Copper(II) PMDTA and copper(II) TMEDA complexes: precursors for the synthesis of dinuclear dicationic copper(II) complexes

Copper(II) cations coordinated with PMDTA (pentamethyldiethylenetriamine) and TMEDA (tetramethylethylenediamine) possess a high synthetic potential. The synthesis of these cations was carried out by metathesis reactions with silver salts. The cationic copper(II) complexes, [Cu(PMDTA)(Me₂CO)Cl]⁺, [Cu(PMDTA)(H₂O)Cl]⁺, [Cu(PMDTA)(DMF)]⁺, [Cu(PMDTA)Cl]⁺, [Cu(PMDTA)OAc]⁺, [Cu(PMDTA)(MeCN)₂]²⁺, [Cu₂(TMEDA)₂Cl₃]⁺ and [Cu(TMEDA)(MeCN)₃]²⁺ were synthesised as PF₆ salts, crystallised and characterised by single-crystal X-ray diffraction.     

Crystal and molecular structure of [Cu(5'-inosine monophosphate) (dipyridylamine) (H2O)]2.4H2O.

The ternary complex [Cu(5′-IMP)(dpa)(H₂O)]₂ has been prepared and its structure analyzed by x-ray diffraction. It has a dimeric structure in which the 5′-IMP ligands coordinate solely through their phosphate groups. This geometry is in marked contrast to that of another $\text{Cu}\text{5′-}\text{IMP}$ ternary complex, [Cu(5′-IMPH)(bipy)(H₂O)₂]⁺, which shows metal binding through the purine base rather than the phosphate group.     

Structural characterization of a metal-based perfusion tracer: Copper(II) pyruvaldehyde bis (N4-methylthiosemicarbazone)

Copper(II) pyruvaldehyde bis(N⁴-methylthiosemicarbazone), Cu(PTSM), has been obtained as a dark red crystalline solid from EtOH-DMSO solvent mixture and structurally characterized by x-ray crystallography. The molecule possesses the expected pseudo-square planar N₂S₂ metal coordination sphere; however, the copper center also interacts through its axial coordination site with the sulfur atom of an adjacent Cu(PTSM) molecule in the crystal lattice. The structure of this compound is compared with the structures of other metal complexes that have been proposed in the nuclear medicine literature as perfusion tracers.     

Oxidation of copper(II)-coordinated diethylenetriamine by hexacyanoferrate(III) ion. A kinetic investigation

The stoichiometry and kinetics of the reaction between [Cu(dien)(OH)]⁺ and [Fe(CN)₆]³⁻ in aqueous alkaline medium are described. The rate equation − (d[Fe(III)]/dt = {k₁[OH⁻]²[[Cu(dien)(OH)]⁺] + k₂[OH⁻] × [[Cu(dien)(OH)]⁺]²}([Fe(III)]/[Fe(II)]) (Fe(III) = [Fe(CN)₆]³⁻; Fe(II) = [Fe(CN)₆]⁴⁻, the 4:4:1 OH⁻/Fe(III)/[Cu(dien)(OH)]⁺ stoichiometric ratio and the nature of the ultimate products identified in the reaction solution suggest the fast formation of a doubly deprotonated Cu(III)-diamido complex which slowly undergoes an internal redox process where the ligand is oxidised to the Schiff base H₂NCH₂CH₂NCHCHNH.The [[Cu(dien)(OH)]⁺]² term in the rate equation is explained with the formation of a transient μ-hydroxo mixed-valence Cu dimer. A two-electron internal reduction of the Cu(III) complex yielding a Cu(I) intermediate is suggested to account for the presence of monovalent copper in a precipitate which forms at relatively high reactant concentrations and in the absence of dioxygen.     

Crystal structure, magnetic and electrochemical properties of five-coordinate copper (II) complexes with 1,10-phenanthroline-5,6-dione

Three new five-coordinate Cu^II complexes, [Cu(tpy)(phen-dione)](PF₆)₂, [Cu(phen)(phen-dione)Cl]PF₆ and [Cu(bpy)(phen-dione)Cl]PF₆ (tpy = 2,2′;6′,2″-terpyridine, phen = 1,10-phenanthroline and phen-dione = 1,10-phenanthroline-5,6-dione) have been prepared and characterized by elemental analysis, IR and UV-Vis spectroscopies and cyclic voltammetry.The complex of [Cu(tpy)(phen-dione)](PF₆)₂ crystallized with one molecule of acetonitrile. The ortep drawing of [Cu(tpy)(phen-dione)](PF₆)₂ · CH₃CN shows that the coordination geometry around Cu^II is a distorted trigonal- bipyramid. Due to the steric hindrance of in the unit cell, the tpy ligands in each complex cation cannot interact in a π-π fashion. The effective magnetic moment (μ_eff) of the complexes was measured by the Evans method. The cyclic voltammograms at Pt disk electrode for these complexes display only one reversible Cu(II)/Cu(I) redox couple.     

