Synthesis,structure, and thermal behavior of discrete Co(II), Ag(I), and Pd(II) complexes with 2,3-bis(2-pyridyl)quinoxaline. Insight into coordination modes

The reactions of 2,3-bis(2-pyridyl)quinoxaline (bpq) with CoCl₂·6H₂O, Ag(CH₃CN)₄BF₄, and PdCl₂(C₆H₅CN)₂ produce [CoCl₂(bpq)]₂·2CHCl₃, [Ag(bpq)CH₃CN]₂(BF₄)₂·2CH₃CN, and [PdCl₂(bpq)], respectively. All the products are discrete 1:1 (metal:bpq) adducts, where the chelation mode of the bpq is dependent upon the metal atoms. The structure of [CoCl₂(bpq)]₂·2CHCl₃ is a centrosymmetric Cl-bridged four-membered dimer, [Co₂Cl₂], in which the bpq is bonded to the cobalt(II) atom in an anisobidentate mode with the nitrogen donors of pyridine and pyrazine rings. For [Ag(bpq)CH₃CN]₂(BF₄)₂·2CH₃CN, each bpq ligand connects two tetrahedral silver(I) ions in a tridentate mode, resulting in a cationic cyclic dimer. The structure of [PdCl₂(bpq)] approximates to a molecular rocking chair with an isobidentate bpq through the nitrogen donors of 2-pyridyl rings. The compounds exhibit significant and characteristic relationships between the structures and their thermal properties. For [CoCl₂(bpq)]₂·2CHCl₃, the solvate chloroform molecules are safely contained up to 144°C, but drastically evaporate above this temperature. The striking feature of [Ag(bpq)CH₃CN]₂(BF₄)₂·2CH₃CN is that the skeletal cyclic dimer is basically retained after dissociation of the coordinated acetonitriles in the solid state.     

Characterisation of metal binding sites for 8-azaadenine. Formation and X-ray structural analysis of methylmercury(II) complexes

The compounds [(CH₃Hg)AAdH]NO₃ (1) and [(CH₃Hg)AAd]·4H₂O (2) have been isolated from aqueous 1:1 solutions of CH₃HgOH and 8-azaadenine (AAdH) at respective pH values of 2 and 5. Their structures have been established by X-ray structural analysis. N9 is the metal binding site in both complexes. Alteration of the metal to ligand ratio to 2:1 at a pH of 5 allows the preparation of [(CH₃Hg)₂AAd]NO₃·H₂O (3) in which the base is coordinated at both N3 and N9. The compound [(CH₃Hg)₃AAdH₋₁]NO₃ (4), in which N1, N6 and N9 function as binding sites for the CH₃Hg⁺ cation, is formed in a 3:1 solution at a pH of 6.5. X-ray structural analyses have been performed on 3 and 4. N8 takes part in weak intermolecular secondary bonds to symmetry related Hg9 atoms in all four complexes. The relevance of the structures to an understanding of the basicities of the nitrogen atoms in 8-azaadenine and their alteration upon metal coordination of N9 and N6 is discussed.     

N,N-diisopropylcarboxylic acid amide complexes of thorium(IV) and uranium(IV) N-thiocyanates; the crystal structure of tetraisothiocyanato tetrakis(N,N-diisopropylacetamide-O)uranium(IV)

