Four-coordinate Nickel Research Articles

O, N Coordination-Mediated Nickel Single-Atom Catalysts for High-Efficiency Generation of H2O2.

Electrochemical selective two-electron oxygen reduction shows great potential for on-site electrochemical production of hydrogen peroxide (H2O2). Herein, we demonstrated the synthesis of Ni single-atom sites coordinated by three oxygen atoms and one nitrogen atom (i.e., Ni-N1O3) supported by oxidized carbon black (OCB) by pyrolyzing nickel-(pyridine-2,5-dicarboxylate) coordination complexes. Aberration-corrected scanning transmission electron microscopy (AC-STEM) combined with X-ray absorption spectroscopy (XAS) proves the presence of atomically dispersed Ni atoms attached on OCB (labeled as Ni-SACs@OCB), in which Ni single atoms are stabilized by a N, O-mediated coordination configuration. This Ni-SACs@OCB catalyst shows high H2O2 selectivity (95%) in a range of 0.2-0.7 V undergoing a two-electron oxygen reduction process, with a kinetic current density of 2.8 mA cm-2 and a mass activity of 24 A gcat.-1 at 0.65 V (vs RHE). In practice, H-cells with Ni-SACs@OCB as catalysts displayed a high H2O2 production rate of 98.5 mmol gcat.-1 h-1 with negligible current loss during testing, suggesting the high H2O2 generation efficiency and robust stability. DFT theoretical calculations revealed that Ni single-atom sites coordinated by O, N coordination exhibit advantages in oxygen adsorption and increased reactivity toward the intermediate species, *OOH, which is beneficial to high selectivity for H2O2 production. This work provides a novel N, O-mediated four-coordinate nickel single-atom catalyst as a promising candidate for practical decentralized production of H2O2.

Single-Oxidation of Ni(II) Complexes of Bidentate Fused N-Heterocyclic Carbene–Phenol Conjugates

The pro-ligands (H2LtBu)+ and (H2LOMe)+ were synthesized as chloride salts. They associate an imidazo [1,5-a] pyridinium ring and an electron-rich 2,4-(di-tert-butyl)phenol or 2-(tert-butyl)-4-methoxyphenol, respectively. The homoleptic Ni(II) complexes of H2LtBu (1) and H2LOMe (2) were prepared and structurally characterized, showing a four-coordinate nickel center with two ligands bound by one phenolate oxygen and one carbene each. Complexes 1 and 2 show two reversible oxidation waves in their cyclic voltammetry curve, at E1/21 = 0.19 V and E1/22 = 0.59 V, and E1/21 = 0.03 V and E1/22 = 0.32 V, respectively. The one-electron oxidized forms were generated and characterized by spectroscopy, while 2+ could be isolated as single crystals. They both demonstrate two remarkable NIR bands indicating radical species in CH2Cl2. The EPR parameters are 2.097, 2.023, and 1.997 (gaverage = 2.039) for 1+ and 2.030, 2.016, and 1.994 (gaverage = 2.013) for 2+. Both gaverage values are slightly higher than those reported for genuine phenoxyl radicals but far below those of Ni(III) complexes, supporting a metalloradical character of 1+ and 2+, whereby one metal d-orbital contributes to the singly occupied molecular orbital (SOMO). A very good agreement is found between DFT calculated and experimental vis–NIR and EPR data. Both metalloradical cations could be converted into Ni(III) species by addition of pyridine. The redox isomerism could be monitored by EPR spectroscopy: the [1•Py]+ species exhibits for instance the g-values 2.157, 2.136, and 2.014 (gaverage = 2.103). The Ni(III) adducts are thermally unstable and undergo reduction back to the neutral precursor at room temperature.

