A Novel 3D Twofold Zn(Ⅱ) Coordination Polymer Constructed by Mixed Flexible Ligands: Synthesis,Crystal Structure and Fluorescence Property

A new Zn(Ⅱ) coordination polymer, {[Zn(1,3-bip)(oba)]·0.5H_2O}n(1),1,3-bip =1,3-bis(imidazole)propane, H_2oba=4,4?-oxybis(benzoate)), have been synthesized and characterized by single-crystal X-ray diffraction, powder XRD, FTIR, TGA and elemental analysis techniques. The single-crystal X-ray diffraction reveals that complex 1 shows a 3D→3D twofold interpenetrating network that can be described as a 4-connected uninodal net with(65.8) topology. In addition, the photoluminescence property of complex 1 was also investigated at room temperature.     

Two Co(Ⅱ) Complexes Constructed from 1-(3,5-Dicarboxybenzyl)-3,5-pyrazole Dicarboxylic Acid:Syntheses,Structures and Magnetic Properties

Two new complexes[Co_2(L)(4,4′-bip)(H_2O)_3]_n (1) and{[Co(L′)_2(phen)]·2H_2O)}_n (2)(H_4L=1-(3,5-dicarboxybenzyl)-3,5-pyrazole dicarboxylic acid,H_3L′=1-(3,5-dicarboxybenzyl)-3-pyrazole carboxylic acid,4,4′-bip=4,4′-bis(1-imidazolyl)biphenyl,phen=1,10-phenanthroline) were synthesized.Complexes 1 and 2have been characterized by IR spectrography,X-ray single-crystal diffraction,elemental analysis and thermogravimetry.1 crystallizes in monoclinic system,space group P2_1/c.Complex 2 crystallizes in monoclinic system,space group I2/a.It is remarkable that in situ hydrothermal decarboxylation was observed during preparing complex 2.In addition,magnetic analysis indicates that antiferromagnetic interaction exists among Co(Ⅱ) ions in complexes 1 and 2.     

Synthesis,Crystal Structure,and Luminescence of a 1D Chain Cd(Ⅱ) Polymerwith 3,3?,5,5?-Benzene-1,3-biyl-tetrabenzoic Acid

A new Cd(Ⅱ) coordination polymer, [Cd(H_2btb)(bpy)]_n(1, H_4btb = 3,3?,5,5?-benzene-1,3-biyl-tetrabenzoic acid, bpy = 2,2?-bipyridine), has been synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric(TG) analyses and single-crystal X-ray diffraction techniques. Complex 1 belongs to monoclinic system, C2/c space group. In 1, two carboxylate groups of the H_4btb ligand adopt bidentate chelating and μ_2-η~1:η~1 coordination modes, respectively, bridging the Cd(Ⅱ) atoms to generate a 1D polymeric ribbon. In addition, the photoluminescence property of complex 1 has also been studied.     

Auxiliary Ligand-tuned Structural Variation of Cd(Ⅱ) Coordination Polymers: Synthesis,Crystal Structures and Luminescent Properties

Two new Cd(Ⅱ) coordination polymers, [Cd(PT)(1,4-BDC)0.5]_n(1) and [Cd(PT)(1,3-BDC)0.5]_n(2)(HPT = 3-(pyridin-2-yl)-1,2,4-triazole, 1,4-H2 BDC = 1,4-benzenedicarboxylic acid, 1,3-H2 BDC = 1,3-benzenedicarboxylic acid), have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction as well as elemental analysis and IR. Complexes 1 and 2 are both three-dimensional coordination polymers with two-dimensional sheet structures bridged by the deprotonated carboxylate ligands. In 1, 1,4-BDC~(2-) bridges the layered network to generate a quadrangular framework, and 2 owns a sexangular framework, which was caused by the different steric hindrance between 1,4-BDC~(2-) and 1,3-BDC~(2-). Their thermal stabilities and photoluminescent properties have been also investigated.     

