Tetranuclear Units Research Articles

Unusual Stabilisation of Remarkably Bent Tetra-Cationic Tetra-radical Intermolecular Fe(III) μ-Oxo Tetranuclear Complexes.

A hitherto unknown series of air stable, π-conjugated, remarkably bent tetra-cation tetra-radical intermolecular Fe(III) μ-oxo tetranuclear complex, isolated from the dication diradical diiron(III) porphyrin dimers, has been synthesised and spectroscopically characterised along with single crystal X-ray structure determination of two such molecules. These species facilitate long-range charge/radical delocalisation through the bridge across the entire tetranuclear unit manifesting an unusually intense NIR band. Assorted spin states of Fe(III) centres are stabilised within these unique tetranuclear frameworks: terminal six-coordinate iron centres stabilise the admixed intermediate spin states while the central five-coordinate iron centres stabilise the high-spin states. Variable temperature magnetic susceptibility measurements indicated strong antiferromagnetic coupling for the Fe(III)-O-Fe(III) unit while the exchange interactions between the Fe centres and the porphyrin π-cation radicals are weaker as supported both by magnetic data and DFT calculations. The nature of orbital overlap between the SOMOs of Fe(III) and π* orbital of the porphyrin was found to rationalise the observed exchange coupling, establishing such a complex magnetic exchange in this tetranuclear model with a significant bioinorganic relevance.

Unusual Stabilisation of Remarkably Bent Tetra‐Cationic Tetra‐radical Intermolecular Fe(III) μ‐Oxo Tetranuclear Complexes

AbstractA hitherto unknown series of air stable, π‐conjugated, remarkably bent tetra‐cation tetra‐radical intermolecular Fe(III) μ‐oxo tetranuclear complex, isolated from the dication diradical diiron(III) porphyrin dimers, has been synthesised and spectroscopically characterised along with single crystal X‐ray structure determination of two such molecules. These species facilitate long‐range charge/radical delocalisation through the bridge across the entire tetranuclear unit manifesting an unusually intense NIR band. Assorted spin states of Fe(III) centres are stabilised within these unique tetranuclear frameworks: terminal six‐coordinate iron centres stabilise the admixed intermediate spin states while the central five‐coordinate iron centres stabilise the high‐spin states. Variable temperature magnetic susceptibility measurements indicated strong antiferromagnetic coupling for the Fe(III)−O−Fe(III) unit while the exchange interactions between the Fe centres and the porphyrin π‐cation radicals are weaker as supported both by magnetic data and DFT calculations. The nature of orbital overlap between the SOMOs of Fe(III) and π* orbital of the porphyrin was found to rationalise the observed exchange coupling, establishing such a complex magnetic exchange in this tetranuclear model with a significant bioinorganic relevance.

A novel mixed azido/phenoxido bridged 1D CuII coordination polymer containing o-vanillin-based compartmental ligand: Synthesis, magnetism, phenoxazinone synthase and catalytic activity in epoxidation of alkenes

A novel 1-D coordination polymer, formulated as [Cu2(L)(N3)3]·H2O (1), has been synthesized by reacting the Schiff base ligand, 2-methoxy-6-((2-(2-hydroxyethylamino)ethylimino) methyl)-phenol (HL), with copper(II) chloride dihydrate in the presence of sodium azide. The X-ray structural analysis shows that compound 1 consists of tetranuclear [Cu2(L)(N3)3]2 units bearing a central double asymmetric μ1,1-N3 bridge and terminal mixed µ1,1-N3/phenoxido bridges that are linked via a double µ1,1,3-N3 bridge forming a 1-D network. The magnetic properties of 1 show the presence of ferromagnetic Cu···Cu interactions through the central double μ1,1-N3 bridge (J1 = 81.7(3) cm−1) coexisting with antiferromagnetic Cu···Cu interactions through the double µ1,1-N3/phenoxido bridge (J2 = –62.3(4)cm−1). Additionally, there is a very weak antiferromagnetic interaction (zJ = –0.12(2) cm−1) through the asymmetric µ1,1,3-N3 bridge connecting the tetranuclear units. Using o-aminophenol (OAP) as a substrate, the phenoxazinone synthase-like catalytic activity of the CuII coordination polymer 1 has been studied. The compound efficiently catalyzes the aerobic oxidation of o-aminophenol in DMF medium with a turnover number Kcat = 31.69 h−1. Moreover, 1 has been used as an active catalyst for the epoxidation of cis-cyclooctene, as a model alkene, with tert-butyl hydroperoxide (TBHP), showing an excellent epoxide yield and selectivity in CHCl3 under reflux conditions. To enlarge the scope of the reaction, the efficacy of the catalytic method has also been investigated in the epoxidation of some other substituted alkenes.

