Experimental and computational studies of the macrocyclic effect of an auxiliary ligand on electron and proton transfers within ternary copper(II)-Histidine complexes

The dissociation of [Cu^II(L)His]^•2+ complexes [L=diethylenetriamine (dien) or 1,4,7-triazacyclononane (9-aneN₃)] bears a strong resemblance to the previously reported behavior of [Cu^II(L)GGH]^•2+ complexes. We have used low-energy collision-induced dissociation experiments and density functional theory (DFT) calculations at the B3LYP/6-31+G(d) level to study the macrocyclic effect of the auxiliary ligands on the formation of His^•+ from prototypical [Cu^II(L)His]^•2+ systems. DFT revealed that the relative energy barriers of the same electron-transfer (ET) dissociation pathways of [Cu^II(9-aneN₃)His]^•2+ and [Cu^II(dien)His]^•2+ are very similar, with the ET reactions of [Cu^II(9-aneN₃)His]^•2+ leading to the generation of two distinct His^•+ species; in contrast, the proton transfer (PT) dissociation pathways of [Cu^II(9-aneN₃)His]^•2+ and [Cu^II(dien)His]^•2+ differ considerably. The PT reactions of [Cu^II(9-aneN₃)His]^•2+ are associated with substantially higher barriers (>13 kcal/mol) than those of [Cu^II(dien)His]^•2+. Thus, the sterically encumbered auxiliary 9-aneN₃ ligand facilitates ET reactions while moderating PT reactions, allowing the formation of hitherto nonobservable histidine radical cations.     

Binding of Cu+ and Cu2+ with peptides: Peptides = oxytocin,Arg8‐vasopressin,bradykinin, angiotensin‐I,substance‐P,somatostatin, and neurotensin

The intrinsic binding ability of 7 natural peptides (oxytocin, arg⁸‐vasopressin, bradykinin, angiotensin‐I, substance‐P, somatostatin, and neurotensin) with copper in 2 different oxidation states (Cu^I/II) derived from different Cu^+/2+ precursor sources have been investigated for their charge‐dependent binding characteristics. The peptide‐Cu^I/II complexes, [M − (n‐1)H + nCu^I] and [M − (2n‐1)H + nCu^II], are prepared/generated by the reaction of peptides with CuI solution/Cu‐target and CuSO₄ solution and are analyzed by using matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight mass spectrometry. The MALDI mass spectra of both [M − (n‐1)H + nCu^I] and [M − (2n‐1)H + nCu^II] complexes show no mass shift due to the loss of ─H atoms in the main chain ─NH of these peptides by Cu⁺ and Cu²⁺ deprotonation. The measured m/z value indicates the reduction of Cu^I/II oxidation state into Cu⁰ during MALDI processes. The number and relative abundance of Cu⁺ bound to the peptides are greater compared with the Cu²⁺ bound peptides. Oxytocin, arg⁸‐vasopressin, bradykinin, substance‐P, and somatostatin show the binding of 5Cu⁺, and angiotensin‐I and neurotensin show the binding of 7Cu⁺ from both CuI and Cu targets, while bradykinin shows the binding of 2Cu²⁺, oxytocin, arg⁸‐vasopressin, angiotensin‐I, and substance‐P; somatostatin shows the binding of 3Cu²⁺; and neurotensin shows 4Cu²⁺ binding. The binding of more Cu⁺ with these small peptides signifies that the bonding characteristics of both Cu⁺ and Cu²⁺ are different. The amino acid residues responsible for the binding of both Cu⁺ and Cu²⁺ in these peptides have been identified based on the density functional theory computed binding energy values of Cu⁺ and the fragment transformation method predicted binding preference of Cu²⁺ for individual amino acids.     

In Situ Generation of ArCu from CuF2 Makes Coupling of Bulky Aryl Silanes Feasible and Highly Efficient

A bimetallic system of Pd/CuF₂, catalytic in Pd and stoichiometric in Cu, is very efficient and selective for the coupling of fairly hindered aryl silanes with aryl, anisyl, phenylaldehyde, p‐cyanophenyl, p‐nitrophenyl, or pyridyl iodides of conventional size. The reaction involves the activation of the silane by Cu^II, followed by disproportionation and transmetalation from the Cu^I(aryl) to Pd^II, upon which coupling takes place. Cu^III formed during disproportionation is reduced to Cu^I(aryl) by excess aryl silane, so that the CuF₂ system is fully converted into Cu^I(aryl) and used in the coupling. Moreover, no extra source of fluoride is needed. Interesting size selectivity towards coupling is found in competitive reactions of hindered aryl silanes. Easily accessible [PdCl₂(IDM)(AsPh₃)] (IDM = 1,3‐dimethylimidazol‐2‐ylidene) is by far the best catalyst, and the isolated products are essentially free from As or Pd (<1 ppm). The mechanistic aspects of the process have been experimentally examined and discussed.     

