Showing papers in "Journal of Coordination Chemistry in 1990"

The Effect of Ligand Structure on Spectral Characteristics and Kinetics of Redox Reactions of Copper(II) and Copper(III) Complexes with Macrocyclic Ligands Containing amide Groups

Abstract: Spectral characteristics of macrocyclic copper(II) and copper(III) complexes with 13- and 14-membered tetraaza ligands containing two amine and two deprotonated amide groups (CuL) have been studied. It was shown that, unlike copper(II) complexes, the spectral properties of copper(III) compounds are more sensitive to such ligand structure parameters as ring size and the presence of benzyl substituents. Rate constants and activation parameters for oxidation of CuIIL by peroxodisulfate and decomposition reactions of CuIIIL in aqueous solutions at pH 5 were also measured. Activation parameters were shown to be dependent on ligand structure and the tendencies of their changes are opposite in these two types of reactions. Decomposition of copper(III) compounds proceeds probably through protonation of the amide group in acidic media and through deprotonation of amine group in alkaline media. The copper(III) complex with a benzyl-substituted 13-membered ligand was found to be most kinetically stable amon...

A Multinuclear NMR Study of Platinum(II) Complexes of N-Phenyl and N-(3-Allyl) Substituted 2-(2-Pyridinemethylene) Hydrazine Carbothioamides

Abstract: Jeutral platinum(II) complexes of type [Pt(LH)Cl], where LH− denotes the N-phenyl and N-allyl-2-(2-yridineraethylene)hydrazine carbothioamide anion, have been prepared and characterized. These com-lexes, as well as the hydrochloride salts of these ligands, have been examined in DMSO-d 6 solution by H, 13C and 195Pt NMR spectroscopy. From the observed chemical shift, the 195Pt-1H and 195Pt-13C oupling constant trends, the mode of coordination of Pt(II) to these ligands has been deduced to be via he thiocarbonyl atom, the pyridyl N(3) and hydrazinic N(2) nitrogen atoms respectively. In these omplexes the resolved 195Pt-13C coupling constants to the carbon atoms of the pyridyl group of the gand follow the order 2J > 3J > 4J, in contrast to trends observed for other simple Pt(II) complexes ivolving a coordinated pyridine molecule. Indications are that in DMSO solution, the complexes Pt(LH)Cl] undergo some solvolysis to yield [Pt(LH)DMSO]+CP.

The Crystal and Molecular Structure of bis [1,2-bis(Diphenylphosphino)Ethane] Silver(I) Nitrate

Abstract: The title compound, [Ag(dppe)2]NO3, is shown to be bis-chelated by two dppe ligands so that the silver atom is four-coordinate; Ag-P 2.488(3), 2 × 2.523(3) and 2.527(3) A. Distortions from ideal tetrahedral geometry are related to the restricted bite distances of the dppe ligands such that the P(1)-Ag-P(2) and P(3)-Ag-P(4) angles are 84.5(1) and 83.8(1)°, respectively. The compound crystallizes in the monoclinic space group P21/n with unit cell dimensions a = 14.834(2), b = 19.795(2), c = 15.856(3) A, β = 93.09(1)° and Z = 4. The structure was refined by a full-matrix least-squares procedure to final R = 0.063 for 3776 reflections with I ≥ 2.5 σ(I).

Ruthenium Carbonyl Complexes of N-Heterocyclic Molecules. Part 2. Preparation, Protonation and Decarbonylation Reactions of Complexes with a Bidentate Terpyridyl Ligand. Structure of [Ru(CO)2(phen)(tpyH)](BF4)3

Abstract: The complexes Ru(CO)2(CF3SO3)2(bidentate) {bidentate = 2,2′-bipyridyI (bpy) or 1,10-phenanthroline (phen)} react with 2,2′:6′,2″-terpyridyl (tpy) forming octahedral [Ru(CO)2(bidentate)(tpy)]2 + compounds (II) which contain a bidentate tpy. Complex II (bidentate = phen) can be protonated to give [Ru(CO)2-(phen)(tpyH)](BF4)3, the structure of which has been established by X-ray crystallography. Treatment of II with trimethylamine N-oxide in methanol at room temperature gives the monocarbonyl compounds [Ru(CO)(bidentate)(tpy)]2+ (IV) which contain a tridentate tpy. Complex IV is also obtained by photolysis of II.

