Synthesis and characterization of monomeric and dimeric palladium(II)–ammonium complexes: their use for the catalytic oxidation of alcohols

The addition of quaternary ammonium salts, R₄NX, to PdCl₂ leads to mononuclear anionic complexes: (R₄N)₂PdX₄. A dinuclear complex, (n-Bu₄N)₂Pd₂Cl₆, has been characterized from the crystallization of the corresponding monomeric species under controlled conditions. These complexes revealed a similar efficiency as mixtures of PdCl₂ and R₄NX for the catalytic oxidation of alcohols using 1,2-dichloroethane as both solvent and stoichiometric oxidant.     

New iron(II) α-iminopyridine complexes and their catalytic activity in the oxidation of activated methylene groups and secondary alcohols to ketones

A set of iron(II) complexes of the general formula [Fe(OTf)(2)L(2)] was synthesized in 32 to 78% isolated yields, where L represents a bidentate α-iminopyridine ligand. Four of the iron complexes were characterized structurally, revealing a rich coordination chemistry, because the coordination geometry of the iron complexes strongly depends on the substitution pattern exhibited by the ligands L. The catalytic activity of the new complexes was demonstrated in the oxidation of cyclohexane, activated methylene groups and secondary alcohols to the corresponding ketones utilizing H(2)O(2) and t-BuOOH as the oxidants. The oxidation of activated methylene groups and secondary alcohols to the corresponding ketones with t-BuOOH gave isolated yields between 22 and 91% (4 h, room temperature, 3% catalyst load). The influence of the structure of the ligand on the activity of the corresponding metal complex is also reported. Furthermore, UV-vis experiments were performed which provided evidence for the formation of an [Fe-O-O-t-Bu] intermediate.     

Interconversion of copper(II) to copper(I): synthesis,characterization of copper(II) and copper(I) 2,2′-biquinoline complexes and their microbiological activity

The complexes [Cu(biq)₂]Cl₂ and [Cu(biq)₂]BF₄·biq (biq?=?2,2′-biquinoline) have been prepared and characterized. The interconversion to copper(I) complex [Cu(biq)₂]BF₄·biq, from [Cu(biq)₂]Cl₂ has been established. The new complexes have been characterized by elemental analysis, conductivity and magnetic measurements, IR, UV-vis and ¹H- and ¹³C-NMR spectroscopy. The X-ray analysis of the complex [Cu(biq)₂]BF₄·biq supports the assumption of the interconversion of copper(II) to copper(I) in this case. The crystal structure shows that geometry around the metal is severely distorted from T_d, and displays many supramolecular motifs incorporating both hydrophobic (aryl···aryl) and hydrophilic (C–H···F) intermolecular interactions. The microbiological activity of the complexes against bacteria and fungi was found to be high against Candida albicans, and slight to moderate against bacteria. The antimicrobial activity of [Cu(biq)₂]BF₄·biq was slightly better than that observed for [Cu(biq)₂]Cl₂ against both bacteria and fungi.     

Zinc(II) ortho-hydroxyphenylhydrazo-β-diketonate complexes and their catalytic ability towards diastereoselective nitroaldol (Henry) reaction

The zinc(II) complexes with ortho-hydroxy substituted arylhydrazo-β-diketonates [Zn(2)(CH(3)OH)(2)(μ-L(1))(2)] (5), [Zn{(CH(3))(2)SO}(H(2)O)(L(2))] (6), [Zn(2)(H(2)O)(2)(μ-L(3))(2)] (7) and [Zn(H(2)O)(2)(L(4))]·H(2)O (8) were synthesized by reaction of a zinc(II) salt with the appropriate hydrazo-β-diketone, HO-2-C(6)H(4)-NHN=C{C(=O)CH(3)}(2) (H(2)L(1), 1), HO-2-O(2)N-4-C(6)H(3)-NHN=C{C(=O)CH(3)}(2) (H(2)L(2), 2), HO-2-C(6)H(4)-NHN=CC(=O)CH(2)C(CH(3))(2)CH(2)C(=O) (H(2)L(3), 3) or HO-2-O(2)N-4-C(6)H(3)-NHN=[CC(=O)CH(2)C(CH(3))(2)CH(2)C(=O) (H(2)L(4), 4). They were fully characterized, namely by X-ray diffraction analysis that disclosed the formation of extensive H-bonds leading to 1D chains (5 and 6), 2D layers (7) or 3D networks (8). The thermodynamic parameters of the Zn(II) reaction with H(2)L(2) in solution, as well as of the thermal decomposition of 1-8 were determined. Complexes 5-8 act as diastereoselective catalysts for the nitroaldol (Henry) reaction. The threo/erythro diastereoselectivity of the β-nitroalkanol products ranges from 8:1 to 1:10 with typical yields of 80-99%, depending on the catalyst and substrate used.     

