Two‐ and Three‐Dimensional Molecular Organization of Schiff‐Base Derivatives

We have designed and synthesized a series of Schiff base derivatives, and studied their structural features in two‐dimensional (2D) and three‐dimensional (3D) states by combining scanning tunneling microscopy (STM) and X‐ray diffraction experiments. The Schiff‐base derivatives with short alkyl chains crystallize easily, which allows a detailed structural analysis by X‐ray diffraction. Due to the strong adsorbate–substrate interactions, those bases with long alkyl chains easily form 2D assemblies on highly oriented pyrolytic graphite (HOPG). The STM images indicate also that the introduction of two methoxy groups into the molecule can change the structure of these 2D assemblies as a result of the increased steric hindrances, for example: the Schiff‐base derivative, bearing both methoxy groups and C₁₆H₃₃ tails, forms 2D Moiré patterns, and an alignment of pairing Schiff‐base molecules may be easily resolved. Conversely, the Schiff base derivative, bearing solely C₁₆H₃₃ tails, forms 2D non‐Moiré patterns. It is demonstrated that the 3D structural features result from the compromise of intermolecular interactions of different molecular moieties. However, there is one more factor, which also governs the 2D structure: the adsorbate‐substrate interaction. The 3D crystal structure may thus help to understand many factors involved in the formation of 2D structures, and would be helpful for designing new molecular assemblies with tailoring functions.     

Metal‐directed supramolecular architectures based on the bifunctional ligand 2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalic acid

By the solvothermal reactions of 2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalic acid (H₂L) with transition‐metal ions, two novel polymeric complexes, namely, poly[diaqua[μ₄‐2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalato]cobalt(II)], [Co(C₁₂H₆N₆O₄)(H₂O)₂]_n, ( 1 ), and poly[[diaqua[μ₄‐2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalato]nickel(II)] dihydrate], {[Ni(C₁₂H₆N₆O₄)(H₂O)₂]·2H₂O}_n, ( 2 ), were isolated. Both polymers have been characterized by FT–IR spectroscopy, elemental analysis and single‐crystal X‐ray diffraction analysis. The complexes have similar two‐dimensional layered structures and coordination modes. Furthermore, the two‐dimensional layered structures bear distinct intermolecular hydrogen‐bonding interactions and π–π stacking interactions to form two different three‐dimensional supramolecular networks based on 4⁴‐subnets. The structural variation depends on the nature of the metal cations. The results of variable‐temperature magnetization measurements (χ_MT?T and χ_M^?1?T) show that complexes ( 1 ) and ( 2 ) display antiferromagnetic behaviour.     

Synthesis and Characterization of Ba[CoSO]: Magnetic Complexity in the Presence of Chalcogen Ordering

Barium thio‐oxocobaltate(II), Ba[CoS_2/2O_2/2], was synthesized by the reaction of equimolar amounts of BaO, Co, and S in closed silica ampoules. The title compound (Cmcm, a=3.98808(3), b=12.75518(9), c=6.10697(4) Å) is isostructural to Ba[ZnSO]. The use of soft X‐ray absorption spectroscopy confirmed that cobalt is in the oxidation state +2 and tetrahedrally coordinated. Its coordination consists of two sulfur and two oxygen atoms in an ordered fashion. High‐temperature magnetic susceptibility data indicate strong low‐dimensional spin–spin interactions, which are suggested to be closely related to the layer‐type crystal structure and perhaps the ordered distribution of sulfur and oxygen. Antiferromagnetic ordering below T_N=222 K is observed as an anomaly in the specific heat, coinciding with a significant lowering of the magnetic susceptibility. Density functional theory calculations within a generalized‐gradient approximation (GGA)+U approach identify an antiferromagnetic ground state within the square‐like two‐dimensional layers of Co, and antiferromagnetic correlations for nearest and next nearest neighbors along bonds mediated by oxygen or sulfur. However, this magnetic state is subject to frustration by relatively strong interlayer couplings.     

