Flexible Bidentate Ligand Research Articles

Stereochemistry of six-coordinated tungsten(VI) complexes having one rigid chiral bidentate ligand and two flexible bidentate ligands: Stereo-selective formation of Δ- and Λ-forms induced by the chiral ligand

Six-coordinated tungsten(VI) complexes with one rigid chiral bidentate ligand, 1,1′-bi-2-naphthol (bino) 1, and two flexible bidentate ligands (f-bls), pinacol (pin) or ethylene glycol (en), were prepared, and their stereochemistry was discussed. Generally, metal complexes with three f-bls produce enantiomeric Δ- and Λ-forms. Other types of isomerism are produced by f-bls, which are attributable to their conformation, i.e., δ- and λ-forms. Although the conformational isomerism of Δ- and Λ-enantiomers produces diastereomers, the energy differences between the diastereomers are small, less than several kcal mol−1. Therefore, the conformational isomerism of f-bls is not significant in coordination chemistry. We found that the introduction of one rigid chiral bidentate ligand controls the Δ- and Λ-stereochemistry of the complex. The conformation of (R)-bino produces the Δ-isomer, and that of (S)-bino affords the Λ-isomer. We also performed theoretical studies to support our observations.

Construction of Entropically Favored Supramolecular Metal–Ligand Trimeric Assemblies Supported by Flexible Pyridylaminophosphorus(V) Scaffolds

The self-assembly reactions of tetratopic metal acceptors with the flexible bidentate ligands are known to yield self-assembled molecular squares of the type [M4L8], triangles of composition [M3L6], or a mixture of these two. In this work, we demonstrate the preferential formation of a trimeric cage assembly of the formula [Pd3(L1)6·(BF4)6] (1a) over the tetrameric cage [Pd4(L1)8·(BF4)8] (1b) by employing a flexible dipodal phosphoramide ligand, [PhPO(NH(3-Py))2] (L1; 3-Py = 3-aminopyridine), in a reaction with [Pd(CH3CN)4·(BF4)2]. The entropically favored trimeric self-assembly of 1a is the predominant species in the solution [dimethyl sulfoxide (DMSO)-d6] at room temperature. In fact, at higher temperatures, 1a was found to be the only product, as observed from the disappearance of the peak due to 1b in the 31P NMR spectrum. However, in a 1:1 mixture of acetonitrile (MeCN)-d3 and DMSO-d6, the tetrameric species 1b is the preferred species, as revealed by the 31P NMR and electrospray ionization mass spectral analyses. The structure of the molecular trimer 1a has been established in the solid state by using single-crystal X-ray diffraction analysis. Interestingly, treatment of an another flexible ligand, [MePO(NH(3-Py))2] (L2), with the same Pd(II) acceptor resulted in exclusive formation of the trimeric cage [Pd3(L2)6·(BF4)6] (2).

Synthesis and Characterization of Co(II) Coordination Polymer with a Flexible Bidentate Ligand

A coordination polymer, {[Co(bib)3](BF4)2}n, was prepared for the first time at room temperature via the reaction between cobalt(II) chloride and flexible linker ligand, 1,4-bis(imidazolyl)butane (bib), in the presence of sodium tetrafluoroborate using a three layers method. The compound was characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction. It crystallizes in the triclinic sp. gr. $$P\bar {1}$$ with the unit cell parameters a = 9.8124(2), b = 22.1804(4), c = 26.9233(5) A and α = 71.910(2)°, β = 89.418(2)°, γ = 86.992(2)°. In the polymeric structure of the compound, the cobalt(II) ions have the CoN6 octahedral geometry and six bib-ligands are coordinated to one metal ion to form an open 3D 2-fold interpenetrated framework (α-polonium-type net, pcu).

Role of Anions in the Formation of Multidimensional Coordination Polymers: Selective Separation of Anionic Toxic Dyes by 3D-Cationic Framework and Luminescent Properties

The role of anions in the formation of diversified coordination polymers (CPs) of a flexible bidentate ligand (L), containing an aliphatic-aromatic spacer (p-xylyl) between amidopyridine moieties, has been explored. The reaction of L with Cd(II) or Cu(II) salts of NO3–, ClO4–, SO42–, and SiF62– resulted in the single crystals of eight CPs. The X-ray diffraction analyses of the single crystals reveal that the CPs contain 1D-zigzag (SiF62–), open (4,4)-network (NO3– and SCN–), and the interpenetrated 2D-networks with (4,4)- and (6,3)-topologies and pseudodiamondoid network (SO42– and ClO4–). These results clearly indicate that the presence of tetrahedral anions favored the interpenetration of the 2D- and 3D-networks. The resultant cationic CPs are explored for their dye adsorption ability based on the charge transfer interaction between the framework and ionic dye. Among all CPs, complex 8 containing a 3D-interpenetrated diamondoid network was found to show remarkable ability for the uptake of anionic dyes ...