Mechanochemical regulation of the nickel species coordination environment on Ni/Beta catalysts to enhance propylene dimerization

Propylene oligomerization over nickel-based catalysts has been developed as an attractive route to produce high-value fine chemicals and clean fuels. In this work, the coordination environment of nickel species on high-loading Ni/Beta catalysts is successfully regulated by mechanochemistry, exhibiting a remarkable promotion in activity for propylene dimerization. The optimized ball-milled catalyst with rich four-coordinated nickel species exhibits a higher initial rate of 139.6 molC3=/(molNi·h) than the conventional impregnated catalyst (57.5 molC3=/(molNi·h)). Mechanochemistry induces a strong metal-support interaction by transforming more Ni species into the zeolite channel to generate four-coordinated Ni cations, boosting the adsorption and activation of propylene. Additionally, in-situ Fourier Transform Infrared experiments reveal that propylene dimerization complies with the Cossee-Arlman mechanism via the initial π-adsorption of propylene instead of σ-adsorption. The steric hindrance of the Ni-alkyl intermediate is critical for product selectivity, driving the dimer distribution away from thermodynamic equilibrium and resulting in preferential 1,2-insertion and 2,2-insertion products.

Theoretical identification of key structural factors for strong magnetic anisotropy in Ni(II) complexes

Single-molecule magnets (SMMs) possess a crucial property called magnetic anisotropy (MA), which has an exceedingly delicate correlation with their structures. In recent years, the study on magneto-structural correlations has emerged as a challenging area in singlemolecule science. Understanding the fundamental physical mechanisms underlying the magneto-structural correlations is essential for building excellent high-temperature SMMs. In this work, we screened various four-coordinated nickel(II) SMMs and studied several key structural factors, such as the lengths and angles of the coordination bonds that may be closely associated with MA. Following that, we developed simple molecular models to deduce the evolution trends of MA with coordination bond angles and lengths. The findings on the magneto-structural correlations stimulated our interest to further explore the crystal structure database. We revealed that the magneto-structural correlation can be well described by a logarithmic function. Guided by such a relationship, we discovered a nickel(II) complex with the strongest MA to date among the tetrahedral-coordinated ones. Our work may be helpful for the empirical synthesis of exceptional high-temperature SMMs.

Materializing efficient methanol oxidation via electron delocalization in nickel hydroxide nanoribbon

Achieving a functional and durable non-platinum group metal-based methanol oxidation catalyst is critical for a cost-effective direct methanol fuel cell. While Ni(OH)2 has been widely studied as methanol oxidation catalyst, the initial process of oxidizing Ni(OH)2 to NiOOH requires a high potential of 1.35 V vs. RHE. Such potential would be impractical since the theoretical potential of the cathodic oxygen reduction reaction is at 1.23 V. Here we show that a four-coordinated nickel atom is able to form charge-transfer orbitals through delocalization of electrons near the Fermi energy level. As such, our previously reported periodically arranged four-six-coordinated nickel hydroxide nanoribbon structure (NR-Ni(OH)2) is able to show remarkable methanol oxidation activity with an onset potential of 0.55 V vs. RHE and suggests the operability in direct methanol fuel cell configuration. Thus, this strategy offers a gateway towards the development of high performance and durable non-platinum direct methanol fuel cell.

Nickel(ii)-methyl complexes adopting unusual seesaw geometries.

We report four-coordinate nickel(ii)-methyl complexes of tris-carbene borate ligands which adopt rare seesaw geometries. Experimental and computational results suggest the structural distortion from threefold symmetry results from a combination of electronic stabilization of the singlet state, strong field donors, and constrained angles from the chelating ligand.

Syntheses of Four-Coordinate Nickel(II)-Phosphine Compounds and a Rapid Suzuki–Miyaura Cross-Coupling Reaction for Short Laboratory Sessions

