Ni Distance Research Articles

Surface structures of [formula omitted] in (√3 × √3 )R30° and (5√3 × 2) phases studied by surface extended X-ray absorption fine structure spectroscopy

The local surface structures of S Ni(111) in the ( √3 × √3) R30° and (5√3 × 2) phases have been investigated by means of polarization-dependent sulfur K-edge surface EXAFS. In the (√3 × √3 ) R30° phase, sulfur adatoms are found to occupy threefold hollow sites with a SNi distance of 2.13 Å and an inclination angle ω of the Sz.sbnd;Ni bonds at 44° from the surface plane. In contrast, in the (5√3 × 2) phase, it is determined that the Sz.sbnd;Ni bond is longer, 2.18 Å, more inclined, ω = 31°, and that the coordination number is not 3 but 4. These results strongly support a picture involving reconstruction of the top nickel layer to form a rectangular structure. Consideration of several models proposed for the (5√3 × 2) phase leads to one which is compatible with both the present results and results recently reported using STM.

Synthesis, spectroscopic and structural studies of alkali metal–nickel periodates MNilO6(M = Na, K, Rb, Cs or NH4)

The dark red-purple nickel(IV) periodataes MNilO6(M = Na, K, Rb, Cs or NH4) have been prepared by peroxohexaoxodisulfate oxidation of mixtures of nickel(II) salts, MNO3 and periodate ions in hot aqueous solution. Powder X-ray diffraction studies showed that the structures adopted the space group P312, with hexagonal close-packed layers of oxide ions. One-third of the octahedral holes in every second layer contained M ions, and in the other layers one-third of the octahedral holes contained I and one-third Ni. The Ni–O,I–O, Ni ⋯ I and Ni ⋯ Ni distances have been determined by a combination of nickel and iodine K-edge extended X-ray absorption fine structure (EXAFS) data. IR, Raman and UV/VIS spectroscopic data for MNiIO6 were obtained. Iodine K-edge EXAFS data have also been obtained for the related periodates M′M″IO6(M″= K or Rb; M″= Ge, Sn, Pb or Mn).

Nickel thioether chemistry: syntheses and crystal structures of [Ni2L2(µ-Cl)2][BF4]2(l = 1,4,7,10-tetrathiacyclododecane, 1,4,8,11-tetrathiacyclotetradecane or 1,5,9,13-tetrathiacyclohexadecane)

Reaction of NiCl2 with 1 molar equivalent of the macrocycles (L) 1,4,7,10-tetrathiacyclododecane ([12]aneS4), 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4) or 1,5,9,13-tetrathiacyclohexadecane ([16]aneS4) and NaBF4 in MeNO2 for 30 min afforded green or blue solutions, from which the complexes [Ni2L2Cl2][BF4]2 can be isolated. The complex [Ni2([12]aneS4)2Cl2][BF4]2·2MeNO2 crystallises in the monoclinic space group C2/m with a= 11.0651(20), b= 13.4977(24), c= 12.7222(21)Å, β= 104.824(21)° and Z= 2. The complex [Ni2([14]aneS4)2Cl2][BF4]2·6MeNO2 crystallises in the triclinic space group P with a= 10.6341(18), b= 11.6481(22), C= 12.2457(25)Å, α= 88.547(7), β= 67.288(12), γ= 68.647(6)° and Z= 1. The complex [Ni2([16]aneS4)2Cl2][BF4]2·2MeNO2 crystallises in the monoclinic space group Ccwith a = 16.024(4), b= 1 3.6862(17), c= 1 9.7329(24)Å, β= 92.042(19)° and Z= 4. Single-crystal structure determinations on each of these products showed the presence of dichloro-bridged dimeric cations exhibiting edge-sharing bioctahedral structures, with the macrocyclic ligands co-ordinated in a cis fashion about the Ni. The Ni–S bond lengths and internal crystallographic symmetry vary significantly between the structures, the shortest distances being observed for [Ni2([14]aneS4)2Cl2]2+[Ni–S 2.3694(22), 2.3765(21), 2.3756(21), 2.3798(21)Å, Ni–Cl 2.4416(20), 2.4252(20)Å]; for [Ni2([12]aneS4)2Cl2]2+, Ni–S 2.412(3), 2.4144(25), 2.373(3), Ni–Cl 2.411(3), 2.382(3)Å and for [Ni2([16]aneS4)2Cl2]2+, Ni–S 2.4098(22)–2.4421 (22), Ni–Cl 2.3860(21 )–2.4205(20)Å. These variations are related to the differing hole sizes of the three tetrathia macrocyles. The Ni ⋯ Ni distances are similar in all three structures, 3.5534(12)–3.5692(12)Å. The complexes [Ni2L2Cl2][BF4]2 exhibit only irreversible electrochemical oxidation and reduction processes according to cyclic voltammetry in MeCN–0.1 mol dm–3 NBun4PF6 at 293 K. Reaction of NiCl2 with 1,4,7-trithiacyclononane ([9]aneS3) and NaBF4 affords the triply bridged dimeric complex [Ni2([9]aneS3)2Cl3]BF4.