The complexes M(NCS)₄·xL (x = 2, M = U, L = Me₃CCON(Prⁱ)₂(dippva); x = 3, M = Th, L = Me₂CHCON(Prⁱ)₂(dipiba) and dippva, M = U, L = EtCON(Pr¹)₂(dippa), dipiba and dippva; x = 4, M = Th, L = MeCON(Prⁱ)₂(dipa), dippa and dipiba, M = U, L = dipa, dippa) and the solvates M(NCS)₄·4dipa·CH₂Cl₂ (M = Th, U) have been prepared. Their i.r. and u.v.-visible (M = U only) spectra are reported. The crystal and molecular structure of U(NCS)₄(dipa)₄· CH₂Cl₂ has been determined by the heavy-atom method from X-ray diffractometer data and refined by least squares to R 0.029 for 1135 independent reflections. The crystal is tetragonal, space group P$\text{4}$2₁c, with Z = 2, a = 15.663(4) and c = 10.512(3) Å. The coordination geometry about the 8-coordinate uranium atom is dodecahedral with the N atoms of the NCS groups occupying the dodecahedral A sites and the ‘dipa’ O atoms the B sites. The bonding distances of UO and UN are 2.363(8), and 2.444(11) Å respectively.     

Trans-bis(benzo(1,3)-thiazole)bis(N,N-dimethylformamide)bis(N-thiocyanato)-cobalt(II): spectroscopy,thermal analysis and crystal structure

Disolution of Co(bzt)₂(NCS)₂ (bzt = benzo 1,3- thiazole) in dimethyl formamide (dmf) produces Co(bzt)₂(NCS)₂(dmf)₂. The stoichionmetry of the complex has been established by a combination of chemical (C, H, N) and thermal analysis. The comlex has an octahedral structure with pairs of ligands in trans configuration as well as a CoN₄O₂ coordination sphere with CoN distances of 2.185(2) Å (bzt); 2.082(2) Å (NCS) and CoN(dmf) of 2.118(2) Å. The infrared and electronic absorption spectra are consistent with this arrangement.     

Proton magnetic resonance study of rotation about carbon-nitrogen bonds in pentakis(1,1-dimethylurea)dioxouranium(VI) and its 1,3-dimethylurea analogue

In CD₃CN solutions the kinetic parameters characterising rotation about the CNMe₂ and CNH₂ bonds in [UO₂(1,1-DMU)₅]²⁺ (1,1-DMU = 1,1- dimethylurea) were determined as: k(265 K) = 39.1 ± 0.4 and 2960 ± 60 s^?1, ΔH3 = 49.1 ± 0.76 and 61.1 ±0.5 kJ mol^?1, ΔS2 = ?28.3 ± 2.7 and 53.1 ± 2.2 J K^?1 mol^?1 respectively from ¹H NMR studies. Resonances arising from the three isomeric 1,3-DMU (= 1,3-dimethylurea) ligands were observed for [UO₂(1,3-DMU)₅]²⁺ in CD₃CN solution and the kinetic parameters characterising their isomerisations were also determined. The three isomers of 1,3-DMU have not previously been detected in solution and it appears that coordination of 1,3-DMU to UO₂²⁺ increases the barrier to rotation about the carbon nitrogen bond, as is also shown to be the case for 1,1-DMU.     

Electrochemical synthesis and crystal structure of iron(II), cobalt(II), nickel(II) and copper(II) complexes of dianionic tetradentate N4 Schiff base ligand

The electrochemical oxidation of anodic metal (iron, cobalt, nickel and copper) in an acetonitrile solution of the potentially chelating Schiff base N,N(dithiodiethylenebis-(aminylydenemethylydene)-bis(1,2-phenylene)ditosylamide (H₂L) afforded stable complexes of empirical formula [ML]. The compounds obtained have been characterized by microanalysis, IR spectroscopy and ES-MS mass spectrometry. The crystal and molecular structures of [FeL]·CH₃CN (1) [CoL]·CH₃CN (2), [NiL]·CH₃CN (3) and [CuL]·CH₃CN (4) have been determined by X-ray diffraction in all complexes, the metal atom is in a distorted tetrahedral environment with the Schiff base acting as a tetradentate N4 donor.     