[NiBr2(PPh3)2] and [NiBr2(dppe)] are prepared from nickel bromide hydrate and phosphine. These brightly colored coordination compounds are then converted into the related organometallic compounds trans-[NiBr(Mes)(PPh3)2] and [NiBr(Mes)(dppe)] (Mes = 2,4,6-Me3C6H2) by reaction with the Grignard reagent MesMgBr. Characterization of the compounds is accomplished by a combination of UV–vis and multinuclear NMR spectroscopies. [NiBr(Mes)(dppe)] is a highly active precatalyst for the Suzuki–Miyaura cross-coupling of 4′-bromoacetophenone and phenylboronic acid. The catalytic reaction is complete in as little as 15–20 min with only a 1 mol % precatalyst loading, and the reaction can be carried out in air. Results are assessed by 1H NMR spectroscopy, or the solid 4-acetylbiphenyl product can be isolated following aqueous workup and recrystallization. The experiments are flexible and accommodate a variety of laboratory schedules and student skill levels. Each experimental component has been designed to be completed within a 3 h laboratory period.

Structure and Properties of a Five-Coordinate Nickel(II) Porphyrin

Axial coordination in nickel(II) porphyrins has been thoroughly investigated and is well understood. However, isolated five-coordinate nickel(II) porphyrins are still elusive after 50 years of intense research, even though they play a crucial role as intermediates in enzymes and catalysts. Herein we present the first fully stable, thoroughly characterized five-coordinate nickel(II) porphyrin in solution and in the solid state (crystal structure). The spectroscopic properties indicate pure high-spin behavior (S = 1). There are distinct differences in the NMR, UV-vis, and redox behavior compared to those of high-spin six-coordinate [with two axial ligands, such as NiTPPF10·(py)2] and low-spin four-coordinate (NiTPPF10) nickel(II) porphyrins. The title compound, a strapped nickel(II) porphyrin, allows a direct comparison of four-, five-, and six-coordinate nickel(II) porphyrins, depending on the environment. With this reference in hand, previous results were reevaluated, for example, the switching efficiencies and thermodynamic data of nickel(II) porphyrin-based spin switches in solution.

Direct CO2 Addition to a Ni(0)–CO Species Allows the Selective Generation of a Nickel(II) Carboxylate with Expulsion of CO

Addition of CO2 to a low-valent nickel species has been explored with a newly designed acriPNP pincer ligand (acriPNP- = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide). This is a crucial step in understanding biological CO2 conversion to CO found in carbon monoxide dehydrogenase (CODH). A four-coordinate nickel(0) state was reliably accessed in the presence of a CO ligand, which can be prepared from a stepwise reduction of a cationic {(acriPNP)Ni(II)-CO}+ species. All three Ni(II), Ni(I), and Ni(0) monocarbonyl species were cleanly isolated and spectroscopically characterized. Addition of electrons to the nickel(II) species significantly alters its geometry from square planar toward tetrahedral because of the filling of the dx2-y2 orbital. Accordingly, the CO ligand position changes from equatorial to axial, ∠N-Ni-C of 176.2(2)° to 129.1(4)°, allowing opening of a CO2 binding site. Upon addition of CO2 to a nickel(0)-CO species, a nickel(II) carboxylate species with a Ni(η1-CO2-κC) moiety was formed and isolated (75%). This reaction occurs with the concomitant expulsion of CO(g). This is a unique result markedly different from our previous report involving the flexible analogous PNP ligand, which revealed the formation of multiple products including a tetrameric cluster from the reaction with CO2. Finally, the carbon dioxide conversion to CO at a single nickel center is modeled by the successful isolation of all relevant intermediates, such as Ni-CO2, Ni-COOH, and Ni-CO.

Anagostic C-H⋅⋅⋅Ni interaction and DFT calculation of bis(μ-N,O-((E)-2-((cyclohexylmethylimino)methyl)phenol)–nickel(II) complex

