Ni4O4 Cubane Research Articles

Spin state and magnetic coupling in polynuclear Ni(II) complexes from density functional theory: is there an optimal amount of Fock exchange?

Reliable prediction of the ground-state spin and magnetic coupling constants in transition-metal complexes is a well-known challenge for density functional theory (DFT). One popular strategy for addressing this long-standing issue involves the modification of the fraction of Fock exchange in a hybrid functional. Here we explore the viability of this approach using three polynuclear metal-organic complexes based on a Ni4O4 cubane motif, having different ground state spin values (S = 0, 2, 4) owing to the use of different ligands. We systematically search for an optimum fraction of Fock exchange, across various global, range-separated, and double hybrid functionals. We find that for all functionals tested, at best there only exists a very narrow range of Fock exchange fractions which results in a correct prediction of the ground-state spin for all three complexes. The useful range is functional dependent, but general trends can be identified. Typically, at least two similar systems must be used in order to determine both an upper and lower limit of the optimal range. This is likely owing to conflicting demands of minimizing delocalization errors, which typically requires a higher percentage of Fock exchange, and addressing static correlation, which typically requires a lower one. Furthermore, we find that within the optimal range of Fock exchange, the signand relative magnitude of Ni-Ni magnetic coupling constants are reasonably well reproduced, but there is still room for quantitative improvement in the prediction. Thus, the prediction of spin state and magnetic coupling in polynuclear complexes remains an ongoing challenge for DFT.

Enhanced water oxidation reaction kinetics on a BiVO4 photoanode by surface modification with Ni4O4 cubane

Ni4O4 cubane is combined with a BiVO4 photoanode via an Al2O3 adsorbed layer for highly efficient and stable photoelectrochemical water oxidation.

Electrochemical Water Splitting by Pseudo‐spinel, Disordered and Layered Lithium Nickel Oxides: Correlation between Structural Motifs and Catalytic Properties

AbstractIn this work, three different structures of lithium nickel oxide (LNO) synthesized by simple methods as inexpensive and efficient electrocatalyst for OER were presented. The catalytic activities of LNO catalysts for OER were pseudo‐spinel (PS‐LiNiO2) > disordered (DO‐LiNiO2) > layered (L‐LiNiO2) lithium nickel oxide. Particularly, PS‐LiNiO2 demonstrated much lower tafel slope of 62 mV dec−1 with the highest durability whereas the layered LNO catalysts exhibited the higher tafel slope of 88 mV dec −1, respectively. To elucidate the origin of high activities of LNO catalysts, three structures of LNO were studied by EXAFS measurements and DFT theoretical calculation. Compared to L‐LiNiO2, PS‐LiNiO2, including Ni4O4 cubane structural motifs, exhibited higher valent states and lower Ni d‐band center to drive the catalytic reaction. Thus, our results demonstrated that the activities of LNO can be optimized by controlling the value states, chemical and local electronic structure of Ni via novel design approaches.

Syntheses, crystal structures and magnetic properties of two Ni4(μ3–phenoxido)4 cubanes: Role of additional bridging carboxylates

The work in the present investigation reports the syntheses, crystal structures, ESI-MS (positive) and variable-temperature and variable-field magnetic properties of two Ni4O4 cubane compounds of composition [NiII4L2(µ1,3-HCO2)2](ClO4)2·2H2O (1) and [NiII4L2(µ1,3-o-ClPhCO2)2](ClO4)2·3H2O (2) derived from the Robson type tetraiminodiphenol macrocyclic ligand H2L (2+2 condensation of 4-ethyl-2,6-diformylphenol and 2,2-dimethyl-1,3-diaminopropane). All the four oxygen atoms of the distorted cubane are phenoxido oxygen atoms, coming from two deprotonated macrocycle, [L]2−, i.e., these compounds are Ni4(μ3–phenoxido)4 cubanes. The nickel(II) centers in each of the two pairs in two opposite faces of the cube are additionally bridged by a syn–syn carboxylate, formate in 1 and o-chlorobenzoate in 2. Variable-temperature and variable-field magnetization data reveal an overall antiferromagnetic interaction in both 1 and 2, where two of the six pathways are ferromagnetic (4.06cm−1 in 1 and 1.58cm−1 in 2) and the remaining four pathways are antiferromagnetic (−3.03cm−1 in 1 and −1.55cm−1 in 2). The possibility of a J versus NiII–O(phenoxo)–NiII angle correlation and the roles of carboxylate moiety as well as energy difference between the first excited state and ground state on magnetic properties have been discussed.

