Metal-organic coordination architectures of azole heterocycle ligands bearing acetic acid groups: Synthesis, structure and magnetic properties

Four new coordination complexes with azole heterocycle ligands bearing acetic acid groups, [Co(L¹)₂]_n (1), [CuL¹N₃]_n (2), [Cu(L²)₂·0.5C₂H₅OH·H₂O]_n (3) and [Co(L²)₂]_n (4) (here, HL¹=1H-imidazole-1-yl-acetic acid, HL²=1H-benzimidazole-1-yl-acetic acid) have been synthesized and structurally characterized. Single-crystal structure analysis shows that 3 and 4 are 2D complexes with 4⁴-sql topologies, while another 2D complex 1 has a (4³)₂(4⁶)-kgd topology. And 2 is a 3D complex composed dinuclear μ_1,1-bridging azido Cu^II entities with distorted rutile topology. The magnetic properties of 1 and 2 have been studied.     

Syntheses, structures and properties of five copper coordination polymers constructed by the triazole ligand

Reactions of different metal salts with 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole (3-abpt) gave rise to five new complexes, namely [Cu₄(CN)₄(3-abpt)₂]_n (1), [CuBr(3-abpt)]_n (2), [CuI(3-abpt)]_n (3), [Cu₃I₃(3-abpt)]_n (4) and [Cu(3-abpt)(SO₄)(H₂O)]_n (5). Compounds 1, 3, 4 and 5 are all 2D structures. Compound 1 is a double-layered polymer with an uncommon 3-nodal 3-connected (10³)(10².4)₄ network, 3 shows a 2D square layered structure, 4 is also a double-layered polymer with 2-nodal 4-connected (3.4.5.6².7)₂(3.4².5².7) network and 5 is a 2D structure which is ultimately stacked with an ABAB repeat pattern. Compound 2 is a 1D coordination polymer which exhibits a ladder-like network. The photoluminescence of 1-2 has also been investigated. The long emission lifetimes of 1-2 could be assigned to metal-to-ligand charge transfer triple excited states [MLCT].     

Quinoxaline-annelated Z-shaped quadruple-bridged orthocyclophanes: synthesis and crystal structures

A three-step synthesis of nineteen Z-shaped quadruple-bridged [6,6] and [6,4]orthocyclophanes comprising two quinoxaline-based sidewalls are described. The synthesis began from the bis-Diels−Alder adducts B1-B3 followed by ruthenium-promoted oxidation of dichloroetheno-bridges in the adducts to generate a bis-α-diketones, which were then condensed with various arene-1,2-diamines (9a-g) to construct sidewalls (phane parts) of Z-shaped quadruple-bridged orthocyclophanes D1-3, D2g, and D3g. Single-crystal structures of six orthocyclophanes (D1a, D2a, D2f, D3f, D2g-α, and D3g-α) were obtained and revealed that the C_Ar−H?π and π?π stacking interactions between N-containing arene rings are the major driving force for molecular assembly and crystal packing, in addition to the interactions involving the polar OCH₃ groups and the solvate molecules.     

Syntheses and crystal structures of diorganotin (IV) moieties with 3-hydroxy-2-pyridinecarboxylic acid

A series of new organotin (IV) complexes with 3-hydroxy-2-pyridinecarboxylic acid (3-OH-2-picH) of two types: R₂SnCl(3-OH-2-pic) (I) (R = Me 1, n-Bu 2, Ph 3, PhCH₂4) and R₂ Sn(3-OH-2-pic)₂ (II) (R = Me 5, n-Bu 6, Ph 7, PhCH₂8)have been synthesized by reactions of diorganotin (IV) dichloride with 3-hydroxy-2-pyridinecarboxylic acid in the presence of sodium ethoxide. All complexes are characterized by elemental analyses, IR spectra and NMR spectra analyses. Among them, complexes 1, 5, 6 and 7 are also characterized by X-ray crystallography diffraction analyses. Complex 1 is a 1D polymeric chain with six-coordinate tin atoms and the packing of complex 1 is stabilized by the C-H?Cl intermolecular weak interactions, thus a 2D network of 1 is formed. Complex 5 is also a 1D polymeric chain with seven-coordinate tin atoms. Complex 6 is a zigzag polymeric chain linked by Sn?O intermolecular weak interactions. Complex 7 is a monomeric complex with distorted octahedral geometry.     

