N-(2-Pyridyl)acetamide complexes of palladium(II), cobalt(II), nickel(II), and copper(II)

N-(2-Pyridyl)acetamide (aapH) complexes of palladium(II), cobalt(II), nickel(II), and copper(II) have been studied by means of magnetic susceptibilities, and infrared, electronic, and PMR spectra. In the octahedral complexes M(aapH)₂X₂(M = Co, Ni, Cu; X = Cl, Br, NCS, NO₃), bidentate aapH is chelated through the pyridine-N and amid-O atomes, whereas in the square-planar Pd(aapH)₂X₂ (X = Cl, Br) unidentate aapH is coordinated through the pyridine-N atom alone. Under alkaline conditions aapH is deprotonated in the presence of palladium(II) to form Pd(aap)₂·4H₂O, aap being an anionic bidentate ligand and chelating through the pyridine-N and amide-O atoms.     

Copper(II) complexes of bidentate ligands containing nitrogen and sulfur donors: Synthesis, structures, electrochemistry and catalytic properties

Two nitrogen and sulfur containing ligands, 1-methyl-4-((4-methylimidazol-5-yl)methylthio)benzene (NS-mim) (1) and 1-methyl-4-(2-pyridylmethylthio)benzene (NS-mpy) (2) were synthesized and a series of their Cu(II) complexes, 3-10, prepared. The imidazole-containing complexes (3-6) have the form [Cu(NS-mim)₂(solvent)₂](X)₂ where X = ClO₄, BF₄and [Cu(NS-mim)₂(Y)₂] where Y = Cl or Br and the pyridine-containing complexes (7-10) have the form [Cu(NS-mpy)₂]X₂ (where X = ClO₄, BF₄) and [Cu₂(NS-mpy)₂Y₄] (where Y = Cl or Br). These complexes were characterized by a combination of elemental analysis, FAB-MS and electrochemistry. The X-ray structure of the imidazole-containing [Cu(NS-mim)₂(DMF)₂](ClO₄)₂ (3) was determined and it showed the copper(II) coordinated only by the nitrogen donors while the sulfurs remain uncoordinated. In comparison, the X-ray structure of the pyridine-containing [Cu₂(NS-mpy)₂(Cl)₄] (9) shows a dinuclear copper(II) complex with the nitrogens and the sulfurs coordinated along with a terminal chloride and two μ-chloro atoms bridging the coppers. Cyclic voltammetry studies indicated that the complexes undergo quasi-reversible one-electron reductions in acetonitrile at potentials between 0.31 and 0.51 V versus SCE. The complexes were found to be active for the oxidation of di-tert-butyl catechol (DTBC) with the rate dependent on the ligand and the counterion present.     

Synthesis and metal complexes of 2,6-bis(1-triazolo)pyridine: X-ray structure of 2,6-bis(1-triazolo)pyridine dihydrochloride

2,6-Bis(1-triazolo)pyridine (1) was synthesized and characterized via IR and NMR. The regiochemistry of the compound was confirmed via single crystal X-ray analysis of the hydrochloride salt. A series of insoluble complexes of the general formulae M(1)₂(X)₂ or M(1)(X)₂ [M=Co(II), Ni(II), Cu(II); X=ClO₄, BF₄, Cl] were prepared and their structures interpreted in light of infrared spectra and composition analysis. The results suggest that first row transition metals are not chelated by 1, but rather form extended coordination polymeric networks. A second family of complexes was prepared using 2,6-bis(1-imidazolo)pyridine to support this interpretation.     

Complexes of d(+)-biotin with Pd(II) and Pt(II)

The reactions of d(+)-biotin with K₂MX₄, where M = Pd(II) or Pt(II) and X = Cl or Br have been studied in acidic, neutral or alkaline aqueous solutions. Complexes of the type trans-M(Bio)₂X₂ have been isolated for both metals and characterized with elemental analyses, conductivity measurments, ir spectra, ¹Hnmr and ¹³Cnmr spectra. The complex of the type [Pd(Bio)Cl₂]₂ has also been isolated from DMF solutions. The results indicate that d(+)-biotin coordinates exclusively through its sulfur atom with these metals in all the complexes in the present study, in the solid state or in solution.     