Sensitive Current Sensor Based on a Lanthanide Framework with Lewis Basic Bipyridyl Sites for Cu2+ Detection.

A new Yb-based three-dimensional metal-organic framework with free Lewis basic sites, [Yb2(ddbpdc)3(CH3OH)2] (referred to as ACBP-6), from YbCl3 and (6R,8R)-6,8-dimethyl-7,8-dihydro-6H-[1,5]dioxonino[7,6-b:8,9-b']dipyridine-3,11-dicarboxylic acid (H2ddbpdc) was synthesized by a conventional solvothermal method. Two Yb3+ are connected by three carboxyl groups to form the [Yb2(CO2)5] binuclear unit, which is further bridged by two carboxyl moieties to produce a tetranuclear secondary building unit. With further ligation of the ligand ddbpdc2-, a 3-D MOF with helical channels is constructed. In the MOF, Yb3+ only coordinates with O atoms, leaving the bipyridyl N atoms of ddbpdc2- unoccupied. The unsaturated Lewis basic sites make this framework possible to coordinate with other metal ions. After growing the ACBP-6 in situ into a glass micropipette, a novel current sensor is formed. This sensor shows high selectivity and a high signal-to-noise ratio toward Cu2+ detection with a detection limit of 1 μM, due to the stronger coordination ability between the Cu2+ and the bipyridyl N atoms.

Highly sensitive fluorescent sensing and photocatalytic degradation performance of two-dimensional Tb-organic network

A novel tetra-nuclear Tb-organic network, named as [Tb4(2-pyia)6(HAc)0.5(2,2′-bipy) (H2O)4.5]·2,2′-bipy·H2O (1), was synthesized hydrothermally based on 5-(pyridin-2-ylmethoxy) isophthalic acid (H2pyia) and 2,2′-bipyridine (2,2′-bipy) ligands, and characterized by single crystal X-ray diffraction, thermogravimetric (TG) analyses, powder X-ray diffraction (PXRD) and infrared (IR) technology. 1 possesses a two-dimensional network based on the tetra-nuclear inorganic building units, and the π-π stacking interactions between the pyia2− ligands and the guest 2,2′-bipy molecules play an important role in the forming of 3D supramolecular structure. 1 exhibits excellent fluorescent sensing performance for Fe3+ (1.26 × 10−8 mol/L), Cr2O72− (8.1 × 10−7 mol/L), 2,4,6-trinitrophenol (TNP) (2.71 × 10−8 mol/L) and tetracycline (TCT) (2.76 × 10−7 mol/L) in aqueous solution with lower detection concentrations. The sensing mechanisms of 1 were investigated by density functional theory (DFT) calculations, ultraviolet–visible (UV-Vis) diffuse reflectance spectroscopy, PXRD and fluorescent lifetime analyses. The activated product of 1 was prepared by heating at 255 °C under constant pressure and used to photo-catalytically degrade TCT. Both 1 and the activated one have good photocatalytic degradation performance for TCT with degradation rates of 84.29% and 96.07%, respectively. The photocatalytic mechanisms were discovered by UV–Vis diffuse reflectance spectroscopy and radical trap experiments. The Tb-organic framework might be an excellent multifunctional fluorescent sensor and a good photocatalytic agent for TCT degradation in the future.

