Ni Distance Research Articles

Synthesis, structure, spectral and magnetic properties of a dinuclear copper(II)/nickel(II) complex bridged by glyoximate groups

A new dinuclear complex of formula [(tmen)(H 2O) 2Ni(Hdmg)(dmg)Cu]·ClO 4 (H 2dmg=dimethylglyoxime, tmen=tetramethylenediamine) has been synthesized. The crystal structure of the complex has been solved by a single-crystal X-ray diffraction method. The structure consists of one cationic dinuclear complex, [(tmen)(H 2O) 2Ni(Hdmg)(dmg)Cu] +, and one anion, ClO 4 −. In the dinuclear cationic complex the copper(II) ion and the nickel(II) ion are bridged by two oximate groups, one through the nitrogen and oxygen atoms and the other only through the oxygen atom. The intramolecular Cu⋯Ni distance is 3.424 Å. The geometry around the copper atom is a distorted square pyramid, and the geometry around the nickel atom is a distorted octahedron. Variable-temperature magnetic susceptibility measurements (75–300 K) on the title complex revealed the occurrence of an intramolecular antiferromagnetic interaction through the oximate bridges. The IR and UV–Vis spectra have also been investigated.

Interaction between heterobinuclear molecules and nature of the ground spin state in oximato-bridged [Cu IIM II] 2 bis-binuclear complexes (M=Cu, Ni, Mn): crystal structure of [Cu(pdmg)Ni(Me 3[12]N 3)(EtOH)](ClO 4) 2

Two new heterobimetallic complexes [Cu(pdmg)Ni(Me 3[12]N 3)(CH 3CH 2OH)](ClO 4) 2 ( 2) and [Cu(pdmg)Mn(bipy) 2](ClO 4) 2 · H 2O ( 3) (H 2pdmg=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime; Me 3[12]N 3=2,4,4-trimethyl-1,5,9-triazacyclododeca-1-ene; bipy=2,2′-bipyridyl) have been prepared and characterized. The structure of 2 has been determined by single-crystal X-ray diffraction methods. It consists of [Cu(pdmg)Ni(Me 3[12]N 3)(CH 3CH 2OH)] 2+ cations and non-coordinated perchlorate anions. The [Cu(pdmg)(CH 3CH 2OH)] complex coordinates to the [Ni(Me 3[12]N 3)] 2+ fragment to afford the binuclear unit doubly-bridged by oximato groups in cis arrangement. The coordination geometry around the copper atom is square-pyramidal, whereas the nickel atom exhibits a trigonal-bipyramidal surrounding. The intramolecular Cu–Ni distance is 3.810(6) Å. In the crystal, two [Cu IINi II] dimeric units are related through an inversion center, giving rise to a bis-binuclear entity with a relatively short intermolecular Cu–Cu separation of 4.175(6) Å. Variable-temperature magnetic susceptibility measurements (2.0–300 K) for 2 correspond to an almost isolated Cu(II)Ni(II) pair with an intrapair interaction parameter J=−143.6(2) cm −1. However, the EPR spectrum at 4.2 K is that of a triplet spin state arising from the interaction between the two doublet spin states within the [Cu IINi II] 2 bis-binuclear entity. The magnetic properties of 3 unambiguously reveal the bis-binuclear nature of this compound, as is the case for the related homometallic complex [Cu(pdmg)Cu(bipy)(H 2O) 2](ClO 4) 2 · H 2O ( 1). The intra- ( J) and interpair ( j) interaction parameters for 3, as deduced from the analysis of its magnetic susceptibility data in the temperature range 2.0–300 K, are −50.9(2) and 1.50(2) cm −1, respectively. The field dependence of the magnetization of 3 at 2.0 K corresponds to that of a nonet state arising from the interaction between two quintuplet spin states within the [Cu IIMn II] 2 bis-binuclear entity. The interaction between the heterobinuclear Cu(II)Mn(II) molecules and its influence on the nature of the ground spin state for 3 are analyzed and discussed in the framework of a spin polarization scheme.

