N4O2 Coordination Sphere Research Articles

Toward 68Ga and 64Cu Positron Emission Tomography Probes: Is H2dedpa-N,N'-pram the Missing Link for dedpa Conjugation?

H2dedpa-N,N'-pram (H2L1), a new chelator derived from the hexadentate ligand 1,2-bis[[(6-carboxypyridin-2-yl)methyl]amino]ethane (H2dedpa), which incorporates 3-propylamine chains anchored to the secondary amines of the ethylenediamine core of the latter, has emerged as a very promising scaffold for preparing 68Ga- and 64Cu-based positron emission tomography probes. This new platform is cost-effective and easy to prepare, and the two pendant primary amines make it versatile for the preparation of bifunctional chelators by conjugation and/or click chemistry. Reported herein, we have also included the related H2dedpa-N,N'-prpta (H2L2) platform as a simple structural model for its conjugated systems. X-ray crystallography confirmed that the N4O2 coordination sphere provided by the dedpa2- core is maintained at both Ga(III) and Cu(II). The complex formation equilibria were deeply investigated by a thorough multitechnique approach with potentiometric, NMR spectrometric, and UV-vis spectrophotometric titrations, revealing effective chelation. The thermodynamic stability of the Ga(III) complexes at physiological relevant conditions is slightly higher than that of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), the common and clinically approved chelator used in the clinic [pGa = 19.5 (dedpa-N,N'-pram) and 20.8 (dedpa-N,N'-prpta) versus 18.5 (DOTA) at identical conditions], and significantly higher for the Cu(II) complexes [pCu = 21.96 (dedpa-N,N'-pram) and 22.8 (dedpa-N,N'-prpta) versus 16.2 (DOTA)], which are even more stable than that of the parent ligand dedpa2- (pCu = 18.5) and that of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) (pCu = 18.5). This high stability found for Cu(II) complexes is related to the conversion of the secondary amines of the ethylenediamine core of dedpa2- into tertiary amines, whereby the architecture of the new H2L1 chelator is doubly optimal in the case of this metal ion: high accessibility of the primary amine groups and their incorporation via the secondary amines, which contributes to a significant increase in the stability of the metal complex. Quantitative labeling of both chelators with both radionuclides ([68Ga]Ga3+ and [64Cu]Cu2+) was observed within 15 min at room temperature with concentrations as low as 10-5 M. Furthermore, serum stability studies confirmed a high radiochemical in vitro stability of all systems and therefore confirmed H2L1 as a promising and versatile chelator for further radiopharmaceutical in vivo studies.

A Comparative Study of Nitrate and Iodide of the Spin-Variable Iron(III) Cation with the N4O2 Coordination Sphere by Mössbauer Spectroscopy

A Comparative Study of Nitrate and Iodide of the Spin-Variable Iron(III) Cation with the N4O2 Coordination Sphere by Mössbauer Spectroscopy

Experimental and theoretical evaluation of N-pyridoxal-salicylic acid hydrazide derived copper(II) complex with 2-methylimidazole

This article deals with the experimental and theoretical evaluations of N-pyridoxal-salicylic acid hydrazide (H2pd-sah) 1 and its mixed-ligand copper(II) complex with 2-methylimidazole, [Cu(pd-sah)(MeImdH)] 2. The compounds were characterized based on spectral (UV/Vis. IR) methods, powder-XRD, elemental analysis, and molar conductivity measurements. Both compounds' molecular structure and charge analysis were computed through B3LYP with 6-311 G (d, p) and LANL2DZ basic set using the Gaussian 09 W program package. The time-dependent density functional theory (TD-DFT) approach is used in gas-phase electronic transitions of 2 using the LANL2DZ basis set. Also, the computed UV-Vis based upon TD-DFT results and IR spectra were simulated for comparison with the experimental ones. The molecular structure based on theoretical investigation reveals that compound 2 adopts a distorted square planer N2O2 coordination sphere around the Cu(II). The ONO donor atoms of hydrazone moiety and one nitrogen of 2-methylimidazole constitute the N2O2 basal plane. Moreover, the in-vitro antioxidant activity was evaluated by DPPH assay in both compounds. In addition, Molecular docking studies were performed to predict the binding interaction between compound 2 and the Human Serum Albumin HSA (PDB ID: 1H9Z). Communicated by Ramaswamy H. Sarma

Modulation of the magnetic and photophysical properties in 3d-4f and 4f-4f' heterobimetallic complexes involving a tetrathiafulvalene-based ligand.