Linear dependence of spin exchange coupling constant on bridge angle in phenoxy-bridged dinickel(II) complexes

A magneto-structural relationship showing linear dependence of antiferromagnetic exchange coupling constant (–J) on Ni–O–Ni bridge angle as well as the intramolecular Ni ⋯ Ni distance has been obtained with a series of phenoxy-bridged macrocyclic dinickel(II) complexes with centrosymmetric structures.

Synthesis, structure, magnetism and electrochemistry of binuclear nickel(II) and copper(II) complexes of an unsymmetrical pentadentate Schiff-base ligand

A new unsymmetrical binucleating ligand, H3L, containing salicylidene and 1-methyl-3-oxobut-1-enyl end groups attached to a 1,3-diaminopropan-2-ol backbone, has been synthesized. Binuclear nickel(II) and copper(II) complexes of this ligand, of the type [M2L(pz)], containing a µ-pyrazolato (pz) exogenous bridging group and a µ-alkoxo endogenous bridge, have been synthesized and characterized. Cyclic voltammetric studies on dimethylformamide solutions of these complexes revealed well resolved waves attributable to sequential one-electron metal-centred reduction processes to yield the species [M2L(pz)]– and [M2L(pz)]2–. Comparison to published electrochemical data on the compounds of analogous symmetrical ligands allows identification of the metal–salicylidene end as the site of the first electron transfer. Magnetic susceptibility studies on powdered samples of [Cu2L(pz)] show medium-strength antiferromagnetic coupling (J12=–129 cm–1) within the binuclear molecules and weaker antiferromagnetic coupling (Jintermol=–41 cm–1) between the molecules. Intermolecular Ni ⋯ Ni contact distances of 3.442(5) and 5.100(4)A are evident in the crystal packing of [Ni2L(pz)]. Crystals of the latter have Z= 2 in a triclinic cell with space group P and dimensions a= 9.084(2), b= 12.185(4), c= 8.269(1)A, α= 98.01(2), β= 100.55(1), γ= 99.03(2)°; R= 0.087 based on 1283 reflections with l 3.0σ(l). The structure shows each nickel(II) ion to have a square-planar trans-N2O2 environment and the whole binuclear molecule to be essentially planar. The Ni(1)⋯ Ni(2) distance is 3.212(4)A.

Polydeckerkomplexe mit μ,η5-2,3-Dihydro-1,3-diborolylnickel-Fragmenten als Stapeleinheiten / Polydecker Complexes with μ,η5-2,3-Dihydro-1,3-diborolylnickel Fragments as Stacking Units

Reactions of 2,3-dihydro-1,3-diboroles 6a–h with (C3H5)2Νi lead to µ,η5-2,3-dihydro-1,3-diborolylnickel triple-decker complexes 7a –h. By slow heating these oily, diamagnetic complexes in a rotating flask polycondensation with formation of black 8a–h as well as of bis(allyl)nickel and hexadiene occurs. The latter can be removed under reduced pressure. The constitution of the polymeric material follows from EXAFS studies. The Ni–Ni distance is 3,35 A, the ring atom Ni bonds are in the range of 2,13 to 2,15 A. Thermogravimetric measurements between 200 and 400°C show a mass loss of 20-40%, depending of the alkyl substituents of the heterocycle. In dynamic difference calorimetry an endothermic process occurs near 420°C. The powder conductivity of the amorphous, air-sensitive material is in the range of 10-2 S • cm-1. Doping with iodine or oxygen causes a decrease in the conductivity of these semi-conductors.