Structure, Charge and Spin Density in Na2Ni(CN)4.3H2O at 295 and 30 K

The earlier reported structure of the title compound, disodium tetracyanonickelate(II) trihydrate, Na2Ni(CN)4.3H2O, has been found to be incorrect and has now been redetermined. The charge distribution has been determined by multipole refinements against single-crystal X-ray diffraction data. In the refinement based on 30 K data a comparison was made between the results obtained using hydrogen positions and displacement parameters from X-ray diffraction with those using the values determined by neutron diffraction. The spin density was investigated by polarized neutron diffraction at 1.6 K. Crystal data: at T = 30 K: a = 7.278 (4), b = 8.856 (5), c = 15.131 (8) Å, α = 89.32 (5), β = 87.39 (4), γ = 83.61 (4)°; at 295 K: a = 7.392 (4), b = 8.895 (4), c = 15.115 (8) Å, α = 89.12 (2), β = 87.46 (2), γ = 84.54 (2)°. The structure contains practically square planar Ni(CN)_4^{2-} ions, which are stacked on top of each other in almost linear chains along the a direction. The separation between the Ni(CN)_4^{2-} planes is rather large, with Ni—Ni distances around 3.7 Å. The six crystallographically independent water molecules are each coordinated to two sodium ions, approximately in the tetrahedral (lone-pair) directions, and the polarizing influence of these sodium ions also appears to be reflected in the deformation density in the lone-pair plane. The charge density based on the deformation functions of all atoms in the structure is compared with the individual densities calculated from the deformation functions of only nickel or the separate water molecules. In this way the effects of simple superposition of the individual densities have been studied. In the planar Ni(CN)_4^{2-} ion the individual deformation density of nickel is in qualitative agreement with that expected from crystal-field theory. As the repulsion from the electrons is much weaker perpendicular to the Ni(CN)_4^{2-} plane than within this plane, the deformation density is considerably larger in the perpendicular direction. However, the largest maxima in the individual deformation density around nickel are not found precisely in the planes defined by nickel and the four cyanide ligands or in the perpendicular direction just mentioned, which illustrates that it is necessary to consider the crystal field due to the whole crystalline environment.

Synthesis, X-ray Crystal Structure and Magnetism of [NiCl2{(bis(2-benzimidazolyl)propane}]2 · (C2H5OH)2 – A Second Example of a Ferromagnetically Coupled Five-Coordinated High-Spin Dichloro-Bridged Nickel(II) Dimer

The ligand bis(2-benzimidazolyl)propane coordinates to NiII with chloride as an anion, thereby forming a dinuclear compound with the formula: [NiCl2(tbz)2]2(C2H6O)2. This compound crystallizes in the space group P21/c. Each five-coordinated NiII ion has a distorted trigonal bipyramidal environment which consist of two asymmetrically bridging Cl anions with distances of 2.3556(17) and 2.4275(16) Å, a terminal Cl anion with a distance of 2.3496(17) Å and two nitrogen atoms of the ligand with distances of 2.022(4) and 2.000(4) Å. The Ni–Ni distance is 3.5891(12) Å, while the Ni–Cl–Ni angle is 97.23(6)°. The magnetic properties of the compound, as studied in the range 5–280 K, have been fitted with a zero-field splitting parameter D (–14.3 cm−1) and a ferromagnetic exchange between the Ni ions in the dinuclear unit (J = +2.5 cm−1). The title compound appears to be the second example for a five-coordinated ferromagnetic dinuclear NiII compound of this type, and its magnetic properties appear to correlate with the ligand structure. With the availability of an increasing number of examples of such species it appears that antiferromagnetic exchange is found for all cases with the chromophore N2ClNiCl2NiClN2 where the MN2 ring is 5-membered. In the case, where this ring is six-membered, the exchange is ferromagnetic.

Bis(μ-{N-[(methylthio)phenylmethylene]methanamineN-oxide}-O:O)bis[bis(1,1,1,5,5,5,-hexafluoropentane-2,4-dionato-O, 4-dionato-O,O')nickel(II)

The title compound, [Ni2(C5HF6O2)4(C9H11NOS)2], crystallizes as a centrosymmetric dimer containing two Ni(hfac)2 moieties bridged by two nitrone ligands (hfac is the 1,1,1,5,5,5-hexafluoropentane-2,4-dionate anion). The Ni⋯Ni distance is 3.2904 (5) Å, with Ni—Onitrone distances of 2.0776 (12) and 2.0974 (12) Å. The average Ni—Ohfac distance is 2.022 (16) Å.

Synthesis, Crystal Structures, and Properties of S-Bridged Pt(II)-Ni(II) Dinuclear Complexes: Conversion of Square-Planar [Ni(aet)2] to Octahedral Geometry by Forming an S-Bridged Structure with Pt(II) (aet = 2-Aminoethanethiolate)

Abstract The reactions of [Ni(aet)2] with [PtCl2(L)] gave a new type of S-bridged dinuclear complexes [Pt(L){Ni(aet)2(H2O)2}]2+ (aet = aminoethanethiolate; L = bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline (5), dmbpy = 4,4′-dimethyl-2,2′-bipyridine). These complexes readily react with L′ to form [M(L){Ni(aet)2(L′)}]2+ (L = bpy, L′ = bpy (3), phen; L = phen, L′ = phen, bpy; L = L′ = dmbpy). A similar reaction of [Ni(aet)2] with [PtCl2(phen)] and phen gave only [Pt(phen){Ni(aet)2(phen)}]2+. The crystal structures of 3 and 5 were determined by X-ray crystallography. The Ni atoms are surrounded by two aet and a bpy or two water molecules to have an approximately octahedral geometry, forming the C2-cis(S)-[Ni(aet)2{bpy or (H2O)2}] unit. The Pt atoms have a square-planar geometry, in which two Cl atoms of the starting [PtCl2(L)] (L = bpy or phen) have been substituted by the two S atoms from the Ni(II) unit. The Pt(II) plane and the Ni(II) equatorial plane are almost coplanar, and the Pt–Ni distance is 3.4987(8) Å (3) and 3.476(4) Å (5). All of the complexes were characterized on the basis of the electronic absorption and infrared spectra and the cyclic voltammetry. The conversion of a square-planar [Ni(aet)2] to an octahedral [Ni(aet)2{(H2O)2 or (L′)}] units was also considered. In the solid state, the water molecule in [Pt(L){Ni(aet)2(H2O)2}]2+ could be readily exchanged by nitrate.

Hydroxamate-Bridged Dinuclear Nickel Complexes as Models for Urease Inhibition

Facile reaction of the model urease complex [Ni2(OAc)3(urea)(tmen)2][OTf] (A) with acetohydroxamic acid (AHA) gives the monobridged hydroxamate complex (I) [Ni2(OAc)2(AA)(urea)(tmen)2][OTf] with a Ni−Ni distance of 3.434(1) A compared to that of 3.5 A in urease (OAc, CH3COO-; tmen, N,N,N‘,N‘-tetramethylethylenediamine; OTf, CF3SO3; AHA, acetohydroxamic acid; AA, acetohydroxamate anion). I is a close model of one proposed mode of urease inhibition by hydroxamic acids, recently observed in the acetohydroxamate-inhibited C319A variant of Klebsiella aerogenes urease. Reaction of [Ni2(OH2)(OAc)4(tmen)2] (B) with AHA gives the dibridged hydroxamate complex (II) [Ni2(OAc)(AA)2(tmen)2][OAc] with a Ni−Ni distance of 3.005(1) A. Infrared spectroscopic studies provide evidence for the bridging acetate groups undergoing carboxylate shifts thereby assisting replacement of acetate by hydroxamate. Both I and II show ferromagnetic exchange coupling.