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1H-benzimidazol-2-yl)-pyridine ligand (L), 1 equivalent of Ln(hfac)3·2H2O/Dy(tta)3·2H2O (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta- = 2-thenoyltrifluoroacetonate) and M(hfac)2·2H2O leads to the formation of heteroleptic 3d-4f dinuclear complexes of formula [MLn(hfac)5(L)]n (M(II) = Cd, Zn, Co, Mn, Ni and Ln(III) = Dy, Yb, Nd) and [ZnDy(tta)2(hfac)3(L)]·(CH2Cl2). Their X-ray structures reveal that the two coordination sites are occupied by one Ln(III) ion and one M(II) transition metal respectively. The M(II) ions are coordinated to the benzoimidazolylpyridine (bzip) moiety in a N2O4 coordination sphere, while the Ln(III) ions are coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety in a N3O6 surrounding. When Dy(III) ion is used a field-induced Single-Molecule Magnet (SMM) behavior is detected with a magnetic relaxation time slightly dependent to the nature of the vicinal divalent transition metal. On the other hand, when the Yb(III) is used, intense, moderated or quenched 2F5/2 → 2F7/2 NIR luminescence is observed when the Yb(III) ion is respectively associated with the Zn(II), Mn(II) and Ni(II)/Co(II) ion. The emission intensity can be modulated in function of the metal-to-ligand charge transfer and d-d transition intensities. The replacement of the divalent transition metal by a trivalent lanthanide leads to the formation of heteroleptic 4f-4f' dinuclear complexes of formula [Ln2-xLn'x(hfac)6(L)]·a(CH2Cl2)·b(C6H14) and [Dy1.11Nd0.89(tta)3(hfac)3(L)]. The coordination selectivity is based on the radius. Among the 4f-4f' series, the Dy(III) derivatives displayed such ion in N2O6 eight-coordinated sphere allowing the observation of SMM behavior. The three compounds [Dy1.21Nd0.79(hfac)6(L)]·2(CH2Cl2)·(C6H14), [Yb1.04Nd0.96(hfac)6(L)] and [YbPr(hfac)6(L)] displayed respectively Nd(III), modarated Yb(III) and intense Yb(III) NIR emissions.

Sterically Encumbered Coordination Sites. Iron(II) Complexes of Jäger‐type ligands with a Terphenyl Backbone

AbstractA Schiff base‐like ligand H2LTerPh featuring a para‐terphenyl backbone was synthesized and converted in two steps to an octahedral iron(II) coordination polymer with 1,2‐bis‐(4‐pyridyl)‐ethylene as bridging ligand. Single crystal X‐ray structure analysis was possible for the free ligand and the two octahedral iron(II) complexes. The Schiff base‐like ligand features a [N2O2]2− coordination sphere for the metal center and the para‐terphenyl backbone introduces intrinsic steric constraint. Characterization of the coordination polymer with an N4O2 coordination sphere around the iron center via magnetic measurements (SQUID) and room temperature Mössbauer spectroscopy revealed HS character in the entire temperature range investigated. Structure modelling with DFT calculations supports the findings, but support also the possibility of spin crossover in solution.

