Synthesis and Crystal Structure of a New Dinuclear Manganese(Ⅱ) Manganese(Ⅲ) Complex of a Macrocyclic Ligand

A mixed-valence dinuclear manganese complex, [Mn ⅡMn ⅢL](ClO 4)·1/2MeOH, where L is a macrocyclic ligand derived from the cyclocondensation of sodium 2,6-diformyl-4-methylphenolate with N,N-bis(2-aminoethyl)-2-hydroxybenzyl amine, was obtained and its structure was determined by X-ray diffraction. The orange crystal is a monoclinic system with space group P2 1/c and lattice parameters a=1.1617(4), b=1.4005(3), c=1.4641(3) nm, β=113.03(2)°, and Z=2. The crystal structure shows that each pendant-arm is bonded in a bidentate fashion to the adjacent metal atom and that both the arms are on the same side of the macrocycle. The two Mn atoms are bridged by two μ 2-phenoxy oxygen atoms of the tetra-imine macrocycle, and each Mn atom, locating in a trigonal prismatic coordination environment(N 3O 3), is six-coordinated by the two imine nitrogen atoms, one tertiary nitrogen atom and a pendant phenol moiety apart from the two oxygen atoms.

Syntheses and Crystal Structures of Two Cyano-bridged Bimetallic Complexes [Ce(DMSO)_4(H_2O)_3Fe(CN)_6]·H_2O and [La(DMSO)_4(H_2O)_3Co(CN)_6]·H_2O(DMSO = Dimethylsulfoxide)

Two new bimetallic cyano-bridged complexes [Ce（DMSO）4（H2O）3Fe（CN）6]·H2O 1 and [La（DMSO）4（H20）3Co（CN）6].H20 2 have been prepared by the ball milling reaction method and structurally characterized by X-ray single-crystal structure analyses. Crystallographic data for 1： C14H32CeFeN6O8S4, Mr= 736.67, monoclinic, space group P2 1/n, a = 14.952（1）, b = 13.7276（9）, c = 15.392（1） A, β= 108.288（1）°, V = 2999.6（4） A3, Z = 4, Dc= 1.631 g/cm^3, g = 2.304 mm^-1, F（000） = 1480, R = 0.0593 and wR = 0.1611; and those for 2： C14H32CoLaN6O8S4, Mr=738.54, monoclinic, space group P21/n, a = 14.945（3）, b = 13.731（3）, c = 15.300（3） A, β= 107.806（1）°, V= 2989.3（11） A^3, Z= 4, Dc = 1.641 g/cm^3, μ = 2.288 mm^-1, F（000） = 1480, R = 0.0383 and wR = 0.1132. In both complexes the lanthanide ion is eight-coordinated in a square antiprism arrangement, and the Fe（Ⅲ） or Co（Ⅲ） ion in a nearly regular octahedral environment The [LnM（CN）6（DMSO）4（H2O）3]·H2O （Ln = Ce and M = Fe for 1; Ln = La and M = Co for 2） species are held together via hydrogen bonds by coordinated water molecules, lattice water molecules and nitrogen atoms of cyanide groups to form a three-dimensional framework.

Synthesis and Crystal Structure of a Cyano-bridged Bimetallic Complex[La(betaine)_2(H_2O)_6Fe(CN)_6]·2H_2O

The title complex [La(betaine)2(H2O)6Fe(CN)6]?2H2O (betaine = (CH3)3NCH2CO2) has been synthesized and characterized by X-ray single-crystal structure analysis. The crystal crystallizes in monoclinic, space group P21/n with a = 15.793(5), b = 8.927(3), c = 22.257(7) ?, β = 110.147(5)o, C16H38FeLaN8O12, Mr = 729.31, Z = 4, V = 2946.0(15) ?3, Dc = 1.640 g/m3, μ(MoKα) = 1.988 mm-1, F(000) =1476, R = 0.0388 and wR = 0.0827 for 4237 observed reflections (I > 2σ(I)). The La3+ ion is nine-coordinated by one cyano nitrogen atom and eight oxygen atoms of two betaine and six water molecules. Each complex molecule is connected to form a 3D network structure by some O–H…O and O–H…N hydrogen bonds.

