Asymmetric salt effects on anion/cation reactions: A comparative study of the [Fe(CN)6]4− + [Co(NH3)5pz]3+ and [Ru(NH3)5pz]2+ + [Co(C2O4)3]3− reactions

The kinetics of electron transfer reactions between [Fe(CN)₆]^4? and [Co(NH₃)₅pz]³⁺ and between [Ru(NH₃)₅pz]²⁺ and [Co(C₂O₄)₃]^3? was studied in concentrated salt solutions (Na₂SO₄, LiNO₃, and Ca(NO₃)₂). An analysis of the experimental kinetic data, k_obs, permits us to obtain the true (unimolecular) electron transfer rate constants corresponding to the true electron transfer process (precursor complex → successor complex), k_et. The variations of both, k_obs and k_et, with salt concentrations are opposite for these reactions. These opposite tendencies can be rationalized by using the Marcus–Hush treatment for electron transfer reactions. The conclusion is that the negative salt effect found for the first reaction ([Fe(CN)₆]^4? + [Co(NH₃)₅pz]³⁺) is due to the increase of the reaction and reorganization free energies when the concentration of salt increases. In the case of the second reaction ([Ru(NH₃)₅pz]²⁺ + [Co(C₂O₄)₃]^3?), the positive salt effect observed is caused by the fact that the driving force becomes more favorable when the concentration of salt increases. Thus, it is shown that for anion/cation electron transfer reactions the kinetic salt effect depends on the charge sign of the oxidant (and the reductant). © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 81–89, 2005     

Oligomeric calix[4]arene‐thiacrown ether for toxic heavy metals

A new oligomeric calix[4]arene‐thiacrown‐4 ( 5 ) was synthesized via a condensation reaction of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis‐(4‐aminobenzyloxy)‐calix[4]arene‐thiacrown‐4 ( 4 ) with adipoyl dichloride. In this oligomerization reaction only five/six calix[4]arene‐thiacrown‐4 units were linked in the oligomeric chain. The complexation studies of 5 were made with liquid–liquid‐ extraction and solid–liquid‐sorption procedures. For comparison, the extraction efficiencies of monomers 1 , 3 , and 4 to selected transition metals are reported. The selectivity of monomers 3 and 4 toward Cu²⁺, Hg²⁺, and Pb²⁺ was lost after oligomerization in the two‐phase extraction systems. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 186–193, 2004     

Kinetics of oxidation of reducing sugars by catalytic amount of osmium(VIII) in presence of periodate

The kinetics of oxidation of some reducing sugars viz. glucose, galactose, fructose, maltose, and lactose by osmium(VIII) in presence of sodium metaperiodate in alkaline medium have been investigated. The reactions are zero order in periodate. The order of reaction in substrate and OH^? decreases from unity to zero at higher [substrate] or [OH^?], respectively. Rate of oxidation is proportional to [Osmium(VIII)]. Osmium(VIII) serves as an effective oxidant which oxidizes reducing sugars and itself reduces to osmium(VI). Role of IO₄^? is to regenerate osmium(VIII) from osmium(VI). An evidence for the complex formation between osmium(VIII) and reducing sugar has also been obtained. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:441–448, 2004.     

C-C and C-H bond activation in the fragmentation of the [M + Ni]+ adducts of aliphatic amino acids

The major metal-containing species formed upon fast atom bombardment of amino acid/Ni⁺² mixtures is the [M + Ni]⁺ adduct, involving reduction of the Ni⁺² to the +1 oxidation state. By contrast, electrospray ionization of amino acid/Ni⁺² mixtures produces predominantly [Ni(M ? H)M]⁺; this species, on collisional activation, produces predominantly [M + Ni]⁺ by elimination of [M - H], presumably a carboxylate radical. The unimolecular fragmentation reactions occurring on the metastable ion time scale for the [M + Ni]⁺ adducts of a variety of α-amino acids have been recorded. The adducts with phenylalanine, α-aminoisobutyric acid and α-aminobutyric acid fragment by elimination of H₂O, H₂O + CO and, to a minor extent, by elimination of CO₂. These reactions are similar to those observed for the [M + Cu]⁺ adducts of α-amino acids. A reaction distinctive for the [M + Ni]⁺ adducts involves formation of the immonium ion RCH=NH ₂ ⁺ . By contrast, the [M + Ni]⁺ adducts with leucine, isoleucine, and norleucine show extensive metastable ion fragmentation by elimination of H₂, CH₄, C₂H₄, C₃H₆, and C₄H₈, with the relative importance of the different fragmentation channels depending on the configuration of the C₄H₉ side chain. These results are interpreted in terms of C-C and C-H bond activation of the C₄H₉ side chain by the Ni⁺. The adducts with valine and norvaline fragment in a fashion similar to the adduct with phenylalanine, except that minor elimination of C₃H₆ is observed.     

