Kinetics of the cis-to-planar interconversion of cis-diaqua(1,4,7,11-tetraazacyclotetradecane)nickel(II) ion

In order to examine the effects of coordinated hydroxide ion and free hydroxide ion in configurational conversion of a tetraamine macrocyclic ligand complex, the kinetics of the cis-to-planar interconversion of cis-[Ni(isocyclam)(H₂O)₂]²⁺ (isocyclam, 1,4,7,11-tetraazacyclotetradecane) has been studied spectrophotometrically in basic aqueous solution. The interconversion requires the inversion of one sec-NH center of the folded cis-complex to have the planar species. Kinetic data are satisfactorily fitted by the rate law, R = k_OH[OH⁻][cis-[Ni(isocyclam)(H₂O)₂]²⁺], where k_OH = 3.84 × 10³ dm³ mol⁻¹ s⁻¹ at 25.0 ± 0.1 °C with I = 0.10 mol dm⁻³ (NaClO₄). The large ΔH^≠, 61.7 ± 3.2 kJ mol⁻¹, and the large positive ΔS^≠, 30.2 ± 10.8 J K⁻¹ mol⁻¹, strongly support a free-base-catalyzed mechanism for the reaction.     

Solution properties of the nickel(II,III) and copper(II,III) complexes of trans-dioxocyclam (trans-dioxocyclam=5,12-dioxo-1,4,8,11-tetraazacyclotetradecane) and the X-ray crystal structure of the N-rac-isomer of the nickel(II) complex

The crystal and molecular structures of the N-rac-isomer of the nickel(II) complex of 14-membered amide-containing macrocycle [NiL¹] · 4H₂O (H₂L¹=5,12-dioxo-1,4,8,11-tetraazacyclotetradecane) have been determined. Two deprotonated amide and two amine donors co-ordinate to the nickel(II) in nearly square planar manner with Ni-N_amine bonds longer than Ni-N_amide ones (1.930 vs. 1.898 Å). Water molecules do not co-ordinate and form hydrogen bond bridges between macrocyclic units in the crystal lattice. The analysis of ¹H NMR data confirmed that the solid-state conformation of the macrocycle in N-rac[NiL¹] is retained in aqueous solution though equilibrated with some amount of N-meso isomer. The comparison of the spectroscopic characteristics of the M(II) and M(III) complexes and the redox potentials of M(III/II) couples (M=Ni and Cu) for ML¹ with those for ML²(H₂L²=5,7-dioxo-1,4,8,11-tetraazacyclotetradecane) revealed a rather small influence of the trans- vs. cis-arrangement of amide donors in co-ordination spheres of the metal ions.     

Novel Cu(II)Cd(II) macrocyclic complex that hydrolyzes an activated phosphate diester

The dinucleating macrocyclic ligand 3,6,9,17,20,23-hexaaza-29,30-dihydroxy-13,27-dimethyl-tricyclo[23,3,1,1^11,15] triaconta-1(28),11,13,15(30),25,26,-hexaene(BDBPH) was synthesized from [2+2] condensation between a diethylenetriamine lead(II) mononuclear complex and diformal-p-cresol. By stepwise synthesis, the heterodinuclear Cu(II)Cd(II) complex was obtained. The single crystal was triclinic, space group P1, with cell constants a=13.2675(10) Å, b=16.4655(13) Å, c=17.9502(14) Å, α=87.78(10), β=68.69(10), γ=74.81(10), V=3517.6(3) Å and Z=4. Potentiometric titration reveals that Cu(II)Cd(II)BDBPHOH species dominate in basic solution from pH 7 to 12. In the hydrolysis of BNP, this dinuclear complex can provide both Lewis acid and base sites to an active phosphate diester in which nucleophilic OH⁻ attacks the substrate to fulfill the hydrolysis cycle. In this system the synergic two functional groups in one catalyst molecule exerted remarkable catalytic activity towards hydrolysis of BNP.     