Formation of Trinuclear Copper(II) Complexes with Three Pyridine Oxime Ligands in Aqueous Solution

Abstract: The protonation and complex formation equilibria of pyridine-2-carboxaldehyde oxime (1), 1-(2-pyridinyl)elhanone oxime (2) and 6-methylpyridine-2-carboxaldehyde oxime (3), HL, with copper(II) ion were studied in aqueous 0.1 M NaCl solution at 25°C by potentiometric titrations with the use of a glass electrode. Application of the least-squares computer program SUPERQUAD to the experimental data indicated that the following complex species are formed: Cu(HL)2 +, CuL+ (ligand 1), Cu(HL)2 2 + (ligands 1 and 3), Cu(HL)L+ CuL2, Cu3L3OH2+ and Cu3L3O + (or Cu3L3(OH)2 +, ligands 1 and 2). The trinuclear complex Cu3L3OH2 + most probably has a triangular Cu3OH central core. In 1:1 molar ratio of ligand to Cu2+ the trimer exists as the predominating complex around pH 4–6 and gives way to the next deprotonated trimer as the pH is increased.

Complex Formation Between Alkaline Earth Cations and 4-(2-Pyridylazo)Resorcinol in Ethanol-Water Mixtures

Abstract: The interaction between alkaline earth cations and 4-(2-pyridylazo)resorcinol in C2H5OH-H2O mixtures has been studied spectrophotometrically. Formation constants for the resulting 1:1 complexes with different amounts of water in ethanol were determined. There is an inverse relationship between the complex formation constant and amount of water in the mixed solvent. In all solvent mixtures used, the stability of the complexes was found to vary in the order Mg2 + > Ca2+ > Sr2+ > Ba2 +. A linear relationship is observed between log Kt for complexes and the mole fraction of ethanol.

Polarographic Studies of Copper(II), Nickel(II) and Cobalt(II) Complexes with D-Mannosamine

Abstract: D.c. polarography was used to establish the coordination equilibria and the stability constants of the species formed at the lower pH range in solutions containing Cu(II), Ni(II) and Co(II) ions and D-mannosamine. Two complexes, ML and ML2, were shown to be present for all three metal ions. The major binding site was shown to be the amino nitrogen donor. The involvement of the protonated hydroxyl oxygen of the aminosugar ligand leads to different stability constants for the complexes with particular aminosugar ligands (e.g., with D-mannosamine, D-galactosamine and D-glucosamine). The polarographic technique was shown to be able to detect minor complexes not seen in potentiometric titrations. It effectively completes potentiometric and spectroscopic studies performed on the systems discussed in this work.

Enantiomeric Recognition of Organic Ammonium Salts by Chiral Pyridino-18-Crown-6 Ligands: A Short Review

Abstract: A short review of enantiomeric recognition of chiral organic ammonium salts by chiral pyridino-18-crown-6 ligands is presented. Topics include preparation of chiral macrocycles and details of enantiomeric recognition as determined by 1H NMR and calorimetry techniques. The chiral pyridino-18-crown-6 ligands containing two tert-butyl or two phenyl substituents on chiral macroring carbon atoms exhibited the highest recognition for the enantiomers of [α-(1-naphthyl)ethyl]ammonium perchlorate of any chiral pyridino-18-crown-6 ligands studied.