Spectroscopic and structural investigation of two (2,2′-bipyridyl)bis(N-protected-aminoacidato)copper(II) complexes,two compounds containing truly CuN2O2 chromophore

The compounds of formula [Cu(bipy)(acleuO)₂] (1) and [Cu(bipy)(ts-β-alaO)₂] (2) (bipy = 2,2′-bipyridil, acleuO = N-acetyl-DL-leucinate anion, ts-β-alaO = N-tosyl-β-alaninate anion) were synthesized and characterized by means of spectroscopic and structural measurements. Complex (1) crystallizes in the monoclinic space group C2/c with cell parameters a = 17.465(4), b = 19.740(5), c = 9.080(2) Å, β = 115.0(1)° with Z = 4; complex (2) crystallizes in the triclinic space group P$\text{1}$, with cell parameters a = 14.489(3), b = 14.308(3), c = 8.659(1) Å, α = 75.0(1), β = 74.6(1), γ = 66.6(1)°, Z = 2. Both structures were solved by conventional Patterson and Fourier methods and refined to R factors of 4.10 and 3.8% respectively. In both crystals the Cu atom is four-coordinated by the nitrogen atoms of a bipy molecule and two carboxylate oxygens of two N-protected aminoacid anions acting as unidentate ligands. The only significant difference between the coordination geometry of (1) and (2) is in the tetrahedral distortion of the coordination plane. Complex (2) is strictly planar, while in complex (1) the distortion expressed by the dihedral angle between the (N)(1)CuN(1′) and O(1)CuO(1′) planes is 20.8°. The electronic and EPR results agree with these different coordination geometries. The infra-red data are consistent with a truly monodentate carboxylate group. The spectroscopic results on a series of previously investigated [Cu(bipy)(N-protected aminoacidato)²] complexes of unknown structures are discussed again in the light of the present structural reports.     

Preparation and structural characterization of di-μ-azido-bis[azido(2-aminopyridine)aquo]dicopper(II), [Cu(2-ampy)(N3)2(H2O)]2

Di-μ-azido-bis[azido(2-aminopyridine)aquo]dicopper(II), [Cu(2-ampy)(N₃)₂(H₂O)]₂, was synthesized and characterized by X-ray crystallography. The crystals are triclinic, space group P$\text{1}$, with a = 7.142(1), b = 7.812(1), c = 9.727(1) Å, a = 96.52(1), β = 95.52(1), γ = 113.47(1)°, and Z = 1. The structure was refined to R_F = 0.030 for 1960 observed MoKα diffractometer data. The dimeric molecule, which possesses a crystallographic inversion center, contains both terminal and μ(1)-bridging azido groups. Each copper(II) atom is further coordinated by a 2-aminopyridine ligand (via its ring N atom) and a water molecule to give a distorted square pyramid, with the metal atom raised by 0.17 Å above the N₄ basal plane [CuN (ring) = 2.001(2), CuN (azide) = 1.962(3)–2.018(2) Å] towards the apical aquo ligand [CuO = 2.371(2) Å]. Each water molecule forms an intramolecular O?HN (amine) acceptor hydrogen bond, and is linked by two OH?N (terminal azide) intermolecular donor hydrogen bonds to adjacent dimeric complexes to yield a layer structure parallel to (001). Infrared and electronic spectral data are presented and discussed.     

Copper(I)-incorporation into spinach apoplastocyanin

Spinach plastocyanin was converted into the apoprotein. CuSO₄ and oxidized Cu(II)- thionein reacted with the apoprotein to Cu(II) plastocyanin. Cu(I) transfer from Cu(I)0-thionein was only 15%. The structural analogue of the copper thiolate chromophore [Cu(I)(thiourea)₃]Cl as well as [Cu(CH₃CN)₄]ClO₄ successfully formed the Cu(I)- holoprotein. Characteristic circular dichroism bands at θ₂₈₄ (?5300 deg·cm²·dmol^?1 and θ₃₁₀ (+3300 deg·cm²·dmol^?1) were seen. Upon oxidation with ferricyanide and dialysis against phosphate buffer the correct Cu(II) binding into the active centre of Cu(II) plastocyanin was confirmed by EPR-measurements. The use of [Cu(I)(thiourea)₃] Cl as a convenient Cu(I) source for reconstitution studies on copper proteins is highly recommended.     

