Acid–Base‐Controlled Stereoselective Metalation of Overhanging Carboxylic Acid Porphyrins: Consequences for the Formation of Heterobimetallic Complexes

Overhanging carboxylic acid porphyrins have revealed promising ditopic ligands offering a new entry in the field of supramolecular coordination chemistry of porphyrinoids. Notably, the adjunction of a so‐called hanging‐atop (HAT) Pb^II cation to regular Pb^II porphyrin complexes allowed a stereoselective incorporation of the N‐core bound cation, and an allosterically controlled Newton’s cradle‐like motion of the two Pb^II ions also emerged from such bimetallic complexes. In this contribution, we have extended this work to other ligands and metal ions, aiming at understanding the parameters that control the HAT Pb^II coordination. The nature of the N‐core bound metal ion (Zn^II, Cd^II), the influence of the deprotonation state of the overhanging COOH group and the presence of a neutral ligand on the opposite side (exogenous or intramolecular), have been examined through ¹H NMR spectroscopic experiments with the help of radiocrystallographic structures and DFT calculations. Single and bis‐strap ligands have been considered. They all incorporate a COOH group hung over the N‐core on one side. For the bis‐strap ligands, either an ester or an amide group has been introduced on the other side. In the presence of a base, the mononuclear Zn^II or Cd^II complexes incorporate the carbonyl of the overhanging carboxylate as apical ligand, decreasing its availability for the binding of a HAT Pb^II. An allosteric effector (e.g., 4‐dimethylaminopyridine (DMAP), in the case of a single‐strap ligand) or an intramolecular ligand (e.g., an amide group), strong enough to compete with the carbonyl of the hung COO^?, is required to switch the N‐core bound cation to the opposite side with concomitant release of the COO^?, thereby allowing HAT Pb^II complexation. In the absence of a base, Zn^II or Cd^II binds preferentially the carbonyl of the intramolecular ester or amide groups in apical position rather than that of the COOH. This better preorganization, with the overhanging COOH fully available, is responsible for a stronger binding of the HAT Pb^II. Thus, either allosteric or acid–base control is achieved through stereoselective metalation of Zn^II or Cd^II. In the latter case, according to the deprotonation state of the COOH group, the best electron‐donating ligand is located on one or the other side of the porphyrin (COO^?>CONHR>COOR>COOH): the lower affinity of COOH for Zn^II and Cd^II, the higher for a HAT Pb^II. These insights provide new opportunities for the elaboration of innovative bimetallic molecular switches.     

Sunlight‐Driven Formation and Dissociation of a Dynamic Mixed‐Valence Thallium(III)/Thallium(I) Porphyrin Complex

Inspired by a Newton’s cradle device and interested in the development of redox‐controllable bimetallic molecular switches, a mixed‐valence thallium(III)/thallium(I) bis‐strap porphyrin complex, with Tl^III bound out of the plane of the N core and Tl^I hung to a strap on the opposite side, was formed by the addition of TlOAc to the free base and exposure to indirect sunlight. In this process, oxygen photosensitization by the porphyrin allows the oxidation of Tl^I to Tl^III. The bimetallic complex is dynamic as the metals exchange their positions symmetrically to the porphyrin plane with Tl^III funneling through the macrocycle. Further exposure of the complex to direct sunlight leads to thallium dissociation and to total recovery of the free base. Hence, the porphyrin plays a key role at all stages of the cycle of the complex: It hosts two metal ions, and by absorbing light, it allows the formation and dissociation of Tl^III. These results constitute the basis for the further design of innovative light‐driven bimetallic molecular devices.     