Self‐Assembly of Oxamidato‐Chelated ReI‐ and MnI‐Based Flexible Dinuclear Horse‐Stirrup‐Like Metallacycles

AbstractThe self‐assembly of M2(CO)10 (M = Mn, Re), oxamide ligands [H2L = N,N′‐dibutyloxamide (dbo), N,N′‐dibenzyloxamide (dbno)], and flexible bidentate linkers [L′ = 1,2‐bis(4‐pyridyl)ethane (bpe), 1,3‐bis(4‐pyridyl)propane (bpp)] afforded MnI‐ and ReI‐based dinuclear metallacycles [(CO)3M(μ‐η4‐L)(μ‐L′)M(CO)3] (1–6). The oxidative addition of oxamide ligands to the equatorial sites and the addition of flexible dipyridyl ligands to the axial sites of facial metal tricarbonyl cores resulted in the formation of dinuclear metallacycles under one‐pot reaction conditions. Metallacycles 1–6 were characterized through elemental analysis, IR, UV/Vis, and NMR spectroscopy. The formation of dinuclear compounds 1 and 4 was ascertained by ESI mass spectrometry. The molecular structures of 2, 3, 5, and 6 were elucidated by single‐crystal X‐ray crystallographic methods, which revealed horse‐stirrup‐like dinuclear frameworks in which the metal centers are orthogonally connected by a bridging oxamide ligand through ON∩NO bis(chelation) and a flexible bidentate ligand through M–N coordination. The first one‐step syntheses of self‐assembled neutral MnI‐based dinuclear metallastirrups containing bis(chelating) oxamide ligands and their rhenium analogues are reported herein.

Tuning the Inclusion Properties and Solid-State Reactivity of Second Sphere Adducts Using Conformationally Flexible Bidentate Ligands

Second-sphere coordination refers to any intermolecular interaction with the ligands directly bound to the primary coordination sphere of a metal ion. In this article, we have successfully applied the second-sphere coordination approach in the construction of versatile host frameworks that can accommodate various guest molecules. We have used a family of bidentate flexible molecules as second-sphere ligands, and the tetrachlorometalate anion [MCl4]2– (where M = Cu, Co, Cd, Zn, and Hg) as the primary coordination sphere to synthesize new second sphere adducts. By introducing an alkyl spacer −(CH2)n– (n = 1, 2, 3, 4) to bibenzylamine (L0), the ligands L1, L2, L3, and L4 with higher degree of flexibility were synthesized. Different guest molecules such as alcohol, acetic acid, acrylic ester, or acetonitrile can be included in the host framework self-assembling diprotonated L1–L4 and [MCl4]2–, leading to a novel type of supramolecular assemblies: CH3CH2OH⊂[L2]2H+·[CuCl4]2– (2), CH3OH⊂[L3]2H+·[MCl4]2– (3), CH3...

Synthesis of di(Imdazolium) and di(Pyrazolium) Salts as Precursors for N-heterocyclic Dicarbene Complexes

Alpha,omega-bis(pyrazol-1-yl)alkanes and alpha,omega-bis(imidazol-1-yl)alkanes with spacers consisting of four to ten methylene groups have been prepared from pyrazole, 3,5-dimethylpyrazole or imidazole and corresponding dibromoalkanes in a superbasic medium KOH-DMSO. The proposed method of synthesis allowed the preparation of new flexible bidentate ligands without the need to use toxic solvents and tedious workup procedures. Bis(pyrazol-1-yl)alkanes were further functionalized for their use as precursors for “non-classical” mesoionic N-heterocyclic carbene ligands. One the first step, iodine atoms were introduced to positions 4 of pyrazole rings by oxidative iodination using I2-HIO3 system. On the next step, nitrogen atoms in positions 2 of pyrazole rings were alkylated using several agents. Reaction with methyliodide unexpectedly led to the formation of only mono-alkylated products even after 7 days of refluxing in a neat alkyliodide. Methylation by trimethyloxonium tetrafluoroborate or methyltriflate led to dimethylated products in high yields. Bis(imidazol-1-yl)alkanes were easily alkylated by methyliodide to give di(imidazolium) salts – precursors to “classic” N-heterocyclic dicarbenes.