A linear Cu-Gd-Cu-Gd complex derived from the assembly reaction of [NaCuH3L] and [Gd(thd)3(H2O)2] (H3L = meso-1,2-diphenyl-1-(2-oxybenzamido)-2-(2-oxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetra-methyl-3,5-heptanedione)

A linear tetranuclear Cu^II-Gd^III-Cu^II-Gd^III complex [Cu^IIL^dpen(meso)Gd^III(thd)₂(H₂O)]₂ was synthesized from the reaction of [NaCu^IIL^dpen(meso)(DMF)] with [Gd^III(thd)₃(H₂O)₂], and the structures and magnetic properties were investigated, where H₃L^dpen(meso) = meso-1,2-diphenyl-1-(2-hydroxybenzamido)-2-(2-hydroxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione. The Cu^II complex component [NaCu^IIL^dpen(meso)(DMF)] has a one-dimensional (1D) chain structure, in which the Na⁺ ion is coordinated by two phenoxo and an ethoxy oxygen atoms of a Cu^II complex and an amido oxygen atom of the adjacent Cu^II unit to produce the 1D structure, in which the diphenylethylenediamine moieties have the array of {(1R,2S)-Na-(1S,2R)}_1∞. The assembly reaction of the Cu^II and Gd^III components gave a linear complex with the array of Cu(1)-Gd(1)-Cu(2)-Gd(2), in which two diphenylethylenediamine moieties have the same chirality of (1R,2S)-(1R,2S) or (1S,2R)-(1S,2R). Two linear Cu(1)-Gd(1)-Cu(2)-Gd(2) units are linked by hydrogen bonds through two water molecules to give a cyclic structure with a center of symmetry. The temperature dependence of the magnetic susceptibilities and field-dependent magnetization revealed the ferromagnetic interaction between the Cu^II and Gd^III ions within the linear chain.     

Cu3(CN)4(NH3)2Hg(CN)2: a novel inter­penetrating framework formed from CuI,CuII, HgII and cyanide bridges

The title compound, poly[diammine­hexa‐μ‐cyano‐di­copper(I)­copper(II)­mercury(II)], [Cu₃Hg(CN)₆(NH₃)₂]_n, has a novel threefold‐inter­penetrating structure of three‐dimensional frameworks. This three‐dimensional framework consists of two‐dimensional network Cu₃(CN)₄(NH₃)₂ complexes and rod‐like Hg(CN)₂ complexes. The two‐dimensional network complex contains trigonal–planar Cu^I (site symmetry m) and octa­hedral Cu^II (site symmetry 2/m) in a 2:1 ratio. Two types of cyanide group form bridges between three coordination sites of Cu^I and two equatorial sites of Cu^II to form a two‐dimensional structure with large hexa­gonal windows. One type of CN⁻ group is disordered across a center of inversion, while the other resides on the mirror plane. Two NH₃ mol­ecules (site symmetry 2) are located in the hexa­gonal windows and coordinate to the remaining equatorial sites of Cu^II. Both N atoms of the rod‐like Hg(CN)₂ group (Hg site symmetry 2/m and CN⁻ site symmetry m) coordinate to the axial sites of Cu^II. This linkage completes the three‐dimensional framework and penetrates two hexa­gonal windows of two two‐dimensional network complexes to form the threefold‐inter­penetrating structure.     

