Aqua substitution from mononuclear Pt(II) complexes with 2-(pyrazol-1-ylmethyl)quinoline non-leaving ligands

The rates of aqua substitution from [Pt{2-(pyrazol-1-ylmethyl)quinoline}(H₂O)₂](ClO₄)₂, [Pt(H₂Qn)], [Pt{2-(3,5-dimethylpyrazol-1-ylmethyl)quinoline}(H₂O)₂](ClO₄)₂, [Pt(dCH₃Qn)], [Pt{2-[(3,5-bis(trifluoromethyl)pyrazol-1-ylmethyl]quinoline}(H₂O)₂](ClO₄)₂, [Pt(dCF₃Qn)], and [Pt{2-[(3,5-bis(trifluoromethyl)pyrazol-1-ylmethyl]pyridine}(H₂O)₂](ClO₄)₂, [Pt(dCF₃Py)], with three sulfur donor nucleophiles were studied. The reactions were followed under pseudo-first-order conditions as a function of nucleophile concentration and temperature using a stopped-flow analyzer and UV/visible spectrophotometry. The substitution reactions proceeded sequentially. The second-order rate constants for substituting the aqua ligands in the first substitution step increased in the order Pt(dCH₃Qn) < Pt(dCF₃Qn) < Pt(H₂Qn) < Pt(dCF₃Py), while that of the second substitution step was Pt(dCH₃Qn) < Pt(dCF₃Qn) < Pt(dCF₃Py) < Pt(H₂Qn). The reactivity trends confirm that the quinoline substructure in the (pyrazolylmethyl)quinoline ligands acts as an apparent donor of electron density toward the metal center rather than being a π-acceptor. Measured pK_a values from spectrophotometric acid–base titrations were Pt(H₂Qn) (pK_a1 = 4.56; pK_a2 = 6.32), Pt(dCH₃Qn) (pK_a1 = 4.88; pK_a2 = 6.31), Pt(dCF₃Qn) (pK_a1 = 4.07; pK_a2 = 6.35), and Pt(dCF₃Py) (pK_a1 = 4.76; pK_a2 = 6.27). The activation parameters from the temperature dependence of the second-order rate constants support an associative mechanism of substitution.     

Copper(I) bromide complexes of two 15-memberd O2S2-macrocycles with different sulfur-to-sulfur separations: dimer and one-dimensional coordination polymer

Abstract

A comparative study on the exo-coordination-based networking of 15-membered O₂S₂-macrocycle isomers (L¹ and L²) induced by interdonor distances is reported. In copper(I) bromide complexation, the isomer L¹ incorporating a shorter sulfur-to-sulfur separation yielded a discrete dimer complex [(μ-Cu₂Br₂)(L¹)₂] (1) in which two macrocycles are bridged by a Cu₂Br₂ square cluster. While, the reaction of copper(I) bromide with the isomer L² incorporating a longer sulfur-to-sulfur separation afforded a double-stranded one-dimensional (1D) coordination polymer {[(μ₄-Cu₂Br₂)(L²)₂]·CH₂Cl₂}_n (2) as a kinetic product which converted to [(μ₄-Cu₂Br₂)(L²)₂]_n (3) with different 1D connectivity pattern as a thermodynamic product. The results indicate as examples of programmed self-assembly that the proposed interdonor distances and the ligand isomerism play decisive roles cooperatively in the topologies of the supramolecular products via different coordination modes.     

Liquid crystalline guanidinium phenylalkoxybenzoates: towards room temperature liquid crystals via bending of the mesogenic core and the use of triflate counter ions

A series of guanidinium salts 1(C _n ) _m –4(C _n ) _m ?X bearing phenyl alkoxybenzoate cores have been synthesised and their mesomorphic properties have been investigated by polarising optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction experiments (small-angle X-ray scattering and wide-angle X-ray scattering). While compounds 1(C₁₂)₁?X and 3(C₁₂)₁?X with one alkoxy chain showed smectic A (SmA) phases irrespective of the counter ion, compounds 1(C₁₂)₂?OTf and 3(C₁₂)₂?OTf with two alkoxy chains displayed SmA phases and the corresponding chlorides 1(C₁₂)₂?Cl and 3(C₁₂)₂?Cl displayed Col_h. Guanidinium salts 1(C _n )₃–4(C _n )₃?X with three alkoxy chains showed Col_h phases. Whereas the use of cyclic guanidinium head groups rather than acyclic ones had only a minor influence on the mesophase properties, melting points were significantly decreased by bent core units instead of linear core units. Replacement of chloride counterions by triflate lead to a further depression of the clearing points and shifted the mesophase towards room temperature.     