A Cd(Ⅱ) Coordination Polymer with cds Topology Constructed by Polycarboxylate and Imidazole-containing Ligand

A new Cd(Ⅱ) coordination polymer,{[Cd(pda)(bimb)]·(H_2O)_(0.5)}_n(1,H_2pda=1,3-phenylenediacetic acid,bimb = 4,4-bis(1-imidazolyl)biphenyl),has been synthesized and characterized by elemental analysis,IR spectroscopy,powder X-ray diffraction(PXRD) analyses and single-crystal X-ray diffraction techniques. Complex 1 shows a 4-connected two-fold interpenetrated three-dimensional(3-D) cds topology. In additional,photoluminescent properties of 1 and its dehydrated product have also been studied.     

Synthesis,Crystal Structure and Magnetic Behavior of a Novel Cd(Ⅱ) Complex with Four Nitroxide Radicals

A novel diamagnetic-metal Cd(Ⅱ) complex with four nitroxide radicals[Cd(IM4Py)4Cl2](IM4Py=2-(4'-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl) was synthesized and characterized by elemental analyses,IR spectra,UV-Vis spectra and X-ray single crystal diffraction.The complex crystallized in triclinic space group P1 with a=0.93285(14) nm,b=1.16827(18) nm,c=1.3660(2) nm,α=112.759(2)°,β=104.524(2)°,γ=92.008(3)°,V= 1.3143(3) nm3,Z=1,Dc=1.335 g/cm3,the final R1=0.0423 and wR2=0.1009.In the title complex,each Cd(Ⅱ) ion adopting a distorted octahedral geometry is coordinated by two Cl-anions and four pyridyl-N atoms from four IM4Py ligands.The magnetic measurements show the weak antiferromagnetic interactions between the nitroxide radicals.     

Synthesis, Structure and Thermochromic Properties of a Copper(Ⅱ) Complex Based on Naphthyl Carboxylate and Benzimidazolyl Ligands

One novel copper(Ⅱ) complex, [Cu(NAA)2(bim)2]·H2O (1, HNAA = a-naphthylacetic acid, bim = benzimidazole) has been synthesized and characterized by X-ray single-crystal diffraction analysis, elemental analysis, and IR spectrum. It crystallizes in monoclinic, space group C2/c with a = 1.15969(12), b = 1.9757(2), c = 1.45763(16) nm, β = 104.712(2)°, V = 3.2298(6) nm3, Z = 4, C38H32N4O5Cu, Mr = 688.22, Dc = 1.418 g/cm-3, μ = 0.729 mm-1, S = 1.039, F(000) = 1428, the final R = 0.0380 and wR = 0.0912 for 2849 unique reflections. In 1, two carboxylate and two benzimidazole ligands coordinate to the central Cu(Ⅱ) atom by a bidentate chelate mode. Interesting, reversible thermochromic properties of 1 can be observed and investigated by thermal analysis method.     

Structure and Fluorescence Property of a 2D Bilayer Cd(Ⅱ) Coordination Polymer Induced by H-bonding and π-π Interaction

Solvothermal reactions of 4,4'-oxybis(benzoic acid) (H2oba) with 1,3-dipyridyl benzene (1,3-dpb) produced a two-dimensional (2D) cadmium(Ⅱ) coordination polymer {[Cd(oba)(dpb)]·H2O}n (1). The complex was characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. It crystallizes in the monoclinic system, space group C2/c with a = 13.6692(9), b = 25.9647(17), c = 8.7912(6) , α = 125.0370(10), γ = 2544.7(3)°, V = 2544.7(3) 3, C30H22N2O6Cd, Mr = 618.91, Dc =1.609 g/cm3, F(000) = 1248, μ = 0.904 mm-1 and Z = 4. The neighboring Cd(Ⅱ) ions are linked by oba2-anions and 1,3-dpb to form an infinitely 2D wavelike sheet, and two such 2D sheets are interlocked with each other by H-bonding to form a 2D → 2D structure. The adjacent two groups of interlocked structures are further linked to form a bilayer 2D supramolecular network by π-π interactions. In addition, the fluorescence property of 1 was also studied.     