Cobalt(II) and nickel(II) complexes with nitrogen-sulfur tripod ligands. Crystal and molecular structure of the five-coordinate complex bromotris(2-tert-butylthioethyl)aminecobalt(II) hexafluorophosphate (NS3Br donor set)

The tripod ligands tris(2-alkylthioethyl)amine, with alkyl = ethyl, iso-propyl, and tert-butyl, give with cobalt(II) and nickel(II) halides high-spin complexes with formulae [MLX₂], [MLX]Y, and [MLX]₂[MX₄] (where X = Cl, Br, I; Y = BPh₄, PF₆). The nickel complexes are either six- or five-coordinate: the coordination number decreases as the bulkiness of the alkyl group bound to the sulfur is increased. All the cobalt complexes contain the five-coordinate cation [CoLX]⁺. The crystal and molecular structure of the [Co(NS₃-t-Bu)Br]PF₆ complex has been determined by standard X-ray methods, and refined to R = 0.061. The crystals are monoclinic, space group P2¹/n. The unit cell dimensions are: a = 27.420 (2), b = 11.923 (4), c = 17.082 (1) Å, β = 102.40 (1)°, Z = 8. The complex cation has a trigonal bipyramidal geometry with the nitrogen and bromine atoms at the apexes, and the three sulfur atoms in the equatorial plane. The tetrahedral distortion is relatively small (mean BrCoS angle = 98.5°), and similar to that found for the [Co (Me₆tren)Br]Br complex [Me₆tren = tris(2-dimethylaminoethyl)amine).     

Template synthesis and structure of mono- and trisubstituted ribbed-functionalized iron(II) clathrochelates

The template condensation of three methylchloroglyoximate molecules with phenylboronic acid and with BF₃ · O(C₂H₅)₂ on an iron(II) ion afforded reactive trichloride phenylboron- and fluoroboron-capped precursors, respectively. The monochloride FeBd₂(CH₃ClGm)(BF)₂ precursor (where Bd²⁻ and CH₃ClGm²⁻ are α-benzyldioxime and methylchloroglyoxime dianions) was synthesized by condensation of macrocyclic iron(II) α-benzyldioximate FeBd₂(BF₂)₂(CH₃CN)₂ with CH₃ClGmH₂. Mono- and trifunctionalized amine, alkylsulfide, and arylsulfide clathrochelate iron(II) tris-dioximates were prepared starting from these precursors by nucleophilic substitution reactions. The complexes obtained were characterized using elemental analysis, PD mass, IR, UV-Vis, ¹H, ¹³C NMR, and ⁵⁷Fe Mössbauer spectra, and X-ray crystallography. An encapsulated low-spin iron(II) ion was found to have distorted trigonal-prismatic coordination N₆-environment in all clathrochelates synthesized.     

Synthesis, structures and spectroscopic properties of palladium(II) complexes with tridentate piperidyl-containing pincer ligands

A new series of square planar palladium(II) complexes with pincer ligands, pip₂NCN⁻ (pip₂NCNH = 1,3-bis(piperidylmethyl)benzene) and pip₂NNN (2,6-bis(piperidylmethyl)pyridine), has been prepared: Pd(pip₂NCN)X (X = Cl, Br, I), [Pd(pip₂NCN)(L)](BF₄) (L = pyridine, 4-phenylpyridine), and [Pd(pip₂NNN)Cl]Cl. The X-ray crystal structures of Pd(pip₂NCN)Br, [Pd(pip₂NCN)(L)]BF₄, and [Pd(pip₂NNN)Cl]Cl confirm the tridentate coordination geometries of the pincer ligands. For the pip₂NCN⁻ complexes, each piperidyl ring adopts a chair conformation with the metal center at an equatorial position on the N(piperidyl) atom. However, one of the piperidyl groups of Pd(pip₂NNN)Cl⁺ adopts a previously unobserved coordination geometry, effectively placing the metal center at an axial position on the N(piperidyl) atom. ¹H NMR and UV-Vis absorption measurements provide additional insight into the electronic structures of these complexes. The ¹H NMR spectra of Pd(pip₂NCN)X (X = Cl, Br, I) are consistent with deshielding of the pip₂NCN⁻ ligand resonances along the Cl < Br < I series, in opposition to the relative halogen electronegativities. It is suggested that this trend is consistent with decreasing filled/filled repulsions between the dπ orbitals of the metal center and the lone pair orbitals of the halide ligands along this series. Electronic absorption spectra support the notion that ligand-to-metal charge-transfer states are stabilized in these palladium(II) complexes relative to their platinum(II) analogues.     

