Double-stranded Helical Chains Research Articles

Homochiral coordination architectures based on a series of pyridyl-alanine derivatives with varied configurations: Structural diversity, photoluminescence and magnetic properties

Six homochiral coordination polymers based on a series of designed pyridyl-alanine derivatives ligands (x,y-H2PDBAla, x, y ​= ​2, 6; 2, 5; 3, 5) and different divalent cations in the absence/presence of ancillary ligands, including [Zn (2,6-PDBAla)]∙3H2O (1), [Cd (2,6-PDBAla)] (2), [Cd (2,5-PDBAla) (H2O)3]·2H2O (3), [Cu3(2,5-PDBAla)2 (bipy)2(H2O)2]·10H2O (4), [Co(3,5-PDBAla) (bpea) (H2O)] (5), [Ni(3,5-PDBAla) (bpee) (H2O)2]·5H2O (6) (H2PDBAla ​= ​pyridine-dicarbonyl-bis(l-alanine), bipy ​= ​4,4′-bipyridine, bpea ​= ​1,2-bis(4-pyridyl)ethane, bpee ​= ​1,2-bis(4-pyridyl)ethylene), were prepared and characterized. Three kinds of pyridyl-alanine derivatives ligands with versatile coordination modes bridge metal ions to generate the diverse structures. In the absence of ancillary ligand, the 2,6-H2PDBAla ligands and Zn(II)/Cd(II) ions react to get the compounds 1 and 2.1 exhibits a one-dimensional (1D) “loop” chain structure with the 14-membered rings, whereas a 3D framework with the qtz topology was observed in 2, in which the right-handed single-stranded and the left-handed double-stranded helical chains coexist. The 2,5-H2PDBAla ligands coordinate with Cd(II)/Cu(II) ions to yield the compounds 3 and 4.3 shows 1D right-handed single-stranded helical chain, and 4 shows a 2D layer constructed from right-handed single-stranded helical chain. The integration of 3,5-H2PDBAla ligands and Co(II)/Ni(II) ions leads to the compounds 5 and 6.5 displays a 2D wavy layer, consisting of the [Co(3,5-PDBAla)] right-handed single-stranded helical chain and the [Co(bpea)]2+ zigzag chain, and 6 displays a 2D layer with sql topology. The photoluminescence spectra of 1, 2 and 3 reveal the corresponding emissions of organic ligands, their maximum emission peaks appear at 402, 401 and 433 ​nm, respectively. Magnetic susceptibility mensuration of 5 gives the J of −12.35 ​cm−1, indicating strong antiferromagnetic interactions between the Co(II) ions.

A zinc(II) coordination polymer containing single- and double-stranded helical chains: synthesis, crystal structure, and thermal and luminescence properties

Abstract A new zinc(II)-based coordination polymer {[Zn(5-fip)(tdbpy)]·(DMF)} n (1) {5-H2fip=5-fluoroisophthalic acid, tdbpy=4,4′-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)bispyridine, DMF=dimethylformamide} has been solvothermally synthesized and structurally characterized. Single-crystal X-ray diffraction revealed that complex 1 shows a unique two-dimensional network architecture containing single-stranded [Zn(5-fip)] n and double-stranded helical [Zn(tdbpy)] n chains. The thermal and luminescence properties of complex 1 have also been studied.

Four Novel Zn (II) Coordination Polymers Based on 4'-Ferrocenyl-3,2':6',3''-Terpyridine: Engineering a Switch from 1D Helical Polymer Chain to 2D Network by Coordination Anion Modulation.