Influence of the anion on the coordination mode of an unsymmetrical N-heterocyclic ligand in Cd(II) complexes: From discrete molecule to one- and two-dimensional structures

Five new 0D–2D Cd(II) complexes, [Cd₂(Hbimt)₂I₄] (1), [Cd(bimt)(Hbimt)Br]_n (2), [Cd(Hbimt)Cl₂(H₂O)]_n (3), {[Cd(Hbimt)(SO₄)(H₂O)₂]·1.5H₂O}_n (4) and [Cd(Hbimt)(SCN)₂]_n (5) (Hbimt = 2-((benzoimidazol-yl)methyl)-1H-tetrazole) have been synthesized by the reactions of Hbimt with suitable cadmium salts. Employment of different anions can influence the coordination modes of the Hbimt ligand, and accordingly result in different structures ranging from 0D to infinite 1D and 2D networks. Complex 1 displays a dimeric structure in which two Cd(II) ions are bridged through two iodine atoms. Complex 2 was caused by deprotonation of the Hbimt ligand, resulting in a 1D helical chain. While in complexes 3 and 4, Hbimt acts as a bidentate bridging ligand which joins two Cd(II) ions, leading to 1D stair-like chains. Complex 5 exhibits a 2D network structure with infinite 1D [Cd₂(SCN)₂]_n chains. The distinct structures of 1, 2, 3, 4 and 5 reveal that the anions and the versatile coordination modes of the ligand play an important role in the structures of the complexes. In addition, the luminescent properties of complexes 1–5 have been investigated in the solid state at room temperature.     

Syntheses,crystal structures,and magnetic and luminescent properties of a series of lanthanide coordination polymers with chelidamic acid ligand

A series of lanthanide(III) complexes with chelidamic acid ligand, [Ln(C₇H₂NO₅)·3H₂O]_n·nH₂O (Ln = La (1), Y (2), Sm (3), and Nd (4)), [Gd₂(C₇H₂NO₅)₃·4H₂O]_n·2nH₂O (5) and [Ce(C₇H₂NO₅)·1.5H₂O]_n (6), have been synthesized by hydrothermal method and structurally characterized by single-crystal X-ray diffraction. Complexes 1–4 are isostructural and possess 2D framework. Complex 5 contains two different Gd(III) ions linked through carboxylate group to form a 2D framework. Complex 6 exhibits a (4⁴) topology 2D network. The variable-temperature magnetic properties of 3 and 5 have been investigated. Furthermore, the photoluminescent properties of 1, 2, 3, and 5 at room temperature were also studied.     

Syntheses, structures and photoluminescence of a series of coordination frameworks based on dicarboxylate anion and bis(imidazole) ligand