Structure and Photophysical Properties of a Chiral 4-Fold Interpenetrated Zn(Ⅱ) Coordination Polymer Tuned by 4,4'-(Hexafluoroisopropylidene)bis(benzoic acid) and 1,3-Di(pyridineyl)benzene

A new three-dimensional(3D) chiral metal-organic coordination polymer, [Zn(dpb)(hfipbb)]n, was obtained under hydrothermal conditions by 1,3-di(pyridineyl)benzene(dpb) and 4,4?-(Hexafluoroisopropylidene)bis(benzoic acid)(H_2hfipbb). The as-prepared sample was characterized by single-crystal X-ray diffraction, PXRD, elemental analysis, IR spectroscopy and TGA analysis. The title coordination polymer crystallizes in orthorhombic, space group P21212, with a=21.923(4), b=23.594(4), c=7.3042(13) ?, V=3778.1(12) ?~3, Dc=1.209 g/cm~3, Mr=687.90, F(000)=1328, μ=0.713 mm~(-1) and Z=4. The compound contains two types of helical chains [Zn(hfipbb)]n and [Zn(dpb)]n which are linked with each other to generate a 3D framework by sharing the same Zn(Ⅱ) cations. It displays a 4-fold interpenetrated 3D framework. In addition, the luminescence, fluorescence lifetime and the second harmonic generation(SHG) efficiency properties in the solid state have been studied.     

Synthesis,Crystal Structure,Fluorescent Property and DFT Calculations of a New Zn(Ⅱ) Complex Based on 3-(2-Pyridyl)-5-(4-pyridyl)-1H-1,2,4-triazole

A new coordination compound Zn(2,4?-bpt)2(H_2O)(1) based on the versatile ligand 2,4?-Hbpt(2,4?-Hbpt = 3-(2-pyridyl)-5-(4-pyridyl)-1H-1,2,4-triazole) was prepared by hydrothermal reactions. The structure of complex 1 has been characterized by X-ray single-crystal diffraction, elemental analysis, X-ray powder diffraction, IR spectrum analysis and thermogravimetric analysis. Single-crystal X-ray diffraction analysis indicates that the complex belongs to monoclinic system, space group C2/c with a = 23.877(3), b = 0.7483(9), c = 1.2492(2) ?, b = 92.681(2)°, V = 2230.6(4) ?3, Z = 4, Dc = 1.572 g/cm~3, m = 1.143 mm~(-1), Mr = 527.85 and F(000) = 1080. The final R = 0.0581 and w R = 0.0898 with I 2s(I). 1 is a 0D motif which is connected by hydrogen bonds to form a corrugated 1D pattern. In addition, 1 shows strong photoluminescent emissions in the solid state at room temperature which can be used as potential optical materials. Theoretical calculations based on density functional theory(DFT) were employed in order to explicate the stability and chemical reactivity of 2,4?-Hbpt with different conformations. The results indicated that conformation I is more stable and prior to coordination in the reactions.     

A New Porous Cadmium(Ⅱ) Complex Based on 1,10-Phenanthroline Derivative and Dicarboxylate:Syntheses,Structure, Thermal Behavior and Luminescence

A new porous Cd(Ⅱ) coordination compound, namely, [Cd(bpdc)(L)2]·3H2O(1, L = 11-fluoro-dipyrido[3,2-a:2,3-c]phenazine and bpdc = 1,1-biphenyl-2,2-dicarboxylate) was synthesized under hydrothermal conditions, and characterized by single-crystal X-ray diffraction. It crystallizes in tetragonal, space group P4122 with a = 9.8486(4), b = 9.8486(4), c = 45.925(4)A, V = 4454.5(5) 3, Z = 4, C50H29 Cd F2N8O7, Mr = 1004.21, Dc = 1.497 g/cm3, F(000) = 2028, μ(Mo Ka) = 0.562 mm-1, R = 0.0566 and w R = 0.1585. Each Cd(Ⅱ) atom is coordinated by one bpdc anion and two L ligands to give a discrete molecule. Neighboring discrete molecules are stacked by π-π interactions among L ligands, resulting in an interesting 1D supramolecular chain. Moreover, the 1D supramolecular chains are packed with each other to give a porous structure, in which an infinite channel is filled with water molecules. In addition, the thermal behavior and luminescent property of 1 have also been studied.     

