Pyridyl-based Ligands Research Articles

Synthesis, characterization, antibacterial properties, mode of action and molecular docking studies of copper pyridyl complexes against drug-resistant bacteria

A series of four new copper complexes containing pyridyl-based ligands of the type [Cu(Cl)2(L)2] were prepared by solid-state methods and evaluated for antibacterial activity. Their elemental analysis showed that the grinding method produced pure complexes. FTIR spectroscopy confirmed the coordination of ligands to copper ions by identifying shifts in vibrational frequencies. Furthermore, their successful synthesis was confirmed by the coordinating bonds being shifted to lower frequencies. Electronic spectra and magnetic susceptibility data proved the complexes to be d9 tetrahedral complexes. Thermal studies of the copper complexes indicated that they had good thermal stability. In the thermal analysis, a recurring pattern emerges as each copper complex experiences multiple mass losses and exhibits characteristic transitions in DSC profiles, shedding light on their distinct thermal behaviors. The mass spectra of the copper complexes showed that the data agreed with the elemental analysis and other elucidation techniques. The complexes displayed characteristic molecular ion peaks and adducts consistent with their calculated masses, substantiating the successful synthesis of these complexes and enhancing understanding of their composition and stability. The copper complexes also displayed solubility in highly polar and heavy solvents thus reduced the chances of forming good-quality crystals. The copper complexes were more effective against Gram-positive bacteria, with CuL4 performing best, notably against MRSA and S. aureus. All of the active complexes were bacteriostatic against MRSA and S. aureus based on the time kill kinetics. Additionally, it was shown that the CuL4 and Cu4PY-H disrupted the S. aureus cell membrane more effectively than the AgSD control. Finally, the CuL4 membrane disruption studies were not significantly different to the AgSD control on MRSA. The results of cell membrane disruption were supported by molecular docking scores, where CuL4 outperformed the other active compounds, and the trends corroborated the experimental results.

Rapid Access to Encapsulated Molecular Rotors via Coordination-Driven Macrocycle Formation.

Macrocycle formation that relies upon trans metal coordination of appropriately placed pyridine ligands within an arylene ethynylene construct provides rapid and reliable access to molecular rotors encapsulated within the macrocyclic framework. Showing no significant close contacts to the central rotors, X-ray crystallography of Ag(I)-coordinated macrocycles provides plausibility for free rotation or wobbling of rotors within the central cavity. Solid-state 13C NMR of Pd(II)-coordinated macrocycles supports the notion of unobstructed movement of simple arenes in the crystal lattice. Solution 1H NMR studies indicate complete and immediate macrocycle formation upon introduction of Pd(II) to the pyridyl-based ligand at room temperature. Moreover, the formed macrocycle is stable in solution; a lack of significant changes in the 1H NMR spectrum upon cooling to -50 °C is consistent with the absence of dynamic behavior. The synthetic route to these macrocycles is expedient and modular, providing access to rather complex constructs in four simple steps involving Sonogashira coupling and deprotection reactions.

A novel multidentate pyridyl ligand: A turn-on fluorescent chemosensor for Hg2+ and its potential application in real sample analysis.

A novel pyridyl-based ligand with multiple binding sites was developed as potential turn on fluorescent probe for mercuric ion. In comparison with other transition metal ions, the ligand displayed a significant optical selectivity and sensitivity for Hg2+ in aqueous solution with a remarkable fluorescence enhancement. The obtained spectroscopic response was related to the inhibition of the photo-chemical mechanism known as photo-induced electron transfer (PET) in the ligand and CN isomerization by Hg2+ binding. A good linearity between fluorescence responses and Hg2+ concentration was obtained in the range 3.3×10-9M-1.6×10-8M and a nanomolar level limit of detection (LOD) (1.4×10-9M~0.28ppb) and limit of quantification (LOQ) (4.8×10-9M~0.93ppb) were obtained. Both LOD and LOQ values are very low compared to the reported permissible Hg2+ level in drinking water (2ppb) by US Environmental Protection Agency (EPA). The possible binding mode between ligand and Hg2+ were determined using Job's plot analysis and density functional theory (DFT) calculations and a complex with 1:1 stoichiometric ratio was suggested. The response of the pyridyl ligand upon Hg2+ addition was noted to be fast without any time delay and reversible. The performance of the ligand at nanomolar level of Hg2+ and real sample application of the proposed method was investigated and satisfactory results were obtained.