Polymerizations of methyl methacrylate and rac-lactide by zinc(II) precatalyst containing N-substituted 2-iminomethylpyridine and 2-iminomethylquinoline

The reaction of [ZnCl₂] with N-cyclopentyl-1-(quinolin-2-yl)methanimine (L_A), N-cyclohexyl-1-(quinolin-2-yl)methanimine (L_B), N-cyclohexyl-1-(pyridin-2-yl)methanimine (L_C), 2,6-diethyl-N-(pyridin-2-ylmethylene)aniline (L_D), N-cyclopentyl-1-(pyridin-2-yl)methanimine (L_E), and N-phenyl-(pyridin-2-yl)methanimine (L_F) in ethanol produced the bidentate [(NN′)ZnCl₂] complexes, [L_AZnCl₂], [L_BZnCl₂], [L_CZnCl₂], [L_DZnCl₂], [L_EZnCl₂] and [L_FZnCl₂], respectively. The molecular structures revealed that the zinc in [L_nZnCl₂] (L_n = L_A ? L_D) showed a distorted tetrahedral geometry involving two nitrogens of N,N’-bidentate ligands and two chloride ligands. Most of these initiators were effective for polymerization of methyl methacrylate (MMA) and polymerization of rac-lactide (rac-LA). [L_CZnCl₂] (with N-cyclohexyl substituted at imine-pyridine moiety) exhibited the highest catalytic activity for MMA polymerization in the presence of modified methylaluminoxane (MMAO) with an activity of 3.33 × 10⁴ g PMMA/mol·Zn·h at 60 °C, giving moderate syndiotactic poly methyl methacrylate (PMMA) with high molecular weight (9.62 × 10⁵ g/mol). The dimethyl derivatives [L_nZnMe₂] (L_n = L_A ? L_F), generated in situ, polymerized rac-LA with moderate activity and yielded a polylactide (PLA) with good number-average molecular weights and narrower polydispersity indices (PDIs). [L_AZnMe₂] effectively initiates the ring-opening polymerization (ROP) of rac-LA to attain heterotactic PLA (P_r = 0.91).     

Synthesis,structural studies,and antibacterial activity of zinc,copper, and silver complexes derived from N′-(1-(pyrazin-2-yl)ethylidene)isonicotinohydrazide

The multidentate Schiff-base ligand N′-(1-(pyrazin-2-yl)ethylidene)isonicotinohydrazide (HL) has been prepared. Reaction with zinc, copper, and silver nitrate afford three complexes, [Zn(HL′)₂](NO₃)₂·3H₂O (1), {[Cu₂(L)₂(NO₃)(H₂O)₂]·NO₃}_n (2) and {[Ag₂(L)₂]·3H₂O}_n (3). These complexes have been characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. In 1, HL is a neutral tridentate ligand, whereas in 2 and 3, HL is a deprotonated tetradentate ligand. The hydrogen bonding interactions between NO₃^? and the host framework result in various supramolecular polymeric structures: a 2-D layer for 1 and 3-D network for 2 and 3. The antibacterial activities of these complexes have been investigated and the results indicate that 3 showed good antibacterial activities.     

Three lanthanide complexes with mixed salicylate and 1,10-phenanthroline: syntheses,crystal structures,and luminescent/magnetic properties

Three new lanthanide complexes incorporating salicylate (HSA or SA) and 1,10-phenanthroline (phen), Ln₃(HSA)₅(SA)₂(phen)₃ [Ln = Ho (1) and Er (2)], and Sm₂(HSA)₂(SA)₂(phen)₃ (3), have been synthesized. X-ray structural analysis reveals that 1 and 2 are isostructural with a trinuclear pattern, and 3 exhibits a binuclear structure. Comparison of the structural differences between 1/2 and 3 suggests that the identity of metal plays an important role in construction of such complexes. The magnetic properties of 1 are discussed. Moreover, 2 and 3 are both photoluminescent materials, and their emission properties are closely related to their corresponding Ln^III centers.     

