0.69(OH)_0.31(2,2′-bipy)₂]⁺ cation, Cl ^– anion and two free H₂O molecules. 2 exhibits a binuclear centrosymmetric moiety built up from two [VOCl₂(4,4'-bipy)(H₂O)] units and one bridging 4,4'-bipy ligand, which provides a rare example of a 4,4'-bipy molecule acting as monodentate ligand. 3 displays a neutral chain [VO(ida)(H₂O)]_n constructed by the linkages of [VO(H₂O)]²⁺ units and ida^2? bridging ligands, while 4 offers the only example of three kinds of oa^2- ligands coexisting within the same anionic chain [(VO)₂(oa)₄^4-]_n. Their spectroscopic properties were investigated, and the magnetic susceptibility of 4 shows antiferromagnetic behavior.     

Metal–organic Coordination Polymers Assembled from Divalent Transition Salts with a Flexible Spacer Ligand: Hydrothermal Syntheses,Crystal Structures,and Luminescent and Magnetic Properties

Seven new metal-organic coordination polymers, [M(tzda)(H₂O)₄] _n [M = Co(1), Ni (2) and Zn(3)], [Zn(tzda)(4,4′-bipy)] _n (4), [Cd(tzda)(4,4′-bipy)_0.5(H₂O)] _n (5) and [M(tzda)(4,4′-bipy)(H₂O)] _n [M = Co(6), Ni(7)] [H₂tzda = (1,3,4-thiadiazole-2,5-diyldithio)diacetic acid, 4,4′-bipy = 4,4′-bipyridine] have been hydrothermally synthesized and structurally characterized by X-ray single crystal diffraction. Compounds 1–3 display similar 1D zigzag chain structure. Compound 4 possesses a 2D-layered architecture generated from [Zn(tzda)] _n moiety with double-chain structure cross-linking 4,4′-bipy spacers, while compound 5 consists of –Cd–OCO–Cd–OCO– chains cross-linked through –CH₂SC₂N₂SSCH₂– spacers of tzda anions and 4,4′-bipy, also showing a 2D-layered structure. The structures of 6 and 7 seem more complicated, in which the [M(tzda)] _n layered subunits are extended to unique 3D framework by the bridging 4,4′-bipy ligand. Photoluminescence investigations reveal that 4 and 5 both display strong blue emissions in the solid state at room temperature, which could be significant in the field of luminescent materials. The magnetic studies of 6 and 7 show both display the characteristics of a weak antiferromagnetic coupling between metal ions in the system mediated by carboxylate bridges.     

Syntheses,structures, and luminescent properties of Zn(II) and Cd(II) complexes: 3-D supramolecules based on 2,6-bis(imino)pyridine ligands constructed by hydrogen bonding interactions

Six 5-coordinate 2,6-bis(imino)pyridine metal complexes, [2,6-(ArN=CMe)₂C₅H₃NMCl₂ · nCH₃CN] (Ar = 4-MeC₆H₄, M = Zn, n = 0.5, Zn1, M = Cd, n = 1, Cd1; Ar = 2,6-Et₂C₆H₃, M = Zn, n = 0.5, Zn2, M = Cd, n = 0.5, Cd2; Ar = 2,4,6-Me₃C₆H₂, M = Zn, n = 1, Zn3, M = Cd, n = 1, Cd3), were synthesized in acetonitrile by the reactions of the corresponding bis(imino)pyridines with ZnCl₂ or CdCl₂ · 2.5H₂O, respectively. The structures of Zn1–Zn3 and Cd1–Cd3 were determined by the single-crystal X-ray diffraction. In all complexes, the ligand is tridentate with further coordination by two chlorides, resulting in a distorted trigonal bipyramid. All complexes self-assemble through hydrogen bonding interactions to form a 3-D supramolecular structure. At 298 K in dichloromethane, all complexes have blue luminescent emissions at 405–465 nm, which can be attributed to ligand-centered π* → π transitions. The zinc and cadmium centers play a key role in enhancing fluorescent emission of the ligands.     