3‐(Pyridin‐4‐yl)acetylacetone: CdII and HgII compete for nitrogen coordination

3‐(Pyridin‐4‐yl)acetylacetone (HacacPy) acts as a pyridine‐type ligand towards Cd^II and Hg^II halides. With CdBr₂, the one‐dimensional polymer [Cd(μ‐Br)₂(HacacPy)Cd(μ‐Br)₂(HacacPy)₂]_∞ is obtained in which five‐ and six‐coordinated Cd^II cations alternate in the chain direction. Reaction of HacacPy with HgBr₂ results in [Hg(μ‐Br)Br(HacacPy)]_∞, a polymer in which each Hg^II centre is tetracoordinated. In both compounds, each metal(II) cation is N‐coordinated by at least one HacacPy ligand. Equimolar reaction between these Cd^II and Hg^II derivatives, either conducted in ethanol as solvent or via grinding in the solid state, leads to ligand redistribution and the formation of the well‐ordered bimetallic polymer catena‐poly[[bromidomercury(II)]‐μ‐bromido‐[aquabis[4‐hydroxy‐3‐(pyridin‐4‐yl)pent‐3‐en‐2‐one]cadmium(II)]‐di‐μ‐bromido], [CdHgBr₄(C₁₀H₁₁NO₂)₂(H₂O)]_n or [{HgBr}(μ‐Br){(HacacPy)₂Cd(H₂O)}(μ‐Br)₂]_∞. Hg^II and Cd^II cations alternate in the [100] direction. The HacacPy ligands do not bind to the Hg^II cations, which are tetracoordinated by three bridging and one terminal bromide ligand. The Cd^II centres adopt an only slightly distorted octahedral coordination. Three bromide ligands link them in a (2 + 1) pattern to neighbouring Hg^II atoms; two HacacPy ligands in a cis configuration, acting as N‐atom donors, and a terminal aqua ligand complete the coordination sphere. Classical O—H…Br hydrogen bonds stabilize the polymeric chain. O—H…O hydrogen bonds between aqua H atoms and the uncoordinated carbonyl group of an HacacPy ligand in a neighbouring strand in the c direction link the chains into layers in the (010) plane.     

Structural Variety of Cobalt(II), Nickel(II), Zinc(II), and Cadmium(II) Complexes with 4,4′‐Azopyridine: Synthesis,Structure and Luminescence Properties

Self‐assembled bi‐ and polymetallic complexes of Co^II, Ni^II, Zn^II, and Cd^II were obtained by the reaction of 4,4′‐azopyridine (azpy) with metal tri‐tert‐butoxysilanethiolates (Co, 1 ; Cd, 2 ), acetylacetonates (Ni, 3 ; Zn, 4 ), and acetates (Cd, 5 ). All compounds were characterized by single‐crystal X‐ray structure analysis, elemental analysis, FTIR spectroscopy, and thermogravimetry. Complexes 1 , 2 and 4 , 5 exhibit diverse structural conformations: 1 is bimetallic, 2 and 4 are 1D coordination polymers, and 5 is a 2D coordination framework formed from bimetallic units. The obtained complexes contain metal atoms bridged by a molecule of azpy. The luminescent properties of 1–5 were investigated in the solid state.     

Investigations on the Structure Diversity and Thermal Degradation Behavior of CdII and ZnII Thiocyanato Coordination Compounds based on 3‐Acetylpyridine as Neutral Co‐Ligand

Reaction of Cd^II and Zn^II thiocyanate with 3‐acetylpyridine leads to the formation of the new Cd^II and Zn^II coordination compounds [Cd(NCS)₂(3‐acetylpyridine)₄] ( 1A ), [Cd(NCS)₂(3‐acetylpyridine)₂]_n ( 1B ), [Cd(NCS)₂(3‐acetylpyridine)]_n ( 1C ) and [Zn(NCS)₂(3‐acetylpyridine)₂] ( 2A ). Compound 1A consists of discrete complexes, in which the metal centers are octahedrally coordinated by four terminal bonded N‐donor co‐ligands and two terminal N‐bonded thiocyanato anions. In compound 2A the metal centers are only tetrahedrally coordinated by two terminal bonded N‐donor co‐ligands and two terminal N‐bonded thiocyanato anions. In compound 1B the Cd^II cations are octahedrally coordinated by two terminal bonded N‐donor co‐ligands and four thiocyanato anions. The metal centers are linked by μ‐1, 3 bridging thiocyanato anions into chains. In compound 1C the metal cations are octahedrally coordinated by two μ‐1, 5 bridging 3‐acetyl‐pyridine ligands and four μ‐1, 3 bridging thiocyanato anions building up a three‐dimensional coordination network. Investigations on the thermal degradation behavior of all compounds using simultaneous differential thermoanalysis and thermogravimetry as well as X‐ray powder diffraction and IR spectroscopy prove that on heating compound 2A decompose without the formation of 3‐acetylpyridine‐deficient intermediates. In contrast, for compound 1A a stepwise decomposition is observed, leading to the formation of the 3‐acetylpyridine‐deficient compound [Cd(NCS)₂(3‐acetylpyridine)₂]_n ( 1B ) which decomposes on further heating     