Synthesis,Crystal Structure,Theoretical Calculation,and Photophysical Property of a New Cd(Ⅱ) Complex Based on N-heterocyclic Ligand and Isophthalic Acid

A new metal-organic coordination complex[Cd(imp)(m-bdc)]_n (1,ipm=5-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-2-methoxyphenol,m-bdc=isophthalic acid) has been synthesized by hydrothermal reaction and characterized by elemental analysis,thermogravimetric (TG) analysis,infrared spectrum (IR) and single-crystal X-ray diffraction.Complex 1 crystallizes in monoclinic,space group C2/c with a=15.373(5),b=16.719(5),c=19.406(6)A,β=106.995(5)°,V=4770(2)A³,C₂₈H₁₈Cd N₄O₆,M_r=618.86,D_c=1.724 g/cm³,μ(Mo Kα)=0.971 mm^–1,F(000)=2480,Z=8,the final R=0.0391 and w R=0.1044 for 4701 observed reflections (I>2σ(I)).Single-crystal X-ray diffraction reveals that 1 exhibits a one-dimensional (1D) double-chain architecture,and the H-bond intersections link the 1D double-chain architecture into a 2D layer structure.TG analysis shows clear courses of weight loss,which corresponds to the decomposition of different ligands.We also study the luminescent properties of complex 1.In addition,to elucidate the essential electronic characters of this complex,theoretical calculation analysis was performed by the PBE0/LANL2DZ method in Gaussian 03 Program.     

Solvothermal Synthesis,Crystal Structure and Luminescent Property of a Two-dimensional Lead(Ⅱ) Compound:[Pb(bmzbc)_2]_n

A two-dimensional coordination polymer, [Pb(bmzbc)_2]_n(1)(Hbmzbc =4-benzimidazole-1-yl-benzoic acid), has been synthesized by the solvothermal reaction of Pb(NO_3)_2 with Hbmzbc at 120 ℃ in ethanol solvent. Compound 1 has been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetry analysis, and IR spectrum. Compound 1 crystallizes in the orthorhombic system, space group Pccn, with a = 12.5801(7), b = 20.0795(11), c = 9.1830(6) ?, V = 2319.6(2) ?~3, Z = 4, C_(28)H_(18)N_4O_4Pb, M_r = 681.65, D_c = 1.952 g/cm~3, μ = 7.319 mm~(-1), F(000) = 1312, the final R = 0.0336 and wR = 0.0965 for 1699 observed reflection with I 2σ(I). In 1, the bmzbc~– ligands bridge the Pb(Ⅱ) ions to generate a 2-D sheet with(4, 4) topology. The complex exhibits turquoise photoluminescent emission with a maximum at 480 nm upon excitation at 300 nm.     

Syntheses,Crystal Structures,and Photoluminescent Properties for One New Cd(Ⅱ) CP Based on 3,5-Bis(4?-carboxy-phenyl)-1,2,4-triazole and 1,4-Bis(imidazol-1-ylmethyl)benzene

One new coordination polymer(CP) [Cd(bct)(bib)]·2(H_2O)(1), based on 3,5-bis(4?-carboxy-phenyl)-1,2,4-triazole(H2 bct) and 1,4-bis(imidazol-1-ylmethyl)benzene(bib), has been synthesized by hydrothermal method, and its structure was determined and characterized by single-crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy, and thermogravimetric analysis. The crystal structure of CP 1 is a three-dimensional framework with(3,5)-connected topology, where the bct ligands adopt a μ3-kO,kO,kO coordination mode connecting with three Cd centers and the bib ligands adopt a μ2-k N,k N coordination mode bridging two Cd ions. It crystallizes in monoclinic system, space group C2/c, with a = 2.6838(4), b = 1.24221(17), c = 1.8011(2) nm, β = 102.939(2)o, V = 5.8522(13) nm3, Z = 8, C30 H27 CdN7O6, Mr = 694.00, Dc = 1.566 g/cm~3, F(000) = 2784, S = 1.055, R = 0.0294 and wR = 0.0731. Furthermore, solid-state photoluminescence measurements show that CP 1 produces strong emissions at room temperature.     