ABSTRACTA new four-coordinated nickel(II) complex [Ni(L)2] (1) (HL = bis(μ-N,O-((E)-2-((cyclohexylmethylimino)methyl)phenol)) has been synthesized. The molecular structure of the complex has been determined by single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic space group P-1 with lattice contents a = 13.543(3), b = 13.592(3), c = 13.766(3) Å, α = 106.31(3)°, β = 118.21(3)°, γ = 103.12(3)°, V = 1939.6(7) Å3, and Z = 3. The final R = 0.0789 and wR = 0.1265 for 6804 observed reflections with I > 2σ(I). The asymmetric unit of 1 consists of 1.5 Ni ions and three L groups. The Ni(II) ions are coordinated to O and N atoms from bidentate ligand L, showing an approximate square planar geometry. The most interesting structural features of 1 is the presence of C-H⋅⋅⋅Ni intermolecular anagostic interactions involving Ni ions in chain motifs, with H⋅⋅⋅Ni distance of 2.94 and 3.02 Ǻ, and C-H⋅⋅⋅Ni bond angle of 120° and 167°. The density functional theory (DFT) calculation of C-H⋅⋅⋅Ni anagostic interactions was consistent with the experimental results.

Nickel-Catalyzed Coupling of Carbon Dioxide with Cyclohexene Oxide by Well-Characterized Bis(N-Heterocyclic Carbene) Carbazolide Complexes

The facile synthesis, structural characterization, and catalytic studies for CO2/epoxide coupling of nickel acetates based on carbazolide-bis(NHC) (NHC = N-heterocyclic carbene) were reported. Treatment of 3,6-di-tert-butyl-1,8-bis(3-alkylimidazolium-1-yl)carbazole salt proligands (bis(R-Im-X)Cz, R = benzyl (Bn), n-butyl (nBu), methyl (Me), X = Br or I) with nickel acetate tetrahydrate in the presence of excess triethylamine generated monomeric four-coordinate nickel complexes [(bis(R-Im)Cz)Ni(OAc)] (R = Bn (3), R = nBu (4), and R = Me (5)). Single-crystal X-ray diffraction of Ni complexes 4 and 5 indicates that the bis(NHC)-carbazolide fragment behaves as a CNC-tridentate pincer ligand to coordinate the metal center, and the ancillary acetate group assumes a terminal acetate bonding mode. Catalysis for coupling of carbon dioxide with cyclohexene oxide (CHO) by these carbazolide-bis(NHC)-ligated Ni complexes was systematically examined. Experimental results displayed that cycloaddition of CHO and CO2 cata...

Synthesis and characterization of a four-coordinate nickel carbamato species (MeSiPiPr2)Ni(OC(O)NHMes) generated from the reaction of (MeSiPiPr2)Ni(NHMes) with CO2

A tridentate silyl pincer complex of nickel was employed to access a 4-coordinate nickel(II) amide complex possessing a Ni–N bond, in which a bond activation is expected at a position that is trans to the silyl donor. Using 2,4,6-trimethylaniline, a synthetically reliable nickel(II)-NHMes species (2Mes) was prepared and its reactivity toward CO2 was investigated. From an instantaneous reaction with CO2, a four-coordinate nickel(II) carbamato species (MeSiPiPr2)Ni(OC(O)NHMes) (4) was successfully generated and fully characterized by various spectroscopic techniques and X-ray crystallography. A corresponding reaction selectively occurs at a trans position to the silyl donor via a normal insertion process of CO2 into a Ni–N bond. Under aerobic conditions, the CO2 reaction of 2Mes gives a nickel(II) carbonato species {(MeSiOPPO)Ni}2-μ-CO3-κ2O,O (5) isolated as a dark orange crystal (29% yield). Its X-ray structure reveals that a dinuclear nickel complex possessing a Si–O single bond and a PO double bond and two square pyramidal nickel centers are bridged by a carbonate anion. The syntheses of nickel complexes and their characterizations by multi-nuclear NMR spectroscopy and X-ray crystallography are described herein.

Chirality at metal and helical ligand folding in optical isomers of chiral bis(naphthaldiminato)nickel(II) complexes.