NMR analyses of two isomeric cyclobutanes from a [2 + 2] photocycloaddition

Complete ¹H and ¹³C NMR assignments are reported for two isomeric cyclobutanes generated from the photochemical [2 + 2] cycloaddition of N‐methylisocarbostyril and 4‐methoxy‐3‐buten‐2‐one. The reaction is 100% regioselective and demonstrates the potential synthetic utility of de Mayo type reactions using an isocarbostyril and a stable β‐dicarbonyl enol derivative. Copyright © 2002 John Wiley & Sons, Ltd.     

Influence of Molecular Structure on the Dimerization Reactivity of Germaaromatic Compounds： a Theoretical Study

Density functional theory (DFT) calculations, at the B3LYP/6-311G** level of theory, were performed to study the reaction mechanism and potential energy surface of the [2 + 2], [4 + 2] and [4 + 4] dimerization reactions of some germaaromatic compounds. The influence of reactant's molecular structure and benzene solvent on the potential energy surface of the studied reactions was investigated. Our calculation results show that [2 + 2] and [4 + 4] reactions are concerted and synchronous processes; while [4 + 2] reactions proceed via a concerted but asynchronous way in general. [2 + 2] and [4 + 2] reactions of germabenzenes and 1-germana- phthalene proceed much more easily than the corresponding [4 + 4] reaction, both thermo- dynamically and kinetically; while most [4 + 2] paths have lower activation barrier than the corres- ponding [2 + 2] ones. As the number of six-membered aromatic rings in reactant molecules becomes larger, [2 + 2], [4 + 2] and [4 + 4] reactions become easier to proceed. The influence of substituents at the Ge atom of germabenzenes on the potential energy surface of [2 + 2] and [4 + 2] reactions correlates with their electronic properties and volume. Solvent effect is not crucial for the potential energy surfaces of the studied reactions.     

Ion-molecule reactions and collision-activated dissociation of C4H 4 +. isomers: A case study in the use of the MS3 capabilities of a pentaquadrupole mass spectrometer

Isomeric C₄H ₄ ^+. radical cations vinylacetylene (a), butatriene (b), methylene cyclopropene (c), and the nonaromatic cyclobutadiene (d), generated, respectively, from the neutral precursors 3-butyn-1-ol (1), 1,4-dichloro-2-butyne (2), benzene (3), and 7,8-benzotricyclo [4.2.2.0^2,5]deca-3,7,9-triene (4), undergo diagnostically different ion-molecule reactions with allene, isoprene, furan, and thiophene. It is speculated that adducts are generated by [2 + 2] cycloadditions with the first reagent and [4 + 2] Dials-Alder cycloadditions with isoprene, furan, and thiophene. The initially formed cycloaddition adducts fragment rapidly, isomerize, or undergo further addition of neutral reagent to yield a complex set of products. With a pentaquadrupole mass spectrometer, MS³ experiments that employ three stages of ion mass analysis are used to help elucidate the ion-molecule reactions and to distinguish the isomeric C⁴H ₄ ^+. ions. Among these experiments, the reaction intermediate spectrum reveals the nature of the intermediates connecting the reactant to a selected product while the sequential product spectrum provides mechanistic and structural information on the adducts and other ion-molecule products. The unique combination of ion-molecule reactions with collision-activated dissociation employed here provides valuable information on the chemistry of ionized cyclobutadiene, including its proclivity to undergo [2 + 2] and [4 + 2] cyc1oadditions.     

Kinetics and mechanism of oxidation of 2‐mercaptosuccinic acid by bis(μ‐oxo)‐ manganese(III,IV)‐cyclam complex in aqueous medium: Influence of externally added copper(II)

Kinetic studies on the oxidation of 2‐mercaptosuccinic acid by dinuclear [Mn₂^III/IV(μ‐O)₂(cyclam)₂](ClO₄)₃] ( 1 ) (abbreviated as Mn^III–Mn^IV) (cyclam = 1,4,8,11‐tetraaza‐cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0–6.0, in the presence of acetate buffer at 30°C by UV–vis spectrophotometry. In the pH region, two species of complex 1 (Mn^III–Mn^IV and Mn^III–Mn^IVH, the later being μ‐O protonated form) were found to be kinetically significant. The first‐order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first‐order dependence on [Cu²⁺] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of μ‐O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV–vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer‐sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170–177 2004     

[2+2]- AND [4+2] cycloaddition reactions of 1,3-diazabutadienes with diphenylketene

1,3-Diazabutadienes react with diphenylketene in [2+2] - and [4+2] cycloaddition reactions, depending on the substitution pattern. Spectroscopic data (IR, ¹H- and ¹³C-NMR) and results of quantummechanical model calculations (ab initio 3-21G) are presented.     