Two macrocyclic pentaaza compounds containing pyridine evaluated as novel chelating agents in copper(II) and nickel(II) overload

Two pentaaza macrocycles containing pyridine in the backbone, namely 3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),14,16-triene ([15]pyN₅), and 3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),15,17-triene ([16]pyN₅), were synthesized in good yields. The acid-base behaviour of these compounds was studied by potentiometry at 298.2 K in aqueous solution and ionic strength 0.10 M in KNO₃. The protonation sequence of [15]pyN₅ was investigated by ¹H NMR titration that also allowed the determination of protonation constants in D₂O. Binding studies of the two ligands with Ca²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ metal ions were performed under the same experimental conditions. The results showed that all the complexes formed with the 15-membered ligand, particularly those of Cu²⁺ and especially Ni²⁺, are thermodynamically more stable than with the larger macrocycle. Cyclic voltammetric data showed that the copper(II) complexes of the two macrocycles exhibited analogous behaviour, with a single quasi-reversible one-electron transfer reduction process assigned to the Cu(II)/Cu(I) couple. The UV-visible-near IR spectroscopic and magnetic moment data of the nickel(II) complexes in solution indicated a tetragonal distorted coordination geometry for the metal centre. X-band EPR spectra of the copper(II) complexes are consistent with distorted square pyramidal geometries. The crystal structure of [Cu([15]pyN₅)]²⁺ determined by X-ray diffraction showed the copper(II) centre coordinated to all five macrocyclic nitrogen donors in a distorted square pyramidal environment.     

Oxidation of malononitrile complex of pentaammineruthenium(II)

The oxidation of Ru(NH₃)₅NCCH₂CN²⁺ complex by the peroxydisulfate ion in the aqueous solution yields two products, Ru(NH₃)₅NHCOCH₂CN²⁺ with λ_max = 373 nm and withλ_max = 863 nm. The distribution of the products and the amount of oxidant required for the maximum yield of the binuclear complex depend on the acidity of the solution. The production of the binuclear complex was favored at lower acid concentrations. The formation of CC bond in the binuclear complex was characterized by both the spectral and the electrochemical results. A mechanism for the oxidation has been proposed by the kinetic studies in the region of 0.001-0.10 M acid concentrations.     

Structure and O2 uptake properties of a novel nickel(II) complex of pyridyl-pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane]

 Novel potentially five-coordinate pyridyl–pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (H₂L) and its homologs (6-methyl and 6,6-dimethyl derivatives)] have been synthesized to study nickel(II) complexation. A purple nickel(II) complex with a deprotonated amide (NiHL) was isolated from aqueous equimolar solution of H₂L and Ni(ClO₄)₂. A yellow nickel(II) complex with two deprotonated amides (NiL) was crystallized from an H₂O/CH₃CN solution of H₂L and Ni(OH)₂. The X-ray crystal study of NiL showed a square-planar nickel(II) complex with the pyridyl–pendant remaining uncoordinated. It is concluded from the visible absorption and NMR study of NiL in aqueous solution that the four-coordinate NiL is in equilibrium with a five-coordinate square-pyramidal nickel(II) complex with the apical coordination of the pyridyl–pendant. A voltammetric study disclosed a low nickel(II/III) redox potential of +0.29 V vs SCE for NiL at pH 9.5 and 25  °C with 0.10 M Na₂SO₄. The nickel(II) complex NiL absorbed an equimolar amount of O₂ at pH 9.5 and 25  °C, and the O₂ was activated to cleave plasmid DNA. Received: 5 August 1996 / Accepted: 24 October 1996     

Further study of the effect of macrocyclic pendant groups on the supramolecular architecture: Synthesis and structures of macrocyclic nickel (II) complexes with trans-butene dicarboxylate

Two nickel (II) complexes with the formula [NiL(H₂O)₂] · 6H₂O (1 · 6H₂O) and [NiH₂L(BDC)]_n (2), where L = 3,10-bis(3-propylcarboxyl)-1,3,5,8,10,12-hexaazacyclo-tetradecane, BDC = trans-butene dicarboxylate, have been synthesized and characterized by elemental analyses, IR spectra and single-crystal X-ray analyses. In 1, the Ni(II) ion is six-coordinated with four nitrogen atoms from the macrocyclic ligand in the equatorial plane and two water molecules in axial position. In 2, the structure is made up of one-dimensional chain of [NiH₂L]²⁺ units with BDC²⁻ anions, in which the Ni(II) ion is also six-coordinated with four nitrogen atoms from the macrocyclic ligand in the equatorial plane and two carboxylate oxygen atoms from the BDC²⁻ group in axial position. In 2, the 1D chains are aligned in a parallel mode.     