The Crystal and Molecular Structure of Bis[1,2-Bis(Diphenylphosphino)Ethane] Dichlororuthenium(II)

Abstract: The title compound, trans -[Ru(dppe)2Cl2], has I symmetry such that the chloride atoms are exactly trans. The coordination geometry is distorted octahedral owing, in part, to the restricted bite distance of the chelating dppe ligands. Important interatomic parameters are Ru-Cl 2.436(1), Ru-P(l), 2.389(1) Ru-P(2) 2.369(1) A and P(I)-Ru-P(2) 82.1(1)°. The compound crystallizes as a dichloromethane solvate in the monoclinic space group C2/c with unit cell dimensions a = 27.995(3), b = 13.85(1), c = 13.265(3) A, β = 105.38(2)° and Z = 4. The structure was refined by a full-matrix least-squares procedure to final R = 0.038 for 3522 reflections with I ≥2.5σ(I).

1H, 13C and 199Hg NMR Studies of the Complexation of HgCl2 by Imidazolidine-2-Thione and its Derivatives

Abstract: Mercury(II) complexes of imidazolidine-2-thione and its derivatives have been synthesized and their 1H, 13C and 199Hg NMR spectra measured. HgCl2 forms L2HgCl2 type complexes (where L = imidazolidine-2-thione and its derivatives). The NH group of the ligand is shifted downfield by about +1.37 ppm in the 1H NMR after complexation. The C-2 carbon in the 13C NMR is shifted by—6.50 ppm for mono N-substituted ligands, but by—5.30 ppm for N,N''-disubstituted ligands. The 199Hg NMR resonance is shifted by about—60 ppm for N-substituted ligands, but—140 ppm shifts were observed for N',N'-disubstituted ligands.

Chromium(III), cobalt(II), nickel(II) and copper(II) complexes of (dimethyl-phosphinyl)methanamine. Crystal structure of fac-tris{(dimethyl-phosphinyl)methanamine-N, O}nickel(II) chloride trihydrate

Abstract: The complexes CrL3Cl3.2H2O (I), CoL3Cl2.3H2O (2), CoL3Br2.H2O (3), NiL3Cl2.3H2O (4) and CuLCl2 (5), where L is (dimethylphosphinyl)methanamine, were synthesized and characterized by infrared and electronic spectra. The X-ray single crystal analysis of 4 (trigonal, space group R 3c, a = 11.340(2), c = 63.708(8) A, V = 7095(2) A, Z = 12) revealed a structure containing tris-chelated fac[NiL3]2 + cations in which L is coordinated via the amino nitrogen and phosphoryl oxygen atoms. The statistically disordered chloride ions and water molecules occupy voids between the cations. On the basis of spectral data, 1,2 and 3 are formulated as consisting of pseudo-octahedral tris-chelate cations [ML3]n + (n = 2 or 3) and non-coordinated halide ions and water molecules. A polymeric structure in which Cu(II) is surrounded by four bridging chlorides and two bridging L ligands is ascribed to 5.

Intermolecular Energy Transfer Between Lanthanide Complexes. 10. Tb(III) Donor and Eu(III) Acceptor Complexes of Triethylenetetra Aminehexaacetic Acid

Abstract: The solution phase coordination chemistry assoicated with the 1:1 complexes of lanthanide ions with triethylenetetraaminehexaacetic acid (TTHA) has been studied by spectroscopic means. It was found that in the pH region of 3 to 7.5, the partially protonated Ln(TTHA) complexes exist as oligomeric species. A well defined polynuclear species has been found to exist between pH 4 and 6, and this characterized by an association constant of 125. Between pH 6 and 8, the oligomeric species apparently dissociate, yielding monomeric lanthanide TTHA complexes above pH 8.