Tris-o-phenanthrolineiron(lll) Complex as a Photoinitiator of Acrylamide Polymerization

Abstract

The blue Tris-o-phenanthrolineiron(m) complex, Fe(phen)₃ ³⁺, formed in aqueous solution by oxidation of the red ferrous phenanthroline complex by nitric acid, is found to be a good photo-initiator of acrylamide (A.AM) polymerization. Systematic study of the kinetics of polymerization of acrylamide by Fe(phen) ₃ ³⁺ in aqueous nitric acid solution in the presence of light of Δ = 365 nm at room temperature showed that the rate of polymerization R_p was dependent on [A.AM]^1,5, [C] ^0,5, I^0,5, and [HCOOH], and the rate of Fe(phen) ₃ ³⁺disappearance, -R_c, was found to be proportional to [A.AM], [C], I, and [HCOOH], where [A.AM], [C] and [HCOOH] refer to the concentrations of acrylamide, Fe(phen) ₃ ³⁺, and formic acid, respectively, and I refers to light intensity. The kinetic observations are consistent with the interaction of the excited Fe(phen) ₃ ³⁺ with acrylamide molecule to produce a radical R. capable of initiation and also reduction of Fe(phen) ₃ ³⁺, to the stable Fe(phen) ₃ ²⁺. The results of the present study differ from those reported for photo initiation by ion pairs of the type Fe ³⁺X ^n- where ×= CI^?, Br^?, C₂O₄ ^2- OH^?, etc., which may be attributed to differences in the photo-behavior of the two systems.     

Three characteristic reactions of alkynes with metal compounds in organic synthesis

Alkynes have two sets of mutually orthogonal π‐bonds that are different from the π‐bonds of alkenes. These π‐bonds are able to bond with transition metal compounds. Alkynes easily bond with the various kinds of compounds having a π‐bond such as carbon monoxide, alkenes, other alkynes and nitriles in the presence of the transition metal compounds. The most representative reaction of alkynes is called the Pauson–Khand reaction. The Pauson–Khand reactions include the cyclization of alkynes with alkenes and carbon monoxide in the presence of cobalt carbonyls. Similar Pauson–Khand reactions also proceed in the presence of other transition metal compounds. These reactions are the first type of characteristic reaction of alkynes. Other various kinds of cyclizations with alkynes also proceed in the presence of the transition metal compounds. These reactions are the second type of characteristic reaction of alkynes. These include cyclooligomerizations and cycloadditions. The cyclooligomerizations include mainly cyclotrimerizations and cyclotetramerizations, and the cycloadditions are [2 + 2], [2 + 2 + 1], [2 + 2 + 2], [3 + 2], [4 + 2], etc., type cycloadditions. Alkynes are fairly reactive because of the high s character of their σ‐bonds. Therefore, simple coupling reactions with alkynes also proceed besides the cyclizations. The coupling reactions are the third type of characteristic reactions of alkynes in the presence of, mainly, the transition metal compounds. These reactions include carbonylations, dioxycarbonylations, Sonogashira reactions, coupling reactions with aldehydes, ketones, alkynes, alkenes and allyl compounds. Copyright © 2008 John Wiley & Sons, Ltd.     

铱催化环加成反应的研究进展

过渡金属催化环加成反应是合成单环及多环化合物的重要方法,也是有机化学的研究热点之一.综述了近年来铱催化环加成反应的研究进展,主要包括了[2+2+1],[2+2+2],[4+2],1,3-偶极环加成反应等,及少量关于[3+2+2],[3+2],[5+1]环加成反应的报道,并讨论了部分铱催化环加成反应机理.     

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.     