Dioxouranium(VI) thiocyanate complexes of schiff bases of p-nitro,chloro, bromo,hydroxy and methoxy aniline and salicylaldehyde

A series of dioxouranium(VI) complexes was synthesised with some Schiff base ligands containing substituent groups at para positions to CHN groups. These molecules were obtained by the condensation of para-nitro, chloro, bromo, hydroxy, methyl and methoxy aniline with salicylaldehyde. The bidentate ligands formed complexes of the type UO₂(NCS)₂ (X-N-Sal)_n·mH₂O, where n = 2, m = 3, x = NO₂, Cl, Br and OH; n = 3, m = 2, x = CH₃ and OCH₃.Conductivity measurements indicate that all the complexes are non-electrolytes in nitromethane solution, whereas in DMF they correspond to 1:1 electrolytes.IR spectral data suggest that the molecules and not the anions of the Schiff base are coordinated to the central uranium atom. IR and Raman spectra suggest that the complexes UO₂(NCS)₂(X-N-Sal)₂· 3H₂O (X = NO₂, Cl, Br) have C_2h molecular symmetry, whereas UO₂(NCS)₂(X-N-Sal)₃·2H₂O (X = OCH₃, CH₃) have C_2v symmetry.The frequencies of UO_2(asym) (IR) and UO_2(sym) (R) in the complexes seem to vary with the various substituents of the Schiff base ligand, in the order:NO₂ > Cl > Br > OH > CH₃ > OCH₃     

Synthesis and crystal and molecular structure of a methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate complex

Bis-Methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate, Dy[O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂]₂(NCS) was prepared from the combination of ethanolic solutions of Dy(NCS)₃·xH₂O and (CH₃O)₂P(O)CH₂C(O)N(C₂H₅)₂. The complex was characterized by infrared and NMR spectroscopy, and single crystal X-ray diffraction methods. The crystal structure was determined at 25 °C from 3727 independent reflections by using a standard automated diffractometer. The complex was found to crystallize in the monoclinic space group P2₁/c with a = 13.282(4) Å, b = 19.168(5) Å, c = 9.648(2) Å, β = 90.09(2)°, Z = 4, V = 2456.4 ų and ?_cald = 1.72 g cm^?3. The structure was solved by standard heavy atom techniques, and blocked least-squares refinement converged with R_f = 4.7% and R_wF = 4.9%. The Dy atom is seven coordinate and bonded in a bidentate fashion to two anionic phosphonate ligands [O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂^?] through the carbonyl oxygen atoms and one of two phosphonate oxygen atoms. In addition, each Dy atom is coordinated to two phosphonate oxygen atoms from two neighboring complexes and to the nitrogen atom of a thiocyanate ion. This coordination scheme gives rise to a two-dimensional polymeric structure. Some important bond distances include DyNCS 2.433(8) Å, DyO(carbonyl)_avg 2.39(2) Å, DyO(equat. phosphoryl)_avg 2.303(8) Å, DyO(axial phosphoryl)_avg 2.25(2), PO(phosphoryl)_avg 1.493(3) Å and CO(carbonyl)_avg 1.25(1) Å.     

Sugar interaction with uranium ion. Synthesis,spectroscopic and stmctural analysis of UO2-sugar complexes containing D-glucuronate moiety

Interaction between D-glucuronic acid and hydrated uranyl salts has been studied in aqueous solution and solid complexes of the type UO₂(D- glucuronate)X·2H₂0 and UO₂(D-glucuronate)₂·2H₂O, where X = CI⁻, Br⁻ or NO₃⁻, are isolated and characterized by means of FT-IR and proton-NMR spectroscopy.On comparison with the structurally identified Ca(D-glucuronate)Br·3H₂O compound, it is concluded that the UO₂²⁺ cation binds to two D- glucuronate moieties in uranylsugar complexes via O6, O5 oxygen atoms (ionized carboxyl group) of the first and O6′, 04 (non-ionized carboxyl group) of the second sugar moiety, whereas in the UO₂(D- glucuronate)₂·2H₂O salt the uranyl ion is bonded to two sugar anions through O6, O6′ oxygen atoms of the ionized carboxyl group, resulting in a six- coordination geometry around the uranium ion. The strong intermolecular hydrogen bonding network of the free acid is rearranged upon sugar metalation and the sugar moiety showed β-anomer conformation both in the free acid and in these uranylsugar complexes.     