Crystal structure and magnetism of 4,4'-bipyridylium di-μ-bromotetrabromodicuprate(II)

Abstract: A new bromocuprate complex of formula C10HI0N2Cu2Br6 has been synthesized and its crystal structure investigated by single-crystal X-ray methods. Stable, black, needle-like crystals are isostructural with the analogous chloride compound.1 The crystals are triclinic, a = 4.1018(5), b = 10.2755(10), c = 11.0355(9) A, a = 113.894(7), β = 94.975(8), γ = 95.935(9)°. The structure was refined by least-squares methods to R = 0.031 and R w = 0.038 for 1930 reflections. It consists of cationic columns formed by stacking of planar (4,4′-bipy H2)2+ cations and anionic columns formed by stacking of nearly planar Cu2Br6 2- anions. Cationic and anionic columns are parallel to the needle axis. The geometry and interionic interactions for the chloride and bromide crystals were compared. The EPR spectrum of a polycrystalline sample of the complex displayed only one broad line centred at 2.08 (T = 293 K). Variable temperature (ca 4.2–290 K.) magnetic susceptibility data indicated an antiferromagnetic superexchange...

Potentiometric and Spectroscopic Studies of Binary and Ternary Copper(II) Complexes with Histidinehydroxamic Acid

Abstract: Because the results concerning the Cu(II)-histidinehydroxamic acid (Hisha) system are somewhat controversial, we have performed a new study of the Cu(II)-Hisha binary system, using potentiometry and e.p.r. techniques. Since the occurrence of ternary complexes in natural systems is very probable, we have also undertaken potentiometric and spectroscopic studies of the Cu(II)-Hisha-His ternary system, where His is histidine.

Synthesis and structure of ferrocene-linked Schiff base porphyrins

Abstract: A series of mono ferrocene Schiff-base porphyrins in which the ferrocene unit is disposed in different orientations to the porphyrin core have been synthesized from meso-5(o- or p)aminophenyl-10,15,20-triphenyl-21,23-H-porphyrin and ferrocenecarboxaldehyde. The optical and magnetic resonance spectral features of these derivs. reveal weak interactions between ferrocene and porphyrin units. The kinetics of metal incorporation into the free-base ferrocenyl porphyrins indicate the steric features induced by the ferrocene unit. Electrochem. redox behavior of the compds. shows that the ferrocene and porphyrin entities behave as independent units. Steady-state photolysis expts. reveal no internal electron-transfer, although the energies of the CT state of porphyrin-ferricenium ion indicate the feasibility of electron transfer in these systems.

Zinc(II) Complexes with Aspartate and Glutamate

Abstract: Aspartate and glutamate have been studied as ligands (L) towards zinc(II) at 25°C and in 1.00 M NaC104 by measuring the electromotive force of galvanic cells containing glass and zinc amalgam electrodes over a wide concentration range of reagents. The experimental data were explained by assuming the formation of mononuclear species of the type ZnHpLr where p ≥ 0 and r ≥ 1. For aspartate, evidence for the complexes ZnL, ZnHL, ZnH2L, ZnL2, ZnHL2, ZnH2L2, ZnL3, ZnHL3 and ZnH2L3 was found, whereas for glutamate, the complexes ZnL, ZnHL, ZnL2, ZnHL2, ZnL3, ZnHL3, ZnH2L3 were found. Evidence for the species ZnH2L was found also in the case of glutamate. The relative stability constants have been determined and compared with those of other ligands and cations.

Synthesis of Potential Tripodal Tellurium Ligands and Their Complexation with Mercury(II)

Abstract: Sodium aryltellurolate (ArTe-Na +, where Ar = 4-MeOC6H4 or 4-EtOC6H4) reacts with tris(2-chloro-ethyl)amine resulting in the potentially tripodal tellurium ligand tris(2-aryltelluroethyl)amine [N(CH2CH2TeAr)3,1]. These newly synthesized (N, Te3) ligands form HgX2.l (X = CI or Br) complexes. IR, 1H and 13C NMR spectra in conjunction with molecular weight measurements suggest that 1 coordinates with mercury(II) through its two tellurium atoms and there is fast exchange between free and coordinated tellurium in solution.

Preparation and Oxygenation of Manganese(II) Complexes of Imines Derived from Salicylaldehyde and Amino Acids

Abstract: Manganese(II) complexes of imines derived from salicylaldehyde and glycine, alanine, valine, phenylalanine and histidine were prepared and identified. Most of these compounds were found to be stable towards dry air but absorbed oxygen readily in many organic media to the extent of O2/Mn equal to I or 0.5. Reversibility was barely observed except for complexes derived from valine and phenylalanine. The histidine analogue showed no reversibility.