Two- and three-dimensional coordination polymers of lanthanide tartrate: synthesis,crystal structures and luminescence

Several new coordination polymers of lanthanide tartrate with three types of topological structures, namely [Ln₂(DL-tart)₃(H₂O)₃] · 1.5H₂O [Ln = La (1), Nd (2), and Sm (3)], [Ln₂(D-tart)₃(H₂O)₂] · 3H₂O [Ln = Eu (4), Tb (5), and Dy (6)], and [Lu(C₄H₄O₆)(C₄H₅O₆)] · 2.5H₂O (7), have been synthesized by hydrothermal synthesis. X-ray crystallographic analysis reveals that 1 is a unique 3-D network, whereas 5 with a 3-D network and 7 with a 2-D network are isomorphous with their analogs. All lanthanide ions are nine-coordinate through oxygen donors. Four different coordination modes of tartrate occur in these complexes. Luminescence spectra reveal that 4, 5, and 6 emit characteristic luminescence of corresponding lanthanide ions.     

Diverse structures,magnetism and photoluminescence of four transition metal coordination compounds based on the semirigid 4-(pyridin-3-yloxy)-phthalic acid

Four transition metal coordination compounds, {[Co(PPDA)(H₂O)₂]}_n (1), {[Ni(HPPDA)₂]}_n (2), {[Cd(PPDA)(H₂O)]?H₂O}_n (3), and {Zn(HPPDA)₂(H₂O)₄}_n (4), were synthesized by assembling transition metal salts with a semirigid ligand 4-(pyridin-3-yloxy)-phthalic acid (H₂PPDA) under hydrothermal conditions. The compounds have been characterized by elemental analyses, IR spectra, TGA, powder X-ray diffraction, and single-crystal X-ray crystallography. Compound 1 exhibits a three-connected 2-D layered structure, 2 shows a (3,6)-connected 2-D layered structure, 3 displays a (3,6)-connected 2-D layered framework based on binuclear units, and 4 is a mononuclear structure, connected to generate a 3-D supramolecular architecture by hydrogen bonds. Compound 2 is thermally stable up to 300 °C. The magnetic properties of 1 and photoluminescent properties of 3 and 4 have been explored.     

Coordination polymers of lanthanides incorporating N,N′-ethylenebis(2-hydroxy-1-naphthylideneiminato): syntheses and crystal structures

Reaction of Ln(NO₃)₃?·?6H₂O with H₂napn (H₂napn?=?N,N′-ethylenebis(2-hydroxy-1-naphthylideneiminato)) and KSCN produces seven new coordination polymers, [La(H₂napn)(SCN)(C₂H₅OH)₂(NO₃)₂] _n (1), [La(H₂napn)₂(SCN)(NO₃)₂] _n (2), and [Ln(H₂napn)_1.5(NO₃)₃] _n [Ln?=?La(3), Sm(4), Eu(5), Dy(6), Er(7)]. Crystal structure analysis reveals that H₂napn functions as a bridging ligand, forming a 1-D chain polymer (1) and 2-D open-frameworks (2–7) with lanthanides. Each metal center of 1–7 is nine-coordinate. Lanthanide contraction is observed in 3–7.     

Structural diversity of a series of urea-based coordination complexes: from water tapes,water-sulfate chains,to supramolecular structures