Comparative investigations on a series of [hexakis(1-(tetrazol-1-yl)alkane-N4)iron(II)] bis(tetrafluoroborate) spin crossover complexes: Methyl- to butyl-substituted species

A series of 1-(tetrazol-1-yl)alkanes [ntz] with n = 1-4 were synthesised as ligands for iron(II) spin crossover complexes. Within this series 1-(tetrazol-1-yl)butane [4tz] was prepared for the first time, whereas 1-(tetrazol-1-yl)methane [1tz], 1-(tetrazol-1-yl)ethane [2tz], 1-(tetrazol-1-yl)propane [3tz] and the [hexakis(ntz)iron(II)]bis(tetrafluoroborate) complexes were prepared according to the literature. Aiming for a comparative study we characterized all four compounds by XRPD, magnetic susceptibility measurements, ⁵⁷Fe-Moessbauer spectroscopy and IR spectroscopy. [Fe(4tz)₆](BF₄)₂ yielded appropriate single crystals and an X-ray structure of the new compound [Fe(4tz)₆](BF₄)₂ is presented. The magnetic and structural properties of all [Fe(ntz)₆](BF₄)₂ are compared and discussed.     

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.     

Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO₄ (1), [Co(TPA)Br]ClO₄ (2), [Co(TPA)(H₂O)]Cl(ClO₄) (3) and [Co₂(TPA)₂(μ-tp)](ClO₄)₂ · 2H₂O (4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV-vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2-300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl⁻ ion in 1, Br⁻ ion in 2, coordinated oxygen atom from H₂O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1-3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣D∣ = 7.3 cm⁻¹, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm⁻¹. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique - the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.     

Novel halogen-bridged bisphosphine nickel(II) complexes

Reaction of [NiCl₂(dtbpe)] (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) with one equivalent of NaBAr^F₄ (BAr^F₄ = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) gives the dinuclear chloro-bridged nickel complex [Ni₂(μ-Cl)₂(dtbpe)₂](BAr^F₄)₂ (1). [Ni(solv)₆](BF₄)₂ reacts with dtbpe to give, depending on the solvent, the fluoro-bridged complex [Ni₂(μ-F)₂(dtbpe)₂](BF₄)₂ (2) (solv = THF) or the mononuclear chelate complex [Ni(MeCN)₂(dtbpe)](BF₄)₂ (3) (solv = MeCN). In 1-3, nickel cations are coordinated in a square-planar fashion according to X-ray crystallography. No Ni-Ni interaction was observed in dinuclear halogen-bridged complexes 1 and 2.     

1,4-Di(1,2,3,4-tetrazol-2-yl)butane as a precursor of new 2D and 3D coordination polymers of Cu(II)

A series of new coordination polymers of Cu(II) have been prepared in a reaction between copper(II) perchlorate or tetrafluoroborate salt and a novel ligand 1,4-di(1,2,3,4-tetrazol-2-yl)butane (bbtz). The compounds were characterised by an elemental analysis, TG measurements, IR, EPR and UV-Vis spectroscopy. Crystal structures of bbtz and five complexes of Cu(II) were determined by a single crystal X-ray diffraction measurement performed at 100 K. The composition and architecture of the obtained complexes strongly depend on the reaction conditions especially on the kind of solvent. Investigated complexes are composed of polymeric macrocations and non-coordinated anions. In all cases the bbtz molecules act as the bidentate ligand coordinated to metal(II) ions via N4, N4^′ nitrogen atoms from tetrazole rings. The complexes {[Cu(bbtz)₂(MeOH)₂]X₂}_∞ (X=ClO₄⁻, BF₄⁻) crystallise from methanol as 2D coordination polymers. In these compounds central metal ions are coplanar linked by molecules of bbtz and a coordination sphere is completed by axially coordinated solvent molecules. The complexes {[Cu(bbtz)₃]X₂}_∞ (X=ClO₄⁻, BF₄⁻) were synthesised in EtOH/H₂O solvent system and posses a common network topology. In this group of complexes each central atom is linked by ligand molecules to six other in plane arranged central atoms resulting in 2D networks. Reactions between Cu(II) salts and bbtz performed in absolute ethanol resulted in the formation of the next type of product. In {[Cu(bbtz)₃](ClO₄)₂·2EtOH}_∞ neighboured copper(II) ions are linked by ligand molecules in the three directions what leads to the formation of 3D net. A crystal of this complex is composed of two mutually interpenetrated 3D networks.     