DNA binding affinity of a macrocyclic copper(II) complex: Spectroscopic and molecular docking studies

The interaction of a novel macrocyclic copper(II) complex, ([CuL(ClO₄)₂] that L is 1,3,6,10,12,15-hexaazatricyclo[13.3.1.1^6,10]eicosane) with calf thymus DNA (ct-DNA) was investigated by various physicochemical techniques and molecular docking at simulated physiological conditions (pH = 7.4). The absorption spectra of the Cu(II) complex with ct-DNA showed a marked hyperchroism with 10 nm blue shift. The intrinsic binding constant (K_b) was determined as 1.25 × 10⁴ M^?1, which is more in keeping with the groove binding with DNA. Furthermore, competitive fluorimetric studies with Hoechst33258 have shown that Cu(II) complex exhibits the ability to displace the ct-DNA-bound Hoechst33258 indicating that it binds to ct-DNA in strong competition with Hoechst33258 for the groove binding. Also, no change in the relative viscosity of ct-DNA and fluorescence intensity of ct-DNA-MB complex in the present of Cu(II) complex is another evidence to groove binding. The thermodynamic parameters are calculated by van't Hoff equation, which demonstrated that hydrogen bonds and van der Waals interactions played major roles in the binding reaction. The experimental results were in agreement with the results obtained via molecular docking study.     

A novel tetranuclear lanthanide(III)-copper(II) complex of the macrocyclic oxamide [PrCu3] (macrocyclic oxamide = 1,4,8,11-tetraazacyclotradecanne-2,3-dione): synthesis, structure and magnetism

A novel tetranuclear lanthanide(III)-copper(II) complex of macrocyclic oxamide, [Pr(CuL)₃(H₂O)₂](SCN)₃ · 1.5H₂O (L = 1,4,8,11-tatraazacyclotradecanne-2,3-dione) (1), has been synthesized, structurally characterized and preliminary investigated by magnetic studies. The structure of the title complex consists of a cationic PrCu₃ core, noncoordinated monovalent SCN⁻ anions and H₂O molecules; the packing diagram shows open channels formed through intermolecular weak interactions. The temperature-dependent magnetic susceptibilities were analyzed by an approximate treatment being enlightened by Matsumoto et al. leading to J = −1.62 × 10⁻² cm⁻¹, Δ = 3.12 cm⁻¹, g_Cu = 2.13, respectively.     

Preparation of new tetraaza macrocyclic nickel(II) and copper(II) complexes bearing N-propionic methyl ester groups

A 14-membered tetraaza macrocycle, 2,13-bis(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane (L²) bearing two N-CH₂CH₂COOMe groups, and its nickel(II) and copper(II) complexes have been prepared and characterized. The nickel(II) and copper(II) complexes of 2-(2-carbomethoxyethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane (L³) containing one N-CH₂CH₂COOMe group have also been prepared. The crystal structure of [NiL²](ClO₄)₂ shows that the complex has a slightly distorted trans-octahedral coordination geometry with two relatively short axial Ni-O (N-CH₂CH₂COOMe group) bonds (2.136(3) Å). In various solvents, however, a considerable proportion of [NiL²]²⁺ exists as a square-planar form, in which the functional pendant arms are not involved in coordination. The proportion of the square-planar isomer varies with solvents in the order of nitromethane ? acetonitrile < H₂O < DMF ? DMSO. In the case of [CuL²](ClO₄)₂, only one N-CH₂CH₂COOMe group is involved in coordination. The N-CH₂CH₂COOMe group of [NiL³](ClO₄)₂ is not directly involved in coordination even in the solid state, though the functional group of [CuL³](ClO₄)₂ is coordinated to the metal ion.     