Four novel ZnII coordination polymers, [(ZnCl2)2(L)2]n (1), [(ZnBr2)2(L)2]n (2), and [(ZnI2)2(L)2]n (3) and {[Zn(SCN)2]1.5(L)3}n (4), have been synthesized based on 4′-ferrocenyl-3,2′:6′,3′′-terpyridine with ZnII ions and different coordination anions under similar ambient conditions. Their structures have been confirmed using single crystal X-ray diffraction analysis, showing that complexes 1–3 are one-dimensional (1D) double-stranded metal ion helical polymer chains and complex 4 is of a two-dimensional (2D) network. The structural transformations of them from a 1D polymer chain to a 2D network under the influence of the coordination anions has been systematic investigated. Furthermore, the optical band gaps have been measured by optical diffuse reflectance spectroscopy, revealing that the ligand and the complexes should have semiconductor properties.

Self-Assembly of Discrete Metallocycles versus Coordination Polymers Based on Cu(I) and Ag(I) Ions and Flexible Ligands: Structural Diversification and Luminescent Properties.

Three new Ag(I) and one Cu(I) coordination compounds with two different positional isomers, propane-1,3-diyl bis(pyridine-4-carboxylate) (L1) and propane-1,3-diyl bis(pyridine-3-carboxylate) (L2), of a bis-(pyridyl-carboxylate) ligand have been synthesized. X-ray diffraction analysis revealed that the self-assembly of L1 with AgCF3SO3 and AgClO4 salts leads to the formation of discrete binuclear metallocycles {Ag(L1)CF3SO3}2 (1) and {Ag(L1)ClO4}2 (2), respectively. However, self-assembly of the other ligand, L2, with AgCF3SO3 and CuCl salts, results in a 1-D zig-zag chain {Ag(L2)CF3SO3}∞ (3) and a 1-D double-stranded helical chain {Cu2Cl2(L2)2}∞ (4) coordination polymers, respectively. Solid emission spectra recorded at room temperature show interesting luminescence properties for all four compounds in the range from 438 to 550 nm, especially for compound 4 that was found to change its emission color when the wavelength of the excitation radiation is switched from 332 to 436 nm.

A three-dimensional cadmium(II) coordination polymer with unequal homochiral double-stranded concentric helical chains.

A homochiral helical three-dimensional coordination polymer, poly[[(μ2-acetato-κ(3)O,O':O)(hydroxido-κO)(μ4-5-nicotinamido-1H-1,2,3,4-tetrazol-1-ido-κ(5)N(1),O:N(2):N(4):N(5))(μ3-5-nicotinamido-1H-1,2,3,4-tetrazol-1-ido-κ(4)N(1),O:N(2):N(4):N(5))dicadmium(II)] 0.75-hydrate], {[Cd2(C7H5N6O)2(CH3COO)(OH)]·0.75H2O}n, was synthesized by the reaction of cadmium acetate, N-(1H-tetrazol-5-yl)isonicotinamide (H-NTIA), ethanol and H2O under hydrothermal conditions. The asymmetric unit contains two crystallographically independent Cd(II) cations, two deprotonated 5-nicotinamido-1H-1,2,3,4-tetrazol-1-ide (NTIA(-)) ligands, one acetate anion, one hydroxide anion and three independent partially occupied water sites. The two Cd(II) cations, with six-coordinated octahedral and seven-coordinated pentagonal bipyramidal geometries are located on general sites. The tetrazole group of one symmetry-independent NTIA(-) ligand links one of the independent Cd(II) cations into 61 helical chains, while the other NTIA(-) ligand links the other independent Cd(II) cations into similar but unequal 61 helical chains. These chains, with a pitch of 24.937 (5) Å, intertwine into a double-stranded helix. Each of the double-stranded 61 helices is further connected to six adjacent helical chains through an acetate μ2-O atom and the tetrazole group of the NTIA(-) ligand into a three-dimensional framework. The helical channel is occupied by the isonicotinamide groups of NTIA(-) ligands and two helices are connected to each other through the pyridine N and carbonyl O atoms of isonicotinamide groups. In addition, N-H···O and O-H···N hydrogen bonds exist in the complex.