Investigations of stable penta- and hexa-coordinate polynuclear Zn(II) and Cd(II) complexes derived from a single-armed salamo-based ligand

A penta-coordinated dinuclear Zn(II) complex, [Zn2(L)(μ-PhCOO)(EtOH)] (1), and a hexa-coordinate tetranuclear Cd(II) complex, [{Cd2(L)(EtOH)(η-OAc)}2]·2CH2Cl2 (2), have been synthesized by reactions of a single-armed salamo-based ligand, H3L, and two kinds of transition metal salts, (Zn(NO3)2·6H2O and Cd(OAc)2·2H2O), respectively. Complexes 1 and 2 have been characterized by elemental analyses, single crystal X-ray diffraction, IR spectra and UV-Vis spectra. Complex 1 is composed of a totally deprotonated ligand (L)3- moiety, two Zn(II) ions, one μ-PhCOO- counter-anion and one coordinated ethanol molecule. The (L)3- unit packages two Zn(II) ions, the μ-PhCOO- counter-anion bridges two adjacent Zn(II) ions and one ethanol molecule coordinates with the Zn2 ion, so that both Zn(II) ions are penta-coordinated with slightly distorted trigonal bipyramidal configurations, and the τ5 values of Zn1 and Zn2 are 0.86 and 0.65, respectively. Complex 2 consists of two discrete and similar electroneutral tetra-nuclear units, 2 A and 2B, and two crystallized dichloromethane molecules. Each unit has a symmetric structure that is made up of two completely deprotonated ligand (L)3- moieties, four Cd(II) ions, two η-OAc- counter-anions and two coordinated ethanol molecules. Fluorescence properties and Hirshfeld surfaces analyses have been studied as well.

Synthesis and Characterisation of Novel Bis(diphenylphosphane oxide)methanidoytterbium(III) Complexes.

Reaction of [YbCp2(dme)] (Cp = cyclopentadienyl, dme = 1,2 dimethoxyethane) with bis(diphenylphosphano)methane dioxide (H2dppmO2) leads to deprotonation of the ligand H2dppmO2 and oxidation of ytterbium, forming an extremely air-sensitive product, [YbIII(HdppmO2)3] (1), a six-coordinate complex with three chelating (OPCHPO) HdppmO2 ligands. Complex 1 was also obtained by a redox transmetallation/protolysis synthesis from metallic ytterbium, Hg(C6F5)2, and H2dppmO2. In a further preparation, the reaction of [Yb(C6F5)2] with H2dppmO2, not only yielded compound 1, but also gave a remarkable tetranuclear cage, [Yb4(µ-HdppmO2)6(µ-F)6] (2) containing two [Yb(µ-F)]2 rhombic units linked by two fluoride ligands and the tetranuclear unit is encapsulated by six bridging HdppmO2 donors. The fluoride ligands of the cage result from C-F activation of pentafluorobenzene and concomitant formation of p-H2C6F4 and m-H2C6F4, the last being an unexpected product.

Open-Framework Iron Fluoride Phosphates Based on Chain, Trinuclear, and Tetranuclear Chain FeIII Building Units: Crystal Structures and Magnetic Properties.

We report the synthesis and characterization of a series of new open-framework iron fluoride-fluorophosphates based on linear, trinuclear, and tetranuclear chain FeIII building units. KFe2(PO3F)2F3 (I) consists of {Fe2(O3F)2F2}10- zigzag chains interconnected by P(O/F)4 tetrahedra forming a three-dimensional (3D) open framework. K2Fe(PO2.5F1.5)2F2 (II) is built up by {Fe(PO2.5F1.5)2F2}2- chains separated by K+ cation layers. The framework for K3Fe3(PO4)(PO3F)2F5 (III) contains two-dimensional {Fe3O4F4(PO3F)2}2- sheets, which are built from trimeric Fe-octahedra insulated by PO3F tetrahedra. The macroanionic framework of K3Fe4(PO4)2F9 (IV) comprises linear {Fe4O8F9}10- chains consisting of tetranuclear magnetic clusters of [Fe4O8F9]10- formed via corner-sharing fluorine atoms decorated with PO4 groups. The magnetic characterization of three iron fluorophosphates reveals diversified magnetism: S = 5/2 spin chains for I, antiferromagnetically coupled triangular Fe units for III, and coupled tetrahedral S = 5/2 spin chains for IV. IV shows strong geometric frustration thanks to its spin motifs of corner-shared tetrahedral clusters.