[Hg₂(L₁)₂I₄] (1), [Cd₂(L₁)₂I₄] (2), {[Cd(L₁)₂(SO₄)(H₂O)]·4H₂O}_n (3), {[Zn₂(L₂)₂(Cl)₄]·0.5H₂O} (4), {[Cu₂(L₂)₂(SO₄)₂(H₂O)₄]·2.5H₂O} (5), and {[Cd(L₂)₂(SO₄)(H₂O)]·3H₂O}_n (6), based on N–(3–picolyl)–N′–(3–pyridyl)urea (L₁) or N–(4–picolyl)–N′–(3–pyridyl)urea (L₂), have been synthesized and characterized by elemental analyses, IR spectra, single-crystal and powder X-ray diffraction, and thermogravimetric analyses. Complexes 1 and 2 are isomorphous and feature similar rectangular metal organic loops, which were further extended into 2-D supramolecular structures through hydrogen bonds. Complex 3 possesses a 2-D sql sheet, and the channels between the neighboring sheets are filled with lattice water molecules, which formed a 1-D water tape. Complex 4 also exhibits a rectangular metal organic loop and a 3-D supramolecular structure with the help of hydrogen bonding interactions. Complex 5 also possesses a metal organic loop, and the water molecules interacted with sulfates, constructing a 1-D water–sulfate tube. Complex 6 features a 1-D loop polymeric chain. Moreover, the solid state luminescences of 1–4 and 6 have been investigated.     

The effect of mesogenic and non-mesogenic crosslinking units on the phase behaviour of side-chain smectic and cholesteric elastomers

Chiral monomer (M₁ ), mesogenic and non-mesogenic crosslinking agents (C₁ and C₂ ), and the corresponding liquid crystalline elastomers (P₁ and P₂ series), have been synthesised. Their chemical structures have been characterised by Fourier transform infrared or ¹H nuclear magnetic resonance and their phase behaviour investigated by differential scanning calorimetry, polarising optical miscoscopy, thermo-gravimetric analysis (TGA) and X-ray diffraction. The effect of the crosslinking unit on the phase behaviour of the elastomers has been studied. M₁ showed a cholesteric oily streak and focal conic texture. C₂ exhibited a nematic enantiotropic thread-like and schlieren texture, and a monotropic fan-shaped texture in the S_A phase. Due to the introduction of the mesogenic crosslinking unit, elastomers, P_2-1 ?P_2-5 , exhibited a cholesteric phase, while elastomers, P_1-1 ?P_1-4 , derived from a non-mesogenic crosslinking unit, exhibit a S_A phase. As the content of the crosslinking unit increased, the T _g of the P₁ series initially decreased and then increased, and the T _i of the series decreased. In the P₂ series the T _g increased, but the T _i initially increased and then decreased. TGA confirmed that all the elastomers had improved thermal stability.     

Construction of acetate-bridged dicopper(II) hybrid organic–inorganic networks with calix[4]arene-derived nitrogenous ligands

The reactions of mono-, bis- and tetrapicolyl-p-tert-butylcalix[4]arene derivatives functionalised in the phenolic positions (L ¹ –L ⁴ ) with copper(II) acetate resulted in the formation of discrete complexes or extended coordination polymers. The centrosymmetric dimer [Cu₂(μ-O₂CCH₃)₄(L ¹ )₂] 1, obtained with monodentate L ¹ , has square pyramidal coordination around the copper centres and a cone conformer of monopicolyl-calix[4]arene acting as an axial ligand, with a molecule of acetonitrile hosted within its cavity. The potentially bidentate L ² acts as a monodentate ligand, affording the complex [Cu₂(μ-O₂CCH₃)₄(L ² )₂] 2, which based on spectroscopic and combustion analysis data has a similar coordination sphere around Cu(II). Compound L ³ bridges two dicopper units in the coordination polymer [Cu₂(μ-O₂CCH₃)₄(μ-L ³ )] _n 3, with the calixarene hosting a molecule of tetrahydrofuran. Finally, compound L ⁴ reacts with 4 equivalents of copper(II) acetate, presumably generating a two-dimensional coordination polymer formulated as [{Cu₂(μ-O₂CCH₃)₄}₂(L ⁴ )] 4.     