A series of reaction-controlled coordination polymers constructed from bis(imidazole) and tetrafluoroterephthalic acid ligands: syntheses, structural diversities, properties

Seven new mixed–ligand coordination polymers, {[Co0.5(bib)0.5(tftpa)0.5]·0.5H2O}n (1), [Cd2(bib)(tftpa)2]n (2), [Ni0.5(bib)0.5(tftpa)0.5]n (3), {[Co0.5(tftpa)(H2O)]·0.5bib·EtOH}n (4), {[Cd0.5(tftpa)(H2O)]·0.5bib·EtOH}n (5), [Cd3(bib)3(tftpa)3(MeOH)3]n (6), and [Cd(bib)(tftpa)(MeOH)]n (7) (bib = 1,4-bis(2-methylimidazol-1-yl)butane, H2tftpa = tetrafluoroterephthalic acid) have been synthesized under different reaction conditions and characterized by elemental analysis, IR, PXRD, single crystal X-ray diffraction analysis and thermogravimetric analysis. Complex 1 exhibits an unusual [2 + 2] interpenetrating diamond framework belonging to class IIIa with the point symbol 66. Complex 2 reveals a (3,4)-connected 3D framework with a unique double-stranded helical chain based on Cd–O–Cd and Cd–(COO)–Cd. Complex 3 presents a 4-fold interpenetrating 3D diamond framework belonging to class Ia with the point symbol 66. Complexes 4 and 5 display a 3D supramolecular architecture built on 2D stacked layers through hydrogen bonding and π–π interactions. Complex 6 also shows a 3D 4-fold interpenetrating diamond framework belonging to class Ia with the point symbol 66. Complex 7 features a 2D + 2D → 2D parallel polycatenated framework with the point symbol 44·62. The structural diversity of complexes 1–7 illustrate that a subtle change can have a marked effect on the crystal architectures. Moreover, the magnetic properties of complexes 1, 3, and 4, and the solid-state photoluminescence results for complexes 2, and 5–7 were also studied.

Rational assembly of Pb(II)/Cd(II)/Mn(II) coordination polymers based on flexible V-shaped dicarboxylate ligand: Syntheses, helical structures and properties

Six new coordination polymers, namely, [Pb(L)(H2O)] (1), [Pb(L)(phen)] (2), [Pb2(L)2(4,4′-bipy)0.5] (3), [Cd(L)(phen)] (4), [Cd(L)(4,4′-bipy)]·H2O (5) and [Mn(L)(4,4′-bipy)]·H2O (6) have been synthesized by the hydrothermal reaction of 2,2′-[hexafluoroisopropylidenebis(p-phenyleneoxy)]diacetic acid (H2L) with Pb(II)/Cd(II)/Mn(II) in the presence of ancillary ligands 4,4′-bipyridine (4,4′-bipy) or 1,10-phenanthroline (phen). Complexes 1 and 4–6 exhibit 2-D structures, and complexes 2–3 display 3-D frameworks, of which L2− ligands join metal ions to single-stranded helical chains of 1, 3–6 and double-stranded helical chains of 2. Complexes 2 and 3 also contain double-stranded Metal–O helices. Topology analysis reveals that complexes 1 and 4 both represent 4-connected sql net, 2 represents 6-connected pcu net, 3 exhibits a novel (3,12)-connected net, while 5 and 6 display (3,5)-connected gek1 net. The six complexes exhibit two kinds of inorganic–organic connectivities: I0O2 for 1, 4–6, and I1O2 for 2–3. The photoluminescent properties of 4–5 and the magnetic properties of 6 have been investigated.