The unprecedented role of a Cu<Superscript>II</Superscript> cryptand in the luminescence properties of a Eu<Superscript>III</Superscript> cryptate complex

Abstract  A Eu^III cryptate complex constructed from a Cu^II cryptand with an L ^tBu ligand, [Eu^IIICu₂^II(L ^tBu)₂(NO₃)₃(MeOH)], and the corresponding Ca^II and Na^I cryptates, [Ca^IICu₂^II(L ^tBu)₂(NO₃)₂(MeOH)₂] and [Na^ICu₂^II(L ^tBu)₂(Me₂CO)](BPh₄), have been synthesized and characterized in order to shed light on the essential role of Cu^II in the luminescence of a Eu^III cryptate. The unprecedented role of a Cu^II cryptand makes it possible to produce lanthanide luminescence in a Eu^III cryptate complex and is successfully elucidated by comparison with the corresponding Ca^II and Na^I cryptates. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structure and Magnetism of two Polynuclear Complexes Containing both Macrocyclic and Azido Ligands

The two complexes of formula [Cu₂(CuL)₂(μ‐N₃)₄] · 2CH₃OH ( 1 ) and [Cu₂(NiL)₂(μ‐N₃)₄] · 2CH₃OH ( 2 ) (CuL and NiL, H₂L = 2,3‐dioxo‐5,6,14,15‐dibenzo‐1,4,8,12‐tetraazacyclo‐pentadeca‐7,13‐dien), were synthesized and structurally determined. The magnetic susceptibility data of 1 and 2 were analyzed. For complex 1 , magnetic measurements show alternating ferromagnetic and antiferromagnetic exchange couplings J₁ = 23.67 cm^–1, J₂ = –189.11 cm^–1, zJ’ = –0.62 cm^–1. For complex 2 , the doubly bridged asymmetric EO promotes a ferromagnetic interaction between Cu^II and Cu^II ions(J = 40.764 cm^–1).     

Reaction of (±)-1,1′-binaphthyl-2,2′-diyl hydrogen phosphate {(±)-phosH} with copper(II), cobalt(II) and iron(II) compounds; Identification by x-ray diffraction of [Co(CH3OH)4(H2O)2][(+)-phos][(−)-phos]. 2CH3OH·H2O

[Cu₂(μO₂CCH₃)₄(H₂O)₂], [CuCO₃·Cu(OH)₂], [CoSO₄·7H₂O], [Co((+)-tartrate)], and [FeSO₄·7H₂O] react with excess racemic (±)- 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate {(±)-PhosH} to give mononuclear Cu^II, Co^II and Fe^II products. The cobalt product, [Co(CH₃OH)₄(H₂O)₂]((+)-Phos)((−)-Phos) ·2CH₃OH·H₂O (7), has been identified by X-ray diffraction. The high-spin, octahedral Co^II atom is ligated by four equatorial methanol molecules and two axial water molecules. A (+)- and a (−)-Phos⁻ ion are associated with each molecule of the complex but are not coordinated to the metal centre. For the other Co^II, Cu^II and Fe^II samples of similar formulation to (7) it is also thought that the Phos⁻ ions are not bonded directly to the metal. When some of the Cu^II and Co^II samples are heated under high vacuum there is evidence that the Phos⁻ ions are coordinated directly to the metals in the products.     

A series of new organic–inorganic compounds templated by the [SiW12O40]4− polyanion

Two couples of new compounds templated by the polyanion [SiW₁₂O₄₀]^4?,[Hbix][Cu^I(bix)]₃[SiW₁₂O₄₀]·4H₂O (1) and [Cu^II(H₂O)(Hbix)₂(bix)]₂[Cu^II(H₂O)₂(Hbix)₂(bix)][SiW₁₂O₄₀]₃·4H₂O (2) (bix = 1,4-Bis(imidazol-1-ylmethyl)benzene), [Cu^I(bbi)]₄[SiW₁₂O₄₀]·2H₂O (3) and [Cu^II(bbi₂)]₂[SiW₁₂O₄₀] (4) (bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) were hydrothermally synthesized, and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses and single X-ray diffraction. Compounds 1 and 2 were synthesized from the same reactants but exhibited distinct structures which could be ascribed to the different ratios of the reactant bix to Cu^II. In compound 1, the higher ratio of bix results in the transformation of the Cu^II to Cu^I, the [SiW₁₂O₄₀]^4? templates direct the Cu^I–bix coordination polymers to form a 3D supramolecular framework with grid-like channels along two directions. The [SiW₁₂O₄₀]^4? templates in compound 2 locate in the voids of the 3D supramolecular network constructed by Cu^II–bix coordination polymers, which exhibits the interdigitation fashion in both the formation of the 2D layer and the 3D framework. Compounds 3 and 4 were synthesized similar to 1 and 2, except for the change of bix to bbi. In compound 3, the Cu^I–bbi polymers form a supramolecular metal–organic host framework with rhombic channels in which the SiW₁₂ templates reside. Compound 4 shows a framework with hexagonal channels constructed by Cu^II–bbi coordination polymers which accommodated the SiW₁₂ templates.     