1D, 2D and 3D coordination polymers of 1,3-phenylene diisonicotinate with Cu(i)/Cu(ii): Cu2I2 building block, anion influence and guest inclusions

The reactions of a flexible bidentate ligand 1,3-phenylene diisonicotinate (L) with Cu(i/ii) salts afforded coordination polymers with varied dimensionalities and guest inclusion capabilities.

Structural variation in ethylenediamine and -diphosphine adducts of (2,6-Me2C6H3S)2Pb: a single crystal X-ray diffraction and 207Pb solid-state NMR spectroscopy study

Coordination complexes of (2,6-Me2C6H3S)2Pb (1) with flexible bidentate ligands have been prepared to explore new bonding environments for Pb(II) thiolates. The reaction of 1 with a series of ethylenediamine and ethylenediphosphine ligands resulted in isolation of the adducts [(2,6-Me2C6H3S)2Pb]2(tmeda) (9), [(2,6-Me2C6H3S)2Pb]3(dmpe) (10) and [(2,6-Me2C6H3S)2Pb]2(dppe) (11) [tmeda = N,N,N',N'-tetramethylethylenediamine; dmpe = bis(dimethylphosphino)ethane; dppe = bis(diphenylphosphino)ethane]. The X-ray crystal structure of 9 shows a dinuclear species in which tmeda is chelating a ψ-trigonal bipyramidal S2N2 Pb centre via axial and equatorial sites. The structure of 10 displays a trinuclear structural unit in which dmpe is chelating a ψ-trigonal bipyramidal S2P2 Pb centre via equatorial sites. Compounds 9 and 10 also contain a second unique metal centre with ψ-tetrahedral S3Pb bonding motifs. The structure of 11 shows the dppe ligand bridging two Pb ψ-tetrahedral S2P metal bonding environments. Static (207)Pb solid-state NMR (SSNMR) spectra of 9-11 and [Ph4As][(PhS)3Pb] (12) were acquired with cross polarization (CP)-CPMG and frequency swept pulse (WURST)-CPMG pulse sequences, and the efficiencies of these pulse sequences are compared. The (207)Pb SSNMR spectra reveal that the lead chemical shift anisotropies (CSA) vary greatly between the different Pb sites, and are generally large in magnitude. DFT calculations are utilized to relate the orientations of the (207)Pb nuclear magnetic shielding tensors to the molecular structures, and to aid in spectral assignment where multiple Pb centres are present. The combination of X-ray diffraction, (207)Pb SSNMR and DFT is shown to be invaluable for the structural characterization of these important structural motifs, and should find wide-ranging application to numerous lead coordination compounds.

A Luminescent Cage‐Like Complex Constructed by Bidentate Pyridine‐Containing Ligand and Silver Nitrate

AbstractThe cage‐like complex, Ag4L4(NO3)4 (1) [L = 1, 4‐bis(pyridine‐2‐ylmethoxy)benzene] was synthesized by the reaction of the flexible bidentate ligand and silver nitrate. It was characterized by elemental analysis, IR spectroscopy, TG, and single‐crystal X‐ray analysis. Complex 1 is reported as the first cage‐like cluster constructed by four nitrate anions bridging two [2+2] macrocycles. A blue luminescent emission and luminescent enhancement effect are observed in complex 1.

Syntheses, Structures and Luminescent Properties of Zinc(II) and Cadmium(II) Complexes With the Ditopic Ligand 1,3-Bis(imidazol-1-ylmethyl)benzene

Three new complexes, namely [Zn(mbix)(SO4)]·CH3OH (1), Cd(mbix)2(NO3)2 (2) and [Cd(mbix)2(H2O)2]·(NO3)2 (3), have been obtained by reactions of flexible bidentate ligand 1,3-bis(imidazol-1-ylmethyl)benzene (mbix) with corresponding zinc(II) and cadmium(II) salts. The structures of these complexes have been determined by the X-ray single crystal diffraction analysis. Complex 1 features a 2D wavy network with (4,4) topology. Complex 2 has a 2D grid network with left- and right-handed helical chains, while complex 3 exhibits twofold parallel interpenetration structure. The differences of three complexes demonstrate that the coordination geometry of metal ions and the ratio of reactants have a great impact on the structure of the supramolecular architectures. The luminescent properties of three complexes are also investigated. Three complexes have been constructed by different zinc(II) and cadmium(II) salts with the flexible mbix ligand. The results demonstrate that the metal ion and the ratio of reagents have an important effect on the structure of these complexes.

