Co/Mn-based 2D coordination polymers: synthesis, structure and ring opening polymerization

Reactions of the tetraphosphine ligand N,N,N',N'-tetra(diphenylphosphanylmethyl)ethylene diamine) (dppeda) or 1,4-N,N,N',N'-tetra(diphenylphosphanylmethyl)benzene diamine (dpppda) with NiCl2, ancillary ligand (C2H5)2NCS2Na (Na(dtc)) and NH4PF6 afforded two binuclear complexes [(dtc)Ni(dppeda)Ni(dtc)](PF6)2 (1) and [(dtc)Ni(dpppda)Ni(dtc)](PF6)2 (2). Compounds 1 and 2 were characterized by elemental analyses, IR spectra, (1)H, (13)C{(1)H} NMR and (31)P{(1)H} NMR, electrospray ionization (ESI) mass spectra, thermogravimetric (TGA) experiments and single crystal X-ray diffraction. The Ni(ii) atoms in both compounds form a square planar coordination geometry while the ligands hold a similar end-to-end coordination mode. Both products can catalyze the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) while 1 exhibited a higher catalytic activity than 2. Influencing aspects such as solvent, temperature, the ratio of ε-CL to catalyst, the presence of benzyl alcohol, concentration of ε-CL and reaction intervals were investigated.

Ring-opening polymerization of ε-caprolactone by Zr(IV) tris(β-diketonates): Electronic character of complexes in initiation and propagation steps

We report the synthesis of the 2,2'-[2,5-bis(carboxymethoxy)-1,4-phenylene]diacetic acid (TALH(4)) ligand and the structures of its adducts with ammonium, namely diammonium 2,2'-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetate, 2NH(4)(+).C(14)H(12)O(10)(2-), (I), lanthanum, namely poly[[aquabis[mu(4)-2,2'-(2-carboxylatomethyl-5-carboxymethyl-1,4-phenylenedioxy)diacetato]dilanthanum(III)] monohydrate], {[La(2)(C(14)H(11)O(10))(2)(H(2)O)].H(2)O}(n), (II), and zinc cations, namely poly[[{mu(4)-2,2'-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetato}zinc(II)] trihydrate], {[Zn(C(14)H(12)O(10))].3H(2)O}(n), (III), and poly[[diaqua(mu(2)-4,4'-bipyridyl){mu(4)-2,2'-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetato}dizinc(II)] dihydrate], {[Zn(2)(C(14)H(10)O(10))(C(10)H(8)N(2))(H(2)O)(2)].2H(2)O}(n), (IV), the formation of all four being associated with deprotonation of TALH(4). Adduct (I) is a diammonium salt of TALH(2)(2-), with the ions located on centres of crystallographic inversion. Its crystal structure reveals a three-dimensional hydrogen-bonded assembly of the component species. Reaction of TALH(4) with lanthanum trinitrate hexahydrate yielded a two-dimensional double-layer coordination polymer, (II), in which the La(III) cations are nine-coordinate. With zinc dinitrate hexahydrate, TALH(4) forms 1:1 two-dimensional coordination polymers, in which every Zn(II) cation is linked to four neighbouring TALH(2)(2-) anions and each unit of the organic ligand is coordinated to four different tetrahedral Zn(II) cation connectors. The crystal structure of this compound accommodates molecules of disordered water at the interface between adjacent polymeric layers to give (III), and it has been determined with low precision. Another polymer assembly, (IV), was obtained when zinc dinitrate hexahydrate was reacted with TALH(4) in the presence of an additional 4,4'-bipyridyl ligand. In the crystal structure of (IV), the bipyridyl and TAL(4-) entities are located on two different inversion centres. The ternary coordination polymers form layered arrays with corrugated surfaces, with the Zn(II) cation connectors revealing a tetrahedral coordination environment. The two-dimensional polymers in (II)-(IV) are interconnected with each other by hydrogen bonds involving the metal-coordinated and noncoordinated molecules of water. TALH(4) is doubly deprotonated, TALH(2)(2-), in (I) and (III), triply deprotonated, viz. TALH(3-), in (II), and quadruply deprotonated, viz. TAL(4-), in (IV). This report provides the first structural characterization of TALH(4) (in deprotonated form) and its various supramolecular adducts. It also confirms the potential utility of this tetraacid ligand in the formulation of coordination polymers with metal cations.