Synthesis, characterization, and photophysical properties of a new class of diorganotin(IV)cupferronato complexes with pyridyl-based ancillary ligands with different conjugated π-system

Five diorganotin(IV) cupferronato complexes have been synthesized and characterized by 1H, 13C and 119Sn NMR, FT-IR, and UV–Vis spectroscopies and elemental analysis (C, H, N). The crystal structure of compound [Me2Sn–(N2PhO2)2]2 as a representative structure was determined by X-ray diffraction. The thermal stability of all prepared compounds was inspected under air atmosphere by thermogravimetric analysis. A series of pyridyl-based ligands with different π-conjugation lengths as ancillary ligands were used to improve, change, and control the optical properties of diorganotin(IV) cupferronato complexes. Examination of the optical properties of the compounds showed that the length of the conjugated π-system of pyridyl ligands has a significant effect on their optical properties. Moreover, the prepared tin complexes were used as light-emitting materials in the fabrication of organic light-emitting diodes.

A three-dimensional supramolecular framework based on the interlinkage of an interpenetrating diamondoid coordination network

In the development of coordination-driven crystalline materials, O- and N-atom donors from carboxylate and pyridyl-based ligands are widely used classes of multidentate bridging ligands composed of several terminal coordinating groups linked by either rigid or flexible spacers. The rigidity of the ligands can play a vital role in the determination of the structures formed. A new CdII supramolecular compound, namely poly[μ-adipato-κ2O1:O4-μ-adipato-κ4O1,O1':O4,O4'-diaquabis[μ-1,4-bis(pyridin-4-yl)-1,3-butadiene-κ2N:N']dicadmium(II)], [Cd2(C6H8O4)2(C14H12N2)2(H2O)2]n, (I), has been synthesized by the self-assembly of Cd(NO3)2·4H2O, adipic acid (hexane-1,6-dioic acid; H2adp) and the dipyridyl ligand 1,4-bis(pyridin-4-yl)buta-1,3-diene (1,4-bpbd) under hydrothermal conditions. Single-crystal X-ray diffraction analysis reveals that each CdII centre is located in a distorted octahedral coordination environment, coordinated by one water O atom, three carboxylate O atoms from two different adp2- ligands and two N atoms from two different 1,4-bpbd ligands. The Cd(H2O) units are interconnected by the μ2,κ2-adp2-, μ2,κ4-adp2- and 1,4-bpbd ligands, which lie across centres of inversion, to give a 66-dia network. Large cavities within a single diamondoid network permit the mutual threefold interpenetration of crystallographically equivalent frameworks. Hydrogen-bonding interactions between the coordinated water molecules and adp2- carboxylate O atoms anchor the interpenetrating networks into a unique three-dimensional supramolecular structure. Topologically, taking the coordinated water molecules and CdII centres as nodes, the whole architecture can be simplified as a binodal (3,7)-connected supramolecular framework. The identity of (I) was further characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and powder X-ray diffraction. The solid-state photoluminescence properties of (I) were also investigated.

New complexes of Cu(II) with dipicolinate and pyridyl-based ligands: An experimental and DFT approach