Syntheses and Crystal Structures of Two Cyano-bridged Bimetallic Complexes [Ln(DMSO)_2(H_2O)(μ-CN)_4Fe(CN)_2] (Ln = Ce and Eu, DMSO = Dimethylsulfoxide) with Layered Structure

Two new bimetallic cyano-bridged complexes [Ln（DMSO）2（H2O）（μ-CN）4Fe（CN）2] （Ln = Ce 1, Eu 2） have been prepared by the grinding reaction method and structurally characterized by X-ray single-crystal structure analysis. Crystallographic data for 1： C10H14CeFeN6O3S2, Mr = 526.36, monoclinic, P2/n, a = 7.852（4）, b = 10.729（5）, c = 11.181（5）A,β = 96.992（8）°, V = 935.0（7） A^3, Z = 2, Dc = 1.870 g/cm^3,/1 = 3.421 mm^-1, F（000） = 512, R = 0.0363 and wR = 0.0971; and those for 2： C10H14EuFeN6O3S2, Mr = 538.20, monoclinic, P21n, a = 7.739（5）, b = 10.668（7）, c = 11.008（7） A,β = 96.943（3）°, V = 902.1（11） A^3, Z = 2, Dc = 1.981 g/cm^3,/1 = 4.499 mm^-1, F（000） = 522, R = 0.0345 and wR = 0.0855. In each complex the lanthanide ion is seven-coordinated in a pentagonal bipyramidal arrangement, and the Fe（Ⅲ） ion is in a nearly regular octahedral environment. The title complexes can be described as two- dimensional （2-D） stair-like structures, which are further connected by hydrogen bonds to form three-dimensional （3-D） frameworks.

Synthesis and Crystal Structure of a Cyano- bridged Bimetallic Complex[La(DMSO)_3(H_2O)_3- Cr(CN)_6]·H_2O (DMSO = Dimethylsulfoxide) with One-dimensional Chain Molecular Structure

The title complex [La(DMSO)3(H2O)3Cr(CN)6]H2O was obtained by the reaction of LaCl37H2O, DMSO and K3[Cr(CN)6] in aqueous solution on a hot water bath. The crystal crystallizes in orthorhombic, space group P212121 with a = 9.827(3), b = 15.037(4), c = 17.633(5) ? C12H26CrLaN6O7S3, Mr = 653.48, Z = 4, V = 2605.7(13) ?, Dc = 1.666 g/m3, (MoKa) = 2.314 mm-1, F(000) = 1300, R = 0.0205 and wR = 0.0481 for 5038 observed reflec- tions (I > 2s(I)). La3+ ion is eight-coordinated by three DMSO molecules, three H2O molecules and two [Cr(CN)6]3- units. The structure of the title complex possesses a cyano-bridged one- dimensional zigzag chain structure with alternating La(DMSO)3(H2O)3 and Cr(CN)6 moieties, which are linked by some hydrogen bonds to form a 3D network structure.

Synthesis and Crystal Structure of a Cyano-bridged Bimetallic Complex:[NdFe(CN)_6(DMF)_4(H_2O)_3]H_2O

A new bimetallic cyano-bridged complex, [NdFe(CN)6(DMF)4(H2O)3]H2O (DMF = N,N-dimethylformamide) 1, has been obtained by the reaction of hexacyanoferrate potassium with neodymium (Ⅲ) chloride in H2O/EtOH/DMF (volume ratio: 2:2:1), and its structure was determined by means of single-crystal X-ray diffraction. The compound crystallizes in space group P21/n of monoclinic system with cell parameters: a = 17.646(1), b = 8.9011(3), c = 19.945(1) ? b = 95.835(2)? V = 3116.6(3) ?, Z = 4, Dc = 1.536 g/cm3, Mr = 720.66, F(000) = 1456, m = 2.166 mm-1, R = 0.0386, wR = 0.1120 and S = 1.061. The central Nd (Ⅲ) ion is coordinated by seven oxygen atoms of four DMF molecules and three water molecules and one nitrogen atom of the bridging cyanide in a slightly distorted square-antiprism arrangement, and the Fe (Ⅲ) ion is in an almost octahedral environment coordinated to six cyano-ligands, of which one cyanide ligand bridges the Nd (Ⅲ) ion to form a bimetallic complex. Molecules of complexes in the crystal lattice are held together by hydrogen bonding, forming a three-dimensional framework.