A New Type of Lanthanide(III) Complex with 3-Hydroxybenzoic Acid, [ML3(H2O)3].2H2O. Crystal and Molecular Structure of Triaquatris(3-Hydroxybenzoato)-Neodymium(III) Dihydrate

Abstract: Triaquatris(3-hydroxybenzoato)neodymium(III) dihydrate, a new type of lanthanide complex with 3-hydroxybenzoic acid, crystallizes in the monoclinic space group C2/c with a = 22.220(8), b = 10.007(6), c = 22.086(8) A, β = 99.33(3)[ddot] and Z = 8. The crystal and molecular structure of the complex has been determined using X-ray diffraction data measured with MoKα radiation. The Nd3+ ion is coordinated to nine oxygen atoms, with Nd-O distances ranging from 2.338(7) to 2.697(6) A. The coordinated oxygen atoms are from three water molecules and six oxygen atoms are from the 3-hydroxybezoate anions. There are three different binding modes for the anion to the Nd3+ ion: mono-, bi- and terdentate.

Structure of bis(isothiocyanato)-bis(4-methylpyridine)zinc(II)

Abstract: Zn(C6H7NUNCS)2, C14H14N4S2Zn, is orthorhombic, space group Fdd, a = 35.144(16), b = 18.119(4), c = 5.078(3)A, Z= 8, D cale= 1.430gcm−3, I= 17.036cm−1, F(000) = 1504. The structure consists of monomeric units in which the Zn(II) cation is tetrahedrally coordinated by two N cs and two N Mcpy atoms, the molecule showing twofold axial symmetry.

Reaction of Triethylaluminum with Bis(Diphenylphosphinoyl)Methane. Synthesis and Molecular Structure of [Al(C2H5)][(Ph2P(O))2C]2[Al(C2H5)2]2

Abstract: Reaction of triethylaluminum with bis(diphenylphosphinoyl)methane in toluene/heptane affords the crystalline condensation product [Al(C2H5)][(Ph2P(O))2C]2[Al(C2H5)2]2. The title compound crystallizes in the monoclinic space group C2/c with unit cell parameters a = 26.157(9), b= 10.261(3), c = 24.607(9) A, β = 120.48(2)[ddot], V = 5691.65 A3 and ρ = 1.23 g cm−3 for Z = 4. Full-matrix least-squares refinement based on 2778 observed reflections converged at R = 0.051, R w = 0.068. During the course of the reaction both of the central methylene C-H bonds of each ligand were cleaved, along with four Al-Et bonds, thereby eliminating four units of ethane, and resulting in a five-coordinate aluminum atom residing in a trigonal bipyramidal environment at the core of the molecule.

Binuclear Complexes of Technetium. Synthesis and Characterization of Binuclear tEchnetium(V) and (VII) Complexes with 3,6-bis(2′-pyridyl)-1,2,4,5-Tetrazine

Abstract: Novel binuclear complexes of heptavalent and pentavalent technetium with the bridging ligand 3,6-bis(2′-pyridyl)-1,2,4,5-tetrazine (bptz) have been prepared and characterized by analysis and optical and vibrational spectroscopy. The heptavalent complexes with the formulation (μ-bptz)[TcO3X]2 (X = Cl, OCH3, OCH2CH3) were synthesized from pertechnetate and the ligand bptz-2HCl in the appropriate alcohol (X = OMe, OEt) or from pertechnetate and bptz in ethanolic aqueous HC1 (for X = Cl). Binuclear complexes of technetium(V) with the formulation (u-bptz)[TcOCl2X]2 (X = OEt, Cl) were prepared in ethanol from TcOCl− 4 and bptz in the absence (X = OEt) and presence (X = Cl) of ethanolic aqueous HC1. The mononuclear technetium(V) complex [TcO2(bptz)2]Cl has also been isolated under certain experimental conditions. Mononuclear complexes of the ligand 4-phenyl-3,6-bis(2′-pyridyl)pyrida-zine (pppz) with formulae TcO3(pppz)Cl and TcO(pppz)Cl3 were prepared from pertechnetate and TcOCl− 4, respectively, with ...