Spectral studies and crystal structures of molybdenum(VI) complexes containing pyridine or picoline as auxiliary ligands: interaction energy calculations and free radical scavenging studies

Three cis-MoO2 complexes [MoO2(CAB)(py)] (1), [MoO2(CAB)(3-pic)] (2) and [MoO2(CAB)(4-pic)] (3) which vary in the nature of the heterocyclic bases in the auxiliary coordination site derived from an ONO donor aroylhydrazone (H2CAB) have been synthesized and characterized by various physicochemical methods. The single-crystal X-ray diffraction studies reveal that the complexes adopt a distorted octahedral N2O4 coordination sphere around the Mo(VI) center in which the ONO donor atoms of hydrazone moiety and one oxido oxygen constitute the NO3 basal plane and the axial position by the other oxido oxygen and nitrogen atom of coordinated pyridine molecule in [MoO2(CAB)(py)] (1) or picoline molecule in [MoO2(CAB)(3-pic)] (2) and [MoO2(CAB)(4-pic)] (3). The hydrogen bonding interaction generates a two-dimensional supramolecular sheet-like architecture in [MoO2(CAB)(py)] (1) and [MoO2(CAB)(3-pic)] (2), whereas a three-dimensional network was observed in [MoO2(CAB)(4-pic)] (3). The interaction energy calculations reveal that the dispersion energy component dominates over other components and [MoO2(CAB)(3-pic)] (2) is found to be energetically more stable. Furthermore, the aroylhydrazone shows free radical scavenging activity, whereas the complexes are inactive.

Kinetic Trapping Effects in Amphiphilic Iron(II) Spin Crossover Compounds.

In this work, the synthesis of four new iron complexes with a Schiff base-like amphiphilic equatorial ligand (L) and dimethylaminopyridine (dmap) or 4,4'-bipyridine (bipy) as axial ligands is reported. Three of the complexes ([FeL(dmap)2] 1, [FeL(dmap)(MeOH)0.5]·MeOH 2, and [FeL(bipy)] n 3 have an iron(II) center, and two of those with an N4O2 coordination sphere (1 and 3) are spin crossover active. Both exhibit a thermal hysteresis (10 K with T1/2 = 131 K for 3 and 23 K with T1/2 = 161 K for 1) where the width depends on the velocity used for the measurement. Additionally, in both cases, the high spin state is trapped by rapid cooling, and a TTIESST was determined to be 121 K (1) and 101 K (3). Single crystals suitable for X-ray structure analysis were obtained for the three different complexes with dmap as axial ligand (1S, 2, and [μ-O-{FeL}2(dmap)] 4). The complex 1S has two dmap molecules in axial position, while the other two structures were obtained for a complex where a dmap ligand is exchanged by methanol and one where the iron(II) center is oxidized to iron(III) to form a dinuclear μ-O-complex. All three complexes were obtained under similar reaction conditions in the presence/absence of oxygen, and all three structures show the formation of lipid layer-like arrangements in the packing.

π–π interaction leading to an inversion-symmetric complex pair of Λ- and Δ-bis[N-2-(R-pyridyl)-2-oxo-1-naphthaldiminato-κ2N,O]zinc(II)

The Schiff base ligands N-2-(R-pyridyl)-2-hydroxy-1-naphthaldimine (HL) react with the zinc(II) nitrate or acetate to give the Λ- and Δ-bis[N-2-(R-pyridyl)-2-oxo-1-naphthaldiminato-κ2N,O]zinc(II), [Zn(L)2] {R = H (1), 4/6-CH3 (2/3)}. EI-mass spectra show the molecular ion peaks at 558 (1) and 586 (2 or 3). Molecular structure determination for 2·0.5CH2Cl2 crystal reveals that two molecules of the N^O-chelate ligands form a tetrahedral N2O2-coordination sphere around the zinc atom, in which one of the pyridyl-N atom is located towards the metal atom at a close contact ([Zn1…N2] = 2.674 Å). Packing analysis explores that one of the Zn-chelate ring metallacycles forms a reciprocal and rather strong π–π interaction (Cg⋯g = 3.517 Å) with the pyridyl ring of an adjacent molecule and vice versa, and results in an inversion-symmetric complex pair with opposite Λ- and Δ-configurations at the metal centre. The packing analysis is further supported by quantitative analysis of intermolecular interactions with the Hirshfeld surface. The optimized structure and excitation state properties by DFT/TDDFT support the solid state molecular structure and electronic spectra in solution, respectively.