Crystal Structure and Magnetic Properties of the Oxamidato-bridged Cu_3 Complex Containing Macrocyclic Ligands

One novel oxamido-bridged trinuclear complex [Cu（CuL）2（ClO4）2] has been syn-thesized and structurally determined.It crystallizes in the monoclinic system,space group P21/n with a = 10.636（4）,b = 11.645（4）,c = 16.038（6） ,β = 91.029（5）°,V = 1986.2（12） 3,C38H32Cl2Cu3N8O12,Mr = 1054.24,Dc = 1.763 Mg/m3,μ（MoKα） = 1.802 mm-1,F（000） = 1066,Z = 2,the final R = 0.0328 and wR = 0.0882 for 3152 observed reflections.The crystal structure is a trinuclear complex in which the CuII ions are bridged by macrocyclic oxamide groups.C-H···O hydrogen bonding interactions link the trinuclear fragment to form a 2D supramolecular architecture.Magnetic measurements indicate that the compound is moderately antiferromagnetically coupled.

The Crystal and Molecular Structure of a New Macrocyclic Ligand, (H_6BDBPH)Br_6·4H_2O

The hexahydro\|bromide salt of a new 24\|membered hexaaza diphenol macrocyclic ligand, （H6BDBPH）Br6·4H2O （C 26H 56N6O6Br6, Mr= 1028.23）, crystallizes in the monoclinic system, space group P21/c, with cell parameters: a=14.441（5）, b=11.482（4）, c=12.090（6）, β=96.92°, V= 1990 （1）3, Z=2, Dc=1.716 g/cm3; F（000） =1024. MoKα radiation, λ= 0.71013), R = 0.0643 and wR = 0.1356 for 3507 independent reflections with I>2σ（I）. The macrocyclic ligand adapts chair form, and the crystallographic inversion center is located in the macrocyclic cavity, and the six bromide ions and four water molecules are situated symmetrically outside the macrocyclic cavity.

THE FIRST BINUCLEAR MOLYBDENUM AND TUNGSTEN COMPLEXES WITH DOUBLY-BRIDGING PYRIDINE-2-THIOLATO LIGANDS.X-RAY CRYSTAL STRUCTURE OF THE COMPLEX[Mo_2(CO)_4(μ-pyS)_2(PPh_3)_2].2C_7H_8

The title complex was obtained by reactions of [Mo(CO)_3(MeCN)_3] with [CuBr(pySH)(PPh_3)_2]or directly with pySH and PPh_3. The latter method can be used to synthesize the corresponding tungsten complex [W_2(CO)_4(μ-pyS)_2(PPh_3)_2].The molecular structure of the title compound was determined by X-ray diffraction method.

Solid-state Synthesis at Low-heating Temperature and Crystal Structure of a Dinuclear Molybdenum Complex with Oxalate Ligand[Bu_4N]_2[Mo_2O_2(OH)_2Cl_4(C_2O_4)]

The title compound was synthesized by the solid-state reaction of (NH_4)_6Mo_7O_(24)·4H_2O, Na_2C_2O_4, NH_2OH·HCl and Bu_4NBr at 90 ℃ for 10 h and crystallized from acetone-ether. The green crystal belongs to the monoclinic space group P2_1/n with a=9. 908(2), b= 17, 873(2), c= 13/450(2) A , β= 90. 09(1 )°,V = 2381. 6 (7 ) A￣3 , D_c = 1. 359 g/cm￣3 , Z= 2. The structure was refined to R =0. 0427 for 2562 reflections. The anion of the title compound can be described as an oxalate ligand (C_2O4￣2 ) bridging two [MoCl_2O(OH)] units, which contain Mo(V)atoms.