Enantiopure bis[{(R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminato-κ(2)N,O}]nickel(ii) complexes {Ar = C6H5 ( or ), p-OMeC6H4 ( or ), and p-BrC6H4 ( or )} are synthesized from the reactions between (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldimine and nickel(ii) acetate. Circular-dichroism spectra and their density-functional theoretical simulation reveal the expected mirror image relationship between the enantiomeric pairs / and / in solution. CD spectra are dominated by the metal-centered Λ- or Δ-chirality of non-planar four-coordinated nickel, this latter being in turn dictated by the ligand chirality. Single crystal structure determination for and shows that there are two symmetry-independent molecules (A and B) in each asymmetric unit that give a Z' = 2 structure. Two asymmetric and chiral bidentate N^O-chelate Schiff base ligands coordinate to the nickel atom in a distorted square planar N2O2-coordination sphere. The conformational difference between the symmetry-independent molecules arises from the "up-or-down" folding of the naphthaldiminato ligand with respect to the coordination plane, which creates right- (P) or left-handed (M) helical conformations. Overall, the combination of ligand chirality, chirality at the metal and ligand folding gives rise to discrete metal helicates of preferred helicity in a selective way. Cyclic voltammograms (CV) show an oxidation wave at ca. 1.30 V for the [Ni(L)2]/[Ni(L)2](+) couple, and a reduction wave at ca. -0.35 V for the [Ni(L)2]/[Ni(L)2](-) couple in acetonitrile.

Four-coordinate nickel(II) and copper(II) complex based ONO tridentate Schiff base ligands: synthesis, molecular structure, electrochemical, linear and nonlinear properties, and computational study.

We report the synthesis, characterization, crystal structures, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations of nickel(ii) and copper(ii) complex based ONO tridentate Schiff base ligands: two mononuclear compounds, [Ni(An-ONO)(NC5H5)] (5) and [Cu(An-ONO)(4-NC5H4C(CH3)3)] (6), and two heterobimetallic species, [M(Fc-ONO)(NC5H5)] (M = Ni, 7; Cu, 8), where An-ONOH2 (3) and Fc-ONOH2 (4) are the 1 : 1 condensation products of 2-aminophenol and p-anisoylacetone and ferrocenoylacetone, respectively. These compounds were characterised by microanalysis, FT-IR and X-ray crystallography in the solid state and in solution by UV-vis and (1)H and (13)C NMR spectroscopy. The crystal structures of 3-5, 7 and 8 have been determined and show for Schiff base complexes 5, 7 and 8 a four-coordinated square-planar environment for nickel and copper ions. The electrochemical behavior of all derivatives 3-8 was investigated by cyclic voltammetry in dichloromethane, and discussed on the basis of DFT-computed electronic structures of the neutral and oxidized forms of the compounds. The second-order NLO responses of 3-8 have been determined by harmonic light scattering measurements using a 10(-2) M solution of dichloromethane and working with a 1.91 μm incident wavelength, giving rather high β1.91 values of 350 and 290 × 10(-30) esu for the mononuclear species 5 and 6, respectively. The assignment and the nature of the electronic transitions observed in the UV-vis spectra were analyzed using time-dependent (TD) DFT calculations. They are dominated by LMCT, MLCT and π-π* transitions.

2-{2,6-Bis[bis(4-fluorophenyl)methyl]-4-chlorophenylimino}-3-aryliminobutylnickel(II) bromide complexes: Synthesis, characterization, and investigation of their catalytic behavior

The series of 2-{2,6-bis[di(4-fluorophenyl)methyl]-4-chlorophenylimino}-3-aryliminobutane derivatives (L1–L5) and their nickel(II) dibromide complexes (Ni1–Ni5) were synthesized, and all organic compounds were fully characterized by the Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy and by elemental analysis, while the nickel complexes were characterized by FT-IR spectroscopy, elemental analysis, as well as by single-crystal X-ray diffraction for two representative examples, namely Ni1 and Ni4. A distorted tetrahedral geometry was observed for these four-coordinate nickel complexes. Upon the activation with either Methylaluminoxane or modified methylaluminoxane as co-catalyst, all nickel complex precatalysts showed very high activity toward ethylene polymerization with activities of up to 107 g(PE)·mol−1(Ni)·h−1, and afforded highly branched polyethylene with a bimodal distribution.