Low‐dimensional coordination polymeric structures in alkali metal complex salts of the herbicide (2,4‐dichlorophenoxy)acetic acid (2,4‐D)

The Li, Rb and Cs complexes with the herbicide (2,4‐dichlorophenoxy)acetic acid (2,4‐D), namely poly[[aqua[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ³O¹:O¹:O^1′]lithium(I)] dihydrate], {[Li(C₈H₅Cl₂O₃)(H₂O)]·2H₂O}_n, (I), poly[μ‐aqua‐bis[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ⁴O¹:O^1′:O^1′,Cl²]dirubidium(I)], [Rb₂(C₈H₅Cl₂O₃)₂(H₂O)]_n, (II), and poly[μ‐aqua‐bis[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ⁵O¹:O^1′:O^1′,O²,Cl²]dicaesium(I)], [Cs₂(C₈H₅Cl₂O₃)₂(H₂O)]_n, (III), respectively, have been determined and their two‐dimensional polymeric structures are described. In (I), the slightly distorted tetrahedral LiO₄ coordination involves three carboxylate O‐atom donors, of which two are bridging, and a monodentate aqua ligand, together with two water molecules of solvation. Conjoined six‐membered ring systems generate a one‐dimensional coordination polymeric chain which extends along b and interspecies water O—H...O hydrogen‐bonding interactions give the overall two‐dimensional layers which lie parallel to (001). In hemihydrate complex (II), the irregular octahedral RbO₅Cl coordination about Rb⁺ comprises a single bridging water molecule which lies on a twofold rotation axis, a bidentate O_carboxy,Cl‐chelate interaction and three bridging carboxylate O‐atom bonding interactions from the 2,4‐D ligand. A two‐dimensional coordination polymeric layer structure lying parallel to (100) is formed through a number of conjoined cyclic bridges, including a centrosymmetric four‐membered Rb₂O₂ ring system with an Rb...Rb separation of 4.3312 (5) Å. The coordinated water molecule forms intralayer aqua–carboxylate O—H...O hydrogen bonds. Complex (III) comprises two crystallographically independent (Z′ = 2) irregular CsO₆Cl coordination centres, each comprising two O‐atom donors (carboxylate and phenoxy) and a ring‐substituted Cl‐atom donor from the 2,4‐D ligand species in a tridentate chelate mode, two O‐atom donors from bridging carboxylate groups and one from a bridging water molecule. However, the two 2,4‐D ligands are conformationally very dissimilar, with one phenoxyacetate side chain being synclinal and the other being antiperiplanar. The minimum Cs...Cs separation is 4.4463 (5) Å. Structure extension gives coordination polymeric layers which lie parallel to (001) and are stabilized by intralayer water–carboxylate O—H...O hydrogen bonds.     

A new ZnII coordination polymer based on 4‐(pyridin‐4‐yl)benzoic and formic acids: in‐situ synthesis,crystal structure and luminescence properties

The title compound, poly[(μ₂‐formato‐κ³O,O′:O)[μ₂‐4‐(pyridin‐4‐yl)benzoato‐κ³N:O,O′]zinc(II)], [Zn(C₁₂H₈NO₂)(HCOO)]_n, has been synthesized in situ and characterized by thermogravimetric analysis (TGA) and single‐crystal and powder X‐ray diffraction analyses. The polymer contains two independent structural units in the asymmetric unit. These are constructed from Zn²⁺ ions, 4‐(pyridin‐4‐yl)benzoate (4‐pbc) bridges and in‐situ‐generated formate ligands, forming two similar two‐dimensional (2D) layer structures. These similar 2D layers are arranged alternately and are linked with each other by dense C—H…O hydrogen bonds to generate a three‐dimensional (3D) supramolecular framework. The crystal is pseudomerohedrally twinned about [201]. Compared with free 4‐Hpbc, the polymer exhibits a red shift and significantly enhanced solid‐state luminescence properties.     

Crystallization kinetics and melting behavior of metallocene short‐chain branched polyethylene fractions

Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short‐chain branch (SCB) distribution as compared with unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used to study the influences of SCB content on the crystallization kinetics, melting behavior, and crystal morphology of four butyl‐branched mPE fractions. The parent mPE of the studied fractions was also investigated for comparative purposes. mPE fractions showed a much simpler crystallization behavior as compared with their parent mPE during the cooling experiments. The Ozawa equation was successfully used to analyze the nonisothermal crystallization kinetics of the fractions. The Ozawa exponent n decreased from about 3.5 to 2 as the temperature declined for each fraction, indicating the crystal‐growth geometry changed from three‐dimensional to two‐dimensional. For isothermal crystallization, the fraction with a lesser SCB content exhibited a higher crystallization temperature (T_c) window. The results from the Avrami equation analysis showed the exponent n values were around 3 (with minor variation), which implied that the crystal‐growth geometry is pseudo‐three‐dimensional. Both of the activation energies for nonisothermal and isothermal crystallization were determined for each fraction with Kissinger and Arrhenius‐type equations, respectively. Double melting peaks were observed for both nonisothermally or isothermally crystallized specimens. The high‐melting peak was confirmed induced via the annealing effect during heating scans. The Hoffman–Weeks plot was inapplicable in obtaining the equilibrium melting temperature (T_m°) for each fraction. The relationship between T_c and T_m for the fractions is approximately T_m = T_c (°C) + 8.3. The POM results indicated that the crystals of parent or fractions formed under cooling conditions did not exhibit the typical spherulitic morphology as a result of the high SCB content. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 325–337, 2002     