Preparation and characterization of a new chiral metal-organic framework with spiranes

Herein we report the first homochiral IRMOF structure with chiral carbocyclic spirolinkers, basic Zn-(R)-spiro[3.3]heptane-2,6-dicarboxylate, named WIG-5. First, (R)-spiro[3.3]heptane-2,6-dicarboxylic acid was prepared involving a HPLC separation on chiral stationary phase, then further transformed into homochiral WIG-5 by the solvothermal reaction with zinc nitrate hexahydrate in dimethyl formamide (DMF). WIG-5 crystallizes in the P212121 space group and is built of two interpenetrated networks with pcu underlying network topology. The tetranuclear secondary building units (SBUs) of WIG-5 are coordinated to two DMF molecules and six (R)-spiro[3.3]heptane-2,6-dicarboxylic acid linkers, that results in the formation of a homochiral distorted MOF-5-like structure. Extensive characterization by single crystal X-ray diffraction, powder X-ray diffraction, polarized light microscopy, infrared microspectroscopy, solid-state vibrational circular dichroism spectroscopy and thermogravimetry/mass spectroscopy has been performed on the new material. Birefringence of large WIG-5 single crystals enables potential optical applications.

Turn-on and blue-shift fluorescence sensor toward L-histidine based on stable CdII metal-organic framework with tetranuclear cluster units.

A novel CdII-based two-fold interpenetrated metal-organic framework (MOF), namely {[Cd2(BTDB)2(4,4-bpy)]·DMF}n (JXUST-14), (H2BTDB = 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid and 4,4-bpy = 4,4-bipyridine), has been prepared and characterized. Single-crystal structure determination reveals that JXUST-14 has a tetranuclear cluster based 6-connected pcu topological network with Schlafli symbol {412·63}. When soaked in common organic solvents and aqueous solutions with diverse pH values of 2-12 for 48 h, JXUST-14 remains stable. JXUST-14 is a highly selective and sensitive luminescent sensor for L-histidine (His) with a detection limit of 11.1 ppm. JXUST-14 is the first CdII-based MOF for the detection of His via turn-on and fluorescence blue-shift effects. Experimental study and theoretical calculation suggest that the sensing process can be mainly attributed to a charge transfer and energy transfer mechanism. More interestingly, LED lamps of JXUST-14 and JXUST-14@His were successfully developed, which endowed efficient sensitivity for His detection and thus provide great potential for future applications.

A 3D MOF based on Adamantoid Tetracopper(II) and Aminophosphine Oxide Cages: Structural Features and Magnetic and Catalytic Properties.

This work describes an unexpected generation of a new 3D metal–organic framework (MOF), [Cu4(μ-Cl)6(μ4-O)Cu(OH)2(μ-PTA=O)4]n·2nCl-EtOH·2.5nH2O, from copper(II) chloride and 1,3,5-triaza-7-phosphaadamantane 7-oxide (PTA=O). The obtained product is composed of diamandoid tetracopper(II) [Cu4(μ-Cl)6(μ4-O)] cages and monocopper(II) [Cu(OH)2] units that are assembled, via the diamandoid μ-PTA=O linkers, into an intricate 3D net with an nbo topology. Magnetic susceptibility measurements on this MOF in the temperature range of 1.8–300 K reveal a ferromagnetic interaction (J = +20 cm–1) between the neighboring copper(II) ions. Single-point DFT calculations disclose a strong delocalization of the spin density over the tetranuclear unit. The magnitude of exchange coupling, predicted from the broken-symmetry DFT studies, is in good agreement with the experimental data. This copper(II) compound also acts as an active catalyst for the mild oxidation and carboxylation of alkanes. The present study provides a unique example of an MOF that is assembled from two different types of adamantoid Cu4 and PTA=O cages, thus contributing to widening a diversity of functional metal–organic frameworks.

Novel Ba2+ and Pb2+ metal-organic frameworks based on a semi-rigid tetracarboxylic acid: syntheses, structures, topologies and luminescence properties.