Two-dimensional (2D) coordination polymers (CPs) have a highly accessible surface area that permits guest molecules to effectively access the micropores in the CPs. Here we report a bottom-up synthesis of 2D cyano-bridged Cu-Pt CP nanoflakes using trisodium citrate as a chelating agent, which controls the nucleation rate and the crystal growth. The lateral sizes of the CP nanoflakes are controlled by changing the amount of trisodium citrate used. We strongly believe that our method will be useful for the preparation of other types of 2D CP nanoflakes. The 2D CPs have many active sites for catalytic and electrochemical reactions, and furthermore the assembled CPs can be used as membrane filters.

A green and nontoxic ring-opening polymerization (ROP) of ε-caprolactone (CL) with appreciably high molecular weight (Mn), low dispersity (PDI), and high conversion was achieved using FeCl3 as a catalyst and Benzyl alcohol as an initiator in solvents at ambient temperature. Effects of Fe compounds, solvents, reaction temperature, catalyst concentration, and monomer concentration were investigated. The kinetic experiments reveal the controlled nature of using FeCl3 as a catalyst.

Synthesis of mono- and tetra-nuclear β-pyridylenolate zinc complexes and their catalysis toward the ring-opening copolymerization of ε-caprolactone and lactide

Two N,N′-bis(3-pyridylmethyl)pyromellitic diimide (3-pmpmd) coordination polymers, namely{[Hg(3-pmpmd)I2]·H2O)}n (1), {[Ni2(3-pmpmd)3 (NO3)4]·2CH3OH}n (2), have been synthesized by reactions of 3-pmpmd with HgI2, Ni(NO3)2, respectively. Both complexes have been characterized by elemental analyses, powder X-ray diffraction, thermogravimetric analyses, IR spectroscopy, and single-crystal X-ray diffraction. In complex 1, the 3-pmpmd ligand adopts Zt-mode conformation, resulting in a typical 1D zigzag chain arranged in a parallel array; in complex 2, the 3-pmpmd ligand adopts Zt-mode and Uc-mode (two conformations), and complex 2 is a 2D (6, 3) network containing 1D quadrangle channels to accommodate the methanol molecules. The structural diversity in both complexes is attributed to the different conformations adopted by the 3-pmpmd ligand. Complex 2 showed remarkably enhanced fluorescence intensity at 340 nm upon the addition of 2 equiv of SCN− anion (NaSCN) with respect to complex 2, which is highly promising for fluorescence sensing of the SCN− anion. The methanol adsorption of complex 2 exhibited a dynamic adsorption property. Two 1D and 2D N,N′-bis(3-pyridylmethyl)pyromellitic diimide (3-pmpmd) coordination polymers have been synthesized; the conformations of 3-pmpmd ligand affects their structural diversity. The enhanced fluorescence intensity sensor for SCN− anion of complex 2 was investigated, which is highly promising for fluorescence sensing SCN− anion.

The Mn2+ and Mo6+ based metal-mercaptoacetate (metal-MA) hybrids were prepared by a simple acid–base titration method. The prepared metal-MA hybrids were analysed by FT-IR spectroscopy, UV–visible spectroscopy, SEM, particle size analyser (PSA), XRD and EDX. The prepared metal-MA hybrids were investigated to assess their catalytic activity for ring-opening polymerization (ROP) of ε-caprolactone (CL) in the absence of an initiator at 160 °C in N2 atmosphere by varying the catalyst concentration and temperature. The catalytic activity of the metal-MA hybrid towards the ROP of CL was evidenced by the FTIR-RI method. The % yield, degradation temperature (Td), melting temperature (Tm) and molecular weight (Mw) of poly(ε-caprolactone) (PCL) were also investigated. The structure of PCL was comprehended by analysing its NMR spectrum. The activation energy (Ea) for the ROP of CL was determined as 10,363 kcal/mol. A linear increase in Mw of PCL with the increasing [M0/I0] ratio was also noticed.Graphical abstract

Hydrothermal reaction of hemimellitic acid (H3hma) and 4-chlorobenzoic acid (Hcba) with erbium oxide yielded a two-dimensional (2D) coordination polymer formulated as [Er4(μ3-OH)4(hma)(cba)5]n·n(Hcba) (1). It is characterized by single crystal X-ray diffraction, powder XRD, infrared (IR) spectroscopy and thermogravimetric analysis (TGA). The compound possesses a centrosymmetric wheel-like core involving 10 Er(III) ions supported by two crystallographically identical hma ligands. Neighboring decanuclear [Er10] wheels are connected to each other by edge-sharing two Er(III) ions along the a-axis and by μ3-OH− along the b-axis, generating a 2D layered erbium–organic network in the ab-plane. The organic moieties of the cba ligands point to the direction of the c-axis, forming a hydrophobic environment.