Unusual solvent influence of formamide on the structural variations of chiral and achiral Mn(II) complexes based on tetrachlorophthalate

Using an achiral ligand 3,4,5,6-tetrachloro-1,2-benzenedicarboxylic acid (1,2-H2BDC-Cl4), a short series of chiral or achiral manganese(II) complexes with the formulae [Mn(1,2-BDC-Cl4)(MF)2(H2O)2]n (1), [Mn(1,2-BDC-Cl4)(DMF)(H2O)2]n (2) and [Mn2(1,2-BDC-Cl4)2(DEF)2(H2O)6]·2H2O (3) (MF=N-methylformamide; DMF=N,N-dimethylformamide and DEF=N,N-diethylformamide) have been spontaneously obtained through the alteration of formamide solvent media, and characterized by single-crystal X-ray diffraction, elemental analysis, IR, thermal gravimetric analyses (TGA) and powder X-ray diffractions (PXRD). Complex 1 crystallizes in the monoclinic P21/c space group and shows a one-dimensional fishbone chain structure, complex 2 crystallizes in the orthorhombic P212121 space group and has a chiral double-stranded helical chain consisting of two single-stranded helices of the same right-handness, and complex 3 crystallizes in the triclinic P1 space group and possesses a dinuclear [Mn(1,2-BDC-Cl4)]2 metallomacrocycle directing a two-dimensional hydrogen-bonded water layer based on both coordinated and lattice water molecules. This remarkable structural difference displays the significant influence of formamide solvents on the formation of such chiral and achiral Mn(II) complexes. The spectroscopic, thermal stability and luminescence properties of 1–3 have also been investigated briefly.

Chiral symmetry breaking of a double-stranded helical chain through bend-writhe coupling.

This paper explores asymmetric elasticity of a double-stranded helical chain, which serves as a minimal model of biopolymers. The model consists of two elastic chains that mutually intertwine in a right-handed manner, forming a double-stranded helix. A simple numerical experiment for structural relaxation, which reduces the total elastic energy of the model monotonically without thermal fluctuations, reveals possible asymmetric elasticity inherent in the helical chain. It is first shown that a short segment of the double-stranded helical chain has a tendency to unwind when it is bent. It is also shown that a short segment of the helical chain has a tendency to writhe in the left direction upon bending. This tendency gives rise to a propensity for a longer segment of the chain to form a left-handed superhelix spontaneously upon bending. Finally, this propensity of the helical chain to form a left-handed superhelix is proposed to be a possible origin of the uniform left-handed wrapping of DNA around nucleosome core particles in nature. The results presented here could provide deeper insights into the roles and significance of helical chirality of biopolymers.

A new (3,3,6)-connected achiral 3D supramolecular network containing unique helical chains based on 1H-benzimidazole-5,6-dicarboxylato and Pb(II)

Abstract A new 1D Pb(II) coordination polymer, {[Pb(Hbidc)(phen)]·H2O}n (1), has been synthesized by a solvothermal method based on 1H-benzimidazole-5,6-dicarboxylato (H3bidc) and 1,10-phenanthroline (phen). Complex 1 features two types of helical chains, a 1D left- and right-handed double-stranded helical chain and a supramolecular helical chain, which interweave into a new (3,3,6)-connected achiral 3D supramolecular network. Notably, the supramolecular helical chains are induced by the different spatial orientations of the 1D double-stranded helical chains. The structure and properties of 1 have been determined by single crystal X-ray diffraction, powder X-ray diffraction (PXRD), elemental analysis (EA), thermogravimetric (TG) analysis and solid state fluorescence spectra.

Crystal Structures and Luminescent Properties of Two Lanthanide(III) Complexes Featuring Double-Stranded Helical Chains of Based on 2-Sulfoterephthalate