Synthesis and structure of copper(II) complexes of two new poly(2-pyridylalkyl)diamine ligands

The new pentapyridyldiamine ligand, L¹, which incorporates two bis(2-pyridylethyl)amine donor domains held together by a 2,6-dimethylenepyridine linker, is readily prepared. In the presence of metal salts, L¹ is unstable due to facile elimination of vinyl pyridine. Complexes of L¹ are therefore difficult to isolate. Nonetheless, a novel copper dimer [Cu₂(L¹)(μ-OH)(CH₃CN)](ClO₄)₃ has been isolated in small quantities along with the interesting monomer [Cu(L²)](ClO₄)₂, in which L² is the tetrapyridyldiamine ligand derived from the decomposition of L¹ by loss of one pyridylethyl `arm'. The crystal structures of the two complexes are reported: the [Cu<sub>2</sub>(L<sup>1</sup>)(μ-OH)(CH<sub>3</sub>CN)]<sup>2+</sup> cation exhibits a μ-hydroxo-bridged dicopper(II) core and a coordinated acetonitrile molecule, akin to a putative intermediate in nitrile hydrolysis, and the chiral [Cu(L<sup>2</sup>)]<sup>2+</sup> cation is revealed to have a five-coordinate copper(II) centre that is stabilised by an intramolecular hydrogen-bond between the 2° amine group and a pendant pyridylethyl `arm'.     

Ternary copper(II) complexes with hippurate derivatives and 1,10-phenanthroline: Synthesis and biological activity

Several new Cu-hippurate derivative-phenanthroline ternary complexes have been prepared. The X-ray structure of one of them, [Cu(hip)(phen)₂]⁺·(hip⁻) (2) (where hip is hippurate and phen is 1,10-phenanthroline) has been solved. The structure of this new compound shows important differences (3D-pattern) to other similar related complexes (2D-pattern). A study of the biological activity of [Cu(hip)(phen)₂]⁺·(hip⁻)·2H₂O (2), [Cu(BGG)(phen)₂]⁺·(BGG⁻)·6H₂O (3), [Cu(B^IGG)₂(phen)](H₂O) (4) and [Cu(I-hip)(bpy)₂]⁺·(I-hip⁻)·3.5H₂O (5) (where I-hip is ortho-iodohippurate, BGG corresponds to benzoylglycilglycine, and B^IGG is ortho-iodobenzoylglycilglycine) is included and compared with the anti-proliferative activity of [Cu(I-hip)(phen)₂]⁺·(I-hip⁻)·7H₂O (1) previously described, resulting in a greater cytotoxic activity of the compounds with 1,10-phenanthroline instead of those with 2,2′-bipyridyl, in the same way that removing iodine substitution or lengthening the peptidic chain diminishes the activity of compounds compared with 1. The presence of an ortho-iodine group and the direct bond between Ar-CO and glycine moieties yield to the best results.     

Spectroscopic and electrochemical properties of heteroleptic cationic copper complexes bis-(diphenylphosphino)alkane-(2,2′-biquinoline)copper(I). Crystal structure of bis(diphenylphosphino)ethane-(2,2′-biquinoline)copper(I) perchlorate

A series of [Cu^(I)(2,2′-biquinoline)(L)](ClO₄) complexes (L = bis(diphenylphosphino)methane (bppm), 1,2-bis(diphenylphosphino)ethane (bppe), 1,4-bis(diphenylphosphino)butane (bppb)) have been synthesized and characterized by elemental analysis, conductivity, ESI-mass, NMR and UV-Vis spectroscopies, cyclic voltammetry, X-ray diffraction ([Cu^(I)(2,2′-biquinoline)(bppe)](ClO₄)) and DFT calculations. These compounds are monometallic species in a distorted tetrahedral arrangement, in contrast with related compounds found as dinuclear according to diffraction studies. The spectroscopic properties are not directly correlated with the length of alkyl chain bridge between the bis-diphenylphosphine groups. In this way, the chemical shift of some 2,2′-biquinoline protons and the metal to ligand charge transfer (Cu to 2,2′-biquinoline) follows the order [Cu(2,2′-biquinoline)(bppm)](ClO₄), [Cu(2,2′-biquinoline)(bppb)](ClO₄), [Cu(2,2′-biquinoline)(bppe)](ClO₄). The same dependence is followed by the potentials to Cu(II)/Cu(I) couple. These results are discussed in terms of inter-phosphorus alkane chain length and tetrahedral distortions on copper.     