Ruthenium(II)/(III) and oxovanadium(IV) complexes of highly conjugated β-diketones and their macrocyclic Schiff base binuclear copper(II) complexes

Ruthenium(II) complexes of the general formula [Ru(PPh3)2(L)(L)]ClO4 [L=2,2-bipyridine or 1,10-phenanthroline;L=2-hydroxy--4-X-phenylcinnamoylacetophenone] have been prepared by reacting L and L with Ru(PPh3)3Cl2 in CH2Cl2. The complexes are diamagnetic and absorb intensely in the visible region, owing to the MLCT transition. Hexacoordinated ruthenium(III) complexes, [RuCl2(PPh3)2(L)], have also been prepared by reacting Ru(PPh3)3Cl3 with -diketones. Solutions of ruthenium(III) complexes show rhombic e.s.r. spectra at 77 K, and distortion from the octahedral symmetry has been identified from the line spacings. The conjugation in diketones favours reversibility in RuII/III and RuIII/IV and stabilize ruthenium in different oxidation states owing to d–* interaction. Oxovanadyl(IV) complexes of the -diketones with a metal-to-ligand ratio of 1:2 and square pyramidal geometry were also prepared. The e.s.r spectra of these complexes show the presence of an unpaired electron in the dxy orbital and the hyperfine splitting constants are sensitive to solvent change. ¶ A new class of highly conjugated Schiff bases obtained from the above diketones and 2-aminothiophenol behave as dibasic, tridentate ligands in their copper(II) complexes. The subnormal magnetic moments and hyperfine splittings of these complexes are ascribed to an antiferromagnetic exchange interaction arising from dimerization. Cyclic voltammograms show that the electron transfer occurs in two steps corresponding to CuII–CuI and CuI–CuI redox states.     

2,2′-Bipyridyl-acetylphenolato mixed ligand copper(II) complexes: syntheses,characterizations and catalytic activity in styrene epoxidation

Two copper(II) complexes, [Cu(bipy)(5-Br-2-hap)(ClO₄)]₂ (1) and [Cu(bipy)(2-hap)(ClO₄)] (2) (where bipy?=?2,2′-bipyridine, 5-Br-2-hap?=?5-bromo-2-hydroxyacetophenone, 2-hap?=?2-hydroxyacetophenone), were synthesized and characterized. The crystal structure of 1 was determined by single crystal X-ray diffraction while 2 was reported earlier. Structural characterization reveals that the presence of bromine in 5-Br-2-hap plays a structure-determining role in dimeric 1 in comparison with the mononuclear 2 where 2-hap was used. Studies of the catalytic potential toward styrene epoxidation in homogeneous system using H₂O₂ as oxidant reveal that 1 is more efficient than 2 with respect to epoxide selectivity.     

The mass spectral fragmentation of copper(II) complexes of cyclic β-diketones

Summary Electron impact mass spectra of several bis(2-trifluoroacetylcycloalkanonato) copper(II) and bis(2-acetylcycloalkanonato) copper(II) chelates, in which the cyclic -diketonate moiety comprises five-, six-, seven-, and eight-membered ring systems, have been recorded. Compared with other copper(II) chelates of acyclic -diketonates, the present series of copper(II) cyclic -diketonates exhibited more pronounced intramolecular reduction reactions accompanied by a remarkably facile hydrogen migration resulting in the formation of the [LCu^(I)-H]⁺ ion as the base peak in all complexes investigated. The proposed fragmentation pathways leading to the formation of a number of important copper-containing daughter ions have been confirmed by metastable scanning of the corresponding parent ion spectra using the defocusing technique.