In this article, ten new coordination frameworks, namely, [Ni(H₂O)₆]·(L3) (1), [Zn(L3)(H₂O)₃] (2), [Cd(L3)(H₂O)₃]·5.25H₂O (3), [Ag(L1)(H₂O)]·0.5(L3) (4), [Ni(L3)(L1)] (5), [Zn(L3)(L1)_0.5]·H₂O (6), [Cd(L3)(L1)_0.5(H₂O)] (7), [CoCl(L3)_0.5(L1)_0.5] (8), [ZnCl(L3)_0.5(L2)_0.5] (9), and [CoCl(L3)_0.5(L2)_0.5] (10), where L1 = 1,1′-(1,4)-butanediyl)bis(imidazole), L2 = 1,1′-(1,4-butanediyl)bis(2-ethylbenzimidazole) and H₂L3 = 3,3′-(p-xylylenediamino)bis(benzoic acid), have been synthesized by varying the metal centers and nitrogen-containing secondary ligands. These structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses and IR spectra. In 1, the L3 anion is not coordinated to the Ni(II) center as a free ligand. The Ni(II) ion is coordinated by water molecules to form the cationic [Ni(H₂O)₆]²⁺ complex. The hydrogen bonds between L3 anions and [Ni(H₂O)₆]²⁺ cations result in a three-dimensional (3D) supramolecular structure of 1. In compounds 2 and 3, the metal centers are linked by the organic L3 anions to generate 1D infinite chain structures, respectively. The hydrogen bonds between carboxylate oxygen atoms and water molecules lead the structures of 2 and 3 to form 3D supramolecular structures. In 4, the L3 anion is not coordinated to the Ag(I) center, while the L1 ligands bridge adjacent Ag(I) centers to give 1D Ag-L1 chains. The hydrogen bonds among neighboring L3 anions form infinite 2D honeycomb-like layers, in the middle of which there exist large windows. Then, 1D Ag-L1 chains thread in the large windows of the 2D layer network, giving a 3D polythreaded structure. Considering the hydrogen bonds between the water molecules and L3 anions, the structure is further linked into a 3D supramolecular structure. Compounds 5 and 7 were synthesized through their parent compounds 1 and 3, respectively, while 6 and 9 were obtained by their parent compound 2. In 5, the L3 anions and L1 ligands connect the Ni(II) atoms to give a 3D 3-fold interpenetrating dimondoid topology. Compound 6 exhibits a 3D three-fold interpenetrating α-Po network structure formed by L1 ligands connecting Zn-L3 sheets, while compound 7 shows a 2D (4,4) network topology with the L1 ligands connecting the Cd-L3 double chains. In compound 8, the L1 ligands linked Co-L3 chains into a 2D layer structure. Two mutual 2D layers interpenetrated in an inclined mode to generate a unique 3D architecture of 8. Compounds 9 and 10 display the same 2D layer structures with (4,4) network topologies. The effects of the N-containing ligands and the metal ions on the structures of the complexes 1-10 were discussed. In addition, the luminescent properties of compounds 2-4, 6, 7 and 9 were also investigated.     

Five novel transition metal coordination polymers with 2D/3D framework structure based on flexible H2tzda and ancillary ligand bpe

Five new transition metal coordination polymers based on H₂tzda and co-ligand bpe, {[M(tzda)(bpe)]·H₂O}_n [M=Zn(1), Cd(2), Mn(3), Co(4)] and [Ni₂(tzda)₂(bpe)₂(H₂O)]_n (5) [H₂tzda=(1,3,4-thiadiazole-2,5-diyldithio)diacetic acid, bpe=1,2-bis(4-pyridyl)ethane], have been hydrothermally synthesized and structurally characterized. Compounds 1-4 feature a 2D-layered architecture generated from [M(tzda)]_n moiety with double-chain structure cross-linking bpe spacers. However, the conformations bpe adopts in 3 and 4 are different from those in 1 and 2 due to the rotation of C-C single bond in bpe. Polymer 5 exhibits an interesting 3D porous framework with 2-fold interpenetration, in which intriguing 1D double helix chains are observed. The photoluminescence properties of 1 and 2 in the solid-state at room temperature are investigated. In addition, variable-temperature magnetic data show weak antiferromagnetic behavior in 3-5.     

Synthesis, crystal structures, and luminescent properties of two types of lanthanide phosphonates

Hydrothermal reactions of different lanthanide(III) salts with an amino-diphosphonate ligand (H₄L=C₆H₅CH₂N(CH₂PO₃H₂)₂) led to two series of lanthanide phosphonates, namely, Ln(H₂L)(H₃L) (Ln=La, 1; Pr, 2; Nd, 3; Sm, 4; Eu, 5; Gd, 6; Tb, 7). Compounds 1-5 feature a one-dimensional (1D) chain structure in which dimers of two edge-sharing LnO₈ polyhedra are interconnected by bridging phosphonate groups, such 1D arrays are further interlinked via strong hydrogen bonds between non-coordinated phosphonate oxygen atoms into a two-dimensional (2D) layer with the phenyl groups of the ligands orientated toward the interlayer space. Compounds 6 and 7 also show a different 1D array in which the LnO₆ octahedra are bridged by phosphonate groups via corner-sharing, such chains are also further interlinked by hydrogen bonds into a 2D supramolecular layer. Compounds 5 and 7 emit red and green light with a lifetime of 2.1 and 3.7 ms, respectively.     