A strategy for the formation of heterometallic coordination polymers based on novel copper(II) and cobalt(III) heteroleptic complexes (acacCN)Cu(dpm) and (acacCN)Co(dpm)(2) (acacCN = 3-cyanoacetylacetonate; dpm = dipyrrin) is presented. Using dipyrrins appended with a p- or m-pyridyl group, dpm-4py and dpm-3py, four novel copper and cobalt complexes were prepared and characterized both in solution and in the solid state. These two classes of complexes show different electrochemical properties upon investigation by cyclic voltammetry in CH(2)Cl(2). While the copper complexes show only irreversible reduction processes, the voltammogram of the cobalt species reveals the presence of two quasi-reversible reductions. In the solid state, the copper(II) compounds self-assemble to form one-dimensional architectures upon coordination of the peripheral pyridyl group to the copper center, as characterized by single-crystal X-ray diffraction. Owing to the filled coordination sphere of the octahedral cobalt centers, the (acacCN)Co(dpm-py)(2) compounds crystallize as isolated molecules. Upon reaction with silver salts, these complexes form crystalline heterometallic architectures with different organization and dimensionality, depending on the nature of the metal center and the position of the nitrogen atom in the pyridyl group. The two copper complexes lead to the formation of trinuclear species, {[(acacCN)Cu(dpm-py)](2)Ag}(+), resulting from coordination of the pyridyl groups to the silver cations. However, while meta-functionalized complexes self-assemble into an extended architecture via weak interaction of the peripheral nitrile of the acacCN ligand to the Ag(+) cation, this interaction is not present in the para-functionalized analogue. In both networks based on the Ag(BF(4)) salt, coordination of the tetrafluoroborate anion to the silver center in the rather rare chelate mode is observed. Upon assembly of the cobalt metallatectons with silver salts, two-dimensional (2D) coordination polymers are obtained in crystalline form, resulting, however, from different sets of interactions. Indeed, no coordination of the peripheral nitrile of the acacCN ligand is observed in the network incorporating the m-pyridyl-appended dpm; coordination of the pyridyl groups to the silver center and d(10)-d(10) interactions lead to a 2D architecture. In the case of the para analogue, a 2D honeycomb network is observed owing to coordination of the Ag(I) ion to two pyridyl nitrogen atoms and to one peripheral nitrile group of a acacCN ligand. This latter polymer represents a geometrical hybrid of the networks reported in the literature based on homoleptic Co(dpm-4py)(3) and Cr(acacCN)(3) complexes.

Binuclear aluminum alkyl complexes 2a–4g supported by linked bis(β-diketiminate) ligands were synthesized via the reaction of AlEt3 or AlMe3 and the corresponding proligand in a 2:1 molar ratio with moderate yields. The isolated complexes were well-characterized by 1H-NMR, 13C-NMR and elemental analysis. The binuclear nature of aluminum complex 2b was further confirmed by an X-ray diffraction study. All complexes 2a–4g could efficiently initiate the ring-opening polymerization (ROP) of e-caprolactone in toluene. The substituents at the aromatic rings and the linker unit in the auxiliary ligands exerted significant influence on the catalytic behavior of the investigated aluminum complexes. Complex 4g (R1 = R2 = Cl) containing propylenyl bridging unit exhibited the highest catalytic activity among these complexes, which might be attributed to the increased electrophilicity of the metal center as well as more opened coordination sphere. The molecular weights of obtained poly(e-caprolactone)s deviating considerably from the theoretical values indicated that the ROP of e-caprolactone by complexes 2a–4g was not well-controlled, which was also judged from the broad molecular weight distributions (MWD = 1.47–2.47) of produced poly(e-caprolactone)s. These complexes proved to be inactive toward the polymerization of rac-lactide alone. In the presence of alcohol the polymerization occurred, which was actually initiated by the decomposition species of the aluminum complex upon the treatment with isopropanol.