Multidentate carboxylate ligands have been widely used in the construction of metal-organic frameworks (MOFs) owing to the rich variety of their coordination modes, which can lead to crystalline products with interesting structures and properties. Two new main-group MOFs, namely, poly[[di-μ-aqua-diaqua(dimethylformamide)[μ7-5,5'-methylenebis(2,4,6-trimethylbenzene-1,3-dicarboxylato)]dibarium(II)] trihydrate], {[Ba2(C23H20O8)(C3H7NO)(H2O)4]·3H2O}n or {[Ba2(BTMIPA)(DMF)(H2O)4]·3H2O}n (1), and poly[[diaqua[μ6-5,5'-methylenebis(2,4,6-trimethylbenzene-1,3-dicarboxylato)]dilead(II)] 2.5-hydrate], {[Pb2(C23H20O8)(H2O)2]·2.5H2O}n or {[Pb2(BTMIPA)(H2O)2]·2.5H2O}n (2), were prepared by the self-assembly of metal salts with the semi-rigid tetracarboxylic acid ligand 5,5'-methylenebis(2,4,6-trimethylisophthalic acid) (H4BTMIPA). Both structures were characterized by elemental analysis (EA), single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectroscopy and thermogravimetric analysis (TGA). Complex 1 reveals a three-dimensional (3D) flu network formed via bridging tetranuclear secondary building units (SBUs) and complex 2 displays a 3D framework with an sqp topology based on one-dimensional metal chains. The BTMIPA4- ligands adopt a rare coordination mode in 2, although the ligands in both 1 and 2 are X-shaped. The luminescence properties of both complexes were investigated in the solid state.

Precise Assembly and Supramolecular Catalysis of Tetragonal- and Trigonal-Elongated Octahedral Coordination Containers

The construction of distorted or irregular coordination polyhedrons with specific shapes and functionalities is highly challenging. Here, we demonstrate a viable strategy for attaining a severely d...

Programmable Synthesis of Silver Wheels.

The synthesis of sandwich-shaped multinuclear silver complexes with planar penta- and tetranuclear wheel-shaped silver units and a central anion, [Agn(2-HPB)2(A-)](OTf-)n-1, nAgA, n = 4 or 5 and A- = OH- or F- or Cl-, is reported, along with complete spectroscopic and structural characterization. An NMR mechanistic study reveals that silver complexes were formed in the following order: 2Ag → 3AgH2O → 5AgOH → 4AgOH. The central hydroxides in 4AgOH and 5AgOH exhibit exotic physical properties due to the confined environment inside the complex. The size of these silver wheels can be tuned by changing the central anion or extracting/adding one silver atom. This study provides the facile way to synthesize discrete wheel-shaped multinuclear silver complexes and provides valuable insights into the dynamics of the self-assembly process.

Three coordination polymers built by quaternary-ammonium-modified isophthalic acid.

Three coordination polymers based on quaternary-ammonium-modified isophthalic acid, namely, catena-poly[[[aqua-μ2-bromido-di-μ3-hydroxido-methanoldinitratotetracopper(II)]-bis{μ4-5-[2-(tripropylazaniumyl)ethoxy]benzene-1,3-dicarboxylato}] nitrate], {[Cu4Br(C19H28NO5)2(NO3)2(OH)2(CH4O)(H2O)]NO3}n, 1, poly[μ3-bromido-μ2-bromido-bromido-μ3-hydroxido-{μ4-5-[2-(tripropylazaniumyl)ethoxy]benzene-1,3-dicarboxylato}tricopper(II)], [Cu3Br3(C19H28NO5)(OH)]n, 2, and poly[bromido{μ3-5-[2-(tripropylazaniumyl)ethoxy]benzene-1,3-dicarboxylato}zinc(II)], [ZnBr(C19H28NO5)]n, 3, were obtained by solvothermal reactions. Coordination polymer (CP) 1 contains tetranuclear Cu4 units, in which the four Cu atoms are linked by two μ3-OH- groups into a Cu4(OH)2 cluster, which are in turn linked by 5-[2-(tripropylazaniumyl)ethoxy]benzene-1,3-dicarboxylate (cpa-) ligands into a chain structure. CP 2 also contains a tetranuclear Cu4(OH)2 cluster and these are linked with CuBr3 units into chains. The chains are then connected by cpa- ligands into a two-dimensional layered structure. CP 3 contains a two-dimensional layer structure built by binuclear Zn2 units and cpa- ligands. The Br- counter-anions of the quaternary ammonium groups all take part in the construction of the polymeric networks.