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Massenspektroskopische Fragmentierung von Kupfer(II)-Komplexen cyclischer -Diketone

Zusammenfassung Es wurden die EI-Massenspektren einiger Bis(2-trifluoracetylcycloalkanato)kupfer(II)-und Bis(2-acetylcycloalkanato)kupfer(II)-Chelate mit fünf-, sechs-, sieben- und achtgliedrigen cyclischen -Diketonat-Liganden gemessen. Im Vergleich zu anderen Kupfer(II)-Chelaten mit offenkettigen -Diketonaten zeigen die cyclischen Komplexe eine ausgeprägte Neigung zu intramolekularen Reduktionsreaktionen, die von einer bemerkenswert leicht erfolgenden Wasserstoffwanderung begleitet sind; dies führt zur Bildung von [LCu^(I)-H]⁺ als Basispeak für alle untersuchten Komplexe. Die vorgeschlagenen Fragmentierungswege, die zur Bildung einer Reihe wichtiger kupferhaltiger Tochterionen führen, wurden durch Untersuchung der entsprechenden metastabilen Mutterionen mittels der Defokussierungsmethode überprüft.

     

Synthesis,spectral, magnetic,electrochemical and catalytic studies of cyclam-based copper(II) and nickel(II) complexes–effect of N-substitution

New N-substituted cyclam ligands 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-1,4,8,11-tetraazacyclotetradecane, 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane, 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-1,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane (L¹–L⁴) were synthesized and mononuclear copper(II) and nickel(II) complexes prepared. The ligands and complexes were characterized by elemental analysis, electronic, IR, ¹H NMR and ¹³C NMR spectral studies. N-alkylation causes red shifts in the λ_max values of the complexes. Copper(II) complexes show one-electron, quasi-reversible reduction waves in the range ?1.04 to ?1.00 V. The nickel(II) complexes show one-electron, quasi-reversible reduction waves in the range ?1.18 to ?1.30 V and one-electron, quasi-reversible oxidation waves in the range +1.20 to +1.40 V. The reduction potential of the copper(II) and nickel(II) complexes of the ligands L¹ to L² and L³ to L⁴ shift anodically on N-alkylation. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment value μ_eff?=?1.70–1.74 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and on the hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalyst were carried out. The tetra-N-substituted complexes have higher rate constants than the corresponding disubstituted complexes.     

The structure and EPR spectra of binuclear copper(II) complexes with acyldihydrazones of β-diketones

The synthesis and structure of binuclear copper(II) complexes with acyldihydrazones of some β-diketones are described. The molecular structure of the copper(II) complex [Cu₂L·4Py] with trifluoroacetylacetone succinyldihydrazone (H₄L) was determined by the single-crystal X-ray analysis. Central atoms are bridged by a chain of seven σ-bonds with a Cu...Cu distance of 8.750 Å. EPR spectra of copper(II) complexes with acyldihydrazones of trifluoroacetylacetone and lower dicarboxylic acids containing from one to four methylene groups in the aliphatic spacer show the seven-line HFS due to spin-spin coupling of unpaired electrons with the two equivalent copper nuclei (g = 2.110, a = (38.5–40.5)⊙10^?4 cm^?1). By extending polymethylene spacer, as well as by modifying starting β-diketone, an exchange interaction between paramagnetic centers is suppressed.     

Synthesis and structures of mono(β-diiminato) copper complexes and their catalytic performances for homo- and copolymerizations of methyl acrylate

A series of mono(β-diiminato) copper complexes bearing different coordinating anions and with different fluorine substitution patterns on the β-diiminato ligands were synthesized. All of the complexes were characterized by physicochemical and spectroscopic methods, and in addition, the structures of two of them were confirmed by X-ray diffraction. The crystal structures revealed a four-coordinate mode around the copper center in a slightly distorted square planar geometry, with the β-diimine and the carboxyl groups coordinated to give six- and four-membered chelate rings. The conjugation of C=C and C=N in the β-diiminato ligands and the resonance between C–O and C=O in the carboxyl groups resulted in extensive delocalization of electrons and the formation of conjugated N–C–C–C–N and O–C–O π-bonds, respectively. When activated by modified methylaluminoxane (MMAO), these complexes can effectively catalyze methacrylate (MA) polymerization with activities up to 54.5 kg/mol Cu h, as well as MA/1-hexene copolymerization with the incorporation of MA over 80 %.     