Copper(I) and Copper(II) Complexes of Creatinine

Abstract: A Cu(II) complex of creatinine (creat) was prepared, with formula Cu(creat)2Cl2, as well as a Cu(I) creatinine complex, Cu(creat H_1)(EtNH2).H2O(EtNH2 = ethylamine). The Cu(II) adduct is complexed with neutral creatinine and IR evidence suggests a tetrahedral geometry for the complex with bonding to the ring amino nitrogen atom. Diamagnetic Cu(creat H_1)(EtNH2).H2O, formed from a redox reaction between Cu(II) and creatinine, is composed of Cu(I) atoms bonded to the deprotonated ring amino nitrogen, with the exocyclic carbonyl group hydrogen bonded to coordinated ethylamine molecules.

Novel 2-(Aryltelluro)Ethylmethyl-Sulfides Synthesis and Ligation with Palladium(II) and Platinum(II)

Abstract: 2-(Aryltelluro)ethylmethylsulfide (1), where aryl = 4-MeOC6H4 (a) and 4-EtOC6H4 (b), has been synthesized by reacting sodium aryltellurolate with CICH2CH2SCH3. 1H and 13C NMR spectra indicate the existence of intramolecular Te←S secondary interactions in 1. IR spectra suggest that both the trans and gauche conformations of two CH2 groups coexist, at least in the solid state. (C6H5CN)2PdCl2 and K4PtCl4 react with 1 to give diamagnetic complexes of the type Pd/PtCl2.1. IR, 1Hand 13C NMR data in conjunction with molecular weight and conductivity measurements suggest that 1 in the complexes acts as a bidentate ligand and two CI (cis to each other), S and Te atoms constitute the square planar geometry around Pd/Pt, as supported by electronic spectra.

Nucleophilic Attack on Dichloromethane. Synthesis and Structure of mer-[Cu(2-(Aminomethyl)Pyridine)3]2+

Abstract: Solutions of copper(II) β-diketone complexes in CH2Cl2 or CHCl3 react with 2-(aminomethyl)pyridine (AMP) to produce Cu(AMP)3 2 +, which precipitates as its chloride salt. mer-[Cu(AMP)3]Cl2·CH2Cl2 is monoclinic, space group P21/c; a = 11.072(1), b = 22.306(3), c = 11.388(2) A; β = 117.39(2)°; Z = 4; R = 0.076; R w = 0.068 for 375 parameters and 3477 reflections with I > I σ (I). The mer-Cu(AMP)3 2 + ion has a tetragonally distorted octahedral geometry; distances from Cu to two trans-oriented pyridine N atoms are elongated (2.420(5) and 2.437(5) A), while the third is normal (2.060(4) A). Distances from Cu to the equatorial NH2 N atoms range from 2.012(5) to 2.048(5) A. The chloride ion in this compound is produced by nucleophilic attack of AMP on the CH2Cl2 solvent.

Hydrophobic Vitamin B12. VII. Ring-Expansion Reactions Catalyzed by Hydrophobic Vitamin B12 in Octopus Azaparacyclophane

Abstract: Ring-expansion reactions of alkyl ligands bound to heptapropyl cobyrinate at the axial site of the nuclear cobalt were found to be markedly favoured in the hydrophobic cavity of an octopus azaparacyclophane, relative to reactions in methanol and benzene, under anaerobic photolysis conditions at 20.0°C. Heptapropyl cobyrinate perchlorate catalyzed the same ring-expansion reactions, which convert 2-methyl-1,3-cyclopentanedione and 3-methyl-2-pyrrolidinone into 1,4-cyclohexanedione and 2-piperidinone, respectively, in the octopus cyclophane by utilizing vanadium trichloride as a co-catalyst under aerobic photolysis conditions.