A ferromagnetic tetranuclear nickel(II) Schiff-base complex with an asymmetric Ni4O4 cubane core

The ferromagnetic tetranuclear nickel(II) complex [Ni4(L)4(CH3OH)2]·2MeOH·8H2O (1) has been synthesized by reacting nickel nitrate hexahydrate with the Schiff base ligand H2L (H2L=N-(2-hydroxyphenyl)-3-methoxy-salicylideneamine). Complex 1 was characterized by analytical, thermogravimetric, optical and magnetic techniques. The solid state structure of 1 was established by single crystal X-ray diffraction analysis. Crystal structure determination shows the formation of a distorted Ni4O4 cubane moiety encapsulated by four Schiff base ligands. Compound 1 crystallizes in the triclinic space group P1¯ with a=12.7624(9)Å, b=15.0477(9)Å, c=16.8589(10)Å, α=94.732(2)°, β=94.308(2)°, γ=99.136(2)° and Z=2. The magnetic properties of complex 1 show a predominant ferromagnetic coupling inside the Ni4 cluster with g=2.240, J1=+0.88cm−1, J2=+0.84cm−1, J3=−0.014cm−1, J4=+1.22cm−1 and D=9.6cm−1.

Polynuclear coordination compounds: a magnetostructural study of ferromagnetically coupled Ni4O4 cubane core motif

A series of tetranuclear nickel(II) complexes [NiII4L14(H2O)4] (1), [NiII4L24(MeOH)3(H2O)] (2), [NiII4L24(H2O)4] (3), [NiII4L34(MeOH)4] (4), [NiII4L44(MeOH)4] (5) have been synthesized by employing alkoxo–phenoxo ligands. All these compounds are characterized structurally and magnetochemically. Single-crystal X-ray diffraction studies suggest all the compounds contain a [Ni4(μ3-OR)4] cubane core motif with the alkoxo oxygen atoms of the ligands and octahedrally coordinated nickel(II) atoms placed alternatively at the corners of the cube. Magnetic susceptibility studies indicate a combination of ferromagnetic and antiferromagnetic exchange interactions between the four metal centers, resulting in an ST = 4 spin ground state in all the NiII4 complexes, which is confirmed by an isothermal magnetization measurement. These data were simulated using the Heisenberg–Dirac–Van Vleck (HDvV) spin Hamiltonian H = −2J1(S1·S2 + S3·S4) − 2J2(S1·S3 + S1·S4 + S2·S3 + S2·S4), affording the parameters J1 = −3.9 cm−1, J2 = +7.55 cm−1,g = 2.06 for 1, J1 = −2.45 cm−1, J2 = +7.3 cm−1,g = 2.055 for 2 and J1 = −3.2 cm−1, J2 = +7.8 cm−1,g = 2.045 for 3 and J1 = −3.9 cm−1, J2 = +8.4 cm−1,g = 2.13 for 4. The differences in the J values result from the differences in the Ni–O–Ni angles in the Ni4O4 cores. It is worth noting that small structural variations were found for the Ni–O–Ni angles of the Ni4O4 cubane cores of compounds 2 and 3 due to the change of terminal MeOH coordination in 2 to terminal H2O coordination in 3. In spite of these slight structural variations, both compounds 2 and 3 posses a ST = 4 spin ground state. Spin ladder calculations based on the magnetostructural data clearly indicate the |J2/J1| ratio is larger than 1.5 and in accord with a nonet spin ground state.

A ferromagnetically coupled single hydroxido bridged tetranuclear nickel(II) Schiff base complex incorporating a Ni4O4 cubane core: Crystal structure and magnetic study