Bis[μ-N,N'-bis(salicylidene)-1,3-propanediaminato]bis(dimethylformamide)di(μ-nitrito)copper(II)dinickel(II)–Dimethylformamide (1/2)

The unit cell of the title compound, [CuNi2(NO2)2(C17H16N2O2)2(C3H7NO)2].2C3H7NO, contains two molecules of the linear heterotrinuclear complex and four solvent molecules. The central CuII ion and the terminal NiII ions have distorted octahedral coordination spheres. The Cu–Ni pairs are each triply bridged, by the O atoms of an N,N'-bis(salicylidene)-1,3-propanediaminato (salpd2−) ligand and by an O and an N atom of a nitrite group. The central CuII ion, located on an inversion centre, has a total of six O atoms in its coordination sphere: two from each salpd2− ligand and one from each bridging nitrite group. The NiII ions are related by the inversion centre and each is coordinated by the two O and two N atoms of a salpd2− ligand and one N atom from a nitrite and an O atom from a dimethylformamide (dmf) ligand. The dmf and nitrite groups are mutually trans about the NiII ion. The Cu—Ni distance is 2.9967 (4) Å.

Nickel Complexes Containing New Carbon−Phosphorus Unsaturated Ligands: First Examples of Phosphavinylidene−Phosphorane [R3PCPR‘] and Phosphavinyl Phosphonium [C(H)(PR3)P(R‘)]+Ligands

Oxidative-addition reactions of Cl2CPN(SiMe3)2 with 1:2 Ni(COD)2/PPh3, Ni(PPh3)4, or (Ph3P)2Ni(C2H4) initially yields the phosphavinyl phosphonium complex Cl(Ph3P)Ni[η2-C(Cl)(PPh3)PN(SiMe3)2] (IIa). Addition of another equivalent of Ni(0) reagent to IIa results in the formation of the novel, dinuclear, phosphavinylidene−phosphorane complex Ni2Cl2(PPh3)2[μ2-η2:η2-C(PPh3)PN(SiMe3)2] (IIIa); the structure of IIIa was established by X-ray diffraction and contains a Ph3PCPR‘ ligand bridged between two four-coordinate, planar nickel atoms in a butterfly arrangement with a Ni−Ni distance that is too long for a significant bonding interaction. The Ph3PCPR‘ ligand, which may be viewed as a phosphavinylidene (CPR) ligand with a phosphine-donor substituent, acts as a six-electron donor to the two nickel atoms. This contrasts with the known diphosphaallene compounds of the types R3PCPR3 and RPCPR that act as two-electron donor ligands. When the reaction of the Ni(0) reagent is performed with Cl2CPMes* (Mes* = 2,4,6-tri-tert-butylphenyl), the mononuclear phosphonio−phosphavinyl complex Cl(Ph3P)Ni[η2-C(H)(PPh3)P(Mes*)] (Va) forms. The structure of Va was established by X-ray diffraction and contains a [C(H)(PR3)P(R‘)] ligand that acts as a three-electron donor to the Ni(PPh3)Cl fragment. This structure also exhibits a puckered, boat-shaped supermesityl ring. Both IIIa and Va exhibit labile PPh3 groups on nickel which are easily substituted with PEt3, but the carbon-bound PPh3 groups could not be substituted with PEt3.

Bis{(μ-acetato)[μ-bis(salicylidene)-1,3-propanediaminato](N,N-dimethylformamide)nickel(II)}cadmium(II)

The structure of the title compound, [Cd(C2H3O2)2{Ni(C3H7NO) (C17H16N2O2)}2], consists of a linear heterotrinuclear unit with a central CdII ion. Both this ion and the terminal NiII ions have pseudo-octahedral coordination. Each pair of metal ions is triply bridged via O atoms from N,N'-bis(salicylidene)-1,3-propanediaminato (SALPN2−) ligands and acetate groups. The coordination around the CdII ion involves four O atoms from two SALPN2− and two acetate ligands. The coordination of the NiII ion is provided by the two O atoms and two N atoms from a SALPN2− ligand and one O atom each from an acetate and a dimethylformamide. The Cd⋯Ni distance is 3.2274 (5) Å.