Syntheses and structures of copper(II) and nickel(II) complexes with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-(4,4′-bithiazole-2,2′-diyl)diacetimidamide ligands: in vitro cytotoxicities and DNA-binding properties

Two complexes of general formula, [M(DABTA)]NO₃ [M = Cu^II (1) or Ni^II (2), DABTA = N,N′-(4,4′-bithiazole-2,2′-diyl)diacetimidamide], have been synthesized and characterized by elemental analyses, molar conductivity measurements, IR and electronic spectra studies and single-crystal X-ray diffraction. The crystal structures show that the two complexes have similar molecular structures in which each metal atom has a square-planar coordination environment. Hydrogen bonding interactions link each complex into a 2-D infinite network. The DNA-binding properties and cytotoxicities of the complexes were investigated. The results suggest that the two complexes can interact with DNA by intercalation, with binding affinities following the order of 1 > 2, which is consistent with their in vitro cytotoxicities.     

Synthesis, crystal structure, spectroscopy and magnetic properties of a dinuclear Cu complex with 3,5-bis(2-pyridyl)pyrazole bridging ligand

A dinuclear Cu^II complex [Cu₂(bpp)₂(H₂O)₂](ClO₄)₂ (1) with 3,5-bis(2-pyridyl)pyrazole (Hbpp), has been synthesized and characterized by elemental analyses, thermal analysis, conductance, UV-vis and IR spectra. The crystal structure of 1, determined by X-ray diffraction technique, reveals that two centrosymmetric Cu^II centers are bridged by a pair of tetradentate anionic bpp ligands, adopting a square-pyramidal environment with the water ligand occupying the axial site. An interesting feature of this structure is the formation of a two-dimensional supramolecular network through O-H?O hydrogen bonds between the water moieties of the cationic [Cu₂(bpp)₂(H₂O)₂]²⁺ subunits and perchlorate anions. The magnetic properties of 1 have been investigated by variable-temperature magnetic susceptibility and EPR measurements. Very strong antiferromagnetic interaction between the Cu^II centers (with H=−JS₁S₂, J=−368.3 cm⁻¹) has been observed, and the magneto-structural correlations was analyzed.     

Synthesis,Characterization, and Electrocatalytic Behavior for Hydrogen Evolution of a Dinuclear Copper(II) Complex of 1-[(2-Carboxymethyl) benzene]-3-[2-carboxybenzene] triazene

A dinuclear copper(II) complex, [Cu^II₂(L)₂] is afforded by the reaction of CuCl₂ · 2H₂O with a triazenido ligand, 1-[(2-carboxymethyl) benzene]-3-[2-carboxybenzene] triazene (H₂L). Structural investigation shows that the copper-copper distance [2.3985(7) Å] is significantly shorter than the sum of the van der Waals radii of Cu (1.40 Å), suggesting that there are metal-metal bonds in [Cu^II₂(L)₂]. In solid, there is a strong antiferromagnetic interaction between copper(II) ions (J = –135.6 cm^–1). In homogeneous environment, [Cu^II₂(L)₂] shows electrocatalytic activities for hydrogen generation both from acetic acid with a turnover frequency (TOF) of 32 mol of hydrogen per mole of catalyst per hour [mol(H₂) · mol^–1(catalyst) · h^–1] at an overpotential (OP) of 941.6 mV, and neutral buffer with a TOF of 512 mol(H₂) · mol^–1(catalyst) · h^–1 at an OP of 836.7 mV.     