Hydrothermal syntheses, crystal structures and properties of three coordination frameworks based on a new semirigid ligand and benzenedicarboxylate

Three novel polymers, {[Cd(m-bdc)(L)]·H₂O}_n (1), [Co(m-bdc)(L)_0.5(H₂O)]_n (2) and [Zn₅(L)₂(p-bdc)₅(H₂O)]_n (3) based on 1,1′-bis(pyridin-3-ylmethyl)-2,2′-biimidazole (L) ligand and benzenedicarboxylate isomers, have been prepared and structurally characterized. Compound 1 exhibits a 2D architecture with (4²·6)(4²·6⁷·8) topology, which is synthesized by L and 1,3-benzenedicarboxylate (m-bdc) ligands. Compound 2 is constructed from 1D chains that are linked by L ligands extending a 2D (4,4) grid. Compound 3 is a 3D framework with (4³)(4⁶·6¹⁸·8⁴) topology, which is composed of trinuclear clusters and five-coordinated metal centers joined through 1,4-benzenedicarboxylate (p-bdc) and L ligands. Moreover, the fluorescent properties of L ligand, compounds 1 and 3 are also determined.     

Syntheses, structures, and photoluminescence of three-dimensional lanthanide coordination polymers with 2,5-pyridinedicarboxylic acid

Four new open-framework coordination polymers of lanthanide 2,5-pyridinedicarboxylates, with the formulas Pr2(pydc)₃(H₂O)₂ (1), Ln(pydc)(Hpydc) (Ln=Tb (2), Er (3), Eu (5)), and Gd(pydc)(nic)(H₂O) (4) (H₂pydc=2,5-pyridinedicarboxylic acid, Hnic=nicotinic acid), have been hydrothermally synthesized and four of them (except Eu (5)) have been structurally characterized. Complex 1 consists of two types of ligand-binding modes contributing to link the PrO₇N(H₂O) polyhedral chains to three-dimensional (3D) open-framework architecture. Complexes 2 and 3 are isostructural and feature unique 3D cage-like supramolecular frameworks remarkably different from that of 1, owing to the different ligand-bridging pattern. Complex 4, however, has the distinct 3D open-framework architecture due to the presence of unexpected nicotinate ligands, which may be derived from pydc ligands via in-situ decarboxylation under the hydrothermal condition.     

Synthesis, structures, luminescent and magnetic properties of four coordination polymers with the flexible 1,3-phenylenediacetate ligands

Four coordination polymers, [Zn(pda)(bpy)(H₂O)]_n·nH₂O (1), [Cd(pda)(prz)(H₂O)]_n (2), [Co₃(μ₃-OH)₂(pda)₂(pyz)]_n·2nH₂O (3) and [Pr₂(pda)₃(H₂O)₂]_n (4) (H₂pda=1,3-phenylendiacetic acid, bpy=4,4′-bipyridine, prz=piperazine and pyz=pyrazine) have been hydrothermally synthesized and characterized. Complex 1 is a 1D wheel-like chain structure, which is further extended into a 3D metal-organic supramolecular framework by H-bonds and π-π stacking interactions. Complex 2 is a 1D ladder-like chain structure, which is also further extended into a 3D metal-organic supramolecular framework by H-bonds. Complex 3 possess a 2D sheet structure with infrequent two pairs of double-helix chains. Complex 4 features a 3D structure. Both 1 and 2 display strong blue fluorescent emission at room temperature. Magnetic susceptibility measurements of complexes 3 and 4 exhibit antiferromagnetic interactions between the nearest metal ions, with C=9.99 and 3.43 cm³ mol⁻¹ K, and θ=−23.9 and −46.3 K, respectively.     

Group 12 metal coordination polymers of 1,2-bis(diphenylphosphino)ethane dioxide: A persistent 1D chain motif and consequent 2D and 3D architectures

A series of group 12 metal coordination polymers with 1,2-bis(diphenylphosphino)ethane dioxide (dppeO₂), {[ZnCl₂(μ-dppeO₂)]·CH₂Cl₂}_n (1·CH₂Cl₂), [ZnBr₂(μ-dppeO₂)]_n (2), [CdI₂(μ-dppeO₂)]_n (4), [(HgI₂)₂(μ-dppeO₂)]_n (5), [Zn(SCN)(μ-SCN)(μ-dppeO₂)]_n (6), and [Cd(NO₃)(μ-SCN)(μ-dppeO₂)]_n (7), have been synthesized and structurally characterized. The structures of the compounds are all based on an infinite 1D chain constructed by four-coordinate metal ions and dppeO₂ ligands adopting the trans bridging coordination fashion. In the coordination polymers 1, 2 and 4, the halide ions act as terminal ligands, leading to discrete 1D chains with alternative MX₂ and dppeO₂ repeating units. The mercury compound 5 features a unique square-wave-like inorganic chain –[Hg(1)–I–Hg(2)–I]–, and the 1D HgI₂(μ-dppeO₂) chains are further linked by HgI₂ bridges to form a 3D network. In the thiocyanate-containing compounds 6 and 7, the 1D chains are linked by one (6) or two (7) bridging SCN^– ions to result in 2D layered structures. Solid-state emission spectra of the coordination polymers show different variations compared to the free dppeO₂ ligand, such as enhancement (1, 2, 6 and 7), shift (3 and 4) and quenching (5) upon metal coordination.     