Thermally stable and robust gadolinium-based metal-organic framework: Synthesis, structure and heterogeneous catalytic O-arylation reaction

Hydrothermal treatment of gadolinium nitrate and 2,6-naphthalenedicarboxylic acid (H2NDC) afforded a new metal-organic framework compound, {[Gd4(NDC)6(H2O)6]·2H2O}n(1). Compound 1 has been characterized by single-crystal X-ray crystallography, elemental analysis, FT-IR spectroscopy, therrmogravimetric analysis (TGA) and powder X-ray diffraction analysis. It is crystallized in the monoclinic system with the P21/n space group. Four crystallographically distinct Gd (III) centres are interconnected with each other through bridged carboxylato oxygen atoms and water molecules to form tetranuclear secondary building units, which are further connected through the carboxylato ligand and the network propagates along the crystallographic ac plane to form a 2D structure. Subsequent reinforcement from the remaining carboxylato oxygen atoms gives rise to a robust 3D framework structure. Thermogravimetric analysis demonstrates that compound 1 is fairly stable after dehydration under a nitrogen atmosphere.Notably, compound 1 is capable of catalyzing the O-arylation reaction efficiently between substituted phenols and bromoarene under heterogeneous conditions at 80 °C to afford unsymmetrical diarylethers.

A copper-based coordination polymer formed through synergistic bridging of 1,2,4-triazole and acetate anions: synthesis, crystal structure and magnetic properties

A Cu(II) coordination polymer, [Cu2(pztrz)2(μ-CH3COO)(CH3COO)]·3H2O (1), derived from mono-substituted 1,2,4-triazole derivative 3-(pyrazinyl)-1,2,4-triazole (Hpztrz) is isolated and structurally characterized. X-ray structural analysis shows that Hpztrz ligands and acetate anions demonstrate different coordination modes in complex 1. The two Cu(II) ions are bridged by the 1,2,4-triazole ring of Hpztrz to form a dinuclear unit, which is further linked by two bridging acetate anions to form a tetranuclear Cu4 unit. Interestingly, each Cu4 unit is connected to another four Cu4 units through the outer pyrazinyl of Hpztrz, resulting in a two-dimensional (2D) layer structure. Consecutive layers are further packed into three-dimensional (3D) structures through interlayer hydrogen-bonding interactions. Furthermore, variable-temperature magnetic susceptibility studies reveal that the antiferromagnetic interactions are mediated through 1,2,4-triazole-N1,N2 bridges and acetate bridges with coupling constants of J1 = − 69.98 cm−1 and J2 = − 2.15 cm−1. Synergistic co-coordination of 1,2,4-triazole and acetate ions with Cu(II) ions led to a dinuclear unit, then to a Cu4 unit and finally to a 2D layer. Consecutive layers are further packed into a 3D framework through interlayer hydrogen-bonding interactions. Furthermore, variable-temperature magnetic susceptibility studies indicated the existence of antiferromagnetic coupling between the Cu(II) ions.

A novel three-dimensional tetranuclear CoII coordination polymer with water hexamers based on the V-shaped tetracarboxylate ligand 4-(2,4-dicarboxylatophenoxy)phthalate.