Pyrazolyl- and Hydrocarbyl-Bridged Binuclear Complexes of Nickel

The binuclear nickel complex Ni2Br2(PMe3)3(μ2-η3:η1-CH2-o-C6H4) (1) reacts with pyrazolyllithium (LiPz) to give the μ-pyrazolyl μ-hydrocarbyl compound Ni2(PMe3)2Br(μ2-η3:η1-CH2-o-C6H4)(μ2-Pz) (2). X-ray studies show a short Ni−Ni distance (2.710(2) A) which suggests the existence of some bonding interaction. The bromide ligand of compound 2 can be replaced by anionic (N3-, 2,5-dimethylpyrrolide) or neutral (PMe3, Me2PCH2CH2PMe2) ligands. Other related complexes containing methyl or tert-butyl substituents on the 3-position or on the 3- and 5-positions of the pyrazolate ligand can be obtained using the corresponding pyrazolylthallium derivatives. The monosubstituted pyrazole complexes exist in solution as equilibrium mixtures of two isomers which differ in the relative position of the pyrazolate substituent. However, only one isomer has been isolated in the solid state.

Laser induced desorption of NO from NiO(100): Characterization of potential energy surfaces of excited states

In order to interpret experimental results such as velocity flux distributions and rotational/vibrational populations of the state resolved UV-laser induced desorption of NO from NiO(100) ab initio calculations at the configuration interaction (CI) and complete active space self consistent field (CASSCF) levels have been performed for the electronic ground state and those excited states which are important for the desorption process. The NO NiO(100) system was described by a NiO 8− 5-cluster embedded in a Madelung field of point charges with NO adsorbed in the on-top position on the central Ni 2+ ion. Two-dimensional potential energy surfaces for several electronic states have been calculated as a function of the NNi distance and the tilt angle of NO towards the surface normal. The excited states involved in the desorption process are charge transfer states in which one electron is transferred from the oxygen 2p-shell into the NO 2π-orbitals. The dependence of the potential energy surfaces on the NNi distance is dominated by a strong Coulomb attraction between the NO − ion formed as an intermediate and the hole created within the cluster. The angular dependence of the potentials favours an upright adsorption geometry if NO − is approaching the surface. This offers an explanation of the strong coupling between translation and rotation, which has been observed experimentally for the system NO NiO(100) , as well as the absence of such a coupling in the system NO NiO(111) .

Bis(didentate) open-chain and tetradentate pseudo-macrocyclic bridging co-ordination modes of N,N′ -bis(1,3-dimethyl-5-nitroso-2,4-dioxopyrimidin-6-yl)butane-1,4-diamine

E. Colacio, J. M. Domínguez-Vera, A. Escuer, R. Kivekäs, M. Klinga, J. Moreno and A. Romerosa, J. Chem. Soc., Dalton Trans., 1997, 1685 DOI: 10.1039/A607956C

Paramagnetic and Semiconducting 1:1 Salts of 1,1‘-Disubstituted Ferrocenes and [Ni(mnt)2]-. Synthesis, Structure, and Physical Properties

The ferrocene-based electron donors 1,1‘-bis[2-(4-(methylthio)phenyl)-(E)-ethenyl]ferrocene (2), 1,1‘-bis[2-(4-methoxyphenyl)-(E)-ethenyl]ferrocene (3), 1,1‘-bis[(1,3-dithiolo[4,5-b][1,3]dithiol-2-ylidene)methyl]ferrocene (4), and 1,1‘-bis[(1,3-benzodithiol-2-ylidene)methyl]ferrocene (5) were found to react with ferrocenium bis(maleonitriledithiolato)nickelate (1−) ([FeCp2]+[Ni(mnt)2]-, 6) to afford the corresponding 1:1 paramagnetic salts 7−10, containing 1,1‘-disubstituted ferrocenium derivatives. SQUID magnetic susceptibility measurements of these new compounds showed a behavior dominated by antiferromagnetic interactions within pairs of [Ni(mnt)2]- ions. Pressed pellets of compounds 7 ([2][Ni(mnt)2]) and 9 ([4][Ni(mnt)2]) are semiconducting, with a relatively large conductivity activation energy (0.85 and 1.13 eV). Crystals of 7 reveal the monodimensional nature of the compound. Each separate stack of [Ni(mnt)2]- ions is flanked by two ferrocenium stacks. Ni−Ni distances alternate between 3.67 and 3.99 Å.