Hydrothermal Synthesis,Crystal Structure and Surface Photo-electric Properties of a New Nickel(Ⅱ) 3-D Metalorganic Framework Constructed from the Rigid 1,4-Bis(imidazol-1-yl) benzene Ligand

A new 3-D nickel(Ⅱ) metal-organic framework(MOFs) with formula [Ni(bib)_2(SO_4)]_n(1), where bib = 1,4-bis(imidazol-1-yl)benzene, has been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis and surface photovoltage spectroscopy(SPS). Complex 1 crystallizes in monoclinic system, space group C2/c with a = 19.5988(6), b = 9.7531(3), c = 11.8146(4) ?, β = 96.185(3)°, V = 2245.20(12) ?~3, C_(24)H_(20)N_8NiO_4S, M_r = 575.25, D_c = 1.702 g/cm~3, Z = 4, F(000) = 1184, μ = 1.011 mm-1, the final R = 0.0293 and w R = 0.0702. X-ray diffraction analyses indicated that the center Ni~(2+) ion is six-coordinated with an O_2N_4 donor set of two μ_2-SO_4~(2–) and four bib ligands, resulting in an ideal octahedral geometry. Topological analysis on complex 1 considers each Ni~(2+) as a 6-connected node, while bib and sulfate ion as linkers, giving an α-Po topology with short Schl?fli symbol 412·63. In the crystal packing, the components interact with pairs of intermolecular C–H×××O hydrogen bonds. The SPS of 1 indicates that there are positive response bands in the range of 300~600 nm showing photo-electric conversion properties.     

A Copper（Ⅱ）-cadmium（Ⅱ） Heterometallic Hexanuclear Complex：[Cd_4Cu_2（pdc）_4（H_2O）_（14）]（H_3pdc=3,5-Pyrazoledicarboxylic Acid）

The title complex 1,[Cd 4 Cu 2 (pdc) 4 (H 2 O) 14 ] (H 3 pdc=3,5-pyrazoledicarboxylic acid),has been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction.Complex 1 crystallizes in triclinic,space group P1 with a=0.67235(10),b=1.27935(18),c=1.28569(17) nm,α=112.633(2),β=102.971(3),γ=97.089(2)o,V=0.9673(2) nm 3,C 20 H 32 Cd 4 Cu 2 N 8 O 30,M r=1441.22,D c=2.474 g/cm 3,μ(MoKα)=3.356 mm 1,F(000)=698,S=1.003,Z=1,the final R=0.0471 and wR=0.0748 for I > 2σ(Ⅰ).In 1,two deprotonated 3,5-pyrazoledicarboxylic acids (pdc 3),one copper(Ⅱ) ion and one cadmium(Ⅱ) ion firstly form a pyrazole-bridged Cu II Cd II dinuclear unit,two of which related by an inversion center are connected by another two cadmium(Ⅱ) ions through chelating carboxylate groups to construct the copper(Ⅱ)-cadmium(Ⅱ) heterometallic hexanuclear complexes.Plenty of hydrogen bond interactions existing in the system further lead to a three-dimensional (3D) supramolecular framework.     

Synthesis,Structure and Characterization of a Cd(Ⅱ) Polymer Based on 6-Hydroxynicotinic Acid

A new 2D layered Cd(II) coordination polymer,[Cd(HnicO)(phen)(NO3)]n 1(H2nicO = 6-hydroxynicotinic acid,phen = 1,10-phenanthroline),has been hydrothermally synthesized and characterized by elemental analysis,IR,and single-crystal X-ray diffraction.It crystallizes in the monoclinic system,space group P21/c with a = 11.1107(2),b = 13.7639(2),c = 12.1457(4) ,β = 108.695(1)°,V = 1759.40(7) 3,Z = 4,Mr = 492.72,F(000) = 976,Dc = 1.860 g/cm3,μ = 1.289 mm-1,the final R = 0.0205 and wR = 0.0550 for 3663 observed reflections(I > 2σ(I)).X-ray single-crystal structural analyses reveal that in complex 1,the H2nicO ligands and Cd(II) nodes define the structure to be(4,4) 2D nets which are further assembled into the final 3D architecture via supramolecular interactions such as hydrogen bonds and aromatic interactions.Moreover,the solid-state luminescent study shows the title polymer possesses intense luminescent property at room temperature.     