Spontaneous resolution of a Δ/Λ-chiral-at-metal pseudo-tetrahedral Schiff-base zinc complex to a racemic conglomerate with C–H⋯O organized 41- and 43-helices

Weak supramolecular interactions can be decisive!

Intermolecular interaction studies of complexes with N4O2 coordination sphere

Intermolecular interaction studies of complexes with N₄O₂ coordination sphere

Crystal structures, DFT calculations, and Hirshfeld surface analyses of two new copper(II) and nickel(II) Schiff base complexes derived from meso-1,2-diphenyl-1,2-ethylenediamine

Two new Ni(II) and Cu(II) complexes of a tetradentate Schiff base ligand (1 and 2, respectively), derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with 2-hydroxy-6-methoxy benzaldehyde, were synthesized and characterized by IR, UV–Vis, 1H NMR spectroscopy, and X-Ray crystallography. The central metal ions in both complexes are coordinated via the N2O2 coordination sphere of the ligand with square-planar geometry. DFT results revealed that the MN and MO interactions (M = Ni, Cu) are weaker than the typical covalent single bond indicating that ionic and electrostatic interactions are dominated in MN and MO bonds. Hirshfeld surface (HS) analyses of the studied structures 1 and 2 have been performed. The study using 3D HSs and 2D fingerprint plots (FPs) highlighted the dominant contacts H⋯H, C⋯H/H⋯C and O⋯H/H⋯O in both structures, and H⋯Cl in 2. The molecular assemblies held by C⋯O/O⋯C (in 1) and C⋯C (in 1 and 2) type dipole–dipole interactions are also found in the crystal packing contributing towards stability. The significant contributions arising from the mentioned interactions in crystal packing are also revealed from the Hirshfeld surface FPs showing a major contribution to total HS area for the H⋯H contacts for both structures.

The silver(I) nitrate complex of the ligand N-(pyridin-2-ylmeth-yl)pyrazine-2-carboxamide: a metal-organic framework (MOF) structure.

The reaction of silver(I) nitrate with the mono-substituted pyrazine carboxamide ligand, N-(pyridin-2-ylmeth-yl)pyrazine-2-carboxamide (L), led to the formation of the title compound with a metal-organic framework (MOF) structure, [Ag(C11H10N4O)(NO3)] n , poly[μ-nitrato-[μ-N-(pyridin-2-ylmethyl-κN)pyrazine-2-carboxamide-κN4]silver(I)]. The silver(I) atom is coordinated by a pyrazine N atom, a pyridine N atom, and two O atoms of two symmetry-related nitrate anions. It has a fourfold N2O2 coordination sphere, which can be described as distorted trigonal-pyramidal. The ligands are bridged by the silver atoms forming -Ag-L-Ag-L- zigzag chains along the a-axis direction. The chains are arranged in pairs related by a twofold screw axis. They are linked via the nitrate anions, which bridge the silver(I) atoms in a μ2 fashion, forming the MOF structure. Within the framework there are N-H⋯O and C-H⋯O hydrogen bonds present.

μ2-Oxido bridged dinuclear vanadium(V) complex: Synthesis and characterization

μ2-Oxido bridged dinuclear vanadium(V) Schiff base complex with the general formula [VO2(L)]2·2CH3OH was synthesized and characterized. The X-ray results show the complex is dinuclear with two μ-O bridging ions, and the vanadium centers have an octahedral N2O4 coordination sphere. The tridentate Schiff base ligand L coordinated to vanadium(V) center as a monoanion in the basal plane. The basal plane is completed by one of the μ-O bridges. The other μ-O bridge coordinated to vanadium(V) center as apical direction. The two oxido bridged connected the two Vv centers together with the Vv-O-Vv angle of 101.21(6)°, the VO distances of 1.70(6) and 2.31(7) Å and the V⋯V separation of 3.113(5) Å. Finally, the complex was calcinated at 600 °C for 3 h. The FT-IR spectrum of the product shows the formation of the V2O5 particles.