The new tetranuclear nickel(II) complex [Ni4(OH)(L)(HL)2(CH3OH)1.5(H2O)1.5]·9H2O (1) has been synthesised by the reaction of NiCl2·6H2O and the Schiff base ligand H3L (H3L=(CH3O)(OH)C6H3CHN–C(CH3)(CH2OH)2), prepared by the 1:1 condensation of 2-amino-2-methyl-1,3-propanediol and o-vanillin, and characterized by different physicochemical methods. Single crystal X-ray structural determination identifies a Ni4O4 cubane moiety as the central part of the complex unit. The presence of a single μ3-hydroxido bridged oxygen occupying only one vertex of the Ni4O4 cubane core is rare in Ni4O4 cubanes (ca. 5% of occurrence). Structural analysis also reveals two similar alkoxido oxygen atoms of the Schiff base coordinating the metals in two different modes; one in the μ3-bridging mode whilst the other binds in a monodentate fashion. The metal centers display distorted octahedral geometries with two different coordination environments. The magnetic properties reveal the presence of ferromagnetic nickel(II)–nickel(II) interactions in the cluster with two different exchange pathways. The magnetic data can be fitted to a Ni4O4 cubane model with g=2.058, J1=+17.2cm−1 and J2=+6.6cm−1. Isothermal magnetization measurements confirm the S=4 spin ground state. Both J values agree with previous magneto-structural correlations in doubly oxido-bridged nickel(II) complexes.

A cubane-like [Ni4O4] cluster and a chloro-bridged dinuclear copper complex incorporating a hydroxyl-rich ligand: syntheses and crystal structures

A tetranuclear cubane-like cluster [Ni4(HL)4(DMSO)2] · 2DMSO · H2O (1) and a dinuclear compound [Cu2Cl2(H2L)2] · 1.5MeOH (2) (H3L = 3-(2-hydroxy-benzylideneamino)propane-1,2-diol) have been prepared and characterized by X-ray single crystal diffraction, IR, and elemental analysis. The X-ray diffraction analysis indicated that the four metals of 1 showed a Ni4O4 cubane arrangement, and two of the six faces of the Ni4O4 cubane were capped by DMSO. Complex 1 is the first reported DMSO capped Ni4O4 cubane cluster. Complex 2 contains a u 2-Cl bridged dinuclear core with each CuII ion exhibiting pseudo square pyramidal geometry.

A unique tetranuclear cubane-like [Ni4O4] complex supported by hydroxyl-rich ligands: Synthesis, crystal structure and magnetic property

The tetranuclear cubane-like complex of the formula [Ni-4(HL1)(3)(HL2)(H2O)(CH3OH)] [CH3COO]center dot 2CH(3)OH center dot CH3CN (1) (H(3)L1=3-(2-hydroxybenzylideneamino)propane-1,2-diol; H(2)L2=3-aminoprppane-1,2-diol) has been prepared by a one-pot reaction of nickel(II) acetate, salicylaldehyde and 3-aminopropane-1,2-diol, where the H(3)L1 ligand was generated in situ via the condensation reaction between salicylaldehyde and 3-aminopropane-1,2-diol. The X-ray diffraction analysis of the complex showed a Ni4O4 cubane arrangement and the coordination environments of four Ni(II) ions are different from each other. Magnetic studies indicated ferromagnetic behavior for the complex. The magnetic data were fitted and the parameters were given as g=2.43, J(1)=15.96, and J(2)=4.116. (C) 2011 Elsevier B.V. All rights reserved.

A Tetranuclear Nickel(II) Cubane Complex with O-Vanillin Ligand

A novel cubane complex with formula of [Ni(μ3-OCH3)L(CH3OH)]4 (1) has been successfully assembled by using o-vanillin as multidentate ligand. Each Ni(II) ion is six coordinate, being bound to four oxygen atoms from four methanol molecules, one phenoxido oxygen atom and one aldehyde oxygen atom from the o-vanillin ligand. The cubane structure is characterized by a Ni4O4 core assembled from four nickel atoms and four deprotonated, bidentate o-vanillin ligands and the cubic array of alternating nickel and oxygen atoms give intracluster metal–metal separations of 3.054(1) and 3.076(1) A respectively. Preliminary magnetic studies suggest the existence of a weak antiferromagnetic coupling between the nickel ions. A novel tetranuclear nickel(II) complex with Ni4O4 cubane core has been assembled by using o-vanillin as multidentate ligand.