The redox properties of (1,6-bis(benzimidazol-2-yl)-2,5-dithiahexane) chloro-copper(II) chloride as studied by cyclic voltammetry

Cyclic voltammetry in acetonitrile has been used to study the redox properties of the compound [Cu-(BBDH)Cl] Cl under various conditions. The nature of the species in solution was studied with the aid of ligand-field spectra and ESR spectra. It appears that in CH₃CN solution two Cu(II) species are predominating, viz. [Cu(BBDH)(CH₃CN)_x]²⁺ and Cu(BBDH)-Cl⁺. Minor species are dimeric in nature, such as [(BBDH)CuCl₂Cu(BBDH)]²⁺, as easily seen from ESR. The relative amount of the two major species was varied using added LiCl, allowing us to determine the nature of both species. The redox potential of the species [Cu(BBDH)Cl]⁺ appeared to be 0.62 V (against a normal hydrogen electrode), which is very high for a Cu(II) compound and in the same area as found for the blue copper proteins. Re-oxidation of Cu(BBDH)⁺ in the presence of LiCl shows that C$\text{l}$ slowly recoordinates after reoxidation.     

Copper(II) compounds of the planar-tridentate ligand 2,6-bis(pyrazol-3-yl)pyridine

The tridentate ligand 2,6-bis(pyrazol-3-yl)pyridine (dPzPy) renders coordination compounds with halide, nitrate and tetrafluoroborate salts of copper. The complexes, which have the form [Cu(dPzPy)X₂] with X=Br and Cl, [Cu(dPzPy)(NO₃)₂](H₂O), and [Cu(dPzPy)₂](BF₄)(SiF₆)_0.5(MeOH)₃ have been characterized by elemental analysis and by IR, EPR and ligand field spectroscopy. The single-crystal X-ray structure of [Cu(C₁₁H₉N₅)Br₂] shows the copper(II) ion to be coordinated by three N atoms of 2,6-bis(pyrazol-3-yl)pyridine and two bromides in a geometry exactly in between a trigonal-bipyramid and a square-pyramid. Each molecule lies on a crystallographic C₂-symmetry axis. They are coupled to one another by a two-dimensional network through NH to Br hydrogen bonds. The crystal structure of [Cu(C₁₁H₉N₅)Cl₂] is analogous to the bromide. The single-crystal X-ray structure of [Cu(dPzPy)₂](BF₄)(SiF₆)_0.5(MeOH)₃ shows the copper ion to be in a Jahn-Teller distorted octahedral N₆ environment of two mer-oriented tridentate ligands.     

Synthesis and crystal structure of a tetranuclear five-coordinated copper(II) complex with Schiff-base of N-(3-carboxylsalicylidene)-4-(2-iminoethyl)-morpholine

A tetranuclear copper(II) complex [Cu₄L₂(CH₃COO)₂(OH)₂]·6H₂O, in which L stands for the dianion of N-(3-carboxylsalicylidene)-4-(2-iminoethyl)morpholine, was synthesized and characterized by elemental analysis, IR, UV-Vis, TGA and X-ray single crystal diffraction. The crystal structure shows that the coordination unit is centrosymmetric with all the Cu(II) ions in square pyramidal coordination geometry. The coordination unit consists of two equivalent parts [Cu₂L(CH₃COO)(OH)], each containing two Cu(II) ions, a tetradentate N₂O₂ Schiff base dianion L²⁻, a CH₃COO⁻, and a OH⁻ anion. In [Cu₂L(CH₃COO)(OH)], the six coordination atoms (N₂O₄) are nearly coplanar, with Cu(1) and Cu(2) enchased in between; the phenolate oxygen and the OH⁻ oxygen as bridging atoms bind the two Cu(II) ions in close proximity; both O₄ around Cu(1) and N₂O₂ around Cu(2) form the basal plane of the coordination square pyramids. The two parts are connected by sharing two μ₃-OH⁻ oxygens and two μ₂-CH₃COO⁻ oxygens from each other, forming four edge-sharing coordination square pyramids around the four Cu(II) ions. A 3D network is formed through hydrogen bonding along a and c axis, and π-π interaction along b axis.     

