FT-IR Spectroscopic Investigation of Hofmann Td-Type Complexes of 2-, and 3-Chloropyridine

Hofmann-type modified clathrate hosts containing 2- or 3-chloropyridine molecules attached to metal (II) tetracyanocadmate frame, with a given formula: M(Clpy)₂Cd(CN)₄ where M = Mn, Ni or Cd; Clpy = 2- or 3-chloropyridine, have been synthesised for the first time. Their FT-IR spectra are reported in the 400–4000 cm^-1 region. All the vibrational modes of coordinated Clpy are characterised. The spectral features of the compounds studied are found to be similar to each other indicating that they have analogous structures. The coordination effect on the Clpy modes is analyzed.     

A Chiral Coordination Polymer of Silver(I) with Saccharinate and Pyridine: Synthesis,Spectral, Thermal,and Structural Characterization of [Ag(sac)(py)]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

The first silver(I) complex of saccharinate (sac) with pyridine (py), [Ag(sac)(py)]_n has been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffractometry. The complex crystallizes in chiral, trigonal space group P3₁21 (No. 152) with unit cell parameters of a = 11.2605(2) Å, c = 17.3300(4) Å, V = 1903.02(6) ų and Z = 6. [Ag(sac)(py)]_n contains monomeric [Ag(sac)(py)] units linked into infinite helices by way of Ag⋅sAg interactions [d(Ag⋅sAg) = 2.909(2) and 2.985(1) Å]. The distorted square-planar environment of Ag is completed by an N-bonded sac [Ag—N = 2.084(2) Å] and a py molecule [Ag—N = 2.116(2) Å]. The N_sac—Ag—N_py angle is 173.85(10)^∘. The one-dimensional chains are crosslinked by C—H⋅sO interactions involving the carbonyl and sulfonyl O atoms of sac and aromatic-ring hydrogen atoms of both sac and py. The thermal stability of the title complex was investigated using thermogravimetry and differential thermal analysis in a static atmosphere of air. The first decomposition stage between 90 and 160^∘C corresponds to removal of the py molecule in a single stage, while the degradation of the sac moiety occurs at two stages in the temperature range 370–515^∘C, giving an end product of metallic Ag.     

A vibrational spectroscopic study of the adsorption of 4,4′-bipyridyl by sepiolite and smectite group clay minerals from Anatolia (Turkey)

The adsorption of 4,4-bipyridyl by natural sepiolite and smectite group clay minerals (bentonite, hectorite and saponite) from Anatolia (Turkey) has been studied using vibrational spectroscopy. Investigation of Fourier-transform infrared and Fourier-transform Raman spectra of adsorbed 4,4-bipyridyl indicate the presence of chemisorbed species. However, any evidence for the generation of anionic species on the surface of the phyllosilicates has not been detected. It is proposed that the adsorbed bipyridyl molecules on sepiolite are centrosymmetric and H-bonded to the surface hydroxyls through both the nitrogen lone pairs as bidentate ligands. The adsorbed bipyridyl molecules on the smectite group clays are coordinated to exchangeable cations both directly and also indirectly through water as monodentate ligands. XRD patterns of the clays studied are also recorded.     

Synthesis and structural characterization of a coordination polymer of silver(I) with saccharinate and nicotinamide

A silver(I)-saccharinato (sac) complex with nicotinamide (nia), [Ag(sac)(nia)] _n has been synthesized and characterized by elemental analysis, IR spectroscopy, DTA-TG analyses and single crystal X-ray diffractometry. The complex crystallizes in monoclinic space group P2₁/n with unit cell parameters of a=7.0258(4) Å, b=24.3784(10) Å, c=8.4301(5) Å, β=109.407(5)°, V=1361.85(13) ų and Z=4. [Ag(sac)(nia)] _n contains [Ag(sac)(nia)] units, which are doubly bridged by both nia and sac ligands, leading to a linear one-dimensional polymeric chains running along the a axis. The silver(I) ion has a highly distorted AgN₂O₂ tetrahedral geometry and the coordination polymer exhibits relatively short intra-chain ligand supported Ag···Ag separations of 3.1593(4) Å. The one-dimensional chains are crosslinked by N–H···O hydrogen bonds and aromatic π(sac)···π(nia) stacking interactions to generate a two-dimensional layer structure. IR spectra and thermal analysis data are in agreement with the crystal structure.     

The effect of solvent composition on swelling and shrinking properties of poly(acrylamide-co-itaconic acid) hydrogels

The peculiarities of the equilibrium swelling ratio and swelling-shrinking kinetics of polyelectrolyte copolymeric hydrogels consisting of acrylamide and itaconic acid (AAm/IA) have been studied in water/nonsolvent (acetone, methanol, ethanol and 1-butanol) mixtures as a function of solvent composition and IA content in the hydrogel. The phase transition of these hydrogels was generated by changing the solvent composition by progressive substitution of water by the nonsolvent. For all P(AAm/IA) hydrogels, the form of the shrinking curves was determined to be strongly dependent on the type of the nonsolvent used. The rate of shrinking of these hydrogels increased in the order 1-butanol < ethanol < methanol < acetone.     