Crystal structures and magnetic interactions in nickel(II) dibridged complexes formed by both phenolate oxygen-azide, or methanlate groups

Tridentate Schiff base ligands L1 and L2, derived from the condensation of 2-hydroxy-3-methoxybenzaldehyde (L) with 2-aminoethanol or 2-aminobutan-1-ol, react with nickel chloride, azide, or thiocyanate to give rise to two dinuclear complexes of formulas [Ni2(L)(L1)2N3]·H2O (1), [Ni2(L2)3(μ1,1-N3)]·2H2O (2), and one tretranuclear complex [Ni2(L2)2(NCS)]2(C2H5OH)2 (3), where L1 = HOCH2CH(C2H5)NCHC6H3(O−)(OCH3) and L2 = HO(CH2)2NCHC6H3(O−)(OCH3). We have characterized these complexes by analytical, crystal structures, and variable temperature magnetic susceptibility measurements. The magnetic properties of the complexes are studied by magnetic susceptibility (χM) vs. temperature measurements. The χM T vs. T plots reveal that compounds 1, 2 and 3 are ferromagnetically coupled. Crystal of two dimers and one tetranuclear nickel (II) complexes were determined. Two dimers are azide/phenolate double bridged, and the tetranuclear is Ni4O4 cubane complex. And magnetic properties show that these compounds are ferromagnetically coupled.

Syntheses, Structures and Magnetic Properties of Heterobridged Dinuclear and Cubane‐Type Tetranuclear Complexes of Nickel(II) Derived from a Schiff Base Ligand

AbstractSyntheses, structures and magnetic properties of a heterobridged μ‐phenoxido‐μ1,1‐NCO dinickel(II) compound [NiII2(HL)3(μ‐NCO)]·2H2O (1) and a heterobridged bis(μ3‐phenoxido)bis(μ3‐alkoxido)tetranickel(II) system, [NiII4(L)2(HL)2(SeCN)2(H2O)2]·C3H7NO·4H2O (2), containing a cubane‐type NiII4O4 core, derived from the tetradentate Schiff base compartmental ligand N‐(2‐hydroxyethyl)‐3‐methoxysalicylaldimine (H2L) were described. Compounds 1 and 2 crystallize in triclinic P$\bar {1}$ and monoclinic P21/c systems, respectively. Compound 2, in which the Ni4O4 cubane core is composed of two μ3‐phenoxido and two μ3‐alkoxido moieties, represents the sole example of this type. The variable‐temperature (2–300 K) magnetic susceptibilities and magnetizations of these two compounds were measured. The interaction between the metal centres in dinuclear compound 1 is weak ferromagnetic, resulting in an ST = 2 ground state at 2 K. The overall interaction observed in 2 is weak ferromagnetic, leading to an unusual ST = 3 ground state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Polynuclear Nickel(II) Complexes: Preparation and Magnetic Properties of NiII4, NiII5, and NiII6 Species with Ligands containing O∩X∩O (X = S, Se or N) Donor Atoms

AbstractA family of bisphenol‐containing ligands with XO2 donor atoms, where X = S, Se, or N, yields [NiII]4 (1) and (2), [NiII]5 (3), and [NiII]6 (4) complexes. Complex 2, 3, and 4 have been structurally characterised by X‐ray diffraction. The compounds were characterised spectroscopically and by variable‐temperature (2−295 K), variable‐field (1, 4, and 7 T) magnetic susceptibility measurements. Analysis of the magnetic data shows predominant ferromagnetic interactions between the nickel centres (SNi = 1) indicating “high‐spin” ground states for 1, 2, and 3, whereas complex 4 shows antiferromagnetic interactions. A plot of J vs. Ni−O−Ni angles for all structurally characterised Ni4O4 cubane cores, including 2, irrespective of their symmetry, shows a large variation of J values within a small range of Ni−O−Ni angles. A simple two‐J model was found to be adequate to describe the magnetic properties of the hexanuclear complex, 4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Single‐Atom O‐Bridged Urea in a Dinickel(II) Complex together with NiII4, CuII2 and CuII4 Complexes of a Pentadentate Phenol‐Containing Schiff Base with (O,N,O,N,O)‐Donor Atoms

AbstractA pentadentate phenol‐containing ligand (H3L) with N2O3 donor atoms yields NiII2 (1), NiII4 (2), CuII2 (3) and CuII4 (4) complexes, which have been structurally characterized by X‐ray diffraction. Complex 1 contains a single‐atom O‐bridged urea. The compounds were characterized by IR, UV/Vis, mass spectrometry, electrochemistry and variable‐temperature (2−295 K) magnetic susceptibility measurements. Analysis of the susceptibility data shows antiferromagnetic interactions between the metal centers indicating a diamagnetic ground state for complexes 1, 3 and 4, whereas complex 2, a tetranuclear NiII cubane, has a complicated low‐lying magnetic structure with a non‐diamagnetic ground state. A plot of J vs. Ni−O−Ni angles for all structurally characterized Ni4O4 cubane cores, including 2, irrespective of their symmetry exhibits a large variation of J values within a small range of Ni−O−Ni angles. The electrochemistry of all complexes was investigated in detail and the ligand‐centered oxidation to a radical‐ligand is inferred from the occurrence of oxidation processes at potentials which are similar. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthesis, crystal structures and properties of six cubane-like transition metal complexes of di-2-pyridyl ketone in gem-diol form