Rational Approach Towards Designing Metallogels From a Urea‐Functionalized Pyridyl Dicarboxylate: Anti‐inflammatory,Anticancer, and Drug Delivery

A structural rationale was adopted to design a series of metallogels from a newly synthesized urea‐functionalized dicarboxylate ligand, namely, 5‐[3‐(pyridin‐3‐yl)ureido]isophthalic acid ( PUIA ), that produces metallogels upon reaction with various metal salts (Cu^II, Zn^II, Co^II, Cd^II, and Ni^II salts) at room temperature. The gels were characterized by dynamic rheology and transmission electron microscopy (TEM). The existence of a coordination bond in the gel state was probed by FTIR and ¹H NMR spectroscopy in a Zn^II metallogel (i.e., MG2 ). Single crystals isolated from the reaction mixture of PUIA and Co^II or Cd^II salts characterized by X‐ray diffraction revealed lattice inclusion of solvent molecules, which was in agreement with the hypothesis based on which the metallogels were designed. MG2 displayed anti‐inflammatory response (prostaglandin E₂ assay) in the macrophage cell line (RAW 264.7) and anticancer properties (cell migration assay) on a highly aggressive human breast cancer cell line (MDA‐MB‐231). The MG2 metallogel matrix could also be used to load and release (pH responsive) the anticancer drug doxorubicin. Fluorescence imaging of MDA‐MB‐231 cells treated with MG2 revealed that it was successfully internalized.     

Dynamic Equilibria in Solvent‐Mediated Anion,Cation and Ligand Exchange in Transition‐Metal Coordination Polymers: Solid‐State Transfer or Recrystallisation?

The solution properties of a series of transition‐metal–ligand coordination polymers [ML(X)_n]_∞ [M=Ag^I, Zn^II, Hg^II and Cd^II; L=4,4′‐bipyridine (4,4′‐bipy), pyrazine (pyz), 3,4′‐bipyridine (3,4′‐bipy), 4‐(10‐(pyridin‐4‐yl)anthracen‐9‐yl)pyridine (anbp); X=NO₃^?, CH₃COO^?, CF₃SO₃^?, Cl^?, BF₄^?; n=1 or 2] in the presence of competing anions, metal cations and ligands have been investigated systematically. Providing that the solubility of the starting complex is sufficiently high, all the components of the coordination polymer, namely the anion, the cation and the ligand, can be exchanged on contact with a solution phase of a competing component. The solubility of coordination polymers is a key factor in the analysis of their reactivity and this solubility depends strongly on the physical properties of the solvent and on its ability to bind metal cations constituting the backbone of the coordination polymer. The degree of reversibility of these solvent‐induced anion‐exchange transformations is determined by the ratio of the solubility product constants for the starting and resultant complexes, which in turn depend upon the choice of solvent and the temperature. The extent of anion exchange is controlled effectively by the ratio of the concentrations of incoming ions to outgoing ions in the liquid phase and the solvation of various constituent components comprising the coordination polymer. These observations can be rationalised in terms of a dynamic equilibrium of ion exchange reactions coupled with Ostwald ripening of crystalline products. The single‐crystal X‐ray structures of [Ag(pyz)ClO₄]_∞ ( 1 ), {[Ag(4,4′‐bipy)(CF₃SO₃)] ? CH₃CN}_∞ ( 2 ), {[Ag(4,4′‐bipy)(CH₃CN)]ClO₄ ? 0.5 CH₃CN}_∞ ( 3 ), metal‐free anbp ( 4 ), [Ag(anbp)NO₃(H₂O)]_∞ ( 5 ), {[Cd(4,4′‐bipy)₂(H₂O)₂](NO₃)₂ ? 4 H₂O}_∞ ( 6 ) and {[Zn(4,4′‐bipy)SO₄(H₂O)₃] ? 2 H₂O}_∞ ( 7 ) are reported.     