A new family of magnetic 2D coordination polymers based on [MV(CN)8]3− (M=Mo,W) and pre-programmed Cu2+ centres

The self-assembly of [M(CN)₈]³⁻ (M=Mo, W) anion and polyamine complexes of Cu^II[Cu(tetren)]²⁺ and [Cu(dien)(H₂O)₂]²⁺ (tetren=tetraethylenepentamine, dien=diethylenetriamine) in acidic aqueous solution gives (tetrenH₅)_0.8{Cu^II ₄[W^V(CN)₈]₄}·7.2H₂O 1, (tetrenH₅)_0.8{Cu^II ₄[Mo^V(CN)₈]₄}·7.2H₂O 2, (dienH₃){Cu^II ₃[W^V(CN)₈]₃}·4H₂O 3 and (dienH₃){Cu^II ₃[Mo^V(CN)₈]₃}·4H₂O 4 2D coordination polymers. All compounds are structure-related: the crystal structures of isomorphous 1–2 and 3–4, respectively, consist of double-layered cyano-bridged {Cu^II[W^V(CN)₈]⁻}_n square grid backbones and non-coordinated fully protonated polyamine countercations as well as H₂O molecules located between the sheets. The magnetic measurements reveal long range ferromagnetic ordering with sharp phase transitions at T_C in range 28–37 K and coercivity in range 30–225 Oe at liquid helium temperature, T=4.3 K.     

Studies on 2-acetylthiophene-2-furoylhydrazone complexes of 3d-bivalent metal ions

Summary Metal(II) complexes of 2-acetylthiophene-2-furoylhydrazone (HL) of the types [VO(HL)SO₄], [Cu(HL)₂Cl₂(H₂O)], [M(HL)₂Cl₂] [M=Co^II, Ni^II, or Zn^II] and [ML₂(H₂O)₂] [M=Co^II, Ni^II, Cu^II or Zn^II] have been prepared and characterized on the basis of elemental analyses, molar conductance, magnetic susceptibility, visible, e.s.r. and i.r. spectral studies. The bonding and stereochemistry of the complexes are discussed.     

Copper(II) and nickel(II) complexes of the pendant arm ligand benzimidazole-2-yl-methyl-functionalized 1,4,7-triazacyclononane

Two novel complexes [ML]·(ClO₄)₂·EtOH·xH₂O M = Cu^II, x = 3; M = Ni^II, x = 2; L = 1-R-4,7-bis(benzimidazole-2-yl-methyl)-1,4,7-triazacyclononane, [R = 1-(benzimidazole-2-yl-methyl)benzimidazole-2-yl-methy], were prepared by a one-pot method using the 1,4,7-triazacyclononane ligand (tacn) and 2-chloromethylbenzimidazole as starting materials. The ES-MS and u.v. spectra of the complexes indicate that they are very stable thermodynamically and kinetically in aqueous solution. The crystal structure of the Cu^II complex shows that the Cu^II centre is octahedrally coordinated by six nitrogen atoms of three benzimidazoles and tacn.     

Mononuclear complexes of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II), with 4-amino-3,5-bis(pyridin-2-yl)-1,2,4 triazole and tris(2-aminoethyl) amine: crystal structure of [Ni(tren)(abpt)](NO3)2(H2O)2.25

Complexes of the type [M(tren)(abpt)](NO₃)₂(H₂O)_n (1–6) [M = Mn^II, Fe^II, Co^II, Cu^II, Zn^II (n = 2), Ni^II (n = 2.25), tren = tris(2-aminoethyl)amine, and abpt = 4-amino-3,5-bis(pyridin-2yl)-1,2,4 triazole] have been prepared. The bonding mode and overall geometry of the complexes have been deduced by elemental analyses, molar conductance values, spectral studies (obtained from FT-IR), ¹H-n.m.r., electronic spectral analyses and magnetic susceptibility measurements. A detailed molecular structure of complex (4) has been determined by single X-ray crystallography.     

Chelatbildung mit 1,3-Diamino-2-methylenpropanen

Chelate Formation with 1,3-Diamino-2-methylene Propane1 1,3-Diamino-2-methylene propane and its N, N′ alkylated derivatives form crystalline chelates with Co^II (1:3), Ni^II (1:1, 1:2 and 1:3), Pd^II (1:1, 1:2), Rh^III (1:1) and Cu^II (1:2). Experiments for preparation of olefin complexes were unsuccessful. By potentiometric measurements the base strengths of the ligands as well as the stability constants of the Co^II, Ni^II, Pd^II, Cu^II, Zn^II, Cd^II chelates were evaluated and the kinetics of the formation of the 1:1 Pd^II complex is investigated. The magnetic behaviour of the Co^II?, Pd^II? and Cu^II? chelates is normal, whereas[Ni(dia)₂(H₂O)₂] (ClO₄)₂ shows anormal behaviour due to configurational isomerism between square planar and octahedral ligand geometry in solid state in type of a LIFSCHITZ -isomerism. The ESR-spectra of the Cu^II?compounds are discussed and the bonding parameters of the Cu? N?bonds were calculated.     