Transmethylation of a four-coordinate nickel(i) monocarbonyl species with methyl iodide

The reaction of a nickel(i) carbonyl species with CH3I revealed the formation of (PNP)NiCOCH3 which differs from its zerovalent congener.

Synthesis, spectral and antibacterial studies on Ni(II) and Zn(II) complexes involving N-furfuryl-N-isopropyldithiocarbamate (f iprdtc) and Lewis bases: X-ray structure of [Ni(f iprdtc)(NCS)(PPh3)

[Ni(fiprdtc)2] (1), [Ni(fiprdtc)(PPh3)(NCS)] (2), [Ni(fiprdtc)(PPh3)2]ClO4 (3), [Zn(fiprdtc)2] (4), [Zn(fiprdtc)2(1,10-phen)] (5) and [Zn(fiprdtc)2(2,2′-bipy)] (6) (f iprdtc=N-furfuryl-N-isopropyldithio- carbamate, 1,10-phen=1,10-phenanthroline and 2,2′-bipy=2,2′-bipyridine) complexes were prepared and characterized by elemental analysis, electronic, IR and NMR spectra and the structure of 2 was determined by single-crystal X-ray crystallography. UV–Vis spectral data of 1–3 are consistent with the formation of square planar complexes. IR spectra of the complexes show the contribution of the thioureide form to the structure. A single-crystal X-ray structural analysis of 2 proved four-coordinated nickel in a distorted square planar arrangement with a S2PN donor set. Significant asymmetry in Ni–S bond distances was observed in [Ni‒ S1=2.1655(8); Ni‒ S2=2.2120(8) Å]. This observation clearly supports the less effective trans of SCN− over PPh3. The observed shielding in N13CS2 chemical shifts of heteroleptic nickel complexes 2 and 3 when compared with homoleptic nickel complex 1 indicates the effect of PPh3 on the mesomeric drift of electron density toward nickel through the thioureide C‒ N bond. The N13CS2 chemical shift of 5 and 6 are additionally deshielded compared with 4 owing to the increase in coordination number. Complexes were screened for in vitro antibacterial activity and significant activity has been found.

C–Cl bond activation of ortho-chlorinated benzamides by nickel and cobalt compounds supported with phosphine ligands

The C-Cl bonds of ortho-chlorinated benzamides Cl-ortho-C(6)H(4)C(=O)NHR (R = Me (1), nBu (2), Ph (3), (4-Me)Ph (4) and (4-Cl)Ph (5)) were successfully activated by tetrakis(trimethylphosphine)nickel(0) and tetrakis(trimethylphosphine)cobalt(0). The four-coordinate nickel(II) chloride complexes trans-[(C(6)H(4)C([double bond, length as m-dash]O)NHR)Ni(PMe(3))(2)Cl] (R = Me (6), nBu (7), Ph (8) and (4-Me)Ph (9)) as C-Cl bond activation products were obtained without coordination of the amide groups. In the case of 2, the ionic penta-coordinate cobalt(II) chloride [(C(6)H(4)C(=O)NHnBu)Co(PMe(3))(3)]Cl (10) with the [C(phenyl), O(amide)]-chelate coordination as the C-Cl bond activation product was isolated. Under similar reaction conditions, for the benzamides 3-5, hexa-coordinate bis-chelate cobalt(III) complexes (C(6)H(4)C(=O)NHR)Co(Cl-ortho-C(6)H(4)C(=O)NR)(PMe(3))(2) (11-13) were obtained via the reaction with [Co(PMe(3))(4)]. Complexes 11-13 have both a five-membered [C,N]-coordinate chelate ring and a four-membered [N,O]-coordinate chelate ring with two trimethyphosphine ligands in the axial positions. Phosphonium salts [Me(3)P(+)-ortho-C(6)H(4)C(=O)NHR]Cl(-) (R = Ph (14) and (4-Me)Ph (15)) were isolated by reaction of complexes 8 and 9 as a starting material under 1 bar of CO at room temperature. The crystal and molecular structures of complexes 6, 7 and 9-12 were determined by single-crystal X-ray diffraction.

