Designing a Phenalenyl-Based Dinuclear Ni(II) Complex: An Electrocatalyst with Two Single Ni Sites for the Oxygen Evolution Reaction (OER)

A new dinuclear Ni(II) complex 1, [Ni2II(dtbh-PLY)2], is synthesized from 9-(2-(3,6-di-tert-butyl-2-hydroxybenzylidene)hydrazineyl)-1H-phenalen-1-one, dtbh-PLYH2 ligand, and structurally characterized by various analytical tools including the single-crystal X-ray diffraction (SCXRD) technique. In the solid state, both Ni(II) metal centers in complex 1 exist in a distorted square planar geometry and display the presence of rare Ni···H-C anagostic interactions to form a one-dimensional (1-D) linear motif in the supramolecular array. Complex 1 is further stabilized in the solid state by π-π-stacking interactions between the highly delocalized phenalenyl rings. The redox features of complex 1 have been analyzed by the cyclic voltammetry (CV) technique in solution as well as in the solid state, revealing the crucial involvement of both the Ni(II) metal centers for undergoing quasi-reversible oxidation reactions on the application of an anodic sweep. A complex 1-modified glassy carbon electrode, GC-1, is employed as an electrocatalyst for oxygen evolution reaction (OER) in 1.0 M KOH, giving an OER onset at 1.45 V, and very low OER overpotential, 300 mV vs the reversible hydrogen electrode (RHE) to reach 10 mA cm-2 current density. Furthermore, GC-1 displayed fast OER kinetics with a Tafel slope of 40 mV dec-1, a significantly lower Tafel slope value than those of previously reported molecular Ni(II) catalysts. In situ electrochemical experiments and postoperational UV-vis, Fourier transform infrared (FT-IR), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) studies were performed to analyze the stability of the molecular nature of complex 1 and to gain reasonable insights into the true OER catalyst.

Phenoxido mediated antiferromagnetic and azide mediated ferromagnetic coupling in two dinuclear ferromagnetic nickel(ii) complexes with isomeric Schiff bases: a theoretical insight on the pathway of magnetic interaction

Two relatively rare mixed phenoxo and azide bridged dinuclear nickel(ii) complexes have been discussed. Both complexes show strong intermolecular hydrogen bonding interactions and exhibit ferromagnetic exchange coupling.

Both end-on and end-to-end azide bridged tetranuclear ferromagnetic nickel(ii) Schiff base complexes

Variable temperature magnetic measurement of a tetranuclear nickel(ii) complex, consisting of two pseudo-dinuclear entities, indicates the presence of intra- and inter-dinuclear ferromagnetic interactions, corroborated by DFT calculations.

Mono- and di-nuclear nickel(ii) complexes derived from NNO donor ligands: syntheses, crystal structures and magnetic studies of dinuclear analogues

Ferromagnetic interaction in dinickel(ii) complexes, supported by DFT calculations, is reported. Bis(phenoxo)-bridged compound is only the second example of ferromagnetically coupled system.

Triple-bridged ferromagnetic nickel(II) complexes: a combined experimental and theoretical DFT study on stabilization and magnetic coupling

Two dinuclear [Ni2L2(o-(NO2)C6H4COO)2(H2O)] (1), [Ni2L2(p-(NO2)C6H4COO)2(H2O)]·0.5CH3OH (2) complexes and one trinuclear [Ni3L2(p-(NO2)C6H4COO)4]·C2H5OH (3) Ni(II) complex have been synthesized using a tridentate Schiff base ligand, 1-[(3-dimethylamino-propylimino)-methyl]-naphthalen-2-ol (HL) along with ortho- and para-nitro benzoate as co-ligands. All these three (1-3) complexes have been characterized by spectral analysis, X-ray crystallography and variable temperature magnetic susceptibility measurements. The structural analyses reveal that complexes 1 and 2 are dinuclear in which two μ2-phenoxido and a water molecule bridge the two Ni(ii) centers to make the complexes face sharing bioctahedra. Complex 3 is a linear triple bridged (phenoxido and carboxylato) trinuclear Ni(II) complex. Variable-temperature magnetic susceptibility studies indicate the presence of ferromagnetic exchange coupling in complexes 1-3 with J values of 25.4, 28.1 and 6.2 cm(-1) respectively. Theoretically obtained J values of 21.4 cm(-1) (for 1), 22.0 cm(-1) (for 2) and 9.3 cm(-1) (for 3) corroborate very well the experimental results. DFT calculation also shows that stronger H-bonding interactions present in the case of carboxylate based coligands stabilise the triple oxido-bridged complexes.