Bridge-bonded CO in Ni(110)−p2mg(2×1)-CO: a SEXAFS study

Surface-extended X-ray-absorption fine-structure measurements have been performed to determine the adsorption site of CO in the densely-packed system Ni(110)−p2mg(2×1)-CO. The analysis shows that CO adsorbs in a tilted configuration on short-bridge sites yielding a nearest-neighbour ONi distance of 2.84±0.05 Å. Tilted CO molecules in on-top positions can be definitely ruled out.

Bridge-bonded CO in Ni(110)-p2mg(2 × 1)-CO: a SEXAFS study

Surface-extended X-ray-absorption fine-structure measurements have been performed to determine the adsorption site of CO in the densely-packed system Ni(110)-p2mg(2 × 1)-CO. The analysis shows that CO adsorbs in a tilted configuration on short-bridge sites yielding a nearest-neighbour ONi distance of 2.84 ± 0.05 A ̊ . Tilted CO molecules in on-top positions can be definitely ruled out.

Synthesis, X‐ray and Electronic Structure of Trinickel Tetradecker Sandwich Complexes {(η5‐C5H5)Ni[μ,η5‐(CR1)2(BR2)2CR3]}2Ni

AbstractThe reduction of the 18‐VE complexes (η5C5H5)Ni[η5‐(CR1)2(BR2)2CR3] (2a, b) with potassium in THF leads to the paramagnetic anions 2–, which react with NiBr2 · DME to give the triple‐decker complexes (η5‐C5H5)Ni[μ,η5‐(CR1)2(BR2)2CR3]Ni(η5‐C5H5) (3a, b) and the tetradecker {(η5‐C5H5)Ni[μ,η5‐(CR1)2(BR2)2CR3]}2Ni (4b). Surprisingly, 4b is also obtained by heating the double‐decker complex 2b and H2AlOCMe3 in THF. The reaction between 2c and AlH3 in Et2O leads to the substitution of the ethoxy groups at the boron atoms and to the formation of the tetradecker 4d with four B–H groups. Heating of the 1,3‐benzodiborole ligand 1e and [(C5H5)Ni(CO)]2 in toluene yields small amounts of 2e and 3e, and the tetradecker 4e. X‐ray structure analyses were performed for 4d and 4e. Complex 4d is centrosymmetric with relatively short nickel‐to‐bridging ligand distances (1.69, 1.70 Å). In the tetradecker 4e the two bridging ligands adopt a synclinal conformation (rotating about 36° resp. 41° against each other). The Ni–Ni distance (3.42, 3.43) is slightly longer than in 4d (3.39 Å). The electronic structures of the tripledecker cation 3+ (32 VE) and of the tetradecker 4 (46 VE) have been investigated by means of the Fenske‐Hall method. The findings are in agreement with the experimental results that 3+ is a triplet species and 4 possesses a closed‐shell electron configuration.

Multiple site coincidences and their resolution in photoelectron diffraction: PF 3 adsorbed on Ni(111)

Using scanned energy mode photoelectron diffraction from the P 2p emission of PF 3 on Ni(111) the adsorption structure has been determined; PF 3 occupies an atop site with a PNi nearest neighbour distance of 2.07 ± 0.03 A ̊ . Using the normal emission data alone, comparison of theory and experiment with reliability factors shows a succession of minima as a function of the PNi distance. These multiple “site” coincidences are very similar to those seen in LEED analyses. The ambiguity is removed not only by the depth of these minima, but more importantly by using selected off-normal emission data sensitive to other scattering path-lengths which also show successive minima, but with a different spatial periodicity.