Synthesis, structure of functionalized N-heterocyclic carbene complexes of Fe(II) and their catalytic activity for ring-opening polymerization of ε-caprolactone

The reaction of anhydrous FeBr₂ with two equivalents of in situ generated anionic aryloxo-functionalized N-heterocyclic carbene [NaO-4,6-di-C(CH₃)₃-C₆H₂-2-CH₂{C(NCHCHNR)}] (R = CH(CH₃)₂, NaL¹; R = CH₂Ph, NaL²) affords two bis-ligand Fe(II) complexes (1) and (2) in good yield, respectively. Attempt to synthesize mono-ligand Fe(II) bromide by the 1:1 molar ratio of NaL to FeBr₂ is unsuccessful, the same complexes of 1 and 2 were obtained. Both of 1 and 2 have been fully characterized by elemental analysis, ¹H NMR spectra and X-ray structure determination. Preliminary studies show that 1 can catalyze the ring-opening polymerization of ε-caprolactone as a single component catalyst. The mechanism of the present ROP of ε-caprolactone has been investigated by the end group analysis.     

Mixed ligand complexes of ruthenium(II) containing α,β-unsaturated-β-ketoaminesand their antibacterial activity

Hexacoordinated Ru^II complexes of the [RuX(CO)(PPh₃)(B)(LL)] type [X = Cl; B = PPh₃, pyridine (py), piperidine (pip) or morpholine (morph); LL = ,-unsaturated--ketoaminate] have been synthesised by reacting [RuHCl(CO)(PPh₃)(B)] (B = PPh₃, py, pip or morph) with the appropriate -ketoamine in a 1:1 molar ratio. The replacement of hydride ion and the triphenylphosphine group by a bidentate chelating ligand from the starting compounds occurs. The complexes were characterised by elemental analyses and spectral (i.r., electronic, ¹H- and ³¹P-n.m.r.) data. Antibacterial activity were also tested for in these new complexes.     

Stereoselectivity in bis(α-amino acid) copper(II) complexes—VII: Thermodynamics of N-benzylproline coordination to copper(II)

In the study of temperature dependence of stability constants of copper(II) complexes with N-benzyl-l-proline and N-benzyl-dl-proline it has been shown that the enantioselectivity in the given system (preference to the formation of meso-structure [Cu(d)(l)]) is caused by large entropy gain which is attended by the replacement of four molecules of water during complexation of d-shaped ligand to the monocomplex [Cu(L)(H₂O)₄] of the l-ligand.     

Electrochemistry of nickel(II) and copper(II) N,N′-ethylenebis(acetylacetoniminato) complexes and their electrocatalytic activity for reduction of carbon dioxide and carboxylic acid protons

The effect of the metal center of [ML] complexes [M = Ni(II), Cu(II); L = N,N′-ethylenebis(acetylacetoniminato)] on their electrochemistry and electrocatalytic activity for the reduction of CO₂ and protons has been studied using cyclic voltammetry and bulk electrolysis. The two complexes exhibit different electrochemistries, which are not significantly dependent on the nature of the solvent. The electrocatalytic activity of [NiL] is significantly higher than that of [CuL] for CO₂ reduction, due to the higher stability of the electrochemically generated [Ni(I)L] complex, relative to the Cu(I) analog. The diffusion coefficient of [NiL] calculated from the steady-state diffusion limiting current is 3.0 × 10^?6 cm² s^?1. The catalytic efficiency of [NiL] in non-aqueous solvents in terms of i _p(CO₂)/i _p(N₂) per nickel center is smaller than that of [Ni(cyclam)]²⁺, but greater than those of sterically hindered mononuclear [Ni(1,3,6,8,10, 13,15-heptaazatricyclo(11.3.1.1) octadecane)]²⁺ or multinuclear [Ni₃ (X)]⁶⁺ where X = 8,8′,8″-{2,2′,2″(-nitrilotriethyl)-tris(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1) octadecane}. Both [NiL] and [CuL] are also electrocatalysts for the reduction of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN.     