Nanostructure evolution in a poly(ether ester) elastomer during drawing and the displacement of hard domains from lamellae

A poly(ether ester) thermoplastic elastomer with a soft block content of 50 wt % has been studied with synchrotron small‐angle X‐ray scattering (SAXS) during strain/relaxation cycles. The rigid nodes of the elastic network are not the hard domains themselves but instead are ordered three‐dimensional assemblies of several hard domains. At a critical elongation, single hard domains are disrupted and dislocated from these assemblies in a peculiar manner. In the ultimate structure, remaining pairs of hard domains form (semi)elastic nodes. The complex two‐dimensional SAXS patterns indicate stacks from tilted lamellae that are destroyed when the sample is strained to double its initial length. With multidimensional chord distribution function analysis, the complex nanostructure and its evolution in the draw experiment have been analyzed. The fundamental hard domains are not lamellae but cylinders (5 nm × 8 nm) arranged on a lattice at cylindrical coordinates (r₁₂, r₃), which are given by the intersections of r₃(r₁₂) = ±1.5r₁₂ ± 13nmn, n being a natural number. A semielastic component is made from hard domains forming other lamellar assemblies, which are characterized by n = 3/2. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1947–1954, 2003     

In situ single‐crystal to single‐crystal (SCSC) transformation of the one‐dimensional polymer catena‐poly[[diaqua(sulfato)copper(II)]‐μ2‐glycine] into the two‐dimensional polymer poly[μ2‐glycine‐μ4‐sulfato‐copper(II)]

The one‐dimensional coordination polymer catena‐poly[diaqua(sulfato‐κO)copper(II)]‐μ₂‐glycine‐κ²O:O′], [Cu(SO₄)(C₂H₅NO₂)(H₂O)₂]_n, (I), was synthesized by slow evaporation under vacuum of a saturated aqueous equimolar mixture of copper(II) sulfate and glycine. On heating the same blue crystal of this complex to 435 K in an oven, its aspect changed to a very pale blue and crystal structure analysis indicated that it had transformed into the two‐dimensional coordination polymer poly[(μ₂‐glycine‐κ²O:O′)(μ₄‐sulfato‐κ⁴O:O′:O′′:O′′)copper(II)], [Cu(SO₄)(C₂H₅NO₂)]_n, (II). In (I), the Cu^II cation has a pentacoordinate square‐pyramidal coordination environment. It is coordinated by two water molecules and two O atoms of bridging glycine carboxylate groups in the basal plane, and by a sulfate O atom in the apical position. In complex (II), the Cu^II cation has an octahedral coordination environment. It is coordinated by four sulfate O atoms, one of which bridges two Cu^II cations, and two O atoms of bridging glycine carboxylate groups. In the crystal structure of (I), the one‐dimensional polymers, extending along [001], are linked via N—H...O, O—H...O and bifurcated N—H...O,O hydrogen bonds, forming a three‐dimensional framework. In the crystal structure of (II), the two‐dimensional networks are linked via bifurcated N—H...O,O hydrogen bonds involving the sulfate O atoms, forming a three‐dimensional framework. In the crystal structures of both compounds, there are C—H...O hydrogen bonds present, which reinforce the three‐dimensional frameworks.     