Syntheses, structural characterization and spectroscopic studies of cadmium(II)-metal(II) cyanide complexes with 4-(2-aminoethyl)pyridine

Three new cadmium(II)-metal(II) cyanide complexes, [Cd(4aepy)2(H2O)2][Ni(CN)4] (1), [Cd(4aepy)2(H2O)2][Pd(CN)4] (2) and [Cd(4aepy)2(H2O)2][Pt(CN)4] (3) [4aepy = 4-(2-aminoethyl)pyridine], have been synthesized and characterized by elemental, thermal, FT-IR and Raman spectral analyses. The crystal structures of 1 and 2 have been determined by single crystal X-ray diffraction technique, in which they crystallize in the monoclinic system and C2/c space group. The M(II) [M(II) = Ni(II), Pd(II) and Pt(II)] ions are coordinated with the carbon atoms of the four cyanide groups in the square planar geometries and the [M(CN)4]2− ions act as counter ions. The Cd(II) ions display an N4O2 coordination sphere with a distorted octahedral geometry, the nitrogen donors belonging to four molecules of the organic 4aepy that act as unidentate ligands and two oxygen atoms from aqua ligands. 3D supramolecular structures of 1 and 2 were occurred by M⋯π and hydrogen bonding (NH⋯N and OH⋯N) interactions. Vibrational assignments of all the observed bands were given and the spectral properties were also supported the crystal structures of the complexes. A possible decompositions of the complexes were investigated in the temperature range 30–800 °C in the static atmosphere.

One dimensional coordination polymers: Synthesis, crystal structures and spectroscopic properties

Two new one dimensional (1D) cyanide complexes, namely [M(4-aepy)2(H2O)2][Pt(CN)4], (4-aepy = 4-(2-aminoethyl)pyridine M = Cu(II) (1) or Zn(II) (2)), have been synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal and elemental analyses techniques. The crystallographic analyses reveal that 1 and 2 are isomorphous and isostructural, and crystallize in the monoclinic system and C2 space group. The Pt(II) ions are coordinated by four cyanide-carbon atoms in the square-planar geometry and the [Pt(CN)4]2− ions act as a counter ion. The M(II) ions display an N4O2 coordination sphere with a distorted octahedral geometry, the nitrogen donors belonging to four molecules of the organic 4-aepy that act as unidentate ligands and two oxygen atoms from aqua ligands. The crystal structures of 1 and 2 are similar each other and linked via intermolecular hydrogen bonding, Pt⋯π interactions to form 3D supramolecular network. Vibration assignments of all the observed bands are given and the spectral features also supported to the crystal structures of the complexes.

Mono, di and heptanuclear metal(II) complexes based on symmetric and asymmetric tetradentate Salamo-type ligands: Syntheses, structures and spectroscopic properties

Mono, di and heptanuclear metal(II) complexes with chemical formulae [Cu(L1)] (1), [Co2(L2)2]·2CH3CN (2) and [Ni7(L3)3(μ3-OEt)2(μ3-OH)6(EtOH)6] (3) have been synthesized by variational tetradentate Salamo-type ligands based on 3,5-dichlorosalicylaldehyde, and characterized by elemental analyses, FT-IR, UV–Vis spectra and X-ray crystallography. The Cu(II) complex 1 is a mononuclear complex with tetracoordinate Cu(II) atom lies in the N2O2 coordination sphere. The Co(II) complex 2 is a dinuclear complex with a central Co2O2 bridged unit via CoO bonds to form a head-to-head dimer, the pentacoordinate Co(II) atoms (Co1 and Co2) have a distorted square pyramidal (τ1=0.454) and trigonal bipyramidal (τ2=0.538) geometries, respectively. Interestingly, the Ni(II) complex 3 is a novel heptanuclear complex with an unprecedented 3:7 ligand to metal stoichiometry. Furthermore, fluorescence properties of the Cu(II) and Ni(II) complexes have been studied.