An AIEgen chemosensor of H2hbih, [(E)-N-(2-hydroxybenzylidene) isonicotinohydrazide], containing an isonicotinic moiety condensated by salicylaldehyde was prepared and characterized. It can detect Zn2+ ions selectively in the “off-on” mode based on the coordination polymerization-induced emission (CPIE), with the limit of detection (LOD) being 2.8 × 10–7 M. The corresponding two-dimensional (2D) coordination polymer of the Zn2+ complex (1) was synthesized to investigate the response mechanism. Powder X-ray diffraction and single-crystal X-ray diffraction proved that complex 1 is the species formed in the detection system. Sensing of Zn2+ cannot be interfered by Cd2+, as confirmed by the molecular Cd2+ complex (2) without the CPIE mechanism. H2hbih can be successfully applied to bioimaging of Zn2+ monitoring in mung beans, larval zebrafish, and inner epidermis cells, which sheds light on a new strategy for designing AIE-based chemosensors via polymerization-induced self-assembly.

A novel two-dimensional coordination polymer, [Pb4(8-Quin)4(Tp)2(DMF)2] n (Tp = terephthalic dianion, 8-Quin = 8-Hydroxyquinolate, and DMF = N,N-dimethylformamide) has been synthesized and characterized by elemental analysis, FT-IR, and single crystal X-ray diffraction. The single crystal X-ray analysis shows that the complex is a two-dimensional (2D) polymer and the dimensionality is further increased to 3D as a result of weak C-H…π and C-H…O interactions.

Crystals of poly[[aqua[μ3-4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylato-κ5O1O1':N3,O4:O5][μ4-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylato-κ7N3,O4:O4,O4':O1,O1':O1]cadmium(II)] monohydrate], {[Cd2(C15H14N2O4)(C16H14N2O6)(H2O)]·H2O}n or {[Cd2(Hcpimda)(cpima)(H2O)]·H2O}n, (I), were obtained from 1-(4-carboxybenzyl)-2-propyl-1H-imidazole-4,5-dicarboxylic acid (H3cpimda) and cadmium(II) chloride under hydrothermal conditions. The structure indicates that in-situ decarboxylation of H3cpimda occurred during the synthesis process. The asymmetric unit consists of two Cd2+ centres, one 4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylate (Hcpimda2-) anion, one 1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylate (cpima2-) anion, one coordinated water molecule and one lattice water molecule. One Cd2+ centre, i.e. Cd1, is hexacoordinated and displays a slightly distorted octahedral CdN2O4 geometry. The other Cd centre, i.e. Cd2, is coordinated by seven O atoms originating from one Hcpimda2- ligand and three cpima2- ligands. This Cd2+ centre can be described as having a distorted capped octahedral coordination geometry. Two carboxylate groups of the benzoate moieties of two cpima2- ligands bridge between Cd2 centres to generate [Cd2O2] units, which are further linked by two cpima2- ligands to produce one-dimensional (1D) infinite chains based around large 26-membered rings. Meanwhile, adjacent Cd1 centres are linked by Hcpimda2- ligands to generate 1D zigzag chains. The two types of chains are linked through a μ2-η2 bidentate bridging mode from an O atom of an imidazole carboxylate unit of cpima2- to give a two-dimensional (2D) coordination polymer. The simplified 2D net structure can be described as a 3,6-coordinated net which has a (43)2(46.66.83) topology. Furthermore, the FT-IR spectroscopic properties, photoluminescence properties, powder X-ray diffraction (PXRD) pattern and thermogravimetric behaviour of the polymer have been investigated.

A series of N-(2-(diphenylphosphino)ethyl)-2-alkyl-5,6,7,8-tetrahydroquinolin-8-amines was prepared and used in individually reacting with iron chloride under nitrogen atmosphere to form their iron(ii) complexes Fe1–Fe6. All compounds were characterized using FT-IR spectroscopy and elemental analyses, the organic compounds were confirmed with NMR measurements, and the iron complexes were submitted to single-crystal X-ray diffraction, revealing Fe1, Fe2, Fe4, Fe5, and Fe6 as either mono- or di-nuclear forms. Forming a binary system in situ with two equivalents of LiCH2SiMe3, all iron complexes Fe1–Fe6 efficiently initiated the ring opening polymerization of ε-caprolactone, achieving the TOF up to 8.8 × 103 h−1. More importantly, the resultant polycaprolactone (PCL) possessed high molecular weights with the Mn range of 9.21–24.3 × 104 g mol−1, being a rare case of the iron(ii) catalyst in producing PCL with such high molecular weight. The 1H NMR and MALDI-TOF investigations demonstrated that the PCLs were linear features capped with a methoxy group or CH2SiMe3 or cyclic structure that varied with the molar ratio of [ε-CL]/Fe.