Six cubane-type complexes comprising similar [M4O4]n+ cores [M = Mn(II), Co(II), Ni(II), Zn(II) or Cd(II)] synthesised in a facile route utilizing the gem-diol form of di-2-pyridyl ketone as a ligand have been characterised by X-ray structural analysis. Complex 1 crystallizes in the cubic space group I 3d, which is the highest symmetry documented in the cubane-like manganese compounds to date, while the other complexes crystallize in much lower crystallographic symmetries. The four metal ions and bridging alkoxo oxygen atoms are located at alternating vertices of a cube, with either pyridyl, acetate or aqua groups on the exterior of the core. Variable temperature magnetic susceptibility measurements indicate the presence of an antiferromagnetic behavior in 2 and ferromagnetic behaviors in 3 and 6. The temperature dependence of the magnetic susceptibility for 6 was fitted with J1 = 6.04 cm−1, J2 = −1.47 cm−1, and g = 2.12. The difference in sign between the J1 and J2 superexchange interactions is in good agreement with the different types of faces present in this Ni4O4 cubane core. Both 4 and 5 show similar ambient and cryogenic temperature emissions in solid state.

Structure of the First Tetranuclear Ni(II) Complex Derived from N-(2-hydroxybenzylidene)-4,6-O-ethylidene-β-d-glucopyranosylamine

Abstract In order to understand the binding nature of the glycosylamines possessing imine functionality, a novel tetranuclear Ni(II) complex of N-(2-hydroxybenzylidene)-4,6-O-ethylidene-β-d-glucopyranosylamine having twisted Ni4O4 cubane core was synthesized and structurally characterized.

Synthesis, structure, and magnetic properties of the low-symmetry tetranuclear cubane-like nickel complex [Ni4(pypentO)(pym)(mu 3-OH)2(mu- Oac)2(NCS)2(OH2)

The tetranuclear [Ni4(pypentO)(pym)(mu 3-OH)2(mu-Oac)2(NCS)2(OH2)] cubane-like complex has been prepared, and its structure and magnetic properties have been studied (pypentO and pym are the deprotonated forms of 1,5-bis[(2-pyridylmethyl)amino]pentane-3-ol and 2-pyridylmethanol, respectively). The X-ray diffraction analysis of this novel nickel complex (C61H74N14O25.5S4Ni8, monoclinic, P2(1), a = 13.9375(14) A, b = 20.6604(18) A, c = 16.6684(19) A, beta = 110.619(12) degrees, Z = 2) showed a Ni4O4 cubane arrangement of four nickel atoms, four mu 3-O bridging ligands (one pypentO, one pym, and two OH-), two syn-syn bridging acetates, and three terminal monodentate ligands (two NCS- and one OH2). In this low-symmetry elongated cubane, the four Ni-Ni long distances (3.18 A) correspond to the faces of the cube including two mu 3-OR bridges, and the two Ni-Ni short distances (2.94 A) correspond to the faces including two mu 3-OR and one acetate bridges. The temperature dependence of the magnetic susceptibility was fitted with J1 = -3.09 cm-1, J2 = 15.0 cm-1, J3 = 6.72 cm-1, and g = 2.27. The differences in sign among the J1, J2, and J3 superexchange interactions is in good agreement with the different types of faces present in this Ni4O4 cubane core. The two faces of the cube, including two mu 3-OR bridges associated with one acetate bridge, exhibit ferromagnetic interactions, while the four faces which include only mu 3-OR bridges exhibit antiferromagnetic interactions. The very small zero field splitting may be attributed to the fact that the ground state is diamagnetic. The nature of the ground state is confirmed by the good simulation of the magnetization curves at 2 and 5 K (diagonalization of the full matrix taking into account all energy levels obtained with the parameter set resulting from the fit of the susceptibility curve). The large differences in J values resulting from small differences in Ni-O-Ni angles in this Ni4O4 core of very low symmetry reflect a quite strong magnetostructural correlation.