Solvent-extraction complex of uranium(VI) with cis,syn, cis-dicyclohexano-18-crown-6

The extraction of U(VI)with dicyclohexano-18-crown-6 (mixed isomers or isomer A) from HCl medium is effective and selective, and can be used for separating and analysing uranium and thorium. However, little is known of the properties of the extraction complex of uranium with crown-ether in organic phase. In this paper we report the preparation, characteristic and structure of the crystalline extraction complex IaUO₂Cl₂HClH₂O, Iabeing isomer A of dicyclohexano-18-crown-6.After extracting uranium(VI) from aqueous hydrochloric acid solution with Ia in 1,2-dichloroethane, the crystalline product of the extraction complex was prepared from the organic phase by diluting with a non-polar solvent at 25 °C. The content of uranium, crown-ether and HCl was determined. The IR spectrum of the crystals shows that the strong hydronium-crown ether/oxygen hydrogen bond absorption is found in the region 2300–2400 cm⁻¹. The chemical shift in the range 9–12 ppm was observed. The ¹H NMR signal of hydronium protons appears at 9.890 ppm. The results of assay correspond to the formula Ia₂·(H₃O⁺)₂·UO₂Cl₄²⁻.Crystal structure of the extraction complex has been determined by X-ray crystallography. Crystals are monoclinic, space group C_2/c (No. 15) a=32.464, b=10.203, c=21.616 Å, β=119.73° and Z=4. In the complex each of the two H₃O⁺ cations is anchored in the crown-ether cavity by three stronger hydrogen bonds (distances approximately 2.65 Å), whereas uranium forms UO₂Cl₄²⁻ with Cl⁻ as counterion about 8 Å away from the H₃O⁺.     

Dioxouranium(VI) complexes with 2,6-acetylpyridinebenzoylhydrazones and -semicarbazones

Benzoylhydrazones and semicarbazones derived from 2,6-diacetylpyridine react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄]₂[UO₂Cl₄] to form air-stable complexes. 2,6-Diacetylpyridinebis(benzoylhydrazone) (H₂L¹), 2,6-diacetylpyridinebis(N4-phenylsemicarbazone) (H₂L²) and the asymmetric proligand 2,6-diacetylpyridine(benzoylhydrazone)(N4-phenylsemicarbazone) (H₂L³) give yellow products of the composition [UO₂(L)]. The neutral compounds contain doubly deprotonated ligands and possess uranium atoms with distorted pentagonal-bipyramidal coordination spheres. The equatorial coordination spheres of the metal atoms can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting complexes have hexagonal-bipyramidal coordination environments with the oxo ligands in axial positions.X-ray diffraction studies on [UO₂(L¹)(DMSO)], [UO₂(L²)], [UO₂(L²)(DMSO)] and [UO₂(L³)] show relatively short U-O bonds to the benzoylic oxygen atoms between 2.273(6) and 2.368(5) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U-N bond lengths: 2.502(7)-2.671(7) Å). The addition of a sixth ligand to the equatorial coordination sphere results in a lengthening of the metal-pyridine bonds.     

Organosilicon(IV) O,O-alkylenedithiophosphates

Tri- and di-organosilicon O,O-alkylenedithiophosphates, R_4−nSi[S₂PO₂G]_n (where R = Ph, Me, G = −C(CH₃)₂·C(CH₃)₂−, −CH₂C(CH₃)₂CH₂−, −CH-CH₃CH₂C(CH₃)₂−, n = 1,2) were synthesized by treatment of organosilicon(IV) chlorides with ammonium O,O-alkylenedithiophosphates in benzene. The compounds are volatile, yellow oily liquids, miscible with common organic solvents and monomeric in refluxing benzene. Like dialkyldithiophosphate derivatives of organosilicon(IV), these cyclic chain derivatives appear to be tetrahedral, the ligand behaving as unidentate.     