An open-framework cobalt molybdate possessing {Mo2O7} building block: hydrothermal synthesis and structural characterization of [CoMo2O7(4,4′-bipy)1.5]

The hydrothermal reaction of Co(COO)₂?·?4H₂O, MoO₃, H₃PO₄ and 4,4′-bipyridine yields bipyridine-ligated cobalt dimolybdate [CoMo₂O₇(4,4′-bipy)_1.5] (1) (4,4′-bipy?=?4,4′-bipyridine) in the triclinic system with space group of P 1 and cell parameters of a?=?7.1951(8)?Å, b?=?11.1708(17)?Å, c?=?11.4514(11)?Å, α?=?98.545(7)°, β?=?90.315(2)°, γ?=?105.777(5)°, V?=?874.88(19)?ų, and Z?=?2. Its structure consists of Co/Mo/O bimetal oxide layers with {Mo₂O₇} building blocks, linked by the coordination of 4,4′-bipy ligand with Co and Mo atoms, into a 3D porous hybrid framework.     

Syntheses and structures of three coordination polymers based on 4-methylbenzenethiolates of Zn(II) and Cd(II) and bipyridine

Using 4-methylbenzenethiolates of Zn or Cd as precursors and 4,4′-bipyridine (4,4′-bpy) as bridges, we have synthesized three new Zn(II)/Cd(II) coordination polymers, {[Cd(4,4′-bpy)₂(NCS)₂] · 2(SC₆H₄CH₃-4)₂} _n (1), {[Zn(4,4′-bpy)(SC₆H₄CH₃-4)₂] · DMF} _n (2) and {[Zn(4,4′-bpy)(SC₆H₄CH₃-4)₂] · H₂O · 0.5CH₃OH} _n (3). Compound 1 is a 2-D sheet-like square polymer in which four 4,4′-bpy ligands and two isothiocyanate ligands complete the octahedral Cd(II) coordination sphere. Compounds 2 and 3 have similar coordination around Zn(II), but have different polymer structures. In 2, Zn(II) centers are linked via a bidentate 4,4′-bipyridine to form 1-D twisted arched chains, which is a new structural type for Zn(II). Compound 3 has 1-D zigzag chains. The 2-D sheets in 1 and 1-D chains in 2 and 3 are assembled via intermolecular C–H ··· π and C–H ··· S interactions into 3-D supramolecular networks. C–H ··· S interactions are a vital factor in constructing the sulfur-containing coordination polymers. Different coordination modes and packing schemes in 1–3 show that the guest molecule has a critical influence on formation of polymers.     

Synthesis,crystal structures and photoluminescence of three new Mn(II) coordination polymers assembled from 2,4′-diphenic acid

Three new metal coordination polymers, [Mn(Hdpa)₂(4,4′-bipy)₂] _n (1), [Mn(dpa)(1,10-phen)(H₂O)] _n (2), and [Mn(dpa)(2,2′-bipy)] _n (3) (H₂dpa = 2,4′-biphenyl-dicarboxylic acid, 4,4′-bipy = 4,4′-bipyridine, 1,10-phen = 1,10-phenanthroline, and 2,2′-bipy = 2,2′-bipyridine), have been synthesized and characterized by elemental analysis, IR, and X-ray diffraction. Single-crystal X-ray analyses reveal that 2,4′-diphenic acid is a bridging ligand, exhibiting three coordination modes to link metal ions: μ ₁-η ¹: η ¹/μ ₀-η ⁰: η ⁰; μ ₂-η ²: η ⁰/μ ₁-η ¹: η ⁰; and μ ₂-η ¹: η ¹/μ ₂-η ¹: η ¹. Intermolecular hydrogen bonds in 1 lead to a zigzag chain. In 2, the 2-D supramolecular arrays extended along b-axis through π–π interactions between 1,10-phen. The dinuclear paddle-wheel second building units (SBUs) constructed by four dpa^2? ligands in 3 are linked by dpa^2? into double-strand chains. The fluorescence of H₂dpa and 1–3 are also determined.