Syntheses, crystal structures and properties of Co(II) complexes with N,N′-bis(3-pyridylmethyl)-1,4-benzenedimethyleneimine (bpb), and Cd(II), Hg(II) complexes with reduced bpb

Five novel coordination polymers, [Co(bpb)₂Cl₂] (1), [Co(bpb)₂(SCN)₂] (2), [Cd(H₄bpb)_0.5(dmf)(NO₃)₂] (3), [Cd₂(H₄bpb)Br₄] (4), and [Hg₂(H₄bpb)I₄] (5) [bpb=N,N′-bis(3-pyridylmethyl)-1,4-benzenedimethyleneimine, H₄bpb=N,N′-bis(3-pyridylmethyl)-1,4-benzenedimethylamine], were synthesized and their structures were determined by X-ray crystallography. In the solid state, complex 1 is a 1D hinged chain, while 2 has 2D network structure with the ligand bpb serving as a bridging ligand using its two pyridyl N atoms. The imine N atoms keep free of coordination and bpb acts as a bidentate ligand in both 1 and 2. Complexes 3, 4, and 5 with reduced bpb ligand, i.e. H₄bpb, show similar 2D network structure, in which ligand H₄bpb serves as a tetradentate ligand. Thermogravimetric analyses for complexes 1-5 were carried out and found that they have high thermal stability. The magnetic susceptibilities of compounds 1, 2 were measured over a temperature range of 75-300 K.     

Synthesis, crystal structures and photoluminescent properties of lanthanide supramolecular complexes with 4-oxo-1(4H)-quinolineacetate

Five new lanthanide supramolecular complexes, namely, [Sm(oqa)₂(H₂O)₄]₂ (ClO₄)₂·(bpy)₂ (1), [Ln(oqa)₃]·2H₂O [Ln=Sm(2), Gd(3)] and [Ln(oqa)₂(NO₃)(H₂O)] [Ln=Pr(4), Eu(5)] (oqa=4-oxo-1(4H)-quinolineacetate, bpy=4,4′-bipyridine), have been synthesized under hydrothermal conditions. These complexes exhibit three typical structure features. Complex 1 possesses a dimeric structure, which is further connected together through hydrogen bonds and π-π attractions, forming a 3D supramolecular framework. Compounds 2-3 are isomorphous and contain 1D ring-like chains, which are further interconnected by the oqa ligands into 2D sheet-like structures. 4 and 5 exhibit eight-connected 3D network of 4²⁴·6⁴-bcu topology. The various coordination modes of carboxylate ligands and the selection of the counterions have clearly affected the topological structures. Furthermore, the solid-state luminescent properties of complexes 1, 2 and 5 were investigated at room temperature and they show intense, characteristic emissions in the visible region.     

Modelling the use of lanthanides(III) as probes at calcium(II) binding sites in biological systems: Preparation and characterization of neodymium(III) and calcium(II) malonamato(-1) complexes