Dissociative adsorption of H2 on Ni(111)

Ab initio configuration interaction calculations are performed to study the dissociative adsorption of H2 on a Ni(111) surface. The lattice is modeled as an embedded three-layer 41-atom cluster. Ni 3d orbitals are explicitly included on seven Ni atoms on the surface. H is preferentially chemisorbed at a threefold site on Ni(111) and the calculated binding energy of 62 kcal/mol, H–Ni distance of 1.86 Å, and H vibrational frequency of 1176 cm−1 are in excellent agreement with experimental data. H adsorbed at bridge and on-top Ni sites is 2.5 and 8.1 kcal/mol less stable, respectively. The heat of reaction H2 (gas)→2 H (ads) is calculated to be 22.0 kcal/mol exothermic. When two H atoms are adsorbed as nearest neighbors to the same Ni atom, threefold sites are preferred with H atoms adsorbed at fcc–fcc, hcp–hcp, or across atom fcc–hcp sites. These structures are consistent with the observed (2×2)−2H low energy electron diffraction pattern. The average adsorption energy per H is calculated to be 62 kcal/mol for the across atom case. Adsorption of H at a threefold site on Ni(111) has a tendency to block adsorption at adjacent threefold sites; coadsorbed H atoms at adjacent sites are unbound by 13.5 kcal/mol relative to H2 at infinite separation. For three H atoms chemisorbed at separated threefold sites sharing a Ni atom with the equal H–H lateral distances of 2.48 Å, the calculated average adsorption energy is 60 kcal/mol per H. Dissociation of H2 at an on-top Ni site has the lowest activation barrier of 1.6 kcal/mol. For the transition state, the H–H bond length, H-surface height, and H–H vibrational frequency are 1.22 Å, 1.38 Å, and 2506 cm−1, respectively. Molecular H2 adsorbed over an on-top site is bound by 3.4 kcal/mol with a slightly stretched H–H bond length of 0.79 Å, H-surface height of 1.85 Å, and H–H stretching frequency of 3396 cm−1.

Crystal structure of a dimeric nickel(II) complex with 3-imidazoline nitroxide radical

The crystal structure of an unusual dimeric Ni(II) complex with 3-imidazoline nitroxide LH=C9H14N2O2 of the formula Ni2(LH)4 has been determined. The structure is molecular, space group P21/c, with a=12.150(3) A, b=11.229(3) A, c=15.780(4) A, β=101.59(3)o, and d calc =1.54 g/cm3, for Z=2; V=2109(1) A3, R=0.059. In the centrosymmetric dimer, the Ni...Ni distance is 3.254(2) A; the coordination polyhedron of Ni is a square pyramid (the coordination number is 5) formed by the donor O and N atoms of LH ligands acting as the bidentate-cyclic and bidentate bridged-cyclic structures. The Ni−O and Ni−N distances are 1.989(7) and 2.032(8) A, respectively (for the atoms forming the pyramid base), and 2.000(8) A to the apical N atom. The Ni atom is displaced from the base to the apex of the pyramid by 0.35 A. The interatomic distances and the bond angles in the ligands agree with those for the previously studied M(LR)2 complexes. The distances between the Ni(II) ions and the $$\begin{array}{*{20}c} \backslash \\ / \\ \end{array} N$$ ∸ O O atoms inside the Ni(LH)2 fragments are 5.39(1) and 5.45(1) A, the intermolecular Ni...O∸ distances exceed 6 A, and the ∸O...O∸ distances are as long as 4.73(1) A.

Electrical Conductivity of Nickel Phosphides

Five nickel phosphides, Ni2P, NiP, NiP2, NiP2 (high pressure form) and NiP3 which have interesting crystal structures have been prepared at high temperatures and high pressures. The electrical resistivity, dc magnetic susceptibility and photoelectron spectrum of nickel phosphides have been studied. Five nickel phosphides show the metallic behavior though their crystal structures and Ni–Ni distances are remarkably different. The relationship between the crystal structures and physical properties of the nickel phosphides is discussed.