Hydrothermal reaction of Eu3+ and Dy3+ salts with monosodium 2-sulfoterephthalate (NaH2stp) gives two 2D lanthanide coordination polymers, [Ln(stp)(H2O)2]n (Ln = Eu (1) and Dy (2)). Single-crystal X-ray diffraction of the complexes reveal that both 1 and 2 crystallize in the triclinic crystal system of Pī space group. For 1, each Eu3+ ion lies in a 9-coordinated slightly distorted tri-capped triangle pyramidal configuration. The stp ligands adopt a μ4-type link to the metal ions to form a 2D layer-like structure, of which there exist the left- and right-handed double-stranded helical chains. For 2, each Dy3+ ion is in a 8-coordinated distorted bi-capped triangle pyramidal geometry. The double-stranded helical chains in 2 differ from those in 1. The thermal stabilities of the two compounds are studied by TGA. The solid state photoluminescence of 1 and 2 are reported. The fluorescent decay curves of the ligand and compounds indicate that 1 has the lifetime of 286.7 μs, τ1 = 0.51 ns and τ2 = 3.07 ns for the ligand, and for 2, τ1 = 0.53 ns and τ2 = 2.71 ns.

Highly stable 3D homochiral coordination polymer with interweaving of double-stranded helices and extended metal-SO4-metal chains

Abstract Solvothermal synthesis of an achiral ligand N,N-bis(3-pyridyl) isophthalamide (bpip) with ZnSO4 under 120 °C yield a novel compound, [Zn(bpip)SO4]n, which displays chiral self-assembly into an infinite double-stranded helical coordination polymer consisting of two single-stranded helices with the same P handedness. These chiral infinite double-stranded helical chains are further interwoven by the 1D Zn–SO4–Zn chains to form a novel 3D framework structure with a rare 65.10 topology. On the basis of the results of TG-DSC analyses, the structure is thermally stable up to ~ 467.4 °C.

PH Influence on the Structural Variations of 4,4′-Oxydiphthalate Coordination Polymers

Five new Zn(II)/ODPT/bpe compounds, namely, {[Zn(bpe)(H2O)2](H2ODPT)·3H2O}n (1), {[Zn4(ODPT)2(bpe)3(H2O)2]2(bpe)·7H2O}n (2), {[Zn2(ODPT)(bpe)2]2·7H2O}n (3), {Zn4(ODPT)2(bpe)}n (4), and {Zn2(ODPT)(bpe)(H2O)2}n (5) (ODPT = 4,4′-oxidiphthalate, bpe =1,2-bis(4-pyridyl)ethane), have been synthesized through a hydrothermal method under different pH conditions, and characterized by single-crystal X-ray diffraction, element analysis, infrared spectra (IR), and thermogravimetric (TG) analyses. Compound 1 shows a 3D network framework constructed by the 1D linear [Zn(bpe)(H2O)4]n2+ cationic chains through extensive hydrogen-bonding. Compound 2 displays an unusual three-dimensional (3D) meso-racemic self-penetrating coordination network with distinct chiral information in the interpenetrating networks. Compound 3 features a novel 4-connected (4·62·83)(42·62·82) topology, also exhibiting an intriguing 3D self-penetrating structure formed by triple- and double-stranded helical chain motifs. Compounds 4 and 5 are based ...

Double-stranded helical lanthanide(III) supramolecular networks with rigid diimine ligands: Synthesis, structure, and physical properties

Two lanthanide coordination complexes [Nd(NO 3) 3(CH 3OH) 2(4,4′-bipy) 2] ( 1) (4,4′-bipy=4,4′-bipyridine) and [4,4′-Hbipy][La(NO 3) 4(H 2O) 2(4,4′-bipy )] ( 2), with a salt of cationic diprotonated 4,4′-bipy, [2(4,4′-H 2bipy)][4(NO 3)] ( 3), have been identified and isolated from a methanol solution of Ln(NO 3) 3·6H 2O, 4,4′-bipyridine and pyrazine in 1:2:1 ratio. Their structures have been determined by single-crystal X-ray diffraction analyses, which reveal that 1 has an interesting three-dimensional supramolecular architecture containing 2 1 double-stranded helical chains through hydrogen bonding and π–π interactions , while 2 and 3 have well defined infinite chiral 3D open networks that undergo self-interpenetration. The electrospray ionization mass spectra (ESI-MS) indicate that the covalent complex has higher stability than the electrostatic bonding one. ESI-MS/MS of these ions reveal that the Ln–O bond forms a stronger coordinated bonding than that of Ln–N system and the nitrate anion remains bound to the lanthanide centers after complete dissociation in methanol solution.