Reactions of N-cyanomethyl groups attached to a tetraaza macrocyclic copper(II) complex leading to the formation of various hetero-functionalized macrocyclic complexes

New hetero-functionalized macrocyclic complexes [CuL²](ClO₄)₂ (I) and [CuL³](ClO₄)₂ (II) bearing one N-CH₂CONH₂ or one N-CH₂C(NH)NH(CH₂)₂CH₃ pendant arm as well as one N-CH₂CN group have been prepared by the selective reaction of water or n-propylamine with one of the two N-CH₂CN groups in [CuL¹](ClO₄)₂ (L¹ = 2,13-bis(cyanomethyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane). The complex [CuL⁴](ClO₄)₂ (III) bearing both N-CH₂CONH₂ and N-CH₂C(NH)NH(CH₂)₂CH₃ pendant arms can be prepared by either the reaction of I with n-propylamine or the hydrolysis of II. The N-CH₂CONH₂ and/or N-CH₂C(NH)NH(CH₂)₂CH₃ groups of I, II, and III are coordinated to the metal ion. The crystal structure of II shows that the complex has distorted square-pyramidal coordination polyhedron with a considerably strong apical Cu-N (N-CH₂C(NH)NH(CH₂)₂CH₃) bond (2.101(6) Å). The addition of HClO₄ (?0.01 M) to an acetonitrile (or DMSO) solution of II or III produces [Cu(HL³)](ClO₄)₃ (IIa) or [Cu(HL⁴)](ClO₄)₃ (IIIa), showing that the N-CH₂C(NH)NH(CH₂)₂CH₃ pendant arm of each complex is readily protonated in the non-aqueous solvent; the resulting N-CH₂C()NH(CH₂)₂CH₃ group of IIa or IIIa is not involved in coordination. However, the N-CH₂C(NH)NH(CH₂)₂CH₃ group of II is not protonated even in ?1.0 M HClO₄ aqueous solution. In the case of III, most of the complex exists as the protonated form [Cu(HL⁴)]³⁺ in ?0.1 M HClO₄ aqueous solutions.     

Synthesis of a novel linear polymer of a macrocyclic polyamine copper (II) complex and its interaction with plasmid DNA

The novel linear polymer of a macrocyclic polyamine copper (II) complex, which has many cyclen groups linked by epichlorohydrin, has been synthesized as a DNA cleavage agent. The structure of the polymer 3 was identified by ¹HNMR and IR and its molecular weight was measured by GPC. The result of agarose gel electrophoresis assay showed that Cu-(II) complex 4 could act as a powerful catalyst for the cleavage of plasmid DNA under physiological conditions.     

From “naked” copper(II) ions and asymmetric macrocyclic complex linkers with a monodentate top and a bidentate top to molecular rectangle and infinite molecular rectangle strands

A molecular rectangle [Cu{CuL¹(NO₃)}(H₂O)(NO₃)]₂ (1) and two infinite molecular rectangle strands {[Cu{CuL¹(NO₃)}₂] · 2H₂O}_∞ (2) and [Cu{CuL²(ClO₄)}₂]_∞ (3) were prepared by reaction of “naked” Cu(II) ions with macrocyclic complex ligands CuL¹ for 1 and 2 and CuL² for 3 in metal-to-ligand molar ratios of 1:1, 1:2 and 1:2, respectively. L¹ and L² denote the dianions of diethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate and diethyl 5,6,7,8,15,16-hexahydro-15-methyl-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate, respectively. The structures of 1-3 were determined by X-ray single-crystal analyses. CuL¹ in 1 and 2 and CuL² in 3 act as angular linkers with a monodentate coordination top and a bidentate one between two Cu(II) nodes to enclose the molecular rectangle of 1 and the rectangular subunits of 2 and 3. The angular shape, the monodentate top plus bidentate top coordination mode and the self-complementarity for π?π interactions of the macrocyclic complex linkers, the ratio between the reactants and the octahedral coordination geometry of the naked Cu(II) ions jointly determined the interesting structures of metallocyclophane 1 and 1D double chain coordination polymers 2 and 3. The cavities of the rectangular molecules of 1 are arranged into infinite strands so that parallel channels occur in the crystal. The molecules of 2 and 3 all pack parallel in the crystals.     