Solid-state vibrational spectroscopy: Part VI. An infrared and raman spectroscopic study of transition metal(II)4-methylpyridine complexes

Infrared (4000–200 cm^?1) and Raman (3500–300 cm^?1 ) spectra are reported for metal(II) halide and thiocyanate 4-methylpyridine complexes of the following stoichiometries: (MX₂(4-Mepy)₂) {M = Mn, Co, Cu or Zn, X = Cl or Br; M = Mn, Ni or Zn, X = NCS}; (MX₂(4-Mepy)₄) {M = Mn, Fe, Co or Ni, X = Cl or Br; M = Mn, Fe, Co, W or Cu, X = NCS}. For a given series of isomorphous complexes there is a correlation between the sum of the differences between the liquid and ligand values of the ν₁, ν₂, ν₃, ν₄, ν₅, ν₆, ν₇, ν₈, ν₉, ν₁₀, ν₁₂, ν₁₃ and ν₁₄ modes of 4-methylpyridine and the strength of the metal-nitrogen bond. Comparison of the shift values of pyridine and 4-methylpyridine complexes supports the suggestion that, unlike the situation in the pyridine complexes, back-donation from the metal to the ligand is unimportant in the 4-methylpyridine complexes.     

Vibrational spectroscopic studies of three dimensional host lattices formed by pyrazine bridges between tetracyanonickelate layers

Three dimensional host lattices have been developed by forming bridges with bidentate pyrazine molecules between adjacent tetracyanonickelate polymeric layers of Ni(II) or Cd(II). The Fourier-transform IR and Raman spectra (4000-200 cm^–1) of the compounds with the general formula M(pyz)Ni(CN)₄, (where M = Ni or Cd) are reported. These host lattices can include benzene molecules but it is found that aniline molecules cannot be included in these structures. They, however, form complexes with the formula M(an)₂Ni(CN)₄, by replacing pyrazine ligands. A monodentate pyrazine complex of Cd(II) with the formula Cd(pyz)₂Ni(CN)₄ has also been prepared.     

Monoclinic and triclinic concomitant polymorphs of di‐μ‐pyridazine‐1κ2N:2κ2N′‐bis­[(saccharinato)silver(I)]

Crystallization of the title compound, di‐μ‐pyridazine‐1κ²N:2κ²N′‐bis­[(2,3‐dihydro‐3‐oxobenzisosulfonazolato‐κN)silver(I)], [Ag₂(C₇H₄NO₃S)₂(C₄H₄N₂)₂], from acetonitrile yields both monoclinic, (I), and triclinic, (II), polymorphs. In both forms, the silver(I) ions have a slightly distorted trigonal AgN₃ coordination geometry and are doubly bridged by two neutral pyridazine (pydz) ligands, generating a centrosymmetric dimeric structure. The saccharinate (sac) ligands are N‐coordinated. The dihedral angles between the sac and pydz rings are 8.43 (7) and 7.94 (8)° in (I) and (II), respectively, suggesting that the dimeric mol­ecule is nearly flat. The bond geometry is similar in both polymorphs. In (I), the dimers inter­act with each other via aromatic π_sac–π_pydz stacking inter­actions, forming two‐dimensional layers, which are further crosslinked by weak C—H⋯O inter­actions. Compound (II) exhibits similar C—H⋯O and π–π inter­actions, but additional C—H⋯π and π⋯Ag inter­actions help to stabilize the packing of the dimers.     

Folded overlapping variance estimators for simulation

We propose and analyze a new class of estimators for the variance parameter of a steady-state simulation output process. The new estimators are computed by averaging individual estimators from “folded” standardized time series based on overlapping batches composed of consecutive observations. The folding transformation on each batch can be applied more than once to produce an entire set of estimators. We establish the limiting distributions of the proposed estimators as the sample size tends to infinity while the ratio of the sample size to the batch size remains constant. We give analytical and Monte Carlo results showing that, compared to their counterparts computed from nonoverlapping batches, the new estimators have roughly the same bias but smaller variance. In addition, these estimators can be computed with order-of-sample-size work.     

Auto-Bäcklund transformations and solitary wave solutions for the nonlinear evolution equation

In the present work, according to the concept of extended homogeneous balance method and with help of Maple, we get auto-Bäcklund transformations for a (2 + 1)-dimensional nonlinear evolution equation. Subsequently, by using these auto-Bäcklund transformation, exact explicit solutions of this equation are obtained.