Synthesis, structure, spectroscopic and magnetic characterization of a novel spin-crossover iron(II) complex with 1-cyclopropyltetrazole ligands

For the first time a 1-cyclopropyl substituted tetrazole (C₃tz) has been used as a potential ligand for iron(II) spin-transition complexes. The complexation of 1-cyclopropyltetrazol with iron(II) tetrafluoroborate yielded a fine powdered product of [Fe(C₃tz)₆](BF₄)₂ being poorly soluble in most common solvents. Single crystals of complex were grown in situ from a solution of ligand and iron(II) hexafluorophosphate, which yielded a hexagonal prismatic crystalline product of [Fe(C₃tz)₆](PF₆)₂. A comparison of XRPD data of the homologues [Fe(C₃tz)₆](BF₄)₂ and [Fe(C₃tz)₆](PF₆)₂ proves them to be homeotypic. The thermally induced spin-crossover phenomenon of [Fe(C₃tz)₆](BF₄)₂ complex shows very abrupt spin transitions, with a spin-crossover temperature T_1/2 ≈ 180 K which is found to be ≈50 K above the T_1/2 of all known iron(II) complexes with n-alkyltetrazoles as ligands. The T_1/2 was determined by temperature-dependent ⁵⁷Fe-Mössbauer, far FT-IR and UV-Vis-NIR spectroscopy as well as temperature dependent magnetic susceptibility measurements (SQUID).     

Synthesis and anomalous magnetic properties of heterometal dinuclear Fe(II)-Cr(III) complex bridged by 3,5-bis(pyridin-2-yl)-pyrazolate

A Cr(III)-Fe(II) dinuclear complex [(nta)Cr(μ-bpypz)Fe(dpea)]BF₄, where bpypz=3,5-bis(pyridin-2-yl)-pyazolate, nta=nitrilotriacetate and dpea=(2-aminoethyl)-bis(2-pyridylmethyl)amine, has been synthesized and structurally characterized by ESI-MS and ²H NMR spectra. The proposed structure is mostly more planar in the bridging moiety as compared to that of the previously reported [(nta)Cr(μ-bpypz)Fe(picen)]BF₄(N,N^′-bis-(2-pyridylmethyl)ethylenediamine(picen)). The dpea complex is found to be a high spin state, but to exhibit no spin-crossover by magnetic susceptibility and Mössbauer spectra measurements; showing a large antiferromagnetic interaction, which could make the spin transition temperature lower and/or destroy spin-crossover, suggesting complementarity between spin-crossover and magnetic interaction.     

Tertiary phosphine complexes of nickel(0) and nickel(I). New dinitrogen complexes of nickel(0)

The reduction of NiX₂(PCy₃)₂ (X = Cl, Br; PCy₃ = tricyclohexylphosphine) in toluene with sodium sand under argon affords [NiX(PCy₃)₂]₂ or Ni(PCy₃)₃. In the same way starting from NiX₂P₂ [X = Cl, Br; P = P(C₂H₅)₃, P(CH₂CH₂CH₂CH₃)₃, P(C₂H₅)₂ C₆H₅] the tetracoordinate Ni(0) complexes NiP₄ are obtained. These give NiP₃(N₂) under nitrogen. The electronic spectra of Ni(0) and Ni(I) complexes, both in the solid state and solution, are reported.     

Synthesis, structures and spectroscopic properties of platinum(II), copper(I) and zinc(II) complexes bearing 4-(p-dimethylaminophenyl)-6-phenyl-2,2′-bipyridine ligand

The reactions of 4-(p-dimethylaminophenyl)-6-phenyl-2,2′-bipyridine (HL) with three metal salts of platinum(II), copper(I) and zinc(II) provide the new complexes [Pt(L)(PPh₃)]ClO₄ (1), [Cu(HL)₂]BF₄ (2), [Cu(HL)(PPh₃)]BF₄ (3) and [Zn(HL)₂](ClO₄)₂ (4). All the structures of these four complexes have been characterized by single crystal X-ray diffraction, and their spectroscopic properties were investigated. Especially for complex 1, upon protonation, the excited state can be tuned from the intraligand charge transfer (ILCT) to the metal-to-ligand charge transfer (MLCT), and such switching in the excited state is acid/base reversible. The time-dependent density functional theory (TD-DFT) calculation was used to interpret the absorption spectra of complex 1, and the calculated result is consistent with those of experiments results. In contrast with 1, the lowest energy absorption at 410-650 nm of complexes 2 and 3 can be assigned to MLCT excited state. In solid state or solution complex 4 exhibits intense photoluminescence attributed to a ILCT transition in nature.     