Synthesis of copper(II) and zinc(II) complexes with chalcone–thiosemicarbazone hybrid ligands: X-ray crystallography,spectroscopy and yeast activity

Four chalcone–thiosemicarbazones (C-TSCs) of the type 2-((E)-3-(4-R-phenyl)-1-phenylallylidene)-N-phenylhydrazinecarbothioamide, where R?=?Cl (HL1), NO₂ (HL2), CH₃ (HL3) or CN (HL4), were prepared in good yields from the reaction of the respective chalcone with 4-phenyl-3-thiosemicarbazide and HCl in EtOH. Reaction of HL with CuCl₂·2H₂O or ZnCl₂ in the presence of Et₃N afforded the complexes [M(L)₂], M?=?Cu(II) or Zn(II). X-ray diffraction analysis revealed that the ligands coordinate in their deprotonated form, in a bidentate fashion through the iminic nitrogen and sulfur atoms. Yeast activities of the compounds were tested, where the ligand HL4 was the most damaging derivative, exhibiting cell viability at about 50%. On the other hand, lipid peroxidation assays revealed that the ligand HL1 was able to better induce membrane damage compared to the other compounds. It has been found that coordination with Cu(II) and Zn(II) did not increase the biological activities of the C-TSCs.     

Synthesis,characterization, and biological activity studies of copper(II)–metal(II) binuclear complexes of dipyridylglyoxal bis(2-hydroxybenzoyl hydrazone)

A new series of copper(II) mononuclear and copper(II)–metal(II) binuclear complexes [(H₂L)Cu] ? H₂O, [CuLM] ? nH₂O, and [Cu(H₂L)M(OAc)₂] ? nH₂O, n = 1–2, M = Co(II), Ni(II), Cu(II), or Zn(II), and L is the anion of dipyridylglyoxal bis(2-hydroxybenzoyl hydrazone), H₄L, were synthesized and characterized. Elemental analyses, molar conductivities, and FT-IR spectra support the formulation of these complexes. IR data suggest that H₄L is dibasic tetradentate in [(H₂L)Cu] ? H₂O and [Cu(H₂L)M(OAc)₂] ? nH₂O but tetrabasic hexadentate in [CuLM] ? nH₂O (n = 1–2). Thermal studies indicate that waters are of crystallization and the complexes are thermally stable to 347–402°C depending upon the nature of the complex. Magnetic moment values indicate magnetic exchange interaction between Cu(II) and M(II) centers in binuclear complexes. The electronic spectral data show that d–d transitions of CuN₂O₂ in the mononuclear complex are blue shifted in binuclear complexes in the sequences: Cu–Cu > Cu–Ni > Cu–Co > Cu–Zn, suggesting that the binuclear complexes [CuLM] ? nH₂O are more planar than the mononuclear complex. The structures of complexes were optimized through molecular mechanics applying MM ⁺force field coupled with molecular dynamics simulation. [(H₂L)Cu] ? nH₂O, [CuLM] ? nH₂O, and the free ligand were screened for antimicrobial activities on some Gram-positive and Gram-negative bacterial species. The free ligand is inactive against all studied bacteria. The screening data showed that [CuLCu] ? H₂O > [(H₂L)Cu] ? H₂O > [CuLZn] ? H₂O > [CuLNi] ? 2H₂O ≈ [CuLCo] ? H₂O in order of biological activity. The data are discussed in terms of their compositions and structures.     