Synthesis, structure and magnetic studies of copper(II)-nickel(II) complexes withN,N′-bis(2-aminopropyl)oxamidocopper(II)

Three novel heterobinuclear complexes have been prepared and identified as [Cu(oxap)Ni(L)2](ClO4)2·ξH2O, where oxap denotes theN,N′-bis(2-aminopropyl)oxamido dianion and L denotes 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) or 5-nitro-1,10-phenanthroline (NO2-phen). The crystal structure of [Cu(oxap)Ni(phen)2]-(ClO4)2·2H2O has been determined. Crystal data: triclinic, space group $$P\bar 1$$ , a=12.079 (6), b=12.409 (4), c=17.261 (8) A, α=70.91 (2), β=86.72 (4), γ=89.19 (3)o. At room temperature, Z=2. The CuII is in a square planar environment and the NiII is in an octahedral environment. The Cu−Ni distance is 5.292 A. The temperature dependences of the magnetic susceptibilities of [Cu(oxap)Ni(phen)2]-(ClO4)2·2H2O and [Cu(oxap)Ni(bipy)2](ClO4)2 have been studied in the 4.2–300 K range, giving the exchange integral J=−92.4 cm−1 for bipy and J=−94.3 cm−1 for phen. These results are commensurate with antiferromagnetic interactions between the adjacent metal ions.

Synthetic and structural chemistry of nickel(II) complexes containing dithiolato and phosphine ligands I. Preparation and crystal structure of Ni2(PPh3)2(edt)2

AbstractA nickel(II) complex containing both dithiolato and phosphine ligands, Ni2(PPh3)2(edt)2 (edt = SCH2CH2S2‐), has been prepared and characterized by X‐ray diffration. The complex crystallizes in the triclinic system, space group P‐1, with a = 10.693(3), b = 17.457 (6), c = 10.606 (3) Å, α = 102.84(2), β = 96.49 (2), γ = 82.56(3); V = 1906.8 Å3; Dc = 1.439 g·cm−3 for Z = 2; the final conventional R was 0.052 based on 3338 observed reflections. Nickel atoms are linked by two sulfur atoms from two edt ligands with the Ni—Ni distance of 2.893 Å, and each Ni atom is coordinated by one phosphorus atom and three sulfur atoms with a square‐planar geometry, where the average length of Ni—S bond is 2.180 Å and Ni—P bond 2.188 Å. The UV‐Vis and 1H NMR spectra have also been recorded.

Structural and magnetic properties of Fe/Ni(111).

Structural, electronic, and magnetic properties of Fe/Ni(111) were studied using the total-energy local-spin-density full-potential linearized-augmented-plane-wave method. The Fe adatoms are found to be located on the hcp sites on the Ni(111) surface with a 3.8% downward relaxation relative to the average Fe and Ni distances in bulk. The spin magnetic moments of the Ni(111) surface atoms are enhanced to 0.63${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ from the bulk value of 0.58${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. This moment is further increased to 0.67${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ after the Fe adsorption because of the enhanced exchange interaction. By contrast, the magnetic moment of the Fe overlayer decreases to 2.33${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ from the value of 2.49${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for the isolated Fe monolayer. Layer-by-layer contact hyperfine-field values are presented that show the differing influence of the valence-electron contributions in affecting the proportionality of the hyperfine field and the magnetic moment.

Synthesis, structural, spectroscopic and magnetic studies of two azido and thiocyanato nickel(II) dinuclear complexes with ferromagnetic interactions

From a newly synthesised tridentate ligand [pepci =N′-(2-pyridin-2-ylethyl)pyridine-2-carbaldimine] two new octahedrally co-ordinated nickel(II) dimers, [{Ni(pepci)(N3)2}2]1 and [{Ni(pepci)(NCS)2}2]2, have been prepared. The crystal structure 1 has been solved. It crystallizes in space group P21/c with four formula weights in a cell measuring a= 9.198(3), b= 17.382(6), c= 19.356(7)A, and β= 99.57(1)°. The structure consists of isolated dimeric units in which the nickel ions are linked by two azide bridging groups in an end-on fashion. Two pepci ligands and two terminal azide groups complete the co-ordination spheres. Inside the dimer, each Ni(pepci)(N3)2 entity is crystallographically non-equivalent. There are two different bridging angles Ni(A)–N(4A)–Ni(B) 102.2(2) and Ni(B)–N(4B)–Ni(A) 101.0(2)°. The co-ordination geometry at each nickel atom is approximately octahedral. The Ni(A)⋯ Ni(B) distance is 3.297(1)A. For complex 2 a dimeric structure involving end-to-end thiocyanate bridging groups is proposed. Magnetic susceptibility data, measured from 4 to 300 K, were fitted to the Ginsberg equation, giving the parameters (cm–1): J=+36.3, D=–18.8, z′J′= 0.0 (N3); and J=+4.9, D=–9.8, z′J′=+0.33 (NCS). The magnetic behaviour of these and related complexes is discussed and some magnetostructural trends are given.