Formation of a Tris Complex in the Vanadium(IV)—Tiron System

Abstract: The formation of a tris complex, VA3, was detected pH-metrically in the oxovanadium(IV)-tiron (1,2-dihydroxybenzene-3,5-disulphonate) system, and its draft stability constant was determined. The slow formation of the tris complex in both acidic and basic solutions was studied in detail via a combined pH-spectrophotometric method. Spectrophotometric titration at 25.0 ± 0.1°C and ionic strength 0.2 moldm−3 (KC1) yielded a log K value of 2.01 ± 0.03 for the formation process VOA2 + H2A = VA3 + H2O.

Synthesis, structure, and properties of tetraethylammonium bis[bis(2-oxyphenyl)-disulfide-O,O',S] manganese(III)

Abstract: The title compound (Et4N)[Mn(MP-MP)2] (1) was obtained by air oxidation of an acetonitrile solution of MnCl2-4H2O and Na2MP. The structure of 1 was determined by single crystal X-ray diffraction methods. Crystal data: C32H36MnNO4S4, monoclinic, P21/c, a = 9.598(3), b = 16.845(3), c = 10.702(3) A, β = 111.20(1)°, V= 1613.1 A3, Z = 2; Mr = 681.84; d x = 1.40g cm−3 F(000) = 712; μ = 6.8cm−1, crystal dimensions 0.40 × 0.20 × 0.20 mm3. The Mn atom is octahedrally and symmetrically coordinated by two MP-MP2- ligands, each providing two phenolate-oxygen and one disulfide-sulfur atoms to form a terdentate. The presence of an S-S bond is revealed by the distance of 2.093 A, which constitutes the first disulphide chelated to the Mn(III) ion. The paramagnetic nature of the high spin Mn(d4) ion is reflected in a value of μcff of 4.83 μB and broad 1H NMR absorptions at 23 ∼ 25ppm and –12∼-17ppm.

A Novel Conformation for a Coordinated Macrocycle: The Crystal Structure of [Ni(12-aneN4)(OH2)2](CIO4)2·H2O; (12-aneN4 = 1,4,7,10-Tetraazacyclododecane)

Abstract: The complex [Ni(12-aneN4)(OH2)2](ClO4)2·H2O (12-aneN4 = 1,4,7,10-tetraazacyclododecane) has been prepared and its structure determined. The complex crystallizes in the orthorhombic space group P212121 With a= 11.173(5), b = 11.976(5) and c = 13.969(4) A. The volume of the unit cell is 1869(1) A3. The total reflections collected for 2.0 ≤ 20 ≤ 50.0° were 1916 with 1895 being unique and 1659 used in the structure determination. Final values of R = 0.053 and R w = 0.057 were obtained. Our results indicate that this six coordinate Ni(II) species has a cis or folded geometry and that the coordinated tetraazamacrocyclic ligand exhibits a conformation that is unprecedented in the literature. In this new conformation three of the hydrogens coordinated to the nitrogens point towards the metal centre while only one hydrogen coordinated to a nitrogen points away from the metal centre.

Structure, Conformation and Reactivity of Organotransition Metal π-Complexes. part 21. X-Ray Crystallographic Characterization of Two Neutral Half-Sandwich Cr(CO)3 Complexes

Abstract: The preferred solid state conformations adopted by two (η6-ligand)Cr(CO)3 (η6-ligand: mesitylene, 1; N- phenyl-2,5-dimethylpyrrole, 2) complexes have been determined via single crystal X-ray crystallographic methods. Iadopts a conformation such that the C 6 ring carbon atoms are eclipsed with respect to the carbonyl ligands. Such a conformation is predictable from both steric and electronic considerations. 2, however, adopts a staggered conformation that must be attributed to the steric requirements of the bulky 2,5-dimethylpyrrole substituent.