A new coordination polymer (CP), namely, poly[[diaquatris[μ2-1,4-bis(1H-imidazol-1-yl)benzene]bis[μ6-4-(2,4-dicarboxylatophenoxy)phthalato]tetracobalt(II)] hexahydrate], {[Co4(C16H6O9)2(C12H10N4)3(H2O)2]·6H2O}n, has been synthesized by solvothermal reaction. The CP was fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffraction. It presents a three-dimensional (3D) structure based on tetranuclear CoII secondary building units (SBUs) with a tfz-d net and point symbol (43)2(46·618·84). The 4-(2,4-dicarboxyphenoxy)phthalic acid (H4dcppa) ligands are completely deprotonated and link {Co4(COO)4}4- SBUs into two-dimensional (2D) layers. Furthermore, adjacent layers are connected by 1,4-bis(1H-imidazol-1-yl)benzene (bib) ligands, giving rise to a 3D supramolecular architecture. Interestingly, there are numerous elliptical cavities in the CP where isolated unique discrete hexameric water clusters have been observed. The results of thermogravimetric and magnetic analyses are described in detail.

Di-aqua-bis-{μ-1,5-bis-[(pyridin-2-yl)methyl-idene]carbonohydrazide(1-)}di-μ-chlorido-tetra-chlorido-tetra-zinc(II).

A tetra-nuclear ZnII complex, [Zn4(C13H11N6O)2Cl6(H2O)2] or {[Zn2(HL)(H2O)(Cl2)](μCl)2[Zn2(HL)(H2O)(Cl)]}2, was synthesized by mixing an equimolar amount of a methanol solution containing ZnCl2 and a methanol solution containing the ligand H2 L [1,5-bis-(pyridin-2-yl-methyl-ene)carbono-hydrazide]. In the tetra-nuclear complex, each of the two ligand mol-ecules forms a dinuclear unit that is connected to another dinuclear unit by two bridging chloride anions. In each dinuclear unit, one ZnII cation is penta-coordinated in a N2OCl2 in a distorted square-pyramidal geometry, while the other ZnII cation is hexa-coordinated in a N3OCl2 environment with a distorted octa-hedral geometry. The basal plane around the penta-coordinated ZnII cation is formed by one chloride anion, one oxygen atom, one imino nitro-gen atom and one pyridine nitro-gen atom with the apical position occupied by a chloride anion. The basal plane of the hexa-coordinated ZnII cation is formed by one chloride anion, one hydrazinyl nitro-gen atom, one imino nitro-gen atom and one pyridine nitro-gen atom with the apical positions occupied by a water oxygen atom and a bridged chloro anion from another dinuclear unit, leading to a tetra-nuclear complex. A series of intra-molecular C-H⋯Cl hydrogen bonds is observed in each tetra-nuclear unit. In the crystal, the tetra-nuclear units are connected by inter-molecular C-H⋯Cl, C-H⋯O and N-H⋯O hydrogen bonds, forming a planar two-dimensional structure in the ac plane.

The effects of the coordination orientation and steric hindrance of ligands on the structural diversity of Pb(II) coordination polymers

Five new lead(II) coordination polymers, [Pb(L)]n (1), [Pb3(L)3]n·4nH2O (2), [Pb2(L)(1,2-bdc)]n·nH2O (3), [Pb2(L)(1,3-bdc)]n·nH2O (4) and [Pb4(L)2(1,4-bdc)2(H2O)2]n·2nH2O (5) (H2L = 4′-(4-carboxyphenyl)-6′-carboxycalte-2,2′-bipyridine, H2(1,2-bdc) = benzene-1,2-dicarboxylic acid, H2(1,3-bdc) = benzene-1,3-dicarboxylic acid and H2(1,4-bdc) = benzene-1,4-dicarboxylic acid) were prepared under hydrothermal conditions. Compound 1 shows a 2D ladder single-layer with the hcb topology. Compound 2 presents a 2D ladder double-layer, which shows a 3-connected hcb topology. Compound 3 exhibits a 1D loop chain based on [Pb4(COO)6] tetranuclear units. Compound 4 displays a (3,4)-connected 3D framework with 3,4T10 topology consisting of [Pb2O2] units. Compound 5 exhibits a self-penetrating 3D network based on [Pb4(COO)2] units, which features an intriguing new topological net. The structural diversity of 1–5 gives some insights that the pH value and coordination orientations of aromatic dicarboxylates play significant roles in construction of coordination polymers. Meanwhile, the hemi-directed or holo-directed coordination geometries depend on coordination numbers of Pb(II) ions. Furthermore, tetrel bonds enhance the structural stability of these Pb(II) coordination polymers.