Syntheses, crystal structures and magnetic properties of a series of μ-phenoxo-μ1,1-carboxylato-μ1,3-carboxylato trinickel(II) compounds

The work in this report describes the syntheses, characterization, crystal structures and magnetic properties of eight linear trinickel(ii) compounds of the composition [Ni(II)3(L(sal-pyr))2(propionate)4] (), [Ni(II)3(L(sal-pyr))2(benzoate)4]·CH3CN (), [Ni(II)3(L(sal-pip))2(acetate)4]·2CH3CN (), [Ni(II)3(L(sal-pip))2(propionate)4] (), [Ni(II)3(L(sal-pip))2(benzoate)4]·CH2Cl2 (), [Ni(II)3(L(sal-mor))2(propionate)4] (), [Ni(II)3(L(sal-mor))2(benzoate)4]·3CH2Cl2 () and [Ni(II)3(L(sal-mor))2(o-Cl-benzoate)4]·2CH3CN·2H2O (), where HL(sal-pyr), HL(sal-pip) and HL(sal-mor) are the 1 : 1 condensation products of salicylaldehyde and 1-(2-aminoethyl)-pyrrolidine, 1-(2-aminoethyl)-piperidine and 4-(2-aminoethyl)-morpholine, respectively. One-half of the trinuclear core in each complex is symmetry related to the second part due to the presence of an inversion centre on the central metal ion and so the terminal nickelcentral nickelterminal nickel angle is 180°. The terminal and central nickel(ii) ions are triply bridged by a phenoxo, a μ1,1-carboxylato and a μ1,3-carboxylato moiety. The μ1,1-carboxylato also acts as a chelating ligand for the terminal metal ion. Both the variable-temperature (2-300 K) susceptibilities at a fixed field strength of 0.1 T and variable-field (up to 7 T) magnetization at different fixed temperatures (2-10 K) were recorded. The magnetic data indicate the ferromagnetic interaction in all the cases with J (Ĥ = -2Jij∑SiSj) values ranging between 2.37 and 3.89 cm(-1) and the single-ion zero-field parameter (D) ranging between 7.21 and 8.94 cm(-1). Satisfactorily simulation of both the χMT vs. T and M vs. H data has been obtained. Comparison of the structures and magnetic properties of compounds with those of the previously published related systems reveals some interesting aspects.

Anion controlled structural and magnetic diversity in unusual mixed-bridged polynuclear NiII complexes with a versatile bis(2-methoxy phenol)diamine hexadentate ligand. An experimental and theoretical magneto-structural study

Six new polynuclear Ni^II complexes with uncommon structures have been magneto-structural studied.

Bis[μ-2-({2-[2-(2-chlorophenoxy)-1-oxidoethylidene]hydrazinylidene}methyl)phenolato]bis[pyridinecopper(II)] methanol disolvate

In the title compound, [Cu2(C15H11ClN2O3)2(C5H5N)2]·2CH3OH, the coordination geometry of the metal centre can be described as square pyramidal. Pairs of pentacoordinated metal centres are bridged by symmetry-related phenolate O atoms about the inversion centre at (½, 0, ½), resulting in a binuclear metal cluster via edge-sharing.