Microporous Metal–Organic Frameworks: Structures, in Situ Formation of Ligand, and Crystal-to-Crystal Transformations

Among these new microporous metal–organic frameworks (MOFs) {[CuI17(L1)12X2]X3(H2O)n}∞ (1, X = Cl, 1a, n = 6; 1b, 1c, n = 5, 1d, n = 3; 2, X = Br, 2a, n = 5; 2b, n = 3; L1 = 3,5-bis(4-aminophenyl)-1,2,4-triazolate), 1a and 2a were obtained through in situ copper-mediated ring conversion of 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole into L1 under hydrothermal conditions, while the others were generated through interesting single-crystal-to-single-crystal transformations with an accompanying color change from red to black. In the process of synthesis, when CuII salt was used as starting reactant, the CuI complex 1a was obtained; so the redox reaction clearly took place under this condition. The fascinating features of these structures are the double-stranded helical chains and the largest metallamacrocycle based on triazolate ever reported. These isomorphous complexes adopt the rare binodal six-connected networks. In the solid state at low temperature (∼273 K), the red crystal sample 1b displays an emission ba...

Syntheses and crystal structures of four 1-D or 2-D coordination polymers based on 1-((benzotriazol-1-yl)methyl)-1 H-1,3-imidazole

In this paper, four coordination polymers, {[Ag(bmi)]·NO 3} n ( 1), [Co(N 3) 2(bmi) 2] n ( 2), [Cu(SCN) 2(bmi) 2] n ( 3), and {[Cu(bmi) 2(CH 3OH)(H 2O)]·(ClO 4) 2} n ( 4) have been synthesized through the reactions of an unsymmetrical ligand 1-((benzotriazol-1-yl)methyl)-1 H-1,3-imidazole (bmi) with Ag(I), Co(II) and Cu(II) salts at room temperature. X-ray diffraction analyses showed that compound 1 exhibits double-stranded helical chain. Compounds 2– 4 display 2-D rhombus grid network structure. The rhombus grid consists of 32-membered rings, and gives the dimensions of ca. 8.9 × 8.9 Å for compound 2, ca. 10.1 × 10.1 Å for compound 3, and ca. 9.7 × 9.5 Å for compound 4. In addition, the 2-D layers of compound 3 are stacked into 3-D structure via π– π interactions, while the 3-D architecture of compound 4 is realized through complicated hydrogen bonds and π– π interactions. The thermal analyses of compounds 1 and 3 indicate that they have high thermal stability and are stable up to 259 °C.

Structural diversity and properties of M(ii) phenyl substituted pyrazole carboxylate complexes with 0D-, 1D-, 2D- and 3D frameworks

Eight new metal complexes with two kinds of phenyl substituted pyrazole carboxylic acid, [Ni(HL1)2(H2O)2] (1), [Cu(HL1)2(H2O)2] (2), [Zn(HL1)2] (3), [Ni(HL2)2(H2O)2] (4), [Ni(HL2)2(HL3)2] (5), [Cu(HL2)2]·2H2O (6), [Zn(HL2)2] (7), [Zn2(HL2)2(L2)] (8) [H2L1 = 5-phenyl-1H-pyrazole-3-carboxylic acid; H2L2 = 3-phenyl-1H-pyrazole-4-carboxylic acid; HL3 = 3-phenyl-1H-pyrazole] were prepared by hydro/solvothermal reactions and structurally characterized. Complexes 1 and 2 have monomeric structures; 3 and 4 exhibit 1-D zig-zag chains; 5 and 6 possess 2D layer structures consisting of rhomboid grids; 7 features a 2-fold interpenetrated 3-D diamondoid framework; while complex 8 holds a 3-D NaCl-like framework. Hydrogen bonding and aromatic π–π stacking interactions link the eight complexes into 2-D (1–3) or 3-D (4–8) supramolecular networks, of which 5, 6 and 8 contain single, single and double-stranded helical chains, respectively. The thermal stabilities of complexes 1–8 and photophysical properties of complexes 3 and 7 were investigated.