Guest‐Induced Transformation of a Porphyrin‐Edged FeII4L6 Capsule into a CuIFeII2L4 Fullerene Receptor

The combination of a bent diamino(nickel(II) porphyrin) with 2‐formylpyridine and Fe^II yielded an Fe^II₄L₆ cage. Upon treatment with the fullerenes C₆₀ or C₇₀, this cage was found to transform into a new host–guest complex incorporating three Fe^II centers and four porphyrin ligands, in an arrangement that is hypothesized to maximize π interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity. The new complex shows coordinative unsaturation at one of the Fe^II centers as the result of the incommensurate metal‐to‐ligand ratio, which enabled the preparation of a heterometallic cone‐shaped Cu^IFe^II₂L₄ adduct of C₆₀ or C₇₀.     

SnIV Porphyrin Scaffolds for Axially Bonded Multiporphyrin Arrays: Synthesis and Structure Elucidation by NMR Studies

A simple, one‐step, supramolecular strategy was adopted to synthesize Sn^IV‐porphyrin‐based axially bonded triads and higher oligomers by using meso‐pyridyl Sn^IV porphyrin, meso‐hydroxyphenyl‐21,23‐dithiaporphyrin, and Ru^II porphyrin as building blocks and employing complementary and non‐interfering Sn^IV?O and Ru^II ??? N interactions. The multiporphyrin arrays are stable and robust and were purified by column chromatography. ¹H, ¹H–¹H COSY and NOESY NMR spectroscopic studies were used to unequivocally deduce the molecular structures of Sn^IV‐porphyrin‐based triads and higher oligomers. Absorption and electrochemical studies indicated weak interaction among the different porphyrin units in triads and higher oligomers, in support of the supramolecular nature of the arrays. Steady‐state fluorescence studies on triads indicated the possibility of energy transfer in the singlet state from the basal Sn^IV porphyrin to the axial 21,23‐dithiaporphyrin. However, the higher oligomers were weakly fluorescent due to the presence of heavy Ru^II porphyrin unit(s), which quench the fluorescence of the Sn^IV porphyrin and 21,23‐dithiaporphyrin units.     

An unusual chain cadmium(II) coordination polymer: catena‐poly[[(2,2′‐bipyridyl‐κ2N,N′)cadmium(II)]‐di‐μ‐chlorido‐[(2,2′‐bipyridyl‐κ2N,N′)cadmium(II)]‐di‐μ‐thiocyanato‐κ2N:S;κ2S:N]

The title complex, [CdCl(NCS)(C₁₀H₈N₂)]_n, represents an unusual Cd^II coordination polymer constructed by two types of anionic bridges and 2,2′‐bipyridyl (bipy) terminal ligands. These two types of bridges are arranged around inversion centers. The distorted octahedral coordination of the Cd^II center is provided by two chloride ions, one N‐ and one S‐donor atom from two thiocyanate ions, and a pair of N atoms from the chelating bipy ligand. Interestingly, adjacent Cd^II ions are interconnected alternately by paired chloride [Cd...Cd = 3.916 (1) Å] and thiocyanate bridges [Cd...Cd = 5.936 (1) Å] to generate an infinite one‐dimensional coordination chain. Furthermore, weak interchain C—H...S interactions between the bipy components and thiocyanate ions lead to the formation of a layered supramolecular structure.     

Synthesis,Crystal Structures,and Properties of Copper(II), Zinc(II), and Cadmium(II) Coordination Polymers Based on 5‐Nitro‐isophthalate and 1,2‐(2‐Pyridyl)‐1,2,4‐triazole

Three coordination polymers, namely {[Cu(5‐nipa)(L²²)](H₂O)₂}_n ( 1 ), [Zn(5‐nipa)(L²²)(H₂O)]_n ( 2 ), and {[Cd₂(5‐nipa)₂(L²²)(H₂O)₃](H₂O)_3.6}_n ( 3 ), were prepared under similar synthetic method based on 1,2‐(2‐pyridyl)‐1,2,4‐triazole (L²²) and ancillary ligand 5‐nitro‐isophthalic acid (5‐H₂nipa) with Cu^II, Zn^II, and Cd^II perchlorate, respectively. All the complexes were characterized by IR spectroscopy, elemental analysis, and powder X‐ray diffraction (PXRD) patterns. Single‐crystal X‐ray diffraction indicates that complexes 1 and 2 show similar 1D chain structures, whereas complex 3 exhibits the 2D coordination network with hcb topology. The central metal atoms show distinct coordination arrangements ranging from distorted square‐pyramid for Cu^II in 1 , octahedron for Zn^II in 2 , to pentagonal‐bipyramid for Cd^II in 3 . The L²² ligand adopts the same (η³,μ₂) coordination fashion in complexes 1 – 3 , while the carboxyl groups of co‐ligand 5‐nipa^2– adopt monodentate fashion in 1 and 2 and bidentate chelating mode in 3 . These results indicate that the choice of metal ions exerts a significant influence on governing the target complexes. Furthermore, thermal stabilities of complexes 1 – 3 and photoluminescent properties of 2 and 3 were also studied in the solid state.     

A Multifunctional Bimetallic Molecular Device for Ultrasensitive Detection,Naked‐Eye Recognition,and Elimination of Cyanide Ions

A new bimetallic Fe^II–Cu^II complex was synthesized, characterized, and applied as a selective and sensitive sensor for cyanide detection in water. This complex is the first multifunctional device that can simultaneously detect cyanide ions in real water samples, amplify the colorimetric signal upon detection for naked‐eye recognition at the parts‐per‐million (ppb) level, and convert the toxic cyanide ion into the much safer cyanate ion in situ. The mechanism of the bimetallic complex for high‐selectivity recognition and signaling toward cyanide ions was investigated through a series of binding kinetics of the complex with different analytes, including CN^?, SO₄^2?, HCO₃^?, HPO₄^2?, N₃^?, CH₃COO^?, NCS^?, NO₃^?, and Cl^? ions. In addition, the use of the indicator/catalyst displacement assay (ICDA) is demonstrated in the present system in which one metal center acts as a receptor and inhibitor and is bridged to another metal center that is responsible for signal transduction and catalysis, thus showing a versatile approach to the design of new multifunctional devices.     

A novel three-dimensional coordination polymer [Cd2(C3H2O4)2(H2O)2(μ 2-hmt)] n (hmt = hexamethylenetetramine): synthesis and crystal structure

The self-assembly of the Cd^II ion, hexamethylenetetramine (hmt) and malonate ligand yields a three-dimensional (3D) coordination polymer [Cd₂(C₃H₂O₄)₂(H₂O)₂( ₂-hmt)] _n with channels. The Cd^II ion is located in a octahedral coordination environment, composed of four oxygen atoms from three malonates, one oxygen atom of water and one nitrogen atom of hmt. Two oxygen atoms of each malonate coordinate to the same Cd^II ion and the other two oxygen atoms connect to adjacent two Cd^II ions respectively to form a two-dimensional infinite network, these networks are bridged by ₂-hmt coordinated to Cd^II ions to product a 3D architecture.     

Poly[bis(μ‐4‐benzoyl‐1‐isonicotinoylthiosemicarbazide‐κ2N:S)dichloridocadmium(II)]

The asymmetric unit of the title complex, [CdCl₂(C₁₄H₁₂N₄O₂S)₂]_n, consists of one Cd^II ion located on the crystallographic inversion centre, one 4‐benzoyl‐1‐isonicotinoylthiosemicarbazide ligand and one chloride ligand. The central Cd^II ion adopts a distorted octahedral coordination geometry formed by two pyridyl N atoms of two ligands, two S atoms of two other ligands and two chloride ligands. The thiosemicarbazide ligands act as bridges, linking the metal ions into a two‐dimensional layered structure parallel to the bc plane. Intermolecular N—H...O hydrogen bonds and C—H...π interactions exist between adjacent layers.     