A rare phenoxido/acetato/azido bridged trinuclear and an unprecedented phenoxido/azido bridged one-dimensional polynuclear nickel(II) complexes: synthesis, crystal structure, and magnetic properties with theoretical investigations on the exchange mechanism

The reaction of a tridentate Schiff base ligand HL (2-[(3-dimethylaminopropylimino)-methyl]-phenol) with Ni(II) acetate or perchlorate salts in the presence of azide as coligand has led to two new Ni(II) complexes of formulas [Ni(3)L(2)(OAc)(2)(μ(1,1)-N(3))(2)(H(2)O)(2)]·2H(2)O (1) and [Ni(2)L(2)(μ(1,1)-N(3))(μ(1,3)-N(3))](n)(2). Single crystal X-ray structures show that complex 1 is a linear trinuclear Ni(II) compound containing a μ(2)-phenoxido, an end-on (EO) azido and a syn-syn acetato bridge between the terminal and the central Ni(II) ions. Complex 2 can be viewed as a one-dimensional (1D) chain in which the triply bridged (di-μ(2)-phenoxido and EO azido) dimeric Ni(2) units are linked to each other in a zigzag pattern by a single end-to-end (EE) azido bridge. Variable-temperature magnetic susceptibility studies indicate the presence of moderate ferromagnetic exchange coupling in complex 1 with J value of 16.51(6) cm(-1). The magnetic behavior of 2 can be fitted in an alternating ferro- and antiferromagnetic model [J(FM) = +34.2(2.8) cm(-1) and J(AF) = -21.6(1.1) cm(-1)] corresponding to the triple bridged dinuclear core and EE azido bridge respectively. Density functional theory (DFT) calculations were performed to corroborate the magnetic results of 1 and 2. The contributions of the different bridges toward magnetic interactions in both compounds have also been calculated.

The importance of an additional water bridge in making the exchange coupling of bis(μ-phenoxo) dinickel(II) complexes ferromagnetic

Two new nickel(II) complexes [Ni(2)L(2)(PhCOO)(2)(H(2)O)] (1), [Ni(2)L(2)(PhCH(2)COO)(2)(H(2)O)] (2) have been synthesized using a tridentate Schiff base ligand, HL (2-[(3-dimethylamino-propylimino)-methyl]-phenol) and the carboxylate monoanions, benzoate and phenylacetate, respectively. The complexes have been characterized by spectral analysis, variable temperature magnetic susceptibility measurement and crystal structure analysis. The structural analyses reveal that both complexes are dinuclear in which the distorted octahedral Ni(2+) ions share a face, bridged by one water molecule and two μ(2)-phenoxo oxygen atoms. A monodentate benzoate or phenylacetate anion and two nitrogen atoms of the chelating deprotonated Schiff base (L) complete the hexa-coordination around the metal ion. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complexes 1 and 2 with J values of 11.1(2) and 10.9(2) cm(-1) respectively. An attempt has been made to rationalize the observed magneto-structural behavior considering the importance of the additional water bridge in the present two complexes and also in other similar species.

Isolation, characterization, and computational studies of the novel [Mo3(mu3-Br)2(mu-Br)3Br6]2- cluster anion

The novel trimolybdenum cluster [Mo(3)(mu(3)-Br)(2)(mu-Br)(3)Br(6)](2-) (1, {Mo(3)}(9+), 9 d-electrons) has been isolated from the reaction of [Mo(CO)(6)] with 1,2-C(2)H(4)Br(2) in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)(4)N(+) (1), Et(4)N(+), Et(3)BzN(+)), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)(4)N(+) salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) A, b = 11.8638(11) A, c = 22.521(2) A, alpha = 90 deg, beta = 109.348(4) deg, gamma = 90 deg, V = 5061.3(9) A(3), Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (mu(eff), 1.55 mu(B), r.t.) is lower than the spin-only value (1.73 mu(B)) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm(-1)). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided.