Polynuclear nickel (II) and copper (II) complexes of hexaazamacrocycles incorporating pairs of diethylenetriamine subunits separated by aromatic spacers

A series of Ni(II) and Cu(II) complexes of the hexaaza macrocycles, 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1^11,15]triaconta-1(29),11(30),12,14,25,27-hexaene (L¹) and 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2^11,14]triaconta-1(26),11(29),12,14(30),24(28),25-hexaene (L²), have been prepared and the crystal structures determined for [Ni₂L¹(O₂CCH₃)₂(H₂O)₂](ClO₄)₂ (1), [Ni₂L²(DMF)₆](ClO₄)₄ · 2H₂O (2), {[Cu₂L²Br(O₂CCH₃)](ClO₄)₂}_n (3), [Cu₂L²(μ-CO₃)(H₂O)₂]₂(ClO₄)₄ · 8H₂O (4), [Cu₂L²(O₂CCH₃)₂](BF₄)₂ (5), and [Cu₂L¹(μ-imidazolate)Br]₂Br₄ · 6H₂O (6). In these complexes, two metal centers are bound per ligand; in 1 and 3-6, the N₃ subunits of L¹ or L² coordinate meridionally to the metal centers, whilst in 2, each N₃ subunit in L² adopts a facial mode of coordination. The binuclear cations in 1 and 2 have chair-like conformations, with the distorted octahedral Ni(II) coordination spheres completed by terminal water and a bidentate acetate ligand in 1 and three DMF ligands in 2. The Cu(II) centers in 3-6 generally reside in square planar environments, although a weakly binding ligand enters the coordination sphere in some cases, generating a distorted square pyramidal geometry. The binuclear [Cu₂L²]⁴⁺ units in 3, 4 and 5 adopt similar bowl-shaped conformations, stabilized by H-bonding interactions between pairs of amine groups from L² and a perchlorate or tetrafluoroborate anion. In 3, the binuclear units are linked through acetate groups, bridging in a syn-anti fashion, to produce a zig-zag polymeric chain structure, whilst 4 incorporates a tetrameric cation consisting of two binuclear units linked via a pair of carbonate bridges. Compound 6 features an imidazolate bridge between the two Cu(II) centers bound by L¹. Pairs of [Cu₂L¹(μ-imidazolate)]³⁺ units are then weakly linked through a pair of bromide anions.     

Synthesis and characterization of nickel(II) and copper(II) complexes with tetradentate Schiff base ligands

The 1:1 condensation of 1,2-diaminopropane and 1-phenylbutane-1,3-dione at high dilution gives a mixture of two positional isomers of terdentate mono-condensed Schiff bases 6-amino-3-methyl-1-phenyl-4-aza-2-hepten-1-one (HAMPAH) and 6-amino-3,5-dimethyl-1-phenyl-4-aza-2-hexen-1-one (HADPAH). The mixture of the terdentate ligands has been used for further condensation with pyridine-2-carboxaldehyde or 2-acetylpyridine to obtain the unsymmetrical tetradentate Schiff base ligands. The tetradentate Schiff bases are then allowed to react with the methanol solution of copper(II) and nickel(II) perchlorate separately. The X-ray diffraction confirms the structures of two of the complexes and shows that the condensation site of the diamine with 1-phenylbutane-1,3-dione is the same.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

Synthesis, characterization and X-ray crystal structures of copper(II) and nickel(II) complexes with potentially hexadentate Schiff base ligands

Copper(II) and nickel(II) complexes of potentially N₂O₄ Schiff base ligands 2-({[2-(2-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}ethoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L¹) and 2-({[2-(4-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}butoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L²) prepared of 5-phenylazo salicylaldehyde (1) and two various diamines 2-[2-(2-aminophenoxy)ethoxy]aniline (2) and 2-[4-(2-aminophenoxy)butoxy]aniline (3) were synthesized and characterized by a variety of physico-chemical techniques. The single-crystal X-ray diffractions are reported for CuL¹ and NiL². The CuL¹ complex contains copper(II) in a near square-planar environment of N₂O₂ donors. The NiL² complex contains nickel(II) in a distorted octahedral geometry coordination of N₂O₄ donors. In all complexes, H₂L¹ behaves as a tetradentate and H₂L² acts as a hexadentate ligand. Cyclic voltammetry of copper(II) complexes indicate a quasi-reversible redox wave in the negative potential range.     

Synthesis and characterization of Cu(II) and Ni(II) complexes of a tripodal ligand containing imidazoles

Two complexes of the formula [MH₃L](ClO₄)₂ [M = Cu(II) (1), Ni(II) (2)] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with the ligand (H₃L) formed by the Schiff base condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 4-methyl-5-imidazolecarboxaldehyde and structurally and magnetically characterized. The structures of 1 and 2 are isomorphous with each other and with the iron(II) complex of H₃L which has been reported previously. The ligand, while potentially heptadentate, forms six coordinate complexes with both metal centers forming three M-N_imine and three M-N_imidazole bonds. The tren central N atom is at a nonbonded distance from M of 3.261 Å for 1 and 3.329 Å for 2. The neutral complex CuHL 3 was prepared by reaction of H₃L with Cu(OCH₃)₂ and the ionic complex Na[NiL] 4 was prepared by deprotonation of 2 with aqueous sodium hydroxide. Magnetic measurements of 1-3 are consistent with the spin-only values expected for S = 1/2 (d⁹, Cu(II)) and S = 1 (d⁸, Ni (II)) systems.     

Octahedral nickel(II) hexamethyleneimine-dithiocarbamato complexes involving bidentate N,N-donor ligands

The nickel(II) complexes of the compositions [Ni(hmidtc)(bpy)₂]ClO₄ (I), [Ni(hmidtc)(phen)₂]ClO₄ (II), [Ni(hmidtc)(phen)₂]SCN (III), [Ni(hmidtc)(phen)₂]PF₆ (IV), [Ni(hmidtc)(phen)₂]BPh₄ (V), [Ni(hmidtc)(phen)₂]AcO·2H₂O (VI) and [Ni(hmidtc)(phen)₂]Br·H₂O (VII), involving a combination of one hexamethyleneimine-dithiocarbamate anion (hmidtc) and two bidentate N,N-donor ligands (2,2′-bipyridine (bpy) for I or 1,10-phenanthroline (phen) for II-VII), have been prepared. The compounds were characterized by elemental analysis, molar conductivity measurements, UV-Vis and IR spectroscopy, magnetochemical measurements and thermal analysis. A single-crystal X-ray analysis of the complex I revealed a distorted octahedral geometry with the nickel(II) ion coordinated by four nitrogen atoms (from two bidentate-coordinated bpy molecules) and two sulfur atoms (from one bidentate-coordinated hmidtc anion), together giving an NiN₄S₂ donor set.     

The role of terminal amino group and histidine at the fourth position in the metal ion binding of oligopeptides revisited: Copper(II) and nickel(II) complexes of glycyl-glycyl-glycyl-histamine and its N-Boc protected derivative

Copper(II) and nickel(II) binding properties of two pseudo tetrapeptides, N-Boc-Gly-Gly-Gly-Histamine (BGGGHa) and Gly-Gly-Gly-Histamine (GGGHa) have been investigated by pH-potentiometric titrations, UV-visible-, EPR-, NMR- and ESI-HRMS (electrospray ionization high resolution MS) spectroscopies, in order to compare the role of N-terminal amino group and imidazole moiety at the fourth position in the complex formation processes. Substantially higher stabilities were determined for the ML complexes of GGGHa, compared to those of BGGGHa, supporting the coordination of the terminal amino group and the histamine imidazole of the non-protected ligand. A dimeric Cu₂H_− 2L₂ species, formed through the deprotonation of peptide groups of the ligands, was found in the GGGHa-copper(II) system. Deprotonation and coordination of further amide nitrogens led to CuH_− 2L and, above pH ~ 10, CuH_− 3L. Experimental data supports a {NH₂,2 × N_amide,N_im} macrochelate structure in CuH_− 2L whereas a {NH₂,3 × N_amide} coordination environment in CuH_− 3L. The first two amide deprotonation processes were found to be strongly cooperative with nickel(II) and spectroscopic studies proved the transformation of the octahedral parent complexes to square planar, yellow, diamagnetic species, NiH_− 2L and above pH ~ 9, NiH_− 3L. In the basic pH-range deprotonation and coordination of the amide groups also took place in the BGGGHa containing systems, leading to complexes with a {3 × N_amide,N_im} donor set, and in parallel the re-dissolving of precipitate. Above pH ~ 11, a further proton release from the pyrrolic NH group of the imidazole ring of BGGGHa occurred providing an additional proof for the different binding modes of the two ligands.     

Versatile nuclearity in copper complexes with ortho functionalized 1,3-bis(aryl)triazenido ligands

The synthesis, characterization and crystal structures of three new copper complexes derived from 1,3-bis(aryl)triazenido ligands bearing either a methoxycarbonyl, methylthio or a hydroxymethyl group in the ortho position of one of the aromatic rings are reported. In addition to the coordination of the triazenido fragment, the Lewis basic groups coordinate to the copper centers to form complexes with different nuclearity: {1-[2-(methoxycarbonyl)phenyl]-3-[4-methylphenyl]}triazene and {1-[2-(methylthio)phenyl]-3-[4-methylphenyl]}triazene form stable dinuclear and tetranuclear Cu(I) complexes, respectively. Reaction of {1-[2-(hydroxymethyl)phenyl]-3-[4-methylphenyl]}triazene with either Cu(I) or Cu(II) results in a novel Cu(II) hexanuclear macrocyclic complex.     

Studies of copper(II) and nickel(II) complexation by bis(1,4,7-triazacyclononane) ligands containing alkene and alkyne bridging groups

The copper(II) and nickel(II) complexes of three new 1,2-bis(1,4,7-triazacyclononane) ligands containing unsaturated four carbon bridging groups is studied by continuous variation UV-Vis spectroscopic and pH potentiometric equilibrium experiments. The cis-butene-2 (L_C) linked ligand may form monomeric MN₆-type complexes while the trans-butene-2 (L_T) and butyne-2 (L_Y) ligands are prevented by their stereochemistry from forming monomeric complexes and form oligomeric complexes. It is determined that the stability of the CuL_C²⁺ complex is not appreciably different from the oligomeric complexes of L_T and L_Y. Single-crystal X-ray structure determinations are made on three square pyramidal Cu₂L⁴⁺ complexes: [Cu₂L_CCl₄] (1), [Cu₂L_YCl₄] (2), and [Cu₂L_T(NO₃)₂(H₂O)₂](NO₃)₂ (3). The structure of [Ni₂(L_C)₂](ClO₄)₄ · 2H₂O (4) is a binuclear dimer that contains two nickel(II) ions sandwiched between two ligands, indicating that bis([9]aneN₃) ligands with four linker atom chains may form either monomeric or oligomeric structures.     

Ditopic bis(oxazolines): Synthesis and structural studies of zinc(II), copper(II) and nickel(II) complexes

The synthesis, crystal structures, magnetic and spectroscopic properties of zinc(II), nickel(II) and copper(II) dinuclear complexes 2-4 of a novel dinucleating polyoxazoline ligand 1 are reported. X-ray analysis revealed that the three complexes are centrosymmetric dinuclear species with an overall S shape, the bisoxazoline moieties pointing toward the aromatic core of the molecule. Magnetic susceptibility measurements suggest that there is a very weak exchange interaction between the copper or nickel ions in complexes 3 and 4.     

A systematic study of ligand intermolecular interactions in crystals of copper(II) complexes of bidentate guanidino derivatives

The synthesis and X-ray structures of copper(II) complexes of the bidentate ligands, N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-N′-phenylguanidino, 2-uanidinobenzimidazolo and N-(4-oxo-3-phenyl-1,3-diazaspiro[4.4]non-1-en-2-yl)guanidino, are reported. These complexes, which possess potential doublet (DA) or triplet (DAD) hydrogen bonding motifs, can form supramolecular structures based on synthons involving hydrogen bonding or phenyl embraces. The changes in supramolecular structure resulting from small changes in ligand structure, as well as from the use of different solvents for their crystallisation, are examined. The structures adopted are compared with others reported previously for complexes of related ligands.     

Dinuclear nickel(II) and zinc(II) complexes of 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methylphenol

Reaction of the symmetrical proligand H₂L with metal(II) acetate and a counteranion to promote crystallisation has given the homodinuclear complexes [Zn₂L(OAc)₂](BF₄)]·2MeOH and [Ni₂L(OAc)₂](BF₄)]·2MeOH the crystal structures of which are reported. These show the presence of a triply bridging (μ-cresolato)bis(μ-carboxylato) dimetal core.     

A tetranuclear copper(II) complex with bis(o-aminobenzaldehyde)thiocarbohydrazone

Bis(o-aminobenzaldehyde)thiocarbohydrazone (HL) forms with copper(II) nitrate a tetranuclear complex [Cu₂(L)(NO₃)₃]₂·2H₂O, in which two dinuclear units are joined by nitrate bridges. The dihydrazone ligand behaves ditopically, providing NNS and NNN binding sites, with the four coppers essentially in a square-pyramidal geometry. The tetranuclear molecule displays intramolecular magnetic interactions, with the antiferromagnetic exchange (−2J = 210(1) cm⁻¹) between the copper(II) ions within each dinuclear moiety dominant over weak interdimer ferromagnetic coupling.     

Preparation of new tetraaza macrocyclic nickel(II) and copper(II) complexes bearing N-propionic methyl ester groups

A 14-membered tetraaza macrocycle, 2,13-bis(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane (L²) bearing two N-CH₂CH₂COOMe groups, and its nickel(II) and copper(II) complexes have been prepared and characterized. The nickel(II) and copper(II) complexes of 2-(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane (L³) containing one N-CH₂CH₂COOMe group have also been prepared. The crystal structure of [NiL²](ClO₄)₂ shows that the complex has a slightly distorted trans-octahedral coordination geometry with two relatively short axial Ni-O (N-CH₂CH₂COOMe group) bonds (2.136(3) Å). In various solvents, however, a considerable proportion of [NiL²]²⁺ exists as a square-planar form, in which the functional pendant arms are not involved in coordination. The proportion of the square-planar isomer varies with solvents in the order of nitromethane ? acetonitrile < H₂O < DMF ? DMSO. In the case of [CuL²](ClO₄)₂, only one N-CH₂CH₂COOMe group is involved in coordination. The N-CH₂CH₂COOMe group of [NiL³](ClO₄)₂ is not directly involved in coordination even in the solid state, though the functional group of [CuL³](ClO₄)₂ is coordinated to the metal ion.     

Preparation, structural, magnetic and thermal properties of two heterobimetallic cyano-bridged nickel(II)-copper(II)/platinum(II) coordination polymers

Two unique bimetalic Pt(II) coordination polymers of composition [Ni(hydeten)₂Pt(CN)₄] (Ni-Pt) and [Cu(hydeten)₂Pt(CN)₄] (Cu-Pt) [hydeten = N-(2-hydroxyethyl-ethylenediamine) or 2-(2-aminoethylamino)ethanol] have been synthesized and structurally characterized by various methods in this study. The crystal structure of Cu-Pt was determined by single-crystal X-ray diffraction analysis. The structure of Cu-Pt forms of infinite 2,2-TT type [-Cu(hydeten)₂-NC-Pt(CN)₂-CN-] chains containing paramagnetic copper atoms bridged by tetracyanoplatinate species. In this complex, Cu(II) centers display an axially elongated octahedron with two chelating hydeten molecules in the equatorial positions and N-bonded bridging cyano groups in the axial positions, whereas Pt(II) centers are four coordinate with four cyanide-carbon atoms in a square-planar arrangement. The decrease of the moments of these complexes in temperature range of 50 305 K can assigned to the antiferromagnetic interactions in the structures. The thermal decomposition of Cu-Pt comprise of five distinguished stages, while the thermal decomposition of Ni-Pt take place four different stages.     

DNA interaction of new copper(II) complexes with sulfonamides as ligands

New copper(II) complexes with sulfonamide ligands have been prepared and characterized. Sulfonamide ligands were prepared through a reaction between 8-aminoquinoline and either 2-mesitylene (Hqmesa), 4-tert-butylbenzene (Hqtbsa), or alpha-toluene (Halphaqtsa) sulfonyl chlorides. The structural analysis carried out for complex [Cu(alphaqtsa)(2)] indicated that the local environment of the Cu(II) cation is between a square planar and a tetrahedral geometry, with stacking of the benzene rings of the sulfonyl ligands between neighbor molecules. Powder EPR spectra at room temperature gave rhombic spectra for the [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] complexes and an axial spectrum for the [Cu(qtbsa)(2)] complex, probably due to the steric hindrance of the methyl groups. Complexes [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] are artificial chemical nucleases that degrade DNA in the presence of sodium ascorbate. A study of the radical scavengers revealed that the ROS (reactive oxygen species) involved in the DNA damage were hydroxyl, singlet oxygen-like species, and superoxide anion.     

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H₂L^m (m = 1−4), [1H-pyrrol-2-ylmethylene]{2-[2-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H₂L¹), [1H-pyrrol-2-ylmethylene]{2-[4-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H₂L²), [1H-pyrrol-2-ylmethylene][2-({2-[(2-{[1H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H₂L³) and [1H-pyrrol-2-ylmethylene][2-({4-[(2-{[1H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H₂L⁴) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML^m (m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL³ and CuL², which have been determined by single crystal X-ray diffraction, indicate that the NiL³ complex has a distorted octahedral coordination environment around the metal while the CuL² complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL² complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.     

New bis(macrocyclic) dinickel(II) complexes obtained by oxidation of bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,7-dien-6-yl)dinickel(II) perchlorate

New bis(macrocyclic) dinickel(II) complexes with bis(Me₂[14]-4,7-dien-6-ylidene), 2a and 2b, were synthesized by oxidation of a dinickel(II) complex with an unsaturated bis(macrocyclic) ligand containing four CN bonds, bis(Me₂[14]-4,7-dien-6-yl) (1). Complex 2a was found to undergo intramolecular cyclization between the methyl group of one macrocycle and the carbon atom of the CN group of the other macrocycle to produce a bis(macrocyclic) dinickel(II) complex bridged by a fivemembered ring (3). The structures of 2b and 3 were determined by X-ray crystallography. The nonsymmetrical bis(macrocyclic) structure of the dinickel(II) complex 3 was reflected in its cyclic voltammogram and ¹H and ¹³C NMR spectra. The catalytic capabilities of these bis(macrocyclic) nickel(II) complexes in the reductive debromination of 1-bromo-4-tert-butylbenzene were also investigated.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Binding of azide and thiocyanate ligands to copper(II) model complexes

Summary Binding of azide to a series of copper(II) complexes has been investigated by absorption, CD and EPR spectroscopy. Axial binding of azide to Cu(II) can be differentiated from equatorial binding through the lower intensity and lack of optical activity of the LMCT band. The affinity of azide for Cu(II) increases with the overall positive charge of the complex. The preliminary data on thiocyanate binding to Cu(II) seem to agree with the trends observed for the corresponding azide adducts.