Syntheses and Crystal Structures of Mono-and Binuclear Copper(Ⅱ) Mixed-ligand Complexes Involving Schiff Base

The mononuclear copper（Ⅱ） complex [Cu（L）（2-AP）] 1 and binuclear copper（Ⅱ） complex [Cu（L）（py）]2 2 （L = C10H11O5NS, taurine o-vanillin, py = prydine, 2-AP = 2-aminopyridine） with mixed ligand have been synthesized and characterized by X-ray diffraction method. Crystal data for 1： orthorhombic, space group Pbca with a = 11.921（4）, b = 15.816（6）, c = 17.076（6） A, V= 3219.7（19） A^3, C15H17CuN3O5S, Z = 8, Mr = 414.92, De = 1.712 g/cm^3,μ（MoKα） = 1.520 mm^-1, F（000） = 1704, the final R = 0.0300 and wR = 0.0705 for 2840 observed reflections with I 〉 2σ（I）; and crystal data for 2： monoclinic, space group P21/c with a = 7.929（3）, b = 17.038（5）, c = 11.734（4） A, β = 98.162（6）°, V = 1569.1（9） A^3, C15H16CuN2O5S, Z = 4, Mr = 399.90, Dc = 1.693 g/cm^3, F（000） = 820,μ（MoKα） = 1.554 mm^-1, the final R = 0.0351 and wR = 0.0848 for 2767 observed reflections （I 〉 2σ（I））. The molecular structure of complex 1 consists of one tetra-coordinated Cu（Ⅱ） atom generating a slightly distorted square plane, and a one-dimensional chain structure is formed by intermolecular hydrogen bonds. Complex 2 consists of a diphenolic hydroxyl O-bridged binuclear copper（Ⅱ） structure. The crystal structures of complexes 1 and 2 reveal that the coordinate copper centers are bound to both nitrogen and oxygen atom donors. The usual N,O-trans arrangement of ligands is observed in both cases.

Syntheses and Crystal Structures of Silver(I) Complexes by Depolymerizing [Ag(C≡CPh)]_n with a NP_3 Ligand

Two silver(I) complexes were prepared by the reaction of [Ag(C≡CPh)]n with NP3 [NP3 = N(CH2CH2PPh2)3] or with NP3 and [Cu(CH3CN)4]ClO4. Complex 1 [(Ag2Cl(NP3)2)(Ag5- (C≡CPh)6)] contains both NP3 and PhC≡C- ligands. The complex cation is (Ag2Cl(NP3)2)+, in which two Ag(NP3)+ cations were bridged by a Cl- donor. The anion is (Ag5(C≡CPh)6)-, where five Ag+ ions are linked by six C≡CPh- to form a pentanuclear cluster. Complex 2 only contains NP3 ligand, where the silver center adopts a trigonal-bipyramidal geometry. Crystal data for 1: C133H116Ag7Cl3- N2P6, Mr = 2789.54, triclinic, space group P1, a = 13.0780(2), b = 15.3678(2), c = 31.2041(3) ?, α = 91.3928(7), β = 90.9328(8), γ = 96.0244(4)o, V = 6233.8(1) ?3, T = 293(2) K, Z = 2, Dc = 1.486 g/cm3, F(000) = 2796, μ = 1.266 mm-1, the final R = 0.0746 and wR = 0.1953 for 16475 observed reflections with I > 2σ(I). Crystal data for 2: C42H42AgClNO4P3, Mr = 861.00, trigonal, space group R3, a = 17.451(1), b = 17.451(1), c = 11.3985(7) ?, V = 3006.0(3) ?3, T = 293(2) K, Z = 3, Dc = 1.427 g/cm3, F(000) = 1326, μ = 0.731 mm-1, the final R = 0.0251 and wR = 0.0663 for 1499 observed reflections with I > 2σ(I).

Two Cobalt(II) Complexes Derived from the Hydrolysis Product of Di-Schiff Base Ligand N,N'-Bis-(1-benzimidazo-2-yl-ethylidene)-ethane-1,2-diamine:Preparation,Characterization and Crystal Structure of the 6-Coordinate Species [CoL_2]X·H_2O (X = ClO_4^-, N