Ligation of alkoxymethylimidazoles towards cadmium(II) and zinc(II). X-ray,spectroscopic, thermal and potentiometric investigation

The stability constants and structure of the complexes of Cd^II and Zn^II with 1-ethoxymethylimidazole (ExMeIm), 1-propoxymethylimidazole (PxMeIm), 1-ethoxymethyl-2-methylimidazole (ExMe-2-MeIm) and 1-propoxymethyl-2-methylimidazole (PxMe-2-MeIm) in aqueous solution have been determined by potentiometric methods. Zn^II form both tetrahedral and octahedral species with the cited ligands according to the configurational equilibrium type: octahedron tetrahedron, but Cd^II prefers octahedral coordination of alkoxymethylimidazole complexes in aqueous solution. Retention of the six-coordination form of Cd^II has also been confirmed by the data obtained for two novel compounds which have been synthesized in the solid state. The crystal and molecular structure of [Cd(ExMeIm)₄(NO₃)₂] (1) has been determined by X-ray diffraction. The coordination geometry around the Cd^II ion can be considered as slightly distorted tetragonal bipyramidal (CdN₄O₂). Additionally, another six-coordinate Cd^II compound with ethoxymethyl-2-methylimidazole [Cd(ExMe-2-MeIm)₄(H₂O)](NO₃)₂ (2) has been characterized by spectroscopic (i.r., far i.r., Raman) ES–MS and t.g.a. methods.     

HgII-Mediated TlI-to-TlIII Oxidation in Dynamic PbII/Tl Porphyrin Complexes

Compared with their purely organic counterparts, molecular switches that are based on metal ion translocations have been underexplored, and more particularly, it remains challenging to control the translocation of several particles in multisite receptors. Recently, bimetallic complexes that undergo double translocation processes have been developed with bis-strapped porphyrin ligands. To implement a redox control for these systems, we have investigated the formation of heterobimetallic lead/thallium complexes, with thallium in the +I and +III oxidation states. Two different complexes were characterized: 1) a Pb^II/Tl^I complex, in which both metal ions interact with the N-core on its different sides, and 2) a Pb^II/Tl^III complex with Tl^III selectively bound to the N-core and Pb^II selectively bound to the strap opposite to Tl^III. These two complexes undergo interconversion between their two degenerate forms (same coordination of the metal ions but on opposite sides) by different intra or intermolecular translocation pathways. In addition, conversion of the Pb^II/Tl^I complex into its Pb^II/Tl^III counterpart was achieved by addition of a stoichiometric amount of Hg^II salt as a sacrificial electron acceptor. These results further contribute to the elaboration of devices that feature redox-controlled compartmentalized double translocations.     

Poly[[(μ2‐biphenyl‐2,4′‐dicarboxylato)[μ2‐1,4‐bis(imidazol‐1‐ylmethyl)benzene]cadmium(II)] 0.15‐hydrate]

The asymmetric unit of the title two‐dimensional coordination polymer, {[Cd(C₁₄H₈O₄)(C₁₄H₁₄N₄)]·0.15H₂O}_n, is composed of one Cd^II cation, one biphenyl‐2,4′‐dicarboxylate (bpdc) anion, one 1,4‐bis(imidazol‐1‐ylmethyl)benzene (bix) ligand and 0.15 solvent water molecules. The coordination environment of the Cd^II cation is defined by four carboxylate O atoms from two different bpdc anions in a chelating mode and two N atoms from two distinct bix ligands, constructing a distorted trigonal prism polyhedron. Two inversion‐related Cd^II cations are bridged together by two positionally disordered bpdc anions, forming a 22‐membered ring with a Cd...Cd distance of 9.1966 (9) Å. These rings are then further linked by two bix ligands, extending into a two‐dimensional layer along (102) with 6³ topology.     