New chiral liquid crystal monomers and cholesteric polyacrylates: synthesis and characterisation

The synthesis of new chiral monomers (M₁ ?M₃ ) based on menthol and the corresponding polyacrylates (P₁ ?P₃ ) is described. The chemical structures, formula and phase behaviour of the obtained monomers and polymers were characterised with FT-IR, ¹H-NMR, elemental analyses, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). The effect of the mesogenic core rigidity, spacer length and menthyl steric effect on the phase behaviour of M₁ ?M₃ and P₁ ?P₃ is discussed. The expected mesophase of the compounds based on menthol can be obtained by inserting a flexible spacer between the mesogenic core and the terminal groups. For the chiral monomers and polyacrylates, their corresponding melting temperature (T _m), glass transition temperature (T _g) and clearing temperature (T _i) increased with an increase of the mesogenic core rigidity; while the T _m, T _g and T _i decreased with increasing the spacer length. M₁ and P₁ showed no mesophase, while M₂ and M₃ all revealed a SmC* and cholesteric phases. P₂ and P₃ only showed a cholesteric phase.     

Syntheses and crystal structures of mononuclear,tetranuclear and hexanuclear organotin compounds with derivatives of p -aminobenzoic acid

Four organotin(IV) compounds, [Bu₆Sn₆O₆(L¹)₆] (1), [Bu₆Sn₆O₆(L²)₄(L³)₂] (2), [Bu₈Sn₄O₂(L²)₄] (3) and [Ph₃Sn(L²)] (4), were obtained by reactions of BuSnOH, Bu₂SnO and Ph₃SnOH with 4-((6-chloropyridin-3-yl)methylamino)benzonic acid (HL¹), 4-((pyridin-2-yl)methylamino)benzonic acid (HL²) and p-aminobenzoic acid (HL³). 1 is a hexameric cluster, existing in a drum-like structure with prismatic Sn₆O₆ core. Compound 2 is a mixed drum, containing two kinds of carboxylic acid anions. Compound 3 possesses a Sn₄O₄ ladder structure. In 2 and 3, two-dimensional supramolecular structures are formed by the intermolecular hydrogen-bonding interactions. Compound 4 is a monomer with a dimer formed through π–π stacking between adjacent L² anions. Compounds 1–4 were characterized by elemental analyses and IR spectra.     

Syntheses and structures of three disulfoxide uranyl complexes

Three disulfoxide uranyl complexes [UO₂(DBSOB)(NO₃)₂] _n (1), [UO₂(DBM)₂]₂(DBSOB) (2), and [UO₂(PMBP)₂]₂(DBSOB) (3) (DBSOB = 1,4-di(butylsulfinyl)butane, HDBM = dibenzoylmethane, HPMBP = 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone) were synthesized and characterized. The [UO₂(NO₃)₂] groups are connected by bridging disulfoxide ligands DBSOB to form a 1-D zigzag chain in 1. Two [UO₂(DBM)₂] or [UO₂(PMBP)₂] groups are connected by a bridging DBSOB to form the dimeric structures of 2 or 3, respectively. Complexes 1, 2, and 3 are the first structurally characterized disulfoxide–actinide compounds. Thermal stabilities of 1, 2, and 3 were investigated.     

Coordination-driven synthesis of Ag(I) compounds based on a double emission ligand consisting of 1,3,4-oxadiazole and cyclotriphosphazene units

A new ligand (L) which consists of cyclotriphosphazene and 1,3,4-oxadiazole units is reported. Two new Ag(I) coordination compounds {[Ag(L)SO₃CF₃] _n (1) and Ag₂L₂(NO₃)₂ (2)} based on L and Ag(I) salts are obtained. Compound 1 features a 1-D chain, in which the ligand L adopts a divergent trans-conformation, whereas 2 is a discrete binuclear Ag(I) molecule in which L adopts convergent cis-conformation. Compounds 1 and 2 are fully characterized by ¹H-NMR, Infrared, elemental analysis, X-ray powder, and single-crystal diffraction. Luminescent properties of 1 and 2 are investigated.     

Coordination Compounds of Strontium: Syntheses,Characterizations, and Crystal Structures of [Sr(μ-ONc)2(HONc)4]2 and Sr5(μ4-O)(μ3-ONep)4(μ-ONep)4(HONep)(solv)4 (ONc = O2CCH2CMe3; Nep = CH2CMe3; solv = Tetrahydrofuran or 1-Methyl-Imidazole)