Synthesis, structure, and redox behaviour of a novel cis-dioxomolybdenum(VI) dinuclear complex with a quadradentate dithiocarbamate

A novel dinuclear cis-dioxomolybdenum(VI) complex [{MoO₂(Bz₂endtc)}₂] coordinated with a quadradentate dithiocarbamate (Bz₂endtc²⁻: ((2-(dithiocarboxybenzylamino)ethyl)benzylamino)-methanedithioate(2−)) has been synthesised. The structural features of [{MoO₂(Bz₂endtc)}₂] have been elucidated by X-ray crystal analysis, elemental analysis and ¹³C NMR, IR and FAB⁺ mass spectroscopy: two almost identical cis-dioxomolybdenum(VI) centres are bridged by the two Bz₂endtc²⁻ ligands and each molybdenum(VI) centre has a distorted octahedral geometry with four sulphur atoms and two terminal oxo ligands lying in a cis position to each other. There is unlikely to be electronic interaction between the two cis-dioxomolybdenum(VI) centres in [{MoO₂(Bz₂endtc)}₂] because the MoMo distance is long (=7.337 Å). In the [{MoO₂(Bz₂endtc)}₂]/PPh₃ system, the oxygen atom transfer reaction (Eq. (A)) occurs to give a tetranuclear oxomolybdenum(VI,V) complex formulated as [MoO₂(Bz₂endtc)₂Mo₂O₃(Bz₂endtc)₂MoO₂] which has one μ-oxomolybdenum(V) moiety.

(A)     

Synthesis and spectroscopic investigation of new nickel(II) complexes with the open chain asymmetric tetraamine 1,4,7,11-tetraazaundecane: Crystal structure of the square-planar complex

The synthesis of the X-ray structurally characterized square-planar [Ni(2,2,3-tet)](ClO₄)₂ (2) from the [Ni(2,2,3-tet)(NH₃)(H₂O)]Cl₂ · 1/2EtOH · H₂O (1), was based on their inter-conversion. The two sets of trans Ni-N bonds display similar to each other lengths (1.900 & 1.910 and 1.996 & 1.966 Å). The relaxation times (T_1,2) of water protons and NMR experiments indicate relatively slow octahedral-sq-planar equilibrium, while in the aqueous solutions of 1, the sq-planar species appear to display a structure analogous to 2 in solution. The square planar geometry, the hydrophilicity of the complex and the asymmetry of the ligand generate the conditions for catalytic site formation.     

The dynamics of formation of the O2-Co bond in the cobalt(II) cyclidene complexes

The kinetics of O₂ binding to a vacant coordination site on the cobalt(II) ion have been determined, revealing a radical-like character for the reaction. Reversible oxygenation of Co(II) cyclidenes (C4, C5, C6, C8, C12-bridged and unbridged) was studied by a cryogenic stopped-flow method. In the presence of axial base, kinetic parameters are insensitive to the nature of the solvent, and negative entropies of activation suggest that dissociation of a solvent molecule is not the rate-determining step for the dioxygen binding process. This is in contrast to the behavior of previously studied Co(II) complexes. A very low activation energy (1–4 kcal mol⁻¹), typical of diffusion controlled processes, was found for dioxygen binding. The binding rate constants for the highest affinity complexes (10⁸ M⁻¹ s⁻¹) are comparable to the values for natural dioxygen carriers. The size of the lacuna primarily affects the dioxygen binding rates, while the axial bases influence the dioxygen dissociation rates.     