Noncovalent Synthesis of Hierarchical Zinc Phosphates from a Single Zn4O12P4 Double‐Four‐Ring Building Block: Dimensionality Control through the Choice of Auxiliary Ligands

In contrast to the well‐known reaction of phosphonic acids RP(O)(OH)₂ with divalent transition‐metal ions that yields layered metal phosphonates [RPO₃M(H₂O)]_n, the 2,6‐diisopropylphenyl ester of phosphoric acid, dippH₂, reacts with zinc acetate in methanol under ambient conditions to afford tetrameric zinc phosphate [(ArO)PO₃Zn(MeOH)]₄ ( 1 ). The coordinated methanol in 1 can be readily exchanged by stronger Lewis basic ligands at room temperature. This strategy opens up a new avenue for building double‐four‐ring (D4R) cubane‐based supramolecular assemblies through strong intercubane hydrogen‐bonding interactions. Seventeen pyridinic ligands have been used to synthesize as many D4R cubanes [(ArO)PO₃Zn(L)]₄ ( 2 – 18 ) from 1 . The ligands have been chosen in such a way that the majority of them contain an additional functional group that could be used for noncovalent synthesis of extended structures. When the ligand does not contain any other hydrogen‐bonding donor–acceptor sites (e.g., 2,4,6‐trimethylpyridine (collidine)), zero‐dimensional D4R cubanes have been obtained. The use of pyridine, lutidine, 2‐aminopyridine, and 2,6‐diaminopyridine, however, results in the formation of linear or zigzag one‐dimensional assemblies of D4R cubanes through strong intermolecular C? H???O or N? H???O interactions. Construction of two‐dimensional assemblies of zinc phosphates has been achieved by employing 2‐hydroxypyridine or 2‐methylimidazole as the exo‐cubane ligand on zinc centers. The introduction of an alcohol side chain on the pyridinic ligand in such a way that the ? CH₂OH group cannot participate in intracubane hydrogen bonding (e.g., pyridine‐3‐methanol, pyridine‐4‐methanol, and 3,5‐dimethylpyrazole‐N‐ethanol) leads to the facile noncovalent synthesis of three‐dimensional framework structures. Apart from being useful as building blocks for noncovalent synthesis of zeolite‐like materials, compounds 1 – 18 can also be thermolyzed at approximately 500 °C to yield high‐purity zinc pyrophosphate (Zn₂P₂O₇) ceramic material.     

Two different one‐dimensional CdII halide coordination polymers constructed through bridging carboxylate ligands

Two cadmium halide complexes, catena‐poly[[chloridocadmium(II)]‐di‐μ‐chlorido‐[chloridocadmium(II)]‐bis[μ₂‐4‐(dimethylamino)pyridin‐1‐ium‐1‐acetate]‐κ³O:O,O′;κ³O,O′:O], [CdCl₂(C₉H₁₂N₂O₂)]_n, (I), and catena‐poly[1‐cyanomethyl‐1,4‐diazoniabicyclo[2.2.2]octane [[dichloridocadmium(II)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′] monohydrate], {(C₈H₁₅N₃)[CdCl₂(C₂O₄)]·H₂O}_n, (II), were synthesized in aqueous solution. In (I), the Cd^II cation is octahedrally coordinated by three O atoms from two carboxylate groups and by one terminal and two bridging chloride ligands. Neighbouring Cd^II cations are linked together by chloride anions and bridging O atoms to form a one‐dimensional zigzag chain. Hydrogen‐bond interactions are involved in the formation of the two‐dimensional network. In (II), each Cd^II cation is octahedrally coordinated by four O atoms from two oxalic acid ligands and two terminal Cl⁻ ligands. Neighbouring Cd^II cations are linked together by oxalate groups to form a one‐dimensional anionic chain, and the water molecules and organic cations are connected to this one‐dimensional zigzag chain through hydrogen‐bond interactions.     

One‐dimensional CuII coordination polymers containing C2h‐symmetric 1,1′:4′,1′′‐terphenyl‐3,3′‐dicarboxylate linkers