Abstract

We have synthesized and characterized two novel Sr compounds: [Sr(μ-ONc)₂(HONc)₄]₂ (1, ONc ? O₂CCH₂CMe₃), and Sr₅(μ_?O)(μ₃?ONep)₄(μ?ONep)₄(HONep)(solv)₄ [ONep ? OCH₂CMe₃, solv = tetrahydrofuran (THF), 2a; 1-methyl-imidazole (Melm), 2b], that demonstrate increased solubility in comparison to the commercially available Sr precursors. The two metal centers of 1 share four unidentate bridging μ-ONc ligands and complete their octahedral geometry through coordination of four monodentate terminal HONc ligands. The structural arrangement of the central core of 2a and 2b are identical, wherein four octahedral Sr atoms are arranged in a square geometry around a μ₄-O ligand. An additional seven-coordinated Sr atom sits directly atop the μ₄-O to form a square-pyramidal arrangement of the Sr atoms, but the apical Sr-O distance is too long to be considered a bond. In solution, compound 1 is disrupted forming a monomer but 2a and 2b retain their structures.     

Three cobalt coordination polymers based on bis(1,2,4-triazol-1-ylmethyl)benzene positional isomer ligands and thiocyanate

The reaction of three positional isomer ligands of bis(1,2,4-triazol-1-ylmethyl)benzene and Co(NCS)₂ gives three coordination polymers [Co(obtz)₂(NCS)₂] _n (1), [Co(mbtz)₂(NCS)₂] _n (2), and {[Co(bbtz)₂(NCS)₂]?·?2DMF} _n (3). Polymers 1 and 2 are comprised of similar 1-D double chains. In 1, each chain forms π–π stacking interactions with four adjacent chains (two above and two below) to extend to a 3-D supramolecular network. Polymer 3 is a neutral 2-D (4,4) network. The dangling NCS^? inserts into the window of adjacent layers in a mutual relationship and result in a 2-D?→?3-D polythreaded network in 3. The thermal stability and the diffuse reflectance UV-Vis spectroscopy of 1, 2, and 3 were measured.     

Metal-directed self-assembly of M3L2 (M=Zn,Cd) metal-organic architectures with a tripodal tris-bidentate chelator

Two discrete M₃L₂ metal-organic architectures, 1 and 2, have been constructed by reaction of a newly designed tripodal tris-bidentate ligand L with M(NO₃)₂ (1: M=Zn; 2: M=Cd). Both complexes together with L have been structurally elucidated by single-crystal X-ray crystallography. Complex 1 exhibits a cationic M₃L₂ coordination architecture bearing three positive charges balanced by three uncoordinated nitrates, while 2 shows a neutral M₃L₂. 1 and 2 both adopt a compressed trigonal prism shape but show no internal cavity due to close ligand-to-ligand interactions. They display totally different intermolecular packing modes in the solid state, which strongly influence the intermolecular π–π interactions. Complex 1 has been arrayed such that each M₃L₂ is surrounded by three neighboring C ₃-symmetry related ones, whereas 2 exhibits a columnar molecular stacking. The distinctive intermolecular packing modes in the solid state between 1 and 2 bring about a small but discernible red shift (4?nm) corresponding to the π–π ^? electronic absorption.     

Synthesis,Characterization, and Structure of Metal(II) (-)-Sparteine Complexes Containing Acetate Ligands

The complexes [Co(C₁₅H₂₆N₂)(C₂H₃O₂)₂] (1), [Ni(C₁₅H₂₆N₂)(C₂H₃O₂)₂] (2), [Cu(C₁₅H₂₆N₂)(C₂H₃O₂)₂] (3) and [Zn(C₁₅H₂₆N₂)(C₂H₃O₂)₂] (4) were prepared from reaction of (?)-sparteine with the corresponding metal(II) acetates in ethanol at stoichiometric ligand to metal ratios. The complexes were characterized by UV-Vis and IR spectroscopies, and magnetic susceptibility measurements. The solid-state structures of 1, 2 and 4 have been determined by X-ray crystallography. The Complexes 1 and 2 display a pseudo-octahedral structure around the metal center, where two acetate ligands coordinate to the metal center in a bidentate fashion, whereas the metal centers in 3 and 4 adopt a pseudo-tetrahedral structure and two acetate ligands in these complexes coordinate to the metal center in a monodentate fashion. The whole set of prepared complexes has been used for comparative structural and spectroscopic studies.