A bioinorganic approach into the problem of the isomorphous substitution of calcium(II) by lanthanide(III) ions in biological systems is discussed. Reactions of malonamic acid (H₂malm) with Ca^II and Nd^III sources under similar conditions yielded the compounds [Ca(Hmalm)₂]_n (1), [Nd(Hmalm)₂(H₂O)₂]_n(NO₃)_n (2) and [Nd(Hmalm)₂(H₂O)₂]_nCl_n·2nH₂O (3·2nH₂O). Their X-ray crystal structure data show that the malonamate(-1) ligand presents two different ligation modes and coordinates through the two carboxylate and the amide-O atoms, thus bridging three Ca^II ions in 1 and two Nd^III ions in 2 and 3·2nH₂O. Complex 1 is a 3D coordination polymer based on neutral repeating units, whereas 2 and 3·2nH₂O are 1D coordination polymers based on the same cationic repeating unit. Hydrogen bonding interactions further stabilize the 3D framework structure of 1 and assemble the 1D chains of 2 and 3·2nH₂O into 3D networks. The three complexes were characterized spectroscopically (IR, far-IR, and Raman) and the thermal decomposition of 2 and 3·2nH₂O was monitored by TG/DTA and TG/DTG measurements. Variable-temperature magnetic susceptibility data for 2 are also reported. The bioinorganic chemistry relevance of our results is discussed.     

Complanadine B, obscurumines A and B, new alkaloids from two species of Lycopodium

A new dimer of C₁₆N₂ type alkaloid, complanadine B (1), and two new C₁₆N type alkaloids, obscurumines A (2) and B (3), have been isolated from the club moss Lycopodium complanatum and L. obscurum, respectively. The structures and stereochemistry of 1-3 were elucidated by combination of 2D NMR spectra and chemical transformation. Complanadine A (4) isolated together with 1 induced secretion of neurotrophic factors from human astrocytoma cells.     

Structural diversity of di and triorganotin complexes with 4-sulfanylbenzoic acid: Supramolecular structures involving intermolecular Sn?O, O-H?O or C-H?X (X = O or S) interactions

Twelve new organotin complexes with 4-sulfanylbenzoic acid of two types: R_nSn[S(C₆H₄COOH)]_4−n (I) (n = 3: R = Me 1, n-Bu 2, Ph 3; PhCH₂4; n = 2: R = Me 5; n-Bu 6, Ph 7, PhCH₂8) and R₃Sn(SC₆H₄COO)SnR₃ · mEtOH (II) (m = 0: R = Me 9, n-Bu 10, PhCH₂12; m = 2: R = Ph 11), along with the 4,4′-bipy adduct of 9, [Me₃Sn(SC₆H₄COO)SnMe₃]₂(4,4-bipy) 13, have been synthesized. The coordination behavior of 4-sulfanylbenzoic acid is monodentate in 1-8 by thiol S atom but not carboxylic oxygen atom. While, in 9-13 it behaves as multidenate by both thiol S atom and carboxylic oxygen atoms. The supramolecular structures of 6, 11 and 13 have been found to consist of 1D molecular chains built up by intermolecular O-H?O, C-H?O or C-H?S hydrogen bonds. The supramolecular aggregation of 7 is 2D network determined by two C-H?O hydrogen bonds. Extended intermolecular C-H?O interactions in the crystal lattice of 9 link the molecules into a 2D network.     

New phlegmarane-type, cernuane-type, and quinolizidine alkaloids from two species of Lycopodium

Two new phlegmarane-type alkaloids, cermizines A (1) and B (2), three new quinolizidine alkaloids, cermizine C (3) and senepodines G (4) and H (5), and a new C₁₆N₂ type alkaloid consisting of a quinolizidine and a piperidine ring, cermizine D (6), as well as two new cernuane-type alkaloids, cernuine N-oxide (7) and lycocernuine N-oxide (8), have been isolated together with cernuine (9) and lycocernuine (10) from the club moss Lycopodium cernuum and L. chinense. The relative stereochemistry of 1-4 and 6, and the absolute stereochemistry of 5, 7, and 8 were elucidated by combination of NOESY correlations, modified Mosher's method, chemical transformations, and computational methods. Cermizine D (6) might be a biosynthetic intermediate of cernuane-type alkaloids such as 7-10.     

Total synthesis of eurypamides, marine cyclic-isodityrosines from the Palauan sponge Microciona eurypa

Total synthesis of eurypamides A, B, and D, 1, 2, and 4, has been successfully accomplished. The Tl(NO₃)₃ (TTN) oxidation of the halogenated bisphenols, 14a, 14b, 24, and 43, effected regio-controlled cyclization to provide the corresponding diaryl ethers, 15a, 15b, 25, and 46. This investigation revealed a structural revision of eurypamide A as to possess (2″S,3″R,4″S)-configuration (47), along with the spectral data of pure 2 and 4, which were previously characterized in a mixture.