Cu(II) complexes with labile apical coordination: Synthesis, crystal structure, H NMR investigation, and oxidation properties of mononuclear [Cu(dien)(2-PhIm)(ClO4)] (1), [Cu(dien)(2-MeBzIm)] (2), complexes

The compounds [Cu(dien)(2-PhIm)(ClO₄)](ClO₄) (1); [Cu(dien)(2-MeBzIm)](ClO₄)₂ (2); where dien = diethylenetriamine, 2-PhIm = 2-phenylimidazole and 2-MeBzIm = 2-methylbenzimidazole, were synthesized and characterized. The complexes possessing [Cu(II)dien] moiety as common, the former containing 2-phenylimidazole, yielded square pyramidal geometry with apical perchlorate coordination [Cu1-O(5) = 2.449 Å], while the latter with 2-methylbenzimidazole formed square planar geometry with weak perchlorate contact [Cu1-O(8) = 2.596 Å] in its apical position. The effect of solvent and the variable temperature ¹H NMR investigation combinedly explore the geometrical rearrangement towards five coordination around Cu(II) metal center by accommodating the solvent molecule in its fifth coordination. Possessing easily labile perchlorate anion, both these complexes were investigated for their oxidation capability using 3,5-di-tert-butyl catechol (DTBC). The rate constant determined for the oxidation of DTBC to corresponding quinone indicates that they are catalytically quite similar and the k_cat of 1 ≈ 2. The crystal structure and the NMR investigations are discussed in detail.     

An unexpected by-product obtained during the preparation of technetium(III) boronic acid adducts of dioximes. The single crystal structure of TcCl(DMG)2(BDI)BEt (DMG=dimethylglyoxime, BDI=butane-2, 3-dione imine-oxime)

An unusual Tc(III) boron-capped imine-oxime complex has been isolated from the reaction of ⁹⁹TcCl₃(CH₃CN)(PPh₃)₂, dimethyl glyoxime (DMG) and ethyl boronic acid (EtB(OH)₂). A single crystal X-ray structure analysis of this molecule ⁹⁹TcCl(DMG)₂(BDI)BEt (BDI=butane-2, 3-dione imine-oxime) shows it to be seven coordinate: TcClC₁₄H₂₅N₆O₅B, a=9.073(2), b=23.686(5), c=19.539(6) Å; β=93.77(2)°, P2₁/n, Z=8. Its structure is very similar to that of previously reported Tc(III) complexes ⁹⁹TcCl(dioxime)₃BR, except that one dioxime ligand on the molecule has been reduced to an imineoxime.     

Synthesis, characterization, and magnetic properties of new binuclear CuCu bis(oxamato) complexes

Two new neutral, binuclear Cu^IICu^II bis(oxamato) complexes with the formula [Cu₂(opba)(pmdta)(MeOH)] · 1/2MeOH · dmf (3) and [Cu₂(nabo)(pmdta)(MeOH)] (4), with opba = o-phenylene-bis(oxamato), nabo = 2,3-naphthalene-bis(oxamato), pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine and dmf = dimethylformamide have been synthesized and their crystal structures have been determined. The structure of 3 consists of dimeric [Cu₂(opba)(pmdta)(MeOH)] entities, joined together by mutual intermolecular Cu?O contacts of the Cu²⁺ ion of one [Cu(opba)]²⁻ complex fragment and one carboxylate atom of the oxamato group of a second [Cu(opba)]²⁻ complex fragment. The structure of 4 consists of neutral binuclear complexes joined together by hydrogen bonds and π-π interactions, giving rise to an unique supramolecular 1D-chain. The magnetic properties of 3 and 4 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, identical values of (−114 ± 2) cm⁻¹ (3) and (−112 ± 2) cm⁻¹ (4) were obtained.     