Chloride ion abstraction from cobalt and nickel chlorides by SnCI 4. Crystal structure of [Ni 2(μ-Cl) 3(THF) 6][SnCl 5(THF)

The reactions of CoCl 2 and NiCl 2 with SnCl 4, in THF gave antiferromagnetic salts of the type [M 2(μ-Cl) 3(THF) 6][SnCl 5(THF)]. The structure of the product with M = Ni was established by X-ray diffraction. The cation, composed of two octahedral nickel(II) ions bonded through three bridging Cl atoms, has an Ni · Ni distance of 2.993(3) Å.

Er2BaNiO5: structure refinement using neutron powder diffraction data

The crystal structure of dierbium barium nickelate, ErzBaNiOs, has been refined from neutron powder diffraction data, collected at room tempera- ture. Results agree with those obtained from single- crystal X-ray diffraction. Sixfold oxygen coordi- nation around the Ni atoms is confirmed and more precise oxygen positions are given. The NiO6 octahedra show an unusual twofold distortion: the Ni--O distances to the two axial O atoms are consid- erably shorter, by 0.3 A, than those to the four equatorial oxygens; these oxygens are distorted from the right angles of a regular octahedron to 79.1 (1) °. Interesting physical properties are suggested by the existence of infinite isolated chains of NiO6 flattened octahedra sharing vertices in the direction of the a axis, with extremely short, 3-75 A, Ni--O(axial)--Ni distances. Orthorhombic, Immm, a = 3.7541 (1), b = 5.7442 (1), c -- 11.3019 (2) A, V-- 243.71 (2) A 3, Z = 2, ,t = 1.594 A, Rwp = 7.52%. Introduction. The Nd2BaNiO5 structure type (ortho- rhombic, Immm) was first described by Schiffler & Miiller-Buschbaum (1986a). Subsequent studies by these authors (Schiffler & Mfiller-Buschbaum, 1986a,b, 1987; Mfiller-Buschbaum & Lang, 1988; Mfiller-Buschbaum & Rfiter, 1989), established this structure for the compounds formed with rare earth from Sm to Tm. Independently, Amador (1989) pre-

Spectroscopic and magnetic properties of two ferromagnetically coupled nickel(II) dimers [{Ni(terpy)(NCX)2}2](terpy = 2,2′ :6′,2″-terpyridine, X = S or Se). Crystal structure of the thiocyanate

Two new binuclear nickel(II) complexes [{Ni(terpy)(NCX)2}2](X = S or Se) have been prepared from 2,2′ :6′,2″-terpyridine (terpy) ligand. The crystal structure of [{Ni(terpy)(NCS)2}2]1 was solved by direct methods and refined by least-squares analysis to a discrepancy factor of 0.050. The crystals are triclinic, space group P, with lattice constants a= 8.822(2), b= 9.569(1), c= 10.906(1)A, and α= 74.35(1), β= 85.19(2), γ= 78.75(2)°. The dimer, whose halves are related by a crystallographic inversion centre, consists of two nickel atoms co-ordinated to two terpy ligands, two terminal NCS ligands and two end-to-end NCS bridging ligands. Each NiII has a distorted-octahedral environment. The Ni ⋯ Ni distance is 5.633(3)A and the bridging angles are 100.0(8) and 159(2)°. The complex [{Ni(terpy)(NCSe)2}2]2 was found to be isomorphous [a= 8.867(3), b= 9.592(4), c= 11.047(3)A, α= 73.64(3), β= 83.44(3) and γ= 76.67(2)°]. Magnetic susceptibility data, measured from 2 to 300 K, were fitted to the Ginsberg equation, giving the parameters J=+4.9 cm–1, D=–4.3 cm–1 and z′ J′=+0.02 cm–1(NCS) and J=+10.1 cm–1, D=–10.0 cm–1 and z′ J′=+0.01 cm–1(NCSe). The magnetic behaviour of these and related complexes is discussed and some magnetostructural trends are given.