Synthesis of new unsymmetrical “end-off” phenoxo bridged copper(II), nickel(II) and zinc(II) complexes: spectral,magnetic, electrochemical,catalytic, and antimicrobial studies

A new class of unsymmetrical end-off, aminomethylated N-methylpiperazine and aminomethylated diethanolamine binucleating ligands, 2-[bis(2-hydroxyethyl)aminomethyl]-6-[(4-methylpiperazin-1-yl)methyl]-4-methylphenol (HL¹) and 2-[bis(2-hydroxyethyl)aminomethyl]-6-[(4-methylpiperazin-1-yl)methyl]-4-acetylphenol (HL²) were synthesized by following sequential aromatic Mannich reactions. Their mononuclear and binuclear Cu(II), Ni(II) and Zn(II) complexes have been synthesized and their formulation was confirmed by analytical and spectral analysis. The mononuclear Cu(II) complexes have a magnetic moment value close to the spin only value with four hyperfine EPR signals. The binuclear Cu(II) complexes have an antiferromagnetic interaction with a broad EPR signal. Electrochemical studies of the complexes reveal that all the redox processes are irreversible. Catecholase activity of Cu(II) complexes and the hydrolysis of 4-nitrophenylphosphate using Cu(II), Ni(II), and Zn(II) complexes were carried out. Spectral, magnetic, electrochemical, and catalytic behaviors of the complexes are compared on the basis of the p-substituent of the phenolic ring. Some of the complexes show significant growth inhibitory activity against pathogenic bacteria and fungi.     

Interactions of zinc(II) complexes with 5′-GMP and their cytotoxic activity

The mechanism of substitution from tetrahedral [ZnCl₂(en)] and square-pyramidal [ZnCl₂(terpy)] complexes (where en = 1,2-diaminoethane or ethylenediamine and terpy = 2,2′:6′,2′′-terpyridine) by guanosine-5′-monophosphate (5′-GMP) have been investigated by ¹H NMR spectroscopy. The substitution reaction of [ZnCl₂(terpy)] complex is faster than the reaction of [ZnCl₂(en)], which was finished after 48?h. Information about the structures of the final products in solution were obtained from the DFT calculations (B3LYP/6-31G(d)) and experimental ¹H NMR data acquired during the course of the reaction. The cytotoxic activity of zinc(II) complexes was tested on human breast cancer cell line MDA-MB-231, human colon cancer cell line HCT-116 and normal human lung fibroblast cell line MRC-5. Both complexes reduced cell viabilities, while [ZnCl₂(terpy)] was significantly cytotoxic on MDA-MB-231 after 72?h, and HCT-116 after 24?h without dose dependence. The differences in reactivity toward 5′-GMP and cytotoxic activity of Zn(II) complexes may be attributed to the very stable square-pyramidal geometry of [ZnCl₂(terpy)] in solution, while weak ligand effect of the en compared to the terpy affected slow interaction of tetrahedral [ZnCl₂(en)] complex with the target bio-molecule.     

Aerobic oxidation of alcohol by model complexes relevant to metal site galactose oxidase: role of copper(I) intermediate,evidence for the generation of end-on copper(II)–OOH species and catalytic promiscuity for oxidation of benzyl alcohol,catechol and o-aminophenol

Transition Metal Chemistry - Tridentate ligands having meridional NNO donor centres were designed and synthesized mimicking the copper coordination in the metal site of galactose oxidase enzyme....     

Novel trinuclear copper(II) complexes with α,β-unsaturated carboxylates and imidazole

A MeOH solution of imidazole reacts with Cu₂A₄(H₂O)₂ [A = CH₂=CHCO^– ₂, CH₂=C(Me)CO^– ₂] to yield novel trinuclear copper(II) carboxylate complexes of general formula: Cu₃A₅(OH)(imH)₃ [(1) A=CH₂=CHCO^– ₂; (2) A = CH₂=C(Me)CO^– ₂; imH = imidazole]. The crystal structure of (2) has been determined. The geometry of one copper(II) atom is distorted trigonal bipyramidal, and the other two copper(II) atoms are distorted square-planar. The i.r. spectra show the presence of the absorption bands of both bidentate ₂-O,O and monodentate carboxylate ligands. The electronic reflectance spectra in the solid state suggest that the d–d transitions of complexes are in a trigonal bipyramidal ligand field and a square-planar ligand field. Room temperature X-band e.s.r. spectra of powdered samples with g _av = 2.140 for (1) and g _av = 2.092 for (2), indicate that there is no spin coupling between the copper(II) atoms.