Three novel octacyanomolybdate(IV)–M(II) [M = Mn and Cu] bimetallic assemblies: crystal structures and magnetic properties

Synthesis, structure characterization, and magnetic properties of three novel cyano-bridged complexes {[Mn^II(bpy)(DMF)₂]₂[Mo^IV(CN)₈]·1.5H₂O} _n (1), [Cu^II(L)]₂[Mo^IV(CN)₈]·6.75H₂O (2), and [Mn^II(bpy)₂]₄[Mo^IV(CN)₈]₂·4MeOH·4H₂O (3) (where DMF = N,N′-dimethylformamide; bpy = 2,2-bipyridine and L = 1,3,6,8,11,14-hexaazatricyclo[12.2.1.1^8,11]octadecane) have been studied. The X-ray single-crystal structure reveals that 1 is a cyanide-bridged 1D infinite chain with the alternating of Mn^II(bpy)(DMF)₂ and Mo^IV(CN)₈ moieties. The neighboring chains interact with each other by hydrogen bonding to form a sheet-like network, and the layers further extend to a 3D network due to the face-to-face π···π stack interactions. For 2, the Mo^IV center adopts a distorted square antiprism coordination environment, while the Cu^II center adopts a distorted square pyramidal geometry. The weak Mo–CN···Cu interactions between neighboring molecules lead to a 2D network structure of 2. For 3, basic structural unit is centrosymmetric and contains four Mn^II centers bridged by two octacyanomolybdate(IV). Here, their magnetic properties have also been studied. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and characterization of mononuclear copper(II) and dinuclear cadmium(II) complexes with di-(2-picolyl)sulfide

The reaction of CuCl₂ · 2H₂O and CdCl₂ with di-(2-picolyl)sulfide (dps) leads to the formation of mononuclear copper(II) and binuclear cadmium(II) complexes, [Cu(dps)Cl₂] · H₂O (1) and [(dps)(Cl)Cd^II(μ-Cl)₂Cd^II(Cl)(dps)] (2). The copper atom in (1) is coordinated to one sulfur and two nitrogen atoms from the dps ligand and two chlorides in a distorted square-pyramidal environment. Complex (2) has two distorted octahedra sharing the basal edge that contain the bridging chloro ligands, each of which resides at a center of inversion. Cyclic voltammetric data show that (1) undergoes two reversible one-electron waves corresponding to Cu^II/Cu^III and Cu^II/Cu^I processes. However, cyclic voltammetry of (2) gives two irreversible reduced waves.     

Fac-mer equilibria of coordinated iminodiacetate (IDA2?) in ternary CuII(ida)(H?1B)? complex formation (B = imidazole, benzimidazole) in aqueous solution

pH potentiometric and spectrophotometric investigations on the complex formation equilibria of Cu^II with iminodiacetate (ida²⁻) and heterocyclic N-bases, viz. imidazole and benzimidazole (B), in aqueous solution in binary and ternary systems using different molar ratios of the reactants indicated the formation of complexes of the types, Cu(ida), Cu(ida)(OH)⁻, (ida)Cu(OH)Cu(ida)⁻, Cu(B)²⁺, Cu(H^-1B)⁺, Cu(ida)(H₋₁B)⁻, (ida)Cu(B)Cu(ida) and (ida)Cu(H₋₁B)Cu(ida)⁻. Formation constants of the complexes at 25 ±1° at a fixed ionic strength,I = 0.1 mol dm⁻³ (NaNO₃) in aqueous solution were evaluated and the complex formation equilibria were elucidated with the aid of speciation curves. Departure of the experimental values of the reproportionation constants(ΔlogK _cu) of ternary Cu(ida)(H₋₁B)⁻ complexes from the statistically expected values, despite their formation in appreciable amounts at equilibrium, were assigned tofac(f)-mer(m) equilibria of the ida²⁻ ligand coordinated to Cu^II, as the N-heterocyclic donors, (H₋₁B)⁻, coordinatetrans- to the N-(ida²⁻) atom in the binary Cu(ida) _f complex to form the ternary Cu(ida) _m (H₋₁B)⁻ complexes