Structural diversity in coordination polymers with angular ditetrazole ligands

Abstract Three new coordination polymers with angular bis(1-tetrazol)diphenyl ligands as bridges, {[Ag(L1)2](NO3) ⋅ 2H2O}∞ [L1 = 4,4'-bis(1-tetrazolyl)diphenyl methane], 1, [Ag(L2)2(NO3)]∞ [L2 = 4,4'-bis(1-tetrazolyl)diphenyl sulfone], 2, and [CuBr(L3)0.5]∞ [L3 = 4,4'-bis(1-tetrazolyl)diphenyl ether], 3, are reported, which show unique 2D structural types. Complex 1 forms 1D double-stranded helical chains where the cavities are threaded by linear hydrogen bondings formed by the co-crystallized water molecules and nitrate anions and complex 2 shows 2D grids involving M4L4 64-membered metallocycles composed of helical chains, while complex 3 exhibits a 2D pleated net comprising 1D channels linked by the double-chain CuBr ribbons.

Roles of halide anions in the structural diversity of Zn(ii) complexes containing the flexible N,N′-di(4-pyridyl)adipoamide ligand

A series of Zn(II) complexes with N,N′-di(4-pyridyl)adipoamide ligands, {[ZnX2(L)]·H2O}∞ (X = Cl, 1, Br, 2 and I, 3; L = N,N′-di(4-pyridyl)adipoamide), [Zn2X4(L)2]·2DMF (X = Cl, 4 and Br, 5) and [Zn2I4(L)2]·4DMF·C4H10O, 6, were prepared and their structures determined by X-ray crystallography. Complexes 1 and 2 form double-stranded helical chains which are supported by the N–H⋯O and O–H⋯X hydrogen bonds involving the guest water molecules and the halide anions, whereas 3 shows sinusoidal chains which are interlinked by the N–H⋯O hydrogen bonds and π–π interactions. Complexes 1–3 represent a unique example that the halide anions show significant effect on folding and unfolding of the Zn(II) double-stranded helical coordination polymers. Complexes 1–3 can be transformed to the corresponding complexes 4–6, which are dinuclear with 34-membered metallocycles. In these complexes, the chloride and bromide anions play the same role in the crystal structures, while the iodide anion is distinct.

Syntheses, crystal structures and properties of silver(i) and copper(ii) complexes with an oxazoline-containing tetradentate ligand

Six new coordination complexes, [AgL]CF3SO3 (1 and 2), [Ag2L2](NO3)2·4CH3NO2 (3), [AgL]NO3·0.5CH3OH (4), [AgL]BF4 (5) and [Cu4L2(OCH3)2(OH)2(NO3)2](NO3)2·0.32H2O (6), were obtained by reactions of the corresponding metal salts with ligand N,N′-bis[4-(4,5-dihydrooxazol-2-yl)-benzyl]ethane-1,2-diamine (L). The results of X-ray crystallographic analysis indicate that complexes 1 and 2 are supramolecular isomers with a wavelike cationic two-dimensional network structure of 1 and a double-stranded helical chain of 2. Complexes 4 and 5 also have helical chain structures with P and M forms. Differing from polymeric structure of 1, 2, 4 and 5, complexes 3 and 6 are a M2L2 molecular rectangle and a M4L2 cage, respectively. The results show that the flexible ligand L can have different conformation and coordination modes leading to complexes with varying structures. Magnetic data show that there are antiferromagnetic interactions in the dimeric unit of complex 6.