PHOTOCHEMICAL ACTIVATION OF CARBON DIOXIDE BY VISIBLE LIGHT MEDIATED BY COBALT(II) AND NICKEL(II) COMPLEXES OF 1,6-BIS(BENZIMIDAZOL-2-YL)-2,5-DITHIAHEXANE (BBDH)

Abstract Reactions between crystalline Ni(NO3)2 or Co(ClO4)2 6H2O and 1,6-bis(benzimidazol-2-yl)-2, 5-dithiahexane (BBDH) in ethanol afford the insolubles [Ni(BBDH)(H2O)2](NO3)2 or [Co(BBDH)(H2O)2](ClO4)2 and coloured solutions. The action of CO2 and visible light on these suspensions at room temperature yields new nickel(II) or cobalt(II) 2- carboxylato benzimidazolates, [O2C-BzIm]2-, of formula [Ni2(BBDH)2(μ2-O2C-BzIm)](NO3)2 (I) (I) and [Co2(BBDH)2(μ2-O2C-BzIm)] (ClO4)2 (II), respectively. The crystal and molecular structure of I and II have been elucidated by single crystal X-ray analysis. The complex I crystallizes in the monoclinic space group C2/c, with a = 15.371(3), b = 13.393(3), c = 22.790 (4) A, and β = 99.54(4)°. The unit cell comprises four formula units with half the binuclear cation complex in the asymmetric unit. The [O2C-BzIm]2- bridges two distorted octahedral nickel(II) ions having a Ni═Ni distance of 5.397(2) A. Complex II crystallizes in the triclinic space group P1, with cell data a...

Structure and Magnetic Properties of a Triply Oxygen. Bridged Dinuclear Ni(II) Complex

[Methylamino-(N,N′-1,3-propyl-disalicylaldiminato)-Ni(II)-bis-(N-methylsalicylaldiminato)- Ni(II)] was synthesized from the condensation of N,N′-1,3-propyl-disalicylaldimine, salicylaldehyde, methylaminohydrochloride, NaOH and Ni(CH3COO)2·H2O, and its crystal structure determined. [C34H37N5O4Ni2], orthorhombic, space group Pbca, a = 12.330( 1), b = 24.967(2), c = 20.616(2)Å, Z = 8. The dinuclear complex contains two octahedrally coordinated nickel atoms which are linked via three oxygen atoms with an average (Ni-O-Ni) angle of 87.2( 1)° and a Ni···Ni distance of 2.884(1)Å. The coordination is completed by three nitrogen atoms. The nickel(II) centers are ferromagnetically coupled (J = 11.5 cm-1) as derived from temperature-dependent magnetic susceptibility measurements in the range 5 - 280 K.

Dinuclear phosphido- and arsenido-bridged early/late transition metal complexes. Efficient catalysts for ethylene polymerization

The reaction of ( η 5-C 5H 5) 2Zr{P(SiMe 3) 2} 2 with Ni(CO) 4 yields the heterodinuclear phosphido-bridged complex ( η 5-C 5H 5)Zr{μ-P(SiMe 3) 2)} 2Ni(CO) 2 ( 1). 1 was characterised spectroscopically and by X-ray structure determination. The central four-membered ZrP 2Ni ring is slightly puckered (dihedral angle between planes ZrP 2/ NiP 2 = 1.8°). The ZrP bond lengths are equivalent (Zr-PI 2.655(l), Zr-P2 2.652(1) Å), as are the NiP bond lengths (Ni-PI 2.264(1), Ni-P2 2.266(1) Å). The long Zr…Ni distance of 3.038(1) Å indicates the absence of a metal-metal bond. The heterodinuclear phosphido- and arsenido-bridged complexes ( η 5-C 5H 5) 2Zr{μ-E(SiMe 3) 2} 2M(CO) n [ E = P; M( CO) n = Ni( CO) 2 ( 1) or Mo(CO) 4 ( 2); and E = As M( CO) n = Cr( CO) 4 ( 3)] react rapidly with methylaluminoxane, yielding catalytically active complexes which rival the known cationic systems for the polymerization of ethylene.