Synthesis, magnetism and X-ray structures of [Cu(2-aminopyrimidine)2(μ-OH)(CF3SO3)]2(2-aminopyrimidine)2, a new hydroxo-bridged dinuclear Cu(II) compound generating extremely small antiferromagnetism

The synthesis, optical and magnetic properties and X-ray crystal structure of [Cu(2-aminopyrimidine)₂(OH)(CF₃SO₃)]₂(2-aminopyrimidine)₂, a new dinuclear hydroxo-bridged copper(II) compound with a CuOCu angle of 97.96° and a very small antiferromagnetic interaction for which the singlet-triplet exchange parameter J, is described. The magnetic exchange coupling is almost negligible and, depending on the actual sample, varies from −1.8 to −7.2 cm⁻¹.     

Chemistry at the apical position of square-pyramidal copper(II) complexes: Synthesis, crystal structures, and magnetic properties of homopolynuclear complexes with azido bridges containing [Cu(AA)(BB)] moieties (AA = acetylacetonate; BB = 1,10-phenanthroline, bipy = 2,2′-bipyridine)

Three new homopolynuclear complexes with azido bridges have been obtained by using [Cu(AA)(BB)]⁺ building-blocks (AA = acetylacetonate; BB = 1,10-phenanthroline or 2,2′-bipyridine). The reaction between [Cu(acac)(phen)(H₂O)](ClO₄) and NaN₃ leads to a mixture of two compounds: a binuclear complex, [{Cu(acac)(phen)}₂(μ_1,3-N₃)](ClO₄) · 2H₂O (1), and a linear tetranuclear one, [{Cu(acac)(phen)(ClO₄)}₂{Cu(phen)(μ_1,1-N₃)₂}₂] (2). The reaction between [Cu(acac)(bipy)(H₂O)](ClO₄) and NaN₃ affords also a mixture of two compounds: [{Cu(acac)(bipy)}₂(μ_1,3-N₃)]₃(ClO₄)₃ · 3.75H₂O (3) and [Cu(acac)(bipy)(N₃)][Cu(acac)(bipy)(H₂O)](ClO₄) (4). The X-ray crystal structures of compounds 1-4 have been solved (for compound 4 the crystal structure was previously reported). In compounds 1 and 3, two {Cu(AA)(BB)} fragments are bridged by the azido anion in an end-to-end fashion. Two isomers, cis and trans with respect to azido bridge, were found in crystal 3. The structure of compound 2 consists of two Cu(II) central cations bridged by two μ_1,1-azido ligands, each of them being also connected to a {Cu(acac)(phen)} fragment through another μ_1,1-azido ligand. The cryomagnetic properties of the compounds 1 and 2 have been investigated and discussed. The magnetic behaviour of compound 1 shows the absence of any interactions between the metallic ions. In the tetranuclear complex 2, the magnetic interactions between the external and central copper(II) ions(J₁), and between the central metallic ions (J₂) were found ferromagnetic (J₁ = 0.36 cm⁻¹, J₂ = 7.20 cm⁻¹).     

Ligand exchange reactions between copper(II) and nickel(II) chelates of different sulphur and selenium containing ligands. VII. Single-crystal ESR study on the mixed ligand chelate system Ph4As[Cu/Zn(mnt)(Et2dtc)] and crystal and molecular structure of Ph4As[Zn(mnt)(Et2dtc)]

The synthesis and crystal and molecular structure of the first zinc(II) mixed ligand chelate containing a dithiolene ligand (maleonitriledithiolate) and N,N- diethyldithiocarbamate are reported. The compound Ph₄As[Zn(mnt)(Et₂dtc)] crystallizes monoclinic, space group P2₁/c with four molecules in the unit cell; a=17.834(3), b=12.056(2), c=16.171(4) Å, β=93.73(2)°.The coordination geometry of the ZnS₄ unit is nearly tetrahedral, with a dihedral angle of 87.6° between the chelate rings. The structure is compared with those of both the patent compounds (Ph₄- As)₂[Zn(mnt)₂] and Zn₂(Et₂dtc)₄. Ph₄As[Zn(mnt)(Et₂dtc)] could be used as the host lattice in single- crystal ESR investigations of the planar Cu mixed ligand complex. The rhombic spin-Hamiltonian parameters g and A^Cu are indicative of a low symmetry of the incorporated [Cu(mnt)(Et₂dtc)]⁻ complex anions. In order to substantiate the experimental findings about the actual structure of the copper molecules, the principal values of g and A^Cu were recalculated by means of Extended Hückel MO calculations. However, the calculations performed for the dihedral angles between the ligand planes varying between 0° and 90° suggest that the rotation of the ligands is not larger than 10°