Flexible Diphosphine Ligands with Overall Charges of 0, +1, and +2: Critical Role of the Electrostatics in Favoring Trans over Cis Coordination

The influence of the formal electrostatic interaction on the cis/trans coordination mode at a PdCl(2) center is investigated in a family of isostructural flexible diphosphine ligands Ph(2)P-X-C(6)H(4)-Y-PPh(2), where X and Y stand for neutral or cationic N,C-imidazolylene linkers. While the neutral and monocationic diphosphine spontaneously behave as classical cis-chelating ligands, only the dicationic diphosphine, where the electrostatic repulsion between the formal positive charges specifically takes place, is observed to behave as a trans-chelating ligand. The crucial role of electrostatics is analyzed on the basis of (31)P NMR data in solution and X-ray diffraction data in the crystal state. Comparative theoretical studies of the cis- and trans-chelated complexes, including EDA, static (31)P NMR, MESP, and AIM analyses, have been undertaken on the basis of DFT calculations in the gas phase or in the acetonitrile continuum. Whereas the cis-coordination mode is shown to be thermodynamically favored for the neutral ligand, the trans-coordination mode is found to be preferred for the dicationic homologue. The stereochemical preference is thus shown to be parallel to the expected effect of the formal electrostatic interaction. The results open perspectives for control of the cis- and trans-chelating behavior of flexible bidentate ligands by more or less reversible charge transfer at the periphery of the coordination sphere of a metallic center.

First Three-Dimensional Inorganic–Organic Hybrid Material Constructed From an “Inverted Keggin” Polyoxometalate and a Copper(I)-Organic Complex

A new polyoxometalate (POM) based on a flexible bidentate ligand and "inverted Keggin" inorganic building block, namely, [Cu(8)L(8)[Mo(12)O(46)(AsPh)(4)](2)]·H(2)O (1), where L is 1,3-bis(1,2,4-triazol-1-yl)propane, has been synthesized under hydrothermal condition. In 1, the "inverted Keggin" [Mo(12)O(46)(AsPh)(4)](4-) building blocks are linked by the one-dimensional (1D) zigzag [Cu(I)(trans-L)](+) chains and [Cu(I)(4)(cis-L)(4)](4+) macrocycles to yield a three-dimensional (3D) framework. The compound 1 represents the first 3D "inverted Keggin" polyoxometalate modified by a transition-metal complex. Topologically, the 3D framework can be considered as an 8-connected net with a Schläfli symbol of 4(22)·6(6). As far as we know, compound 1 is the highest-connected uninodal network topology presently known for POM-based materials. The compound was characterized by its IR spectrum, UV-vis spectrum, thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD) patterns. Remarkably, compound 1 exhibits photocatalytic activity for dye degradation under visible light irradiation and shows good stability toward visible-light photocatalysis.

Two coordination polymers displaying unusual threefold 1D→1D and threefold 2D→3D interpenetration topologies

Self-assembly of long V-shaped ligands and metal salts in the presence of a flexible bidentate ligand provides two types of three-fold interpenetrating networks showing unprecedented 1D→1D and 2D→3D motifs.

Probing the dimensions of semi-rigid inner functionalised U-shaped bis-porphyrin cavities

The synthesis of a series of open U-shaped bis-porphyrin cavity molecules is described, with bridged bicyclic backbones to confer rigidity, and a pendant substituted aromatic probe unit suspended on the inside of the cavity. The dimensions and flexibility of the bis-zincporphyrin cavity were probed using several different techniques. Initially the molecular ruler concept was employed, using flexible bidentate ligands as guests with a range of possible linear dimensions. Secondly, NMR methods were employed with rigid bidentate ligand guests of fixed lengths, and thirdly diffusion based NMR methods were utilised. The range of inter-porphyrin distances estimated by these methods suggests that these types of open-cavity systems have a surprising degree of flexibility.

Syntheses, Structures and Spectroscopic Studies of Silver(I) Coordination Polymers Bridged by Flexible Bidentate Ligands

The reaction of Ag2SO4 and bpp (bpp = 1,3-bis(4-pyridyl)propane) in H2O afforded the complex [Ag2(bpp)2(SO4) · 6.5H2O·CH3OH]n, 1. The IR and TGA have been recorded and the structure has been determined. Crystal data for 1: Space group C2/c, a = 17.885(4), b = 25.230(6), c = 8.832(2) Å, β = 105.437(4)°. V = 3841(1) Å3, Z = 8 with final residuals R1 = 0.0710 and wR2 = 0.1620. The complex shows a three-dimensional supramoleclar structure constructed with two-dimensional infinite [Ag2(bpp)2]n sheetlike layers pillared by Ag-Ag interactions and Ag····O (SO4) interactions in the solid state.