Synthesis,crystal structure and characterization of a three‐dimensional CdII coordination polymer constructed from 2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalate

Bifunctional organic ligands are very popular for the design of coordination polymers because they allow the formation of a great diversity of structures. In the title coordination polymer, the new bifunctional inversion‐symmetric ligand 2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalic acid (abbreviated as H₂bttpa) links Cd^II cations, giving rise to the three‐dimensional Cd^II coordination polymer catena‐poly[diaqua[μ₄‐2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalato‐κ⁴O¹:O⁴:N⁴:N^4′]cadmium(II)], [Cd(C₁₂H₆N₆O₄)(H₂O)₂]_n or [Cd(bttpa)(H₂O)₂]_n. The asymmetric unit consists of half a Cd^II cation, half a bttpa²⁻ ligand and one coordinated water molecule. The Cd^II cation is located on a twofold axis and is hexacoordinated in a distorted octahedral environment of four O and two N atoms. Four different bttpa²⁻ ligands contribute to this coordination, with two carboxylate O atoms in trans positions and two triazole N atoms in cis positions. Two aqua ligands in cis positions complete the coordination sphere. The fully deprotonated bttpa²⁻ ligand sits about a crystallographic centre of inversion and links two Cd^II cations to form a chain in a μ₂‐terephthalato‐κ²O¹:O⁴ bridge. This chain extends in the other two directions via the triazole heterocycles, producing a three‐dimensional framework. O—H…O hydrogen bonds and weak C—H…N interactions stabilize the three‐dimensional crystal structure. The FT–IR spectrum, X‐ray powder pattern, thermogravimetric behaviour and solid‐state photoluminescence of the title polymer have been investigated. The photoluminescence is enhanced and red‐shifted with respect to the uncoordinated ligand.     

A novel cadmium(II) coordination polymer with a four‐connected (4,4)‐net based on a trinuclear cadmium(II) node

In the title cadmium(II) coordination polymer, poly[tri‐μ₄‐adipato‐bis(2‐phenyl‐1H‐1,3,7,8‐tetraazacyclopenta[l]phenanthrene‐κ²N⁷,N⁸)tricadmium(II)], [Cd₃(C₆H₈O₄)₃(C₁₉H₁₂N₄)₂]_n, one of the Cd atoms is in a distorted pentagonal bipyramidal coordination environment, surrounded by five O atoms from three adipate (adip) ligands and two N atoms from one 2‐phenyl‐1H‐1,3,7,8‐tetraazacyclopenta[l]phenanthrene (L) ligand. A second Cd atom occupies an inversion center and is coordinated by six O atoms from six adip ligands in a distorted octahedral geometry. The carboxylate ends of the adip ligands link Cd^II atoms to form unique trinuclear Cd^II clusters, which are further bridged by the adip linkers to produce a two‐dimensional layer structure. Topologically, each trinuclear Cd^II cluster is connected to four others through six adip ligands, thus resulting in a unique two‐dimensional four‐connected framework of (4,4)‐topology. This work may help the development of the coordination chemistry of 1,10‐phenanthroline derivatives.     

One‐ and two‐dimensional CdII coordination polymers constructed from 2‐(2‐methyl‐1H‐benzimidazol‐1‐yl)acetate ligands

The one‐ and two‐dimensional polymorphic cadmium polycarboxylate coordination polymers, catena‐poly[bis[μ₂‐2‐(2‐methyl‐1H‐benzimidazol‐1‐yl)acetato‐κ³N³:O,O′]cadmium(II)], [Cd(C₁₀H₉N₂O₂)₂]_n, and poly[bis[μ₂‐2‐(2‐methyl‐1H‐benzimidazol‐1‐yl)acetato‐κ³N³:O,O′]cadmium(II)], also [Cd(C₁₀H₉N₂O₂)₂]_n, were prepared under solvothermal conditions. In each structure, each Cd^II atom is coordinated by four O atoms and two N atoms from four different ligands. In the former structure, two crystallographically independent Cd^II atoms are located on twofold symmetry axes and doubly bridged in a μ₂‐N:O,O′‐mode by the ligands into correspondingly independent chains that run in the [100] and [010] directions. Chains containing crystallographically related Cd^II atoms are linked into sheets viaπ–π stacking interactions. Sheets containing one of the distinct types of Cd^II atom are stacked perpendicular to [001] and alternate with sheets containing the other type of Cd^II atom. The second complex is a two‐dimensional homometallic Cd^II (4,4) net structure in which each Cd^II atom is singly bridged to four neighbouring Cd^II atoms by four ligands also acting in a μ₂‐N:O,O′‐mode. A square‐grid network results and the three‐dimensional supramolecular framework is completed by π–π stacking interactions between the aromatic ring systems.