Two new one‐dimensional Cu^II coordination polymers (CPs) containing the C_2h‐symmetric terphenyl‐based dicarboxylate linker 1,1′:4′,1′′‐terphenyl‐3,3′‐dicarboxylate (3,3′‐TPDC), namely catena‐poly[[bis(dimethylamine‐κN)copper(II)]‐μ‐1,1′:4′,1′′‐terphenyl‐3,3′‐dicarboxylato‐κ⁴O,O′:O′′:O′′′] monohydrate], {[Cu(C₂₀H₁₂O₄)(C₂H₇N)₂]·H₂O}_n, (I), and catena‐poly[[aquabis(dimethylamine‐κN)copper(II)]‐μ‐1,1′:4′,1′′‐terphenyl‐3,3′‐dicarboxylato‐κ²O³:O^3′] monohydrate], {[Cu(C₂₀H₁₂O₄)(C₂H₇N)₂(H₂O)]·H₂O}_n, (II), were both obtained from two different methods of preparation: one reaction was performed in the presence of 1,4‐diazabicyclo[2.2.2]octane (DABCO) as a potential pillar ligand and the other was carried out in the absence of the DABCO pillar. Both reactions afforded crystals of different colours, i.e. violet plates for (I) and blue needles for (II), both of which were analysed by X‐ray crystallography. The 3,3′‐TPDC bridging ligands coordinate the Cu^II ions in asymmetric chelating modes in (I) and in monodenate binding modes in (II), forming one‐dimensional chains in each case. Both coordination polymers contain two coordinated dimethylamine ligands in mutually trans positions, and there is an additional aqua ligand in (II). The solvent water molecules are involved in hydrogen bonds between the one‐dimensional coordination polymer chains, forming a two‐dimensional network in (I) and a three‐dimensional network in (II).     

Oligonucleotides Containing Disaccharide Nucleosides

Disaccharide nucleosides with 2′‐O‐(D ‐arabinofuranosyl), 2′‐O‐(L ‐arabinofuranosyl), 2′‐O‐(D ‐ribopyranosyl), 2′‐O‐(D ‐erythrofuranosyl), and 2′‐O‐(5‐azido‐5‐deoxy‐D ‐ribofuranosyl) substituents were synthesized. These modified nucleosides were incorporated into oligonucleotides (see Table). Single substitution resulted in a ΔT_m of +0.5 to −1.4° for DNA/RNA and a ΔT_m of −0.8 to −4.7° for DNA/DNA duplexes. These disaccharide nucleosides can be well accommodated in RNA/DNA duplexes, and the presence of a NH₂−C(5″) group has a beneficial effect on duplex stability.     

Two coordination polymers constructed by 5‐[(4‐carboxyphenoxy)methyl]benzene‐1,3‐dicarboxylic acid and 2,2′‐bipyridine: syntheses,structures and luminescence properties

Coordination polymers (CPs) have attracted increasing interest in recent years. In this work, two new CPs, namely poly[[aquabis(2,2′‐bipyridine‐κ²N,N′){μ₃‐5‐[(4‐carboxylatophenoxy)methyl]benzene‐1,3‐dicarboxylato‐κ⁴O¹,O^1′:O³:O⁵}(μ‐formato‐κ³O:O,O′)dicadmium(II)] monohydrate], {[Cd₂(C₁₆H₉O₇)(HCO₂)(C₁₀H₈N₂)₂(H₂O)]·H₂O}_n ( 1 ), and poly[[(2,2′‐bipyridine‐κ²N,N′){μ₃‐5‐[(4‐carboxylphenoxy)methyl]benzene‐1,3‐dicarboxylato‐κ⁴O¹,O^1′:O³:O⁵}manganese(II)] sesquihydrate], {[Mn(C₁₆H₁₀O₇)(C₁₀H₈N₂)]·1.5H₂O}_n ( 2 ), have been prepared using the tricarboxylic acid 5‐[(4‐carboxyphenoxy)methyl]benzene‐1,3‐dicarboxylic acid and 2,2′‐bipyridine under hydrothermal conditions. CP 1 displays a two‐dimensional layer structure which is further extended into a three‐dimensional (3D) supramolecular structure via intermolecular π–π interactions, while CP 2 shows a different 3D supramolecular structure extended from one‐dimensional ladder chains by intermolecular π–π interactions. In addition, the solid‐state luminescence spectra of 1 and 2 were studied at room temperature.     