Hydrothermal Synthesis and Crystal Structure of a New 2D Zinc（Ⅱ） Coordination Polymer with 2-Aminoethanesulfonic Acid

A new 2D Zn(Ⅱ) coordination polymer [Zn(TAU)2]n (1, HTAU=2-aminoethane- sulfonic acid) constructed by 2-aminoethanesulfonic acid ligand has been hydrothermally synthesized by the reaction of Zn(CH3COO)2 and 2-aminoethanesulfonic acid with a 1:2 mole ratio and characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy and thermogravimetric analysis. Crystal structural analysis reveals it crystallizes in monoclinic, space group P21/c with a=8.672(4), b=6.523(3), c=9.134(5) , β=115.441(5)°, V=466.6(4) 3, Mr=313.65, Z=2, Dc=2.232 Mg·m-3, F(000) =320, μ(MoKα)=3.091 mm-1, the final R=0.0358 and wR=0.0919 for 2026 observed reflections with Ⅰ > 2σ(Ⅰ). In the structure, each zinc(Ⅱ) ion is coordinated in a slightly distorted octahedron, and each μ3-TAU– acts as a bridge to bond three neighboring Zn(Ⅱ) ions to form an infinite 2D network structure.     

Synthesis,Structure and Highly Enhanced Phosphorescence of a Cadmium (Ⅱ) Coordination Polymer Assembled with 1,4-Naphthalenedicarboxylic Acid and 2-Propylimidazole

One cadmium(Ⅱ)coordination polymer[Cd(1,4-NDC)(PPIM)₂]_n(1,1,4-H₂NDC=1,4-na-phthalenedicarboxylic acid,PPIM=2-propylimidazole),has been synthesized under hydrothermal conditions and structurally characterized by elemental analysis,TGA and X-ray single-crystal diffraction.Complex 1 crystallizes in monoclinic with space group P2₁/n,a=8.8292(2),b=16.6936(4),c=16.7869(4)?,β=99.701(2)°,V=2438.86(10)?³,Z=4,Dc=1.489 Mg/m³,F(000)=1112,μ=0.932 mm^–1,S=1.076,the final R=0.0360 and wR=0.0850.In 1,the 1,4-NDC ligand bridges the Cd(Ⅱ)to form a 1D infinite chain,which are connected through N–H···O hydrogen bond to form a 2D layer then to an overall 3D supramolecular structure.The time-resolved measurements indicate that 1 shows highly prolonged phosphorescent lifetime about 452 times in comparison with that of pristine PPIM ligand.Single-crystal analysis and theory calculations indicate that strong coordination bonds and complete separation of HOMOs and LUMOs in the rigid matrix of 1 promote the long-last phosphorescence emission.     

Synthesis, Characterization and Crystal Structure Determination of a Thiocyanato Bridged One-dimensional Polymeric Complex of Cadmium(Ⅱ)

A new one-dimensional polymeric complex [Cd(SCN)2(H2O)]L (L = N,N?-bis(furan- 2-ylmethylene)hydrazine) has been synthesized and characterized by IR, UV spectra, TG-DTA technique and single-crystal X-ray diffraction analysis. It crystallizes in triclinic, pace group P1 with a = 5.9268(8), b = 10.8678(15), c = 13.3671(19) , α = 109.295(2), β = 95.092(2), γ = 97.8580(10)°, V = 796.70(19) 3, Z = 2, C12H10CdN4O3S2, Mr = 434.76, μ = 1.648 mm–1, Dc = 1.812 g/cm3, F(000) = 428, R = 0.0308 and wR = 0.0769. The crystal structure reveals that the structure of [Cd(SCN)2(H2O)]n features di-μ-1,3-thiocyante bridges and 1D chains. The octahedrally coordinated Cd atom is surrounded by one oxygen atom from water molecule, three S atoms and two Natoms from five di-μ-1,3 thiocyanato bridges. The Cd atoms are connected by two di-μ-1,3 thiocyanato bridges with the Cd(1)…Cd(1A) separation of 4.239(1)  and Cd(1)…Cd(1B) of 5.852(1). In addition, the one-dimensional straight chain structure is further connected by multiform intermolecular N-H…O hydrogen bonds and π…π interactions to form a three-dimensional supramolecular structure.