Synthesis, crystal structures and Hirshfeld surface analyses of two new Salen type nickel/sodium heteronuclear complexes

Two new heteronuclear Nickel(II)/Sodium(I) complexes of a side-off compartmental Schiff base ligand were synthesized and characterized by spectroscopic methods. Crystal structures of both of the complexes were also obtained. The Schiff base ligand was synthesized from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with 2-hydroxy-3-methoxybenzaldehyde. In both of the complexes the Ni(II) ion is coordinated to the inner N2O2 coordination sphere with square-planar geometry and the Na(I) ion is coordinated to the outer O2O2′ coordination sphere. In Complex (1) with general formula [Ni(L)Na(CH3OH)(ClO4)] the sodium ion is seven coordinated while in (2) with general formula [{Ni(L)Na(OH2)}2(μ-Ni(CN)4)] the sodium ion is six coordinated. Intermolecular interactions in two studied complexes were analyzed using 3D Hirshfeld surfaces and corresponding 2D fingerprint plots. This analysis showed that the H … H and C … H/H … C contacts for both structures (altogether 67.5% of total Hirshfeld surface area for (1) and 77.6% for (2)) and the O … H/H … O (24.2%) for (1) and the N … H/H … N (8.1%) contacts for (2) were the characteristic intermolecular contacts in the related crystal structures.

Crystal structure of catena-poly[[[trans-bis(aceto-nitrile-κN)diaquacobalt(II)]-μ-pyrazine-κ(2) N:N'] dinitrate

The central structural motif of the title coordination polymer, [Co(NO3)2(C4H4N2)(CH3CN)2(H2O)2] n , is a chain composed of Co(II) ions linked by bis-monodentate bridging pyrazine ligands through their N atoms. The Co(II) ion is located on an inversion center and is additionally coordinated by two O atoms of water mol-ecules and two N atoms of aceto-nitrile mol-ecules. The resultant N4O2 coordination sphere is distorted octa-hedral. The linear cationic chains extend parallel to the a axis and are aligned into layers parallel to the ac plane. Nitrate anions are situated in the space between the Co(II) chains and form O-H⋯O hydrogen bonds with the coordinating water mol-ecules, leading to a three-dimensional network structure. Weak C-H⋯O hydrogen bonds are also present between pyrazine or aceto-nitrile mol-ecules and the nitrate anions.

Schiff base ligand derived from (±)trans-1,2-cyclohexanediamine and its Cu(II), Co(II), Zn(II) and Mn(II) complexes: Synthesis, characterization, styrene oxidation and hydrolysis study of the imine bond in Cu(II) Schiff base complex

A Schiff base ligand (H2L) derived from 2?-hydroxypropiophenone and (?)trans-1,2-cyclohexanediamine was synthesized. The reactions of MCl2.xH2O (M =Cu(II), Co(II), Zn(II) and Mn(II))with the di-Schiff base ligand (H2L) were studied. This ligand when stirred with 1 equivalent of CuCl2.2H2O in the solution of ethanol and chloroform undergoes partial hydrolysis of the imino bond and the resultant tridentate ligand (HL?)immediately forms complex[CuL?Cl]?3/2CHCl3(1)with N2O coordination sphere. Under the same condition, the reaction of H2L with MCl2.xH2O (M = Co(II) (3), Zn(II) (4) and Mn(II) (5)) gave complexes[ML]?1/2CHCl3?3/2H2O (3-5)with N2O2 coordination sphere and no hydrolytic cleavage was occurred. Also, the reaction of H2L with CuCl2.2H2O in THF gave the complex CuL (2)with N2O2 coordination sphere. The ligand and complexes were characterized by FTIR, UV-Vis, 1H NMRand elemental analysis. The homogeneous catalytic activity of the complexes1, 3 and 5wasevaluated for the oxidation of styrene using tert-butyl hydroperoxide (TBHP) as oxidant. Finally, the copper(II) complex(1)encapsulated in the nanopores of zeolite-Y by flexible ligand method (CuL?-Y)and its encapsulation was ensured by different studies. The catalytic performance of heterogeneous catalyst in the styrene oxidation with TBHP was investigated. The catalytic tests showed that the homogenous and heterogeneous catalysts were active in the oxidation of styrene.

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.