Silver Coodination Polymers with Flexible Ligands. Syntheses, Crystal Structures, and Effect of the Counteranion and the Solvent on the Structure of Complexes [AgLX]∞ of the Bis(Phenylthio)methane Ligand L1 with Silver(I) Salts, X = ClO4-, BF4-, CF3COO-, CF3SO3-, CF3CF2CF2COO-, and -OOCCF2CF2COO-

A number of complexes were synthesized to rationalize the structures of Ag(I) complexes with a small flexible bidentate ligand, bis(phenylthio)methane, when the anion is varied. We compared two similar “spherical” anions, ClO4- (1) and BF4- (2), as well as two slightly “elongated” ones, CF3COO- (3) and CF3SO3- (4, 5). Complexes with a longer anion, CF3CF2CF2COO- (6), and a diacid, -OOCCF2CF2COO- (7), were also investigated. All the compounds studied form a 1D-coordination polymer. The coordination polymers of 1−4 are of the type [Ag−ligand−]∞ and adopt two distinct conformations: gauche−trans−gauche for 1, 2, and 4, and gauche−gauche−gauche for 3. The anions in 1−4 are coordinated to the silver atoms through a single O or F atom. All these 1D-chains are associated through weak van der Waals interactions into 2D-layer structures. Solvent-induced supramolecular isomerism was observed with the CF3SO3- anion. With diethyl ether, the 1D-coordination polymer of 4 was observed, as indicated above, while a two-stranded chain comprising a 16-membered macrocyclic structure, Ag4L14, was noted when petroleum ether was used, 5. The macrocycles are connected through a small cyclic (CF3SO3···Ag···)2 dimeric unit. Another type of double-stranded ladder-like structure was noted for 6. Each of the two heptafluorobutyrate anions is coordinated through its oxygen atoms to two distinct silver atoms to form a dimeric unit. This, in turn, is connected to another unit through two Ag−S coordination bonds. The repeat unit of this coordination polymer is based on a 10-membered Ag4L12 macrocycle. In compound 7, with the tetrafluorosuccinate anion, one observes another type of 1D-polymer best described as a [Ag2−tetrafluorosuccinate−]∞ chain reinforced by Ag−ligand−Ag bonds. Most complexes containing fluorine atoms have C(H)···F or C(H2)···F short contacts (2.998−3.203 Å) that correlate with an FTIR absorption band around 521 cm-1. Relatively short Ag···Ag interactions are found in both 6 and 7.

New diphosphine ligands based on diphenyl ether for the Pd-catalyzed CO/ethene copolymerization

The catalytic activity and selectivity of palladium(II) complexes of new, flexible bidentate ligands in the CO/ethene copolymerization reaction have been found to change considerably with the steric properties of the ligands.

8-(2-Pyridylmethoxy)quinoline: a new N,O,N′-tridentate ligand and X-ray crystal structures of its mononuclear palladium(II), copper(II) and nickel(II) complexes

The synthesis of the new N,O,N′-tridentate ligand 8-(2-pyridylmethoxy)quinoline ( 2) is described. X-ray crystal structures of its mononuclear complexes with palladium(II) chloride, copper(II) chloride and nickel(II) nitrate are reported. The ligand acts as a flexible bidentate or tridentate ligand, according to the requirements of the coordinated metal.

New Inorganic–Organic Coordination Polymers Generated from Rigid or Flexible Bidentate Ligands and Co(NCS)2·xH2O

The coordination chemistry of the long rigid bidentate Schiff-base ligands 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (L1), 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene (L2), and of the flexible ligand 1,3-bis(4-pyridyl)propane with Co(NCS)2·xH2O has been investigated. Three new coordination polymers were prepared and fully characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. The magnetic behavior of all compounds was also investigated and found to follow the Curie law. [Co(NCS)2(L1)2·2CH2Cl2]n (1, monoclinic, C2/m; a= 11.995(2) Å, b=14.596(3) Å, c=10.846(2) Å, β=110.99(3)°, Z=2) features a two-dimensional non-interpenetrating distorted square pattern. [Co(NCS)2(L2)2]n (2, monoclinic, P21/n; a=9.5315(19) Å, b=17.299(4) Å, c=9.6646(19) Å, β=99.11(3)°, Z=2) features a one-dimensional ring-like chain motif. Important C–H···S hydrogen bonding interactions exist in 2, which play a significant role in aligning the polymer strands in the crystalline solid. [Co(1,3-bis(4-pyridyl)propane)2(NCS)2·0.33 H2O]n (3, monoclinic, P21/n; a=18.701(4) Å, b=16.593(3) Å, c=20.696(4) Å, β=114.45(3)°, Z=4) exhibits a polymeric pattern similar to that of 1. All three compounds feature similar {CoN6} pseudooctahedral coordination spheres.