Microstructure and Magnetic Properties of Carbon‐Coated Nanoparticles

Abstract

In the present work, microstructure and superparamagnetic properties of two types of carbon‐coated magnetic Ni and Fe nanoparticles [Ni(C) and Fe(C)] are reviewed. High‐resolution transmission electron microscopy (HRTEM), electron diffraction (SAED), and x‐ray diffraction (XRD) analyses have been used to reveal the distinct structural morphologies of Ni and Fe nanoparticles. Moreover, novel carbon‐coated Ni nanoparticle assemblies offer us great opportunities for studying the mechanism of superparamagnetism in particle assemblies. Magnetization measurements [M(T) and M(H) curves] for assemblies of Ni nanoparticles indicate that modified superparamagnetic properties at T > T _B, have been found in the assemblies of Ni(C) particles. The blocking temperature, T _B, is determined to be near 115K under a certain applied field. Above T _B, the magnetization M(H, T) can be described by the classical Langevin function L using the relation, M/M _s (T = 0) = coth (μH/kT) ? kT/μH. It is suggested that these assemblies of carbon‐coated Ni nanoparticles have typical single‐domain, field‐dependent superparamagnetic relaxation properties. Finally, Mössbauer spectra and hyperfine magnetic fields at room temperature for the assemblies of Fe(C) nanoparticles confirm their distinct nanophases that were detected by structural analysis. Modified superparamagnetic relaxation is observed in the assemblies of Fe(C) nanoparticles, which is attributed to the nanocrystalline nature of the carbon‐coated nanoparticles.     

Three Cadmium(II) Coordination Polymers based on Mixed 1,2‐Naphthalenedicarboxylate and Bis(pyridyl) Co‐ligands: Structural Diversities and Photoluminescent Properties

Hydrothermal reactions of Cd(OAc)₂ · 2H₂O with 1,2‐naphthalic anhydride in the absence/presence of different rigid/flexible bis(pyridyl) co‐ligands, produce three distinct coordination polymers, namely [Cd(ndc)]_n ( 1 ), {[Cd₅(ndc)₄(bpp)₂(OH)₂](H₂O)₄}_n ( 2 ), and [Cd₅(ndc)₄(bpy)₂(OH)₂]_n ( 3 ) [ndc = 1,2‐naphthalenedicarboxylate, bpp = 1,3‐bis(4‐pyridyl)propane, and bpy = 4,4′‐bipyridine]. Complex 1 contains dinuclear [Cd₂O₂] clusters as secondary building units (SBUs) and shows a two‐dimensional (2D) kgd network. Complexes 2 and 3 possess one‐dimensional (1D) chains based on pentanuclear [Cd₅(μ₃‐OH)₂(COO)₂] units as SBUs, which are further extended to afford 2D sql sheet via flexible bpp in 2 and three‐dimensional (3D) pcu network via rigid bpy in 3 , respectively. The structural diversities indicate that the bis(pyridyl) co‐ligands with different flexibility play a key role on the formation of the final supramolecular structures. The complexes were characterized by X‐ray crystallographic, IR, elemental, thermal stability, and powder X‐ray diffraction analyses. In addition, the photoluminescent properties in solid state were also investigated.     

CdII and CoII coordination polymers constructed from benzene‐1,4‐dicarboxylic acid and 2‐(pyridin‐3‐yl)‐1H‐benzimidazole ligands

In poly[aqua(μ₃‐benzene‐1,4‐dicarboxylato‐κ⁵O¹,O^1′:O¹:O⁴,O^4′)[2‐(pyridin‐3‐yl‐κN)‐1H‐benzimidazole]cadmium(II)], [Cd(C₈H₄O₄)(C₁₂H₉N₃)(H₂O)]_n, (I), each Cd^II ion is seven‐coordinated by the pyridine N atom from a 2‐(pyridin‐3‐yl)benzimidazole (3‐PyBIm) ligand, five O atoms from three benzene‐1,4‐dicarboxylate (1,4‐bdc) ligands and one O atom from a coordinated water molecule. The complex forms an extended two‐dimensional carboxylate layer structure, which is further extended into a three‐dimensional network by hydrogen‐bonding interactions. In catena‐poly[[diaquabis[2‐(pyridin‐3‐yl‐κN)‐1H‐benzimidazole]cobalt(II)]‐μ₂‐benzene‐1,4‐dicarboxylato‐κ²O¹:O⁴], [Co(C₈H₄O₄)(C₁₂H₉N₃)₂(H₂O)₂]_n, (II), each Co^II ion is six‐coordinated by two pyridine N atoms from two 3‐PyBIm ligands, two O atoms from two 1,4‐bdc ligands and two O atoms from two coordinated water molecules. The complex forms a one‐dimensional chain‐like coordination polymer and is further assembled by hydrogen‐bonding interactions to form a three‐dimensional network.     