A 31P and 15N NMR study of the synergistic extraction of uranyl nitrate by tributylphosphate and Di-2-ethylhexyl phosphoric acid

Low temperature ³¹P and ¹⁵N NMR spectroscopy was used to investigate the species forming in the organic layer following the extraction of uranium from nitric acid solutions with the synergistic mixture, TBP-DEHPA. It was found that the complex formed during extraction was a mixed nitrato complex UO₂(NO₃)A·TBP. Although the existence of the complex UO₂A₂·χTBP may be demonstrated in model systems, the complex does not form under actual extraction conditions.     

Infrared and Raman studies of [UO2(salen)(L)] (L=H2O and CH3OH)

The infrared and Raman spectra of [UO₂(salen)(H₂O)] and [UO₂(salen)(CH₃OH)] (salen=N,N′-ethylenebis(salicylideneimine) have been recorded. Assignments for the fundamental vibrations are proposed on the basis of C_2v symmetry for the former species and C_s for the latter. The calculated values of the stretching force constant of the uranyl group, F_UO, are 6.87 and 6.63 mdyn Å⁻¹ for [UO₂(salen)(H₂O)] and [UO₂(salen)(CH₃OH)], respectively. The corresponding values of the UO bond lengths calculated as 1.738 and 1.745 Å.     

Resolution,structures, and vibrational circular dichroism of helicoidal trinickel and tricobalt paddlewheel complexes

It has been recently shown that enantiomers of the helicoidal paddlewheel complex [Co₃(dpa)₄(CH₃CN)₂]²⁺ (dpa = the anion of 2,2′-dipyridylamine) can be resolved using the chiral [As₂(tartrate)₂]²⁻ anion (AsT) and that these complexes demonstrate a strong chiroptical response in the ultraviolet-visible and X-ray energy regions. Here we report that the nickel congener, [Ni₃(dpa)₄(CH₃CN)₂]²⁺, can likewise be resolved using AsT. Depending on the stereochemistry of the enantiopure AsT anion, one or the other of the trinickel enantiomers crystallize from CH₃CN and diethyl ether in space group P42₁2 as the (NBu₄)₂[Ni₃(dpa)₄(CH₃CN)₂](AsT)₂·[solvent] salt. After resolution, the AsT salts were converted into the PF₆⁻ salts by anion exchange, with retention of the chirality of the trinickel complex. The enantiopure [Ni₃(dpa)₄(CH₃CN)₂](PF₆)₂·2CH₃CN and [Co₃(dpa)₄(CH₃CN)₂](PF₆)₂·CH₃CN·C₄H₁₀O compounds crystallize in space groups C2 and P2₁, respectively. Both the Ni(II) and Co(II) complex cations are stable towards racemization in CH₃CN. Vibrational circular dichroism (VCD) data obtained in CD₃CN demonstrate the expected mirror image spectra for the enantiomers, the observed peaks arising from the dpa ligand. The VCD response is significant, with Δε values up to 6 Lmol⁻¹ cm⁻¹ and vibrational dissymmetry factors on the order of 10⁻³. Density functional theory calculations well reproduce the experimental spectra, showing little difference between the peak position, sign, and intensity in the VCD for the cobalt and nickel complexes. These results suggest that VCD enhancement of these peaks is unlikely, and their remarkable intensity may be due to their rigid helicoidal structure.     