Vinyl polymerization by cobaltic ions in aqueous solution. Part II. Polymerization of acrylonitrile and methyl acrylate

Polymerization of methyl acrylate in HClO₄ and HNO₃ was studied in the temperature range 10–15°C. The kinetics of the polymerization were found to be very simple, involving initiation and termination by cobaltic ions. Kinetic studies on polymerization of acrylonitrile in HClO₄ and HNO₃ revealed that water oxidation, and monomer oxidation were side reactions as in the case of methyl methacrylate. Experimental evidence favored the simultaneous initiation by Co³⁺ and CoOH²⁺ species. In H₂SO₄, certain unusual features were encountered. At low [Co³⁺], linear termination as well as termination by mutual combination occurred. Another interesting aspect was that CoSO₄⁺ initiated at low [Co³⁺]. This was unlike the case of other monomers in H₂SO₄. The rates of polymerization and rates of cobaltic ion disappearance were measured with respect to changes in [M], [Co³⁺], [H⁺], temperature, etc. The various rate constants were evaluated.     

Comparison of Nonheme Manganese- and Iron-Containing Flavone Synthase Mimics

Heme and nonheme-type flavone synthase enzymes, FS I and FS II are responsible for the synthesis of flavones, which play an important role in various biological processes, and have a wide range of biomedicinal properties including antitumor, antimalarial, and antioxidant activities. To get more insight into the mechanism of this curious enzyme reaction, nonheme structural and functional models were carried out by the use of mononuclear iron, [Fe^II(CDA-BPA*)]²⁺ (6) [CDA-BPA = N,N,N’,N’-tetrakis-(2-pyridylmethyl)-cyclohexanediamine], [Fe^II(CDA-BQA*)]²⁺ (5) [CDA-BQA = N,N,N’,N’-tetrakis-(2-quinolilmethyl)-cyclohexanediamine], [Fe^II(Bn-TPEN)(CH₃CN)]²⁺ (3) [Bn-TPEN = N-benzyl-N,N’,N’-tris(2-pyridylmethyl)-1,2-diaminoethane], [Fe^IV(O)(Bn-TPEN)]²⁺ (9), and manganese, [Mn^II(N4Py*)(CH₃CN)]²⁺ (2) [N4Py* = N,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine)], [Mn^II(Bn-TPEN)(CH₃CN)]²⁺ (4) complexes as catalysts, where the possible reactive intermediates, high-valent Fe^IV(O) and Mn^IV(O) are known and well characterised. The results of the catalytic and stoichiometric reactions showed that the ligand framework and the nature of the metal cofactor significantly influenced the reactivity of the catalyst and its intermediate. Comparing the reactions of [Fe^IV(O)(Bn-TPEN)]²⁺ (9) and [Mn^IV(O)(Bn-TPEN)]²⁺ (10) towards flavanone under the same conditions, a 3.5-fold difference in reaction rate was observed in favor of iron, and this value is three orders of magnitude higher than was observed for the previously published [Fe^IV(O)(N2Py2Q*)]²⁺ [N,N-bis(2-quinolylmethyl)-1,2-di(2-pyridyl)ethylamine] species.     

The physicochemical properties of some imidazolium-based ionic liquids and their binary mixtures

The density, viscosity and conductivity of ionic liquids (ILs), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]), 1-octyl-3-methylimidazolium chloride ([omim][Cl]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim] BF4]), 1-hexyl- 3-methylimidazolium chloride ([hmim][Cl]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]), and the [omim][BF4] + [omim][Cl], [hmim][BF4] + [hmim][Cl], and [hmim][PF6] + [hmim][Cl] binary mixtures were studied at dif- ferent temperatures. It was demonstrated that the densities of both the neat ILs and their mixtures varied linearly with temper- ature. The density sensitivity of a binary mixture is between those of the two components. The excess molar volumes (VE) of [hmim][BF4] + [hmim][Cl] and [hmim][PF6] + [hmim][Cl] mixtures are positive in the whole composition range. For [omim][BF4] + [omim][Cl], the VE is also positive in the [omim][Cl]-rich region, but is negative in the [omim][BF4]-rich re- gion. The viscosity or conductivity of a mixture is in the intermediate of those of the two neat ILs. For all the neat ILs and the binary mixtures studied, the order of conductivity is opposite to that of the viscosity. The Vogel-Tammann-Fulcher (VTF) equations can be used to fit the viscosity and conductivity of all the neat ILs and the binary mixtures. The neat ILs and their mixtures obey the Fractional Walden Rule very well, and the values of the Walden slopes are all smaller than unit, indicating obvious ion associations in the neat ILs and the binary mixtures.     