Two‐Dimensional Monovalent Copper Halide Coordination Polymers Incorporating Anti‐Conformation 3,3′‐Bipyridine

Hydrothermal treatment of aqueous mixtures of copper(II) halides and 3,3′‐bipyridine (3,3′‐bpy) has afforded the coordination polymers [CuCl(3,3′‐bpy)]_n ( 1 ) and [Cu₂Br₂(3,3′‐bpy)]_n ( 2 ), which were analyzed via single crystal X‐ray diffraction, infrared spectroscopy, and elemental analysis. The structure of 1 consists of two‐dimensional (2‐D) layers constructed from the linkage of castellated one‐dimensional (1‐D) [CuCl]_n stepped chains through anti‐conformation 3,3′‐bpy tethers. Compound 2 presents a related 2‐D sheet motif, albeit built from infinite 1‐D [Cu₂Br₂]_n ladders strutted by 3,3′‐bpy ligands in anti conformation. In both cases neighboring 2‐D sheets stack into 3‐D via weak C–H···halogen interactions.     

Synthesis and characterization of a cadmium(II)–organic supramolecular coordination compound based on the multifunctional 2‐amino‐5‐sulfobenzoic acid ligand

Much attention has been paid by chemists to the construction of supramolecular coordination compounds based on the multifunctional ligand 5‐sulfosalicylic acid (H₃SSA) due to the structural and biological interest of these compounds. However, no coordination compounds have been reported for the multifunctional amino‐substituted sulfobenzoate ligand 2‐amino‐5‐sulfobenzoic acid (H₂asba). We expected that H₂asba could be a suitable building block for the assembly of supramolecular networks due to its interesting structural characteristics. The reaction of cadmium(II) nitrate with H₂asba in the presence of the auxiliary flexible dipyridylamide ligand N,N′‐bis[(pyridin‐4‐yl)methyl]oxamide (4bpme) under ambient conditions formed a new mixed‐ligand coordination compound, namely bis(3‐amino‐4‐carboxybenzenesulfonato‐κO¹)diaquabis{N,N′‐bis[(pyridin‐4‐yl)methyl]oxamide‐κN}cadmium(II)–N,N′‐bis[(pyridin‐4‐yl)methyl]oxamide–water (1/1/4), [Cd(C₇H₆NO₅S)₂(C₁₄H₁₄N₄O₂)₂(H₂O)₂]·C₁₄H₁₄N₄O₂·4H₂O, (1), which was characterized by single‐crystal and powder X‐ray diffraction analysis (PXRD), FT–IR spectroscopy, thermogravimetric analysis (TG), and UV–Vis and photoluminescence spectroscopic analyses in the solid state. The central Cd^II atom in (1) occupies a special position on a centre of inversion and exhibits a slightly distorted octahedral geometry, being coordinated by two N atoms from two monodentate 4bpme ligands, four O atoms from two monodentate 4‐amino‐3‐carboxybenzenesulfonate (Hasba⁻) ligands and two coordinated water molecules. Interestingly, complex (1) further extends into a threefold polycatenated 0D→2D (0D is zero‐dimensional and 2D is two‐dimensional) interpenetrated supramolecular two‐dimensional (4,4) layer through intermolecular hydrogen bonding. The interlayer hydrogen bonding further links adjacent threefold polycatenated two‐dimensional layers into a three‐dimensional network. The optical properties of complex (1) indicate that it may be used as a potential indirect band gap semiconductor material. Complex (1) exhibits an irreversible dehydration–rehydration behaviour. The fluorescence properties have also been investigated in the solid state at room temperature.     

An unusual three‐dimensional chiral threefold polycatenating network self‐assembled from inclined two‐dimensional (4,4) layer motifs

In the coordination compound poly[diaqua(μ₂‐4,4′‐bipyridine)(μ₂‐4‐carboxylatocinnamato)nickel(II)], [Ni(C₁₀H₆O₄)(C₁₀H₈N₂)(H₂O)₂]_n, both the 4‐carboxylatocinnamate and 4,4′‐bipyridine (4,4′‐bpy) ligands act as bidentate bridges, connecting the Ni^II centres in an octahedral coordination geometry into a two‐dimensional (4,4) layer. Each layer polycatenates two other identical layers, thus giving a rare 2D → 3D polycatenating network (2D and 3D are two‐ and three‐dimensional, respectively), with a mutually parallel arrangement of the layers. The chiral 4,4′‐bpy ligands link the Ni^II centres into chiral chains, thus introducing chirality into the layer and the resulting 3D network.