Synthesis, characterization and thermal decomposition of dioxouranium(VI) complexes with N,N-diarylidene-S-propyl-thiosemicarbazone: Crystal structure of [UO2(L)(C4H9OH)]

Reactions of salicyl- and 3,5-dichlorosalicylaldehyde-S-propyl-thiosemicarbazones with salicyl- and 3,5-dichlorosalicylaldehyde in the presence of UO₂(CH₃COO)₂ in different alcohols yielded stable solid complexes corresponding to the general formula [UO₂(L)ROH] (R: propyl-, butyl-, pentyl-, and octyl-). The complexes were characterized by means of elemental analysis, IR and ¹H NMR spectroscopies. The thermal stabilities of the alcohol solvated complexes were investigated in air and nitrogen atm., and determined their decomposition phases. In the crystal structure of the [UO₂(L)(C₄H₉OH)], the U(VI) centre is seven-coordinated in a distorted pentagonal bipyramidal geometry involving O,O,N,N atoms of two phenolic and two imine groups and one oxygen atom of alcohol molecule in basal plane and two O atoms of dioxo group in apical positions. The title structure is stabilized by one intramolecular interaction of types C-H?Cl and by two intermolecular interactions of types O-H?O and C-H?π (benzene) leading to the molecular chain along the [0 1 0] direction.     

Some metal alloxides

Tetraalloxygermanium(IV), (CH₂·CH·CH₂·O)₄Ge, has been synthesized from germanium tetrachloride, allyl alcohol, and ammonia. The alloxides [(CH₂·CH· CH₂·O)₄Ti]₂and[(CH₂·CH·CH₂O)₅M]₂ (M = Nb and Ta) have been synthesized by reactions of the corresponding metal isopropoxides with allyl alcohol followed by removal of the isopropanol by azeotropic distillation with benzene. These four metal alloxides can be purified by distillation under reduced pressure. The spectroscopic properties of these new compounds are discussed.     

Further crystallographic evidence of NH· · ·π (system) and CO· · ·π (system) interactions: The structures of bis(diarylhydrazonecarbonyl)methylene derivatives [{ArPhCNNH—C(O)}2CH2] (Ar = Ph, 2‐C5H4N, 2‐C4H3S)

In this study are reported the syntheses of three bis(diarylhydrazonecarbonyl)methylene derivatives [{ArPhCNNH C(O)}₂CH₂] [Ar = 2 C₅H₄N (5), C₆H₅ (6), and 2‐C₄H₃S (7)], obtained by condensation of corresponding hydrazones with carbon suboxide, C₃O₂. The solid‐state self‐assembly of these carbonyl derivatives, giving rise to polymeric and dimeric networks, is described. In the formation of these structural features, in addition to N—H· · ·OC intermolecular hydrogen bonds, stabilizing intramolecular NH· · · π (systems) and intermolecular CO· · ·π (systems) interactions also seem to play an important role. Solution ¹H‐nmr data of compounds 5–7 indicate that the polymeric and dimeric structures are not maintained in solution and show the occurrence of keto‐enolic equilibria. © 1999 John Wiley & Sons, Inc. Biopoly 49: 541–549, 1999     

Complexes of binucleating ligands. XVII. Some 3-atom N,C bridged palladium(II) complexes

The acetate-bridged complex, LPd₂(CH₃CO₂), in which L^3? is a binucleating ligand, reacts with 2-vinylpyridine in the presence of methanol or ethanol to generate the 3 atom N,C bridged complexes LPd₂(2-C₅H₄N·CH·CH₂OR) (R = Me or Et) whose ¹H and ¹³C nmr spectra indicate the presence in solution of two slowly interconverting forms at room temperature. The ¹H and ¹³C nmr spectra of two closely related pairs of 3 atom N,C bridged complexes of the form LPd₂(2-C₅H₄N·CH·X) and LPd₂ (HN = C(CH₃)·CH·X) (where X = COCH₃ or COOCH₃) show that the complexes with pyridine-containing bridges exist in solution at room temperature in two distinguishable forms whilst the corresponding imine-bridged complexes behave as single species. The existence of two forms of the complexes with pyridine-containing 3 atom N,C bridges, the natures of which are discussed in this paper, appears to be a consequence of steric interaction between the pyridine α hydrogen atom and the closely adjacent oxygen donor of L.