Co-ordination compounds derived from dimethylhydrazones of cyclohexane-1,2-dione, 2-acetyl- and 2-benzoylpyridines and 4-bezoylpyridine

The 1,1-dimethylhydrazones of cyclohexane-1,2-dione (CDDMH), 2-acetylpyridine (APDMH) and 2-benzoylpyridine (2BPDMH) from tetrahedral complexes MX₂L (M = Co(II), Zn(II); X = Cl, Br) in which the ligand is chelating through the methylene nitrogen atoms (CDDMH) or one methylene and one pyridine nitrogen atom (APDMH, 2BPMDH). Octahedral complexes CoX₂L₂ (X = Cl, NCS; L = APDMH, 2BPDMH) have also been isolated but no tris-ligand complexes. The ligand 4-benzoylpyridine-dimethylhydrazone (4BPDMH) does not chelate but forms tetrahedral complexes MX₂(4BPDMH)₂ in which the unidentate ligand co-ordinates through the pyridine nitrogen atom.     

Two new Fe(II) spin crossover complexes with tetrazol-1-yl-cycloalkane ligands

Two new 1-(tetrazol-1-yl)cycloalkanes [C_ntz] with n = 5 and 6 were synthesised as ligands for iron(II) spin crossover complexes. Just recently, the [Fe(C₃tz)₆](BF₄)₂ showed that the rigid cyclopropyl-substituent of the tetrazole yielded a rather abrupt and complete spin transition at T_½ ≈ 190 K [1]. Aiming for a deeper insight into the factors governing the spin transition behavior such as abruptness and spin transition temperature we synthesized the two new homologous complexes [Fe(C₅tz)₆](BF₄)₂ and [Fe(C₆tz)₆](BF₄)₂ which were characterized by XRPD, magnetic susceptibility measurements, DSC, ⁵⁷Fe-Mössbauer, UV-Vis-NIR and MIR spectroscopy. The magnetic and structural properties of both [Fe(C_ntz)₆](BF₄)₂ with n = 5 and 6 are also compared with the [Fe(C₃tz)₆](BF₄)₂ and its structural peculiarities are discussed.     

Seven coordinate complexes of metal(II) nitrates

ESR spectra at both X and Q band are reported for manganese(II) ions doped into the seven coordinate complexes M(L)₃(NO₃)₂ (M = Co, Ni, Zn or Cd; L = pyridine or substituted pyridine). The zero field splitting parameters D and λ (= E/D) are deduced. All complexes show considerable deviation from cubic symmetry, as can be expected for a seven coordinate structure. The distinctly lower D value of Ni(Mn)(pyridine)₃(NO₃)₂, as compared to the analogous cobalt and zinc complex, suggests a geometry tending towards an octahedral structure. The steric hindrance by the substituent reduces the D value.     

Magnetic coupling in trinuclear partial cubane copper(II) complexes with a hydroxo bridging core and peripheral phenoxo bridges from NNO donor Schiff base ligands

Three new trinuclear copper(II) complexes, [(CuL¹)₃(μ₃-OH)](ClO₄)₂·3.75H₂O (1), [(CuL²)₃(μ₃-OH)](ClO₄)₂(2) and [(CuL³)₃(μ₃-OH)](BF₄)₂·0.5CH₃CN (3) have been synthesized from three tridentate Schiff bases HL¹, HL², and HL³ (HL¹ = 2-[(2-amino-ethylimino)-methyl]-phenol, HL² = 2-[(2-methylamino-ethylimino)-methyl]-phenol and HL³ = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol). The complexes are characterized by single-crystal X-ray diffraction analyses, IR, UV-vis and EPR spectroscopy, and variable-temperature magnetic measurements. All the compounds contain a partial cubane [Cu₃O₄] core consisting of the trinuclear unit [(CuL)₃(μ₃-OH)]²⁺ together with perchlorate or fluoroborate anions. In each of the complexes, the three copper atoms are five-coordinated with a distorted square-pyramidal geometry except in complex 1, in which one of the Cu^II ions of the trinuclear unit is six-coordinate being in addition weakly coordinated to one of the perchlorate anions. Variable-temperature magnetic measurements and EPR spectra indicate an antiferromagnetic exchange coupling between the Cu^II ions of complexes 1 and 2, while this turned out to be ferromagnetic for complex 3. Experimental values have been fitted according to an isotropic exchange Hamiltonian. Calculations based on Density Functional Theory have also been performed in order to estimate the exchange coupling constants in these three complexes. Both sets of values indicate similar trends and specially calculated J values establish a magneto-structural correlation between them and the Cu-O-Cu bond angle, in that the coupling is more ferromagnetic for smaller bond angle values.