The reactions of Co（C1O4）2·6H2O and Co（NO3）2.6H2O with the di-Schiff base ligand N,N＇-bis-（1-benzimidazo-2-yl-ethylidene）-ethane-1,2-diamine （LA） in ethanol have been investigated. The reactions of LA with excess amount of cobalt salts yield the six-coordinate complexes [CoL2]（ClO4）E·H2O 1 and [CoL2]（NO3）E·H2O 2 as isolatable products （L= N-（1- benzimidazo-2-yl-ethylidene）-ethane-1,2-diamine）, where L is a tri-dentate mono-Schiff base ligand, resulting from the hydrolysis of the precursor di-Schiff base LA. Both complexes were characterized by X-ray crystallography. Crystal data for complex 1： monoclinic, space group P21/c, a = 11.9214（10）, b = 23.5828（17）, c = 14.0387（12）A, β = 135.219（4）°, C22H30Cl2CoN8O9, Mr = 680.37, V = 2780.1（4） A^3 ,Z = 4, Dc = 1.625 g/cm^3,μ（MoKa） = 0.876 mm^-1, F（000） = 1404, the final R = 0.0725 and wR = 0.1530 for 5726 observed reflections （I 〉 2σ（I））. Crystal data for complex 2： monoclinic, space group P21/c, a = 18.2162（16）, b = 10.0610（6）, c = 18.593（2）A, β = 130.099（3）°, C22H30CoN10O7, Mr = 605.49, V = 2606.5（4） A3 Z = 4, Dc = 1.543 g/cm^3,μ（MoKa） = 0.722 mm^-1, F（000） = 1260, the final R = 0.0619 and wR = 0.1429 for 5194 observed reflections （I 〉 2σ（I））. X-ray diffraction analysis reveals that each cobalt atom in the two complexes is chelated by six nitrogen atoms from two tridentate iigands L, exhibiting a slightly distorted octahedral coordination sphere. In both complexes, the strong hydrogen-bonding interactions between the lattice waters and N-H groups of the ligands result in 1D chains which are further connected by ClO4^- （or NO3^-） groups to form a 3D framework. In complex 2, the strong π-π interactions increase the stability of the structure.

A Trinuclear Ni(Ⅱ) Mixed-ligand Complex Containing Pentadentate N-butyl-salicylhydrazide and Monodentate Imidazole:Synthesis, Characterization and Crystal Structure

A novel trinuclear nickel（II） complex [Ni3（bushz）z（Himdz）2（H20）2].2DMF （1, bushz = N-butylsalicylhydrazide, Himdz = imidazole, DMF = N,N-dimethyl-forrnamide） has been synthesized and characterized by X-ray single-crystal diffraction characterization. Complex 1 crystallizes in the monoclinic system, space group P2 1/c with a = 7.706（7）, b = 14.882（6）, c = 18.639（6） A, β = 108.08（2）°, V= 2032（1） A3, Dc = 1.525 g/cm3, Mr = 932.95, Z= 2, F（000） = 972,μ = 1.442 mm-1, the final R = 0.0359 and wR = 0.0771. The three nickel（II） atoms in 1 are arranged in a strictly linear structure and exhibit alternating square-planar and octahedral geometries. The complex is connected to form a supramolecule with an infinite three-dimensional network through intermolecular hydrogen bonds. The electrochemical studies reveal that redox of Ni3＋/Ni2＋ in the complex is a quasi-reversible process. The thermal stability of the title complex was also studied.

Synthesis and Crystal Structure of A Bimetallic Terbium Complex Tb2 {μ-CH2 SiMe2 NC6 H3 ^iPr2 -2, 6}3 （THF）3

The reaction of 2, 6-^iPr2CbH3NHSiMe3 with Tb（CH2SiMe3）3（THF）2 in benzene at room temperature afforded a binuclear terbium complex Tb2 {μ-CH2 SiMe2 NC6 H3 ^iPr2 -2, 6}3（THF）3. X-ray diffraction revealed that Tb atoms were bridged by three methylene units. One Tb atom was six-coordinated by two nitrogen atoms, three methylene carbons, and one THF molecule, while the other Tb atom was six-coordinated by one nitrogen atom, three methylene carbons, and two THF molecules. Both Tb atoms adopted a distorted trigonal prism geometry.

Synthesis and Crystal Structure of a Novel Tetranuclear Manganese(II) Complex with a Tripodal Peptide Ligand

The title complex, [Mn2(O-Py3A)(DPK-CH3O)(CH3OH)]2?2ClO4?4CH3OH (C64H70Cl2- Mn4N12O22, Py3AH = N-(bis(2?-pyridyl)methyl)-2-pyridinecarboxamide, DPK = di-2-pyridyl ketone) has been synthesized and its crystal structure was determined by X-ray diffraction. It crystallizes in the monoclinic system, space group P21/n with a = 12.667(9), b = 16.793(12), c = 17.070(13) ?, β = 100.997(13)o, V = 3565(5) ?3, Dc = 1.537 g/cm3, Mr = 1649.98, Z = 2, μ(MoKα) = 0.851 mm-1 and F(000) = 1696. The final R and wR are 0.0639 and 0.1320, respectively for 3979 observed reflec- tions with I > 2σ(I). In the tetranuclear complex, each Mn(II) atom is six-coordinated and the four Mn(II) atoms are coplanar, exhibiting a parallelogram arrangement; while the deprotonated ligands are oxidized to O-Py3A2- anions and cleaved to DPK-CH3O– anions (the monoanion of mono- methylated diol of DPK) furthermore.