Stabilité en solution aqueuse de complexes de métaux lourds avec des ligands diaza-polyoxamacrocycliques

Stability in aqueous solution of some complexes of heavy metals with diaza-polyoxamacrocyclic ligands Stability of metal complexes (Mⁿ⁺ = Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Pb²⁺, Ag⁺ and Cd²⁺) with five diaza-polyoxamacrocycles (L = [2.1.1], [2.2.1], [2.2.2], [2.1] and [2.2] ) have been determined at 25°, in 0.1 M Et₄N⁺ClO aqueous solutions, by means of potentiometric titrations. All cations form MLⁿ⁺ complexes; Cu²⁺ also forms the MHL⁽ⁿ⁺¹⁾⁺ protonated species with both [2.2.1] and [2.1.1] ligands. The stability of these complexes has been discussed in terms of structure and by considering the ionic radii of the cations together with the radii of the macrocyclic cavities. Different behaviour is observed between some of these complexes and the well known alkali and alkaline-earth cryptates, partly due to the more covalent nature of bonds formed by the investigated cations and the donor sites of the ligands. The effect of the substitution of two oxygen by two sulfur atoms in the pentadentate ligand [2.1] on the stability of the complexes is reported.     

Synthesis and crystal structures of two three-dimensional vanadium polyoxoanion-bridged macrocyclic metal complexes

The reactions of transition metal macrocyclic complexes [ML](ClO₄)₂ (L?=?5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, M?=?Ni, Cu) with NH₄VO₃ under hydrothermal conditions gave two coordination polymers, namely [NiL]₂[V₆O₁₇] and [CuL]₂[V₆O₁₇]. Single-crystal X-ray diffraction analyses indicated that the central Ni(II)/Cu(II) atom displays a distorted six-coordinate octahedral coordination geometry by coordination with four nitrogen atoms of L, and two oxygen atoms of [VO₄] tetrahedrons. Compounds [NiL]₂[V₆O₁₇] and [CuL]₂[V₆O₁₇] show three-dimensional structures, which are constructed through the connections of dodecanuclear [V₁₂O₃₂]^4? rings with [NiL]²⁺ in [NiL]₂[V₆O₁₇], and [V₈O₂₂] _n ^4n? chains with [CuL]²⁺ in [CuL]₂[V₆O₁₇], respectively, generating one-dimensional channels.     

Speciation of the Vanadium(III) Complexes with 1,10-Phenanthroline, 2,2′-Bipyridine,and 8-Hydroxyquinoline

The complex species formed between vanadium(III) and 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), and 8-hydroxyquinoline (8hq) were studied in aqueous solution by means of electromotive forces measurements, emf(H), at 25 °C with 3.0 mol⋅dm⁻³ KCl as the ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic vanadium(III) species formed in solution. Analysis of the vanadium(III)–phen system data shows the formation of [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes. In the vanadium(III)–bipy system the [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes were observed, and in the vanadium(III)–8hq system the complexes [V(OH)L]⁺, [V(OH)₂L], [VL₂]⁺ and [VL₃] were detected.     

Metal Complexes with Macrocyclic Ligands. Part XXXIX. Mono- and binuclear copper(II) complexes of a bridging bis[1, 4, 7-triazacyclononane]

The new bis-macrocycle 1, 1′-[(1H-pyrazol-3], 5-diyl)bis(methylene)bis[1, 4, 7-triazacyclononane] ( 1 ) was synthesized and its complexation with Cu²⁺ studied. Potentiometric and spectrophotometric titrations indicate that, in addition to the mononuclear species [Cu(LH₂)]⁴⁺, [Cu(LH)]³⁺, [CuL]²⁺, and [Cu(LH_?1)]⁺, binuclear complexes such as [Cu₂L]⁴⁺, [Cu₂(LH_?1)]³⁺, and [Cu₂(LH_-2)]²⁺ are also formed in solution. The stability constants and spectral properties of these are reported. The binuclear species [Cu₂(LH_?1)]³⁺ specifically reacts with an azide ion to give a ternary complex [Cu₂(LH_?1)(N₃)]²⁺, the stability and structure of which were determined spectrophotometrically and by X-ray diffraction, respectively. The two Cu²⁺ ions are in a square-pyramidal coordination geometry. The axial ligand is one of the N-atoms of the 1, 4, 7-triazacyclononane ring, whereas at the base of the square pyramid, one finds the other two N-atoms of the macrocycle, one N-atom of the pyrazolide and one of the azide, both of which are bridging the two metal centres. In [Cu₂(LH_?1)(N₃)]²⁺, a strong antiferromagnetic coupling is present, thus resulting in a species with a low magnetic moment of 1.36 B.M. at room temperature.