PH Values Dependent Helicity of 1D Homochiral Helical Chains

The reaction of a racemic four-coordinated nickel(II) complex [Ni(α-rac-L)](ClO4)2 with l-Leu− in acetonitrile/water under basic conditions gave two six-coordinated diastereomers of {[Ni(SS-L)(l-Leu)](ClO4)}n (Δ-1) and {[Ni(RR-L)(l-Leu)](ClO4)}n (a-2). While the reaction of [Ni(α-rac-L)](ClO4)2 with d-Leu− in acetonitrile/water under basic condition generated two six-coordinated diastereomers of {[Ni(RR-L)(d-Leu)](ClO4)}n (Λ-1) and {[Ni(SS-L)(d-Leu)](ClO4)}n (b-2) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, Leu− = leucine anion). Δ-1 and Λ-1 belong to supramolecular stereoisomers in which the [Ni(SS-L)(l-Leu)]+ and [Ni(RR-L)(d-Leu)]+ monomers are linked through the intermolecular hydrogen bonding interactions to form 1D homochiral right- and left-handed helical chains, respectively, while the connections of [{Ni(RR-L)}(l-Leu)]+/[{Ni(SS-L)}(d-Leu)]+ in a-2/b-2 through similar intermolecular hydrogen bonding interactions give 1D zigzag chains instead of 1D helical chains. In contrast, ...

Structural variations of nickel complexes in NiS4 and NiS2PN coordination environments: spectral and single-crystal X-ray structural studies on bis(4-methylpiperidinecarbodithioato-S,S′)nickel(II) and (4-methylpiperidinecarbodithioato-S,S′)(thiocyanato-N)(triphenylphosphine)nickel(II)

Abstract[Ni(4-mpipdtc) 2 ] and [Ni(4-mpipdtc)(PPh 3 )(NCS)] (4-mpipdtc = 4-methylpiperidinecarbodithioate anion) have been characterized by electronic, IR, and NMR spectroscopy, single crystal X-ray analysis, and cyclic voltammetry. IR spectra of the complexes show the contribution of the thioureide form to the structures. 1 H NMR spectra show the deshielding of α-CH 2 protons on complexation. 13 C NMR spectra shows interesting differences between the N 13 CS 2 carbon signals of the parent complex [Ni(4-mpipdtc) 2 ] and the mixed ligand complex [Ni(4-mpipdtc)(PPh 3 )(NCS)]. The N 13 CS 2 carbon signal for [Ni(4-mpipdtc)(PPh 3 )(NCS)] is observed at 204.85 ppm with an upfield shift of about 3.8 ppm compared with that found in [Ni(4-mpipdtc) 2 ] (201.06 ppm). The observed shielding in [Ni(4-mpipdtc)(PPh 3 )(NCS)] indicates the effect of PPh 3 on the mesomeric drift of electron density toward nickel through the thioureide C-N bond. Single crystal X-ray analysis of [Ni(4-mpipdtc) 2 ] and [Ni(4-mpipdtc)(PPh 3 )(NCS)] confirms the presence of four-coordinated nickel in a distorted square-planar arrangement with the NiS 4 and NiS 2 PN chromophores, respectively. The C-N (thioureide) bond lengths of [Ni(4-mpipdtc)(PPh 3 )(NCS)] are shorter than those found in [Ni(4-mpipdtc) 2 ], because of the presence of the π-acid (triphenylphosphine) in [Ni(4-mpipdtc)(PPh 3 )(NCS)]. Significant asymmetry in Ni-S bond distances was observed in Ni(4-mpipdtc)(PPh 3 )(NCS)] (2.162(2) and 2.211(2) A). This observation clearly supports the less effective trans effect of SCN - over PPh 3 . The piperidine ring in the dithiocarbamate fragment is in the normal chair conformation.Graphical Abstract[IMAGE]