The three novel mononuclear copper(II) complexes with dipicolinate and pyridyl-based ligands [Cu(dipic)(L)(OH2)] (L=4-picoline, vinylpyridine, 4-styrylpyridine; dipic2−=dipicolinate) were afforded and structurally characterized. X-ray diffraction studies accounted for slight distorted square-pyramidal structures in which the dianion dipic2− acts as a tridentate ligand in a mer-fashion, the N-donor species occupy an in-plane position, and a water molecule was detected apically coordinated. To assess the effect of the nature of the pyridyl-substituent (para position) on electronic properties, other complexes were also synthesized: [Cu(dipic)(py)(OH2)], [{Cu(dipic)(OH2)}2(μ-pyz)] and [{Cu(dipic)(OH2)}(μ-pypy){Cu(dipic)}] (py=pyridine, pyz=pyrazine, pypy=(E)-1,2-bis(pyridine-4-yl)ethane). Absorptive behavior in the UV–VIS region was studied in solution and in the solid state (reflectance measurements).Additionally, geometry and population analyses were conducted by means of DFT calculations. Electronic UV–VIS spectra were simulated for both dinuclear complexes in the framework of the TD-DFT methodology to assign the origin of the absorption bands.

A series of novel Anderson-type polyoxometalate-based MnII complexes constructed from pyridyl-derivatives: assembly, structures, electrochemical and photocatalytic properties

Three novel Anderson-type polyoxometalates (POMs)-based metal–organic complexes (MOCs), namely, [Mn2(4-pdtz)2[CrMo6(OH)5O19](H2O)4] (1), {Mn(3-dpye)0.5[CrMo6(OH)6O18](H2O)}·(3-H2dpye)0.5 (2), [Mn2(3-H2dpye)(TeMo6O24)(H2O)6]·4H2O (3) (4-pdtz = 4-pyridino-bistriazol, 3-dpye = N,N′-bis(3-pyridinecarboxamide)-1,2-ethane), were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex 1, the [CrMo6(OH)5O19]4− (CrMo6) polyoxoanions bridge the MnII ions to generate a 1D Mn–CrMo6 inorganic chain, on which the 4-pdtz ligands hang. In 2, the adjacent CrMo6 polyoxoanions are linked by MnII ions to form a 2D inorganic layer, which is further linked by 3-dpye forming a 3D metal–organic framework (POMOF). Interestingly, the large voids of the 3D POMOF accommodate free protonated 3-H2dpye molecules. In complex 3, the adjacent TeMo6O246− (TeMo6) polyoxoanions are linked by MnII ions to form a 1D inorganic chain, the protonated 3-H2dpye act as bidentate ligands connecting two MnII centers with the oxygen atoms from amide groups, forming a steady 2D metal organic layer. The effects of various coordination behaviors of the pyridyl-based ligands and central metal ions on the structures of the title complexes have been discussed. The title complexes exhibit excellent electrocatalytic activity towards the reduction of bromate and hydrogen peroxide. In addition, the redox potentials of complex 3 is highly sensitive to pH and may be used as a kind of potential pH sensor. The photocatalytic properties of the title complexes under UV and visible irradiation have been investigated in detail.

Homobimetallic hydride and dihydrogen complexes of ruthenium bearing N-heterocyclic carbene ligands

A series of new homobimetallic hydride complexes of ruthenium bearing N-heterocyclic carbene ligand of the type [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (4,4’-bpy = 4,4’-bipyridine) (2), [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyen)] (4,4’-dpyen = 1,2-bis(4-pyridyl)ethylene) (4), and [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyan)] (4,4’-dpyan = 1,2-bis(4-pyridyl)ethane) (5) has been synthesized and characterized starting from [RuHCl(IMes)(PPh3)(CO)] (1). The pyridyl-based ligands, (4,4’-bpy), (4,4’-dpyen), and (4,4’-dpyan) in these complexes act as the bridging ligands between the two ruthenium fragments. The bridging ligand in these bimetallic complexes is very labile. Reaction of these complexes with PMe3 led to extensive substitution of not only the bridging ligand but also the PPh3 ligands. Reaction of complexes 2, 4, and 5 with HOTf at low temperatures result in the formation of the corresponding dihydrogen complexes, [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-bpy)][OTf]2 (9), [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyen)][OTf]2 (10), and [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyan)][OTf]2 (11), respectively. These are the first examples of homobimetallic ruthenium dihydrogen complexes bearing NHC ligands. The intact nature of the H–H bond in these derivatives was established by variable temperature 1H (400 MHz) spin-lattice relaxation time (T1, ms) measurements and from the H, D coupling constants of the corresponding HD isotopomers. The H–H distances (dHH) in these complexes fall in the range 0.95–0.98 Å. Hydrogen evolution takes place upon warming the dihydrogen complexes generated at low temperatures, indicating the labile nature of the H2 ligand in these complexes. The X-ray crystal structure of [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] complex (2) has been determined.

Copper oxide surfaces modified by alkylphosphonic acids with terminal pyridyl-based ligands as a platform for supported catalysis

Self-assembled monolayer (SAM) films of phosphonates have been successfully formed via reaction of 11-hydroxyundecylphosphonic acid or 4,4′-di(methylenephosphonic acid)-2,2′-bipyridine with the oxide layer of copper via the Tethering by Aggregation and Growth (TBAG) deposition method. The hydroxyl-terminated SAM was further modified with isonicotinic acid or 4,4′-dicarboxy-2,2′-bipyridine through a Steglich esterification reaction. These three surfaces derivatized with pyridyl-based ligands are potential platforms for supported catalysis. As a proof of concept, [Ru(CO)3Cl2]2 was bound to the surfaces through the pyridyl-based ligands to yield tethered analogs of the known carbon dioxide reduction catalyst, [Ru(bpy)(CO)2Cl2]. Surface modification reactions were confirmed through specular reflectance infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Characteristic core binding energies were observed in the XPS analyses for phosphorus (P 2p), nitrogen (N 1s), and ruthenium (Ru 3p and Ru 3d), verifying the presence of the various surface functionalizations. IR and XPS data indicate that the phosphonate binding to the copper surface is tridentate in nature.

From ring-in-ring to sphere-in-sphere: self-assembly of discrete 2D and 3D architectures with increasing stability.

Directed by increasing the density of coordination sites (DOCS) to increase the stability of assemblies, discrete 2D ring-in-rings and 3D sphere-in-sphere were designed and self-assembled by one tetratopic pyridyl-based ligand with 180° diplatinum(II) acceptors and naked Pd(II), respectively. The high DOCS resulted by multitopic ligand provided more geometric constraints to form discrete structures with high stability. Compared to reported supramolecular hexagons and polyhedra by ditotpic ligands, the self-assembly of such giant architectures using multitopic ligands with all rigid backbone emphasized the structural integrity with precise preorganization of entire architecture, and required elaborate synthetic operations for ligand preparation. In-depth structural characterization was conducted to support desired structures, including multinuclear NMR ((1)H, (31)P, and (13)C) analysis, 2D NMR spectroscopy (COSY and NOESY), diffusion-ordered NMR spectroscopy (DOSY), multidimensional mass spectrometry, TEM and AFM. Furthermore, a quantitative definition of DOCS was proposed to compare 2D and 3D structures and correlate the DOCS and stability of assemblies in a quantitative manner. Finally, ring-in-rings in DMSO or DMF could undergo hierarchical self-assembly into the ordered nanostructures and generated translucent supramolecular metallogels.

ChemInform Abstract: The Pyridyl Group in Ligand Design for Selective Metal Ion Complexation and Sensing

AbstractReview: 173 refs.

The pyridyl group in ligand design for selective metal ion complexation and sensing

Factors in polypyridyl ligands that control their thermodynamic metal ion selectivity in aqueous solution, and their use in selective fluorescent sensing, are examined. Preorganization of polypyridyl ligands ranging from bidentate to tetradentate by bridging benzo groups, as are present in 1,10-phenanthroline (phen) compared to 2,2'-bipyridyl (bpy), is discussed. The role of solvation is considered in relation to the relative affinity of ligands containing pyridyl groups for divalent and trivalent metal ions in aqueous solution. The effects of steric clashes between H atoms on polypyridyl ligands in decreasing complex stability are evaluated, as well as the effect of chelate ring size on metal ion selectivity. Phen ligands with other donor groups present at the 2 and 9 positions, such as alcohols, amides, carboxylates, and oximes are discussed. The design of pyridyl-based ligands for the separation of Am(III) from lanthanide(III) ions is considered, as well as ligands for the removal of metal ions such as Cu(II) or Zn(II) in neurological diseases such as Alzheimer's. The design of pyridyl-based fluorescent sensors for selective sensing of metal ions is examined in terms of the role of spin-orbit coupling constants (ζ), paramagnetism, and steric effects in the development of selective fluorescent sensors that operate via chelation enhanced fluorescence (CHEF). It is concluded that for lighter metal ions with smaller ζ values such as Zn(II) and Ca(II), and to a lesser extent Cd(II), that the CHEF effect can be achieved with pyridyl-containing fluorophores that coordinate directly to the metal ion. The way in which steric effects can be used to decrease the CHEF effect in Zn(II) relative to Cd(II) to enable selective sensing of the latter is analyzed. For heavier metal ions such as Hg(II) and Pb(II), because of their large ζ values which quench fluorescence, it is concluded that the fluorophore should be tethered to the metal-binding part of the sensor, and prevented from binding to the metal ion by steric and electronic factors. How Hg(II) can quench the CHEF effect by π-contact with fluorophores such as the anthracenyl group, which at first sight might not seem able to bond with metal ions, is examined.

Three- and Eight-Fold Interpenetrated ThSi2 Metal–Organic Frameworks Fine-Tuned by the Length of Ligand

Two new interpenetrated ThSi2 networks, {[Ag4(bipy)4(ox)]·2OH·16H2O}n (1) and {[Ag2(dpb)2(ox)]·10H2O}n (2) (bipy = 4,4′-bipyridine, dpb = 1,4-di(pyridin-4-yl)benzene and Na2ox = sodium oxalate), were constructed from bidentate pyridyl-based organic tectons incorporating ox auxiliary ligand. Interestingly, both 1 and 2 are 3D frameworks with the same ThSi2 topology but with substantial changes in the interpenetration degrees, which are well controlled by employing the pyridyl-based ligands with different lengths. The thermal stabilities and photoluminescence behaviors of them were also discussed.

Synthesis and Structural characterization of half-sandwich iridium macro-metallacycles containing 1,5-dihydroxy-9,10- anthraquinone ligand

Treatment of binuclear complex [Cp*2Ir2(μ-dhaq)Cl2] (H2dhaq = 1,5-dihydroxy-9,10-anthraquinone) with pyrazine or bifuncational pyridyl-based ligands (4,4′-bipyridine (bpy), E-1,2-bis(4′-pyridyl)ethene (bpe), and 2,5-bis(4′-pyridyl)- 1,3,4-oxadiazole (bpo)) in the presence of AgOTf (OTf = CF3SO3) in CH3OH, gave the corresponding tetranuclear complexes, with a general formula of [Cp*4Ir4(μ-dhaq)2(μ-L)2](OTf)4 (2a–2d), respectively. The molecular structure of [Cp*4Ir4(μ-dhaq)2(μ-pyrazine)2](OTf)4 (2a) has been determined by single-crystal X-ray analysis, revealing that the metal centers were connected by pyrazine and bis-bidentate dhaq2− ligands to construct a “slope” rectangular cavity with the dimension of 7.4 × 8.8 × 6.9 Å. 2a also exhibited unique properties in host–guest behavior.

Main group pyridyl-based ligands; strategies to mixed metal complexes

Tris-2-pyridyl ligands of the type [Y(2-py)(3)](n-) containing metallic or semi-metallic bridgehead atoms (Y) are a relatively new innovation in the area of main group coordination chemistry. This review highlights the major classes of ligands currently available, compares their coordination chemistry to their more well known non-metallic counterparts and explores the way in which they can be used to form heterometallic complexes in a targeted way.

Solvothermal synthesis, structures and physical properties of four new complexes constructed from multi-variant tricarboxylate ligand and pyridyl-based ligands

Solvothermal reactions of partially or wholly deprotonated biphenyl-3,4′,5-tricarboxylate (H3L) with nitrates of cadmium, manganese and cobalt, in the presence or absence of auxiliary 4,4′-bipyridine (bipy) and 1-(3,5-di(1H-imidazol-1-yl)phenyl)-1H-imidazole (timp) ligands in H2O–DMF, produce four new complexes, namely, {[Cd3(L)2(H2O)9]·(H2O)5}n (1), {[Cd2(HL)2(timp)(H2O)4]·(H2O)4}n (2), {Mn(HL)(bipy)0.5(H2O)}n (3), {Co(HL)(bipy)0.5(H2O)}n (4). Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and thermogravimetric analysis. Complex 1 possesses a three-dimensional (3D) framework composed of two-dimensional (2D) T-shaped molecular bilayer motifs polycatenated with each other. In complex 2, multicarboxylate ligands and timp ligands link Cd centers to generate one-dimensional (1D) ladder structures which are further connected by π–π interactions to form a 3D supramolecular structure. Complexes 3 and 4 are isostructural and possess 2D networks. Magnetic susceptibility measurements indicate that complexes 3 and 4 exhibit ferromagnetic coupling between adjacent Mn(II) ions and Co(II) ions. The photoluminescent properties of 1 and 2 have been studied in the solid state at room temperature.

Synthesis, structure, photophysical and electrochemiluminescence properties of Re(i) tricarbonyl complexes incorporating pyrazolyl–pyridyl-based ligands

Three rhenium carbonyl complexes 1-3 were synthesized by reaction of the appropriate bidentate pyrazolyl-pyridyl-based ligand L1, L2 (L1 = 2-[1-{4-(bromomethyl)benzyl}-1H-pyrazol-3-yl]pyridine; L2 = 1,4-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene) with [Re(CO)(5)Cl] in toluene. They were characterized by elemental analyses, ESI-MS, (1)H spectroscopy, and X-ray crystallography for 1 and 2. Compounds 1-3 exhibit bright yellow-green luminescence in the solid state and in solution at 298 K with the lifetimes in the microsecond range. It is noteworthy that the luminescent quantum efficiencies of compounds 1-3 are between 0.040 and 0.051, which are much higher than that of the [Re(bpy)(CO)(3)Cl] complex (= 0.019) (M. M. Richter et al., Anal. Chem., 1996, 68, 4370; J. Van Houten et al., J. Am. Chem. Soc., 1976, 98, 4853). Electrogenerated chemiluminescence (ECL) was observed in solutions of these complexes in the absence or presence of coreactant tri-n-propylamine (TPrA) or 2-(dibutylamino)ethanol (DBAE) by stepping the potential of a Pt disk working electrode. The ECL spectra are identical to the photoluminescence spectra, indicating that the chemical reactions following electrochemical oxidation or reduction form the same (3)MLCT excited states as that generated in the photoluminescence experiments. In most cases, the ECL quantum efficiencies of complexes 1-3 are comparable to that of the [Re(L)(CO)(3)Cl] (L = bpy or phen) system. Oxygen tends to substantially decrease ECL intensities of the three rhenium complexes-TPrA system, which could allow them to be used as oxygen sensors.

Studies of rheniumtricarbonyl complexes of tripodal pyridyl-based ligands

The reaction of N-benzoyl and N-acetyl tris(pyridin-2-yl)methylamine 1b and 1c (LH = tpmbaH and tpmaaH) with [Re(CO) 5Br] has been investigated and shown to proceed via the initial formation of a cationic rheniumtricarbonyl complex [(LH)Re(CO) 3]Br in which coordination of the ligand occurs via the three pyridine rings. For tpmbaH 1b, but not tpmaaH 1c, this initial complex 2b readily undergoes the loss of HBr to give a neutral octahedral complex 4b [(L)Re(CO) 3] where coordination occurs via two of the pyridine rings and the deprotonated amide nitrogen. The 1H NMR spectrum of the latter complex 4b is very unusual in that at room temperature the signals for the 3-H protons on the coordinated pyridine rings are not visible due to extreme broadening of these resonances. Comparison with the analogous complex 7 from N-benzoyl bis(pyridin-2-yl)methylamine 6b (bpmbaH) confirms that this is due to rotation of the uncoordinated pyridine ring. The structure of the cationic complex 3d [(LH)Re(CO) 3]Br formed from N-benzyl tris(pyridin-2-yl)methylamine 1d (bz-tpmaH) is also discussed. The crystal structures of complexes [(tpmba)Re(CO) 3] 4b, [(bz-tpmaH)Re(CO) 3]Br 3d and [(bpmba)Re(CO) 3] 7 have been determined. In all complexes the coordination geometry around Re is distorted octahedral with a fac-{Re(CO) 3} + core.

Structurally characterized group 4 metal alkoxides modified with the pyridyl-based ligands 2-mercapto pyridine n-oxide and 3,3′-dihydroxy-2,2′-bipyridine

An investigation of a series of substituted pyridyl-based ligands was undertaken using 2-mercapto pyridine n-oxide (H-2MPO) and 3,3′-dihydroxy-2,2′-bipyridine (H 2-OBPy) as the modifying reagents of a series of titanium alkoxides. The resultant products were identified as (2MPO) 2Ti(OR) 2 [OR = OCHMe 2 ( 1), OCH 2CMe 3 ( 2), OCMe 3 ( 3)] and [(OR) 2M(μ c-OBPy)] 3 where M⧹OR = Ti⧹OCH 2CMe 3 ( 4) along with Zr⧹OCMe 3 ( 5) from Zr(OCMe 3) 4 (μ c = chelating bridging). The structure of 1– 3 were found to adopt similar monomeric structures with octahedrally (Oh) bound Ti metal centers using two terminal OR and two chelating 2MPO derivatives. Switching to the OBPy ligand, cyclic trinuclear species with Oh bound metals that employed two terminal OR and two μ c-OBPy ligands were isolated. The two rings of the bridging OBPy were rotated such that one O and one N from different rings chelate to a single metal. The synthesis and characterization of these compounds and comparison to appropriate literature species are presented.

Synthesis and Crystal Structures of Multidimensional Coordination Polymers Based on W/Cu/S Clusters with Flexible Imidazole Ligands

Reactions of [WES3]2- (E = S, O) with CuX (X = NCS, CN, I) in the presence of bix (bix = 1,4-bis(imidazole-1-ylmethyl)benzene) in DMF or CH3CN resulted in the formation of two novel 2D --> 3D interpenetrating coordination polymers [S2W2S6Cu4(bix)2]n (1) and {[WS4Cu4(NCS)2(bix)3].CH3CN}n (2), a noninterpenetrating 3D polymer {[WS4Cu2(bix)].DMF}n (3), and two 2D sheet polymers [WS4Cu3(CN)(bix)]n (4) and {[OWS3Cu3(bix)2][I].DMF.2H2O}n (5), depending on the reaction temperature and the reagents used. Compound 1 contains a hexagonal prism of W2Cu4S6 cluster core, which serves as a 4-connecting node to link equivalent nodes via bix ligands, forming a 2D (4,4) net. In 2, a WCu4S4 core, which also acts as a 4-connecting node, connects the neighboring nodes either through single or double bix bridges, affording a different 2D (4,4) sheet. Inclined interpenetration occurs between two stacks of 2D sheets in the total structure of 1, while 2 involves a parallel interpenetration between the adjacent layers, both creating a 3D network. Compounds 1 and 2 represent the first examples of interpenetrating (4,4) frameworks with clusters as nodes and bidentate pyridyl-based ligands as linkers. Unlike 1 and 2, compound 3 has a noninterpenetrating 3D network, which is composed of the inorganic 1D (WS4Cu2)n chains linked by cis and trans bix ligands. Compound 4 features an inorganic 1D (WS4Cu3)n chain structure, which is linked by CN groups and bix ligands to form an infinite 2D network. Compound 5 is a 2D layer polymer with large inner cavities.