Synthesis and structure of metallomacrocycles based on isothiosemicarbazides

New isothiosemicarbazide-based heteronucleating ligands have been synthesised by Ba 2+-templated (1:1) macrocyclisation of the polyetherdialdehydes, 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)bis(2-hydroxybenzaldehyde) and 3,3′-(3,6,9-trioxaundecane-1,11-diyldioxy)bis(2-hydroxybenzaldehyde), by using S-methylisothiosemicarbazide as the diamine building block. Thus, the linear polyether dialdehydes (2-hydroxybenzaldehyde-3-yl)-O-(CH 2CH 2 O) n -(3-yl-2-hydroxybenzaldehyde), with n = 3 and 4, react wit S-methylisothiosemicarbazide in the presence of Ba(CF 3SO 3) 2 and Ni(CH 3COO) 2·4H 2O to give two nickel/barium complexes 5 and 6, the crystal structures of which are described. 5: triclinic, P 1, a=9.886(3), b=12.376(4), c=13.845(6) A ̊ , α=73.97(3), β=88.58(3), γ=83.26(3)°, Z=1 ; 6: triclinic, P 1 , a=10.767(2), b=13.221(2), c=15.986(2) A ̊ , α=102.57(1), β=101.13(1), γ=109.91(1)°, Z=2 . Treatment of these complexes with an aqueous solution of guanidinium sulfate yields the respective Ba free metallomacrocycles. The crystal structure of one of these ( 3·H 2O) has been determined. 3·H 2O: triclinic, P 1, a=8.106(3), b=11.836(4), c=13.174(4) A ̊ , α=88.22(3), β=76.64(3), γ=70.30(3)°, Z = 2 . Its geometry is compared with its parent compound 5. It reveals that coordination of the Ba 2+ cation (0.6 Å above the mean plane of the O atoms) has little influence on the conformation of the macrocycle. The polyether ring in the two Ba complexes differs in size yet the Ba…Ni distances are remarkably similar (3.664(5) versus 3.723(3) Å) suggesting that the two metal atoms although not bonding may be touching.

A heterodinuclear anti oximate-bridged copper(II)-nickel(II) complex: crystal structure and magnetic properties

The crystal structure of [Cu(ClO 4)(μ-L)Ni(CTH)](ClO 4)·H 2O (where H 2L is α,ω-bis(1,3-dimethyl-5-nitrosouracil-6-yl-amine)propane and CTH is d, l-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) has been determined by X-ray methods. The complex crystallizes in the monoclinic space group C2/ c with a=41.848(16), b=12.738(3), c=20.005(7) A ̊ , β=114.92(2)° . The structure consists of discrete dimetallic cations [Cu(ClO 4)(μ-L)Ni(CTH)] +, one perchlorate anion and one non-bonded disordered molecule of water. Within the dinuclear cation, copper(II) and nickel(II) are bibridged by an exocyclic oxygen atom of the uracil ring and an anti nitroso-oximato group, resulting in a Cu···Ni distance of 4.972(2) Å. The copper(II) ion occupying the inside site of the double deprotonated ligand L 2− exhibits a N 4O distorted square-pyramidal coordination environment, whereas the nickel(II) ion is in a distorted octahedral geometry. Magnetic susceptibility measurements in the temperature range 300-2 K revealed the occurrence of a strong antiferromagnetic exchange interaction between copper(II) and nickel(II) ions with a J value of −136.4 cm −1. Magnetic and structural parameters of this and other related complexes are compared in order to know how the type of NO bridging conformation affects the magnetic properties.

Surface structure of (√3 × √3)R30° and (5√3 × 2) phases of S/Ni(111)

Surface EXAFS has revealed that the sulfur atom is located at the 3-fold hollow site with the SNi distance of 2.13 Å in (√3 × √3)R30°S/Ni(111) phase and that the SNi bond of 2.18 Å is more inclined and the coordination number is 4 in the (5√3 × 2) phase. A new reconstruction model consistent with EXAFS and STM is presented.