Unexpected Synthesis and Crystal Structure of Macrocyclic Nickel Complex Involving Rare S-Cl Bond

A novel complex of [NiL（OOCNH2C2H3SClO3）]·H2O was obtained unexpectedly by the reaction of [Ni（rac-L）]（ClO4）2 with l-cysteine （L=5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra- azacyclotetradecane）, and characterized by EA, IR, ESI-MS and single-crystal X-ray diffraction. It crystallizes in the orthorhombic system, space group P212121 with a=9.211（12）, b=14.942（19）, c=19.002（2）, Mr=563.80, V=2615.3（6）3 , Z=4, Dc=1.432 g/cm3 , F（000）=1204, μ=0.966 mm-1 , the final R=0.0565 and wR=0.1515. The central nickel（Ⅱ） ion displays a distorted six-coordinate octahedral coordination geometry by coordination with four nitrogen atoms of L, and one oxygen and one nitrogen atoms of l-cysteine. The sulfur atom of l-cysteine instead of oxygen atom links directly with the chlorine atom of perchlorate. The title complex is the first example of perchlorate salt involving the sulfur atom.

Syntheses and Crystal Structures of Two Silver(I) Complexes Isolated by the Reaction of [Ag(PPh_3)_2(MeCN)](SbF_6) with a N_6 Ligand

Two silver(I) complexes were obtained by the reaction of a N6 ligand with [Ag(PPh3)2(MeCN)](SbF6). In complex [AgL1(PPh3)](SbF6) 1, the silver center is bound to three N donors of the nitrogen ligand and P donor of one triphenylphosphine group, forming an irregular AgN3P tetrahedron. In complex [Ag(PPh3)4](SbF6) 2, the Ag+ ion is coordinated to four triphenyl- phosphine groups, affording a tetrahedral geometry. Crystal data for complex 1: C30H37AgF6N6PSb, Mr = 856.25, orthorhombic, space group Pbca, a = 19.0702(9), b = 15.9047(7), c = 21.498(1) ?, V = 6520.5(6) ?3, Z = 8, Dc= 1.744 g/cm3, F(000) = 3408, μ = 1.544 mm-1, the final R = 0.0367 and wR = 0.1077 for 5325 observed reflections with I > 2σ(I); and those for 2: C72H60AgF6P4Sb, Mr = 1392.70, trigonal, space group R3, a = 14.4577(6), b = 14.4577(6), c = 51.544(2) ?, V = 9330.5(7) ?3, Z = 6, Dc= 1.487 g/cm3, F(000) = 4224, μ = 0.913 mm-1, the final R = 0.0352 and wR = 0.1089 for 3498 observed reflections with I > 2σ(I).

Molecular and Supramolecular Structures of a Nickel(Ⅱ) Complex with a Macrocyclic Ligand

The crystal structure of the title complex, [NiL], has been determined by using X-ray analysis (H2L = 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(methoxycarbonyl)-1,4,8,11-tetraazacyclotetra- deca-7,11-diene). Crystal data: C22H18N4O6Ni, Mr = 493.11, triclinic, space group P, a = 9.128(6), b = 9.941(7), c = 12.396(8) ? a = 107.11(1), b = 106.14(1), g = 97.69(1), V = 1003.9(11) 3, Z = 2, Dc = 1.631 g/cm3, m(MoKa) = 1.018 mm-1, F(000) = 508, R = 0.0584 and wR = 0.0981 for 1724 observed reflections with I > 2s(I). The Ni(II) atom is coordinated by four nitrogen donors of the macrocyclic ligand with a slightly distorted square-planar geometry. In the crystal, the CH…O hydrogen bonds link the complex molecules to form infinite 1D chains which are further linked by p…p stacking interactions to form chain-pairs.