Synthesis, characterization and kinetic studies of the cis-[RuCl2(cyclen)] complex

We report here the synthesis, characterization and kinetic studies of cis-[RuCl₂(cyclen)]⁺ in aqueous solution, where cyclen is the macrocyclic ligand 1,4,7,10-tetraazacyclododecane. The complex releases one Cl⁻ producing cis-[RuCl(OH)(cyclen)]⁺ in aqueous solution at pH 4.60. The product of this reaction was characterized by Ultraviolet-Visible (UV-Vis) spectrum in comparison to the synthesized cis-[RuCl(OH)(cyclen)](BF₄)·2H₂O. The electrochemical data showed that E_pc of the Ru(III/II) peak increases as the macrocycle ring size decreases and also when the trans conformation is changed to cis. The chloride affinity of Ru(III) depends on the macrocycle ring size since cis-[RuCl₂(cyclam)]⁺ (cyclam=1,4,8,11-tetraazacyclotetradecane) does not release chloride for at least 12 h. The overall effect between cyclam and cyclen reflects the fact that the electron involved in the reduction enters a nonbonding π-d orbital and its energy is affected by the macrocyclic ligand.     

Conformational characterization of square planar nickel(II) tetraaza macrocyclic complexes by proton NMR. Crystal structure of [Ni(13aneN4)]ZnCl4

Conformations in solution of several diamagnetic nickel(II) complexes of macrocyclic tetraaza ligands are elucidated using proton NMR. There are six possible configurational isomers of planar [Ni(13aneN₄)]²⁺ (13aneN₄ = 1,4,7,10-tetraazacyclotridecane due to the orientation of the N---H protons above or below the plane of the macrocyle. Using NMR it is shown that in aqueous solution the [Ni(13aneN₄)]²⁺ complex has the R,S,R,S or trans-II configuration. A single-crystal X-ray study demonstrates the same configuration of the nitrogen atoms in the complex [Ni(13aneN₄)]ZnCl₄. In the case of the 14-membered ring macrocyle cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane), previous NMR studies revealed the presence, in aqueous solution, of the previously unobserved trans-I or R,S,R,S isomer, whose spectrum is examined in greater detail here. Solution structures of nickel(II) complexes of bicyclam (1,5,8,12-tetraazabicyclo[10.2.2]hexadecane) and dachden (N, N′-bis(2-aminoethyl)-1,4-diazacycloheptane) are also reported.     

Cd(II) complexes with N8 and N4O4 donor macrocyclic ligands

The coordination capability of the octaaza 24-membered (L¹) and the tetraoxotetraaza 28-membered (L²) macrocycle ligands - with different sizes, nature and number of the donor atoms - has been investigated with nitrate and perchlorate Cd(II) salts. The complexes were prepared in 1:1 and 2:1 Cd:L molar ratio. The characterization by elemental analysis, IR, LSI mass spectrometry, conductivity measurements and ¹H NMR spectroscopy, together with the crystal structure of the complexes [CdL¹](NO₃)₂ · 0.5H₂O, [CdL¹](ClO₄)₂ and [CdL²(CH₃CN)₂](ClO₄)₂ · CH₃CN · H₂O confirms the formation of mononuclear complexes in all cases. The [CdL¹](NO₃)₂ · 0.5H₂O and [CdL¹](ClO₄)₂ present a mononuclear endomacrocyclic structure with the metal ion coordinated by the eight donor nitrogen atoms from the macrocyclic backbone in a square antiprism geometry. The complex [CdL²(CH₃CN)₂](ClO₄)₂ · CH₃CN · H₂O is also mononuclear, but the cadmium ion is in an octahedral environment coordinated by four amine nitrogen atoms from the macrocyclic framework and two nitrogen atoms from two acetonitrile molecules. The ether oxygen atoms from the ligand are not coordinated.     

New macrocyclic Cu(II)-bischelates with paddle wheel Cu2-acetate cage

Two novel bolaamphiphile based dicarboxylic ligands L1H₂ and L2H₂ are synthesized by desymmetrizing aromatic anhydrides. The corresponding Cu(II) complexes [Cu(L1) · EtOH]₂ (1), [Cu(L2) · (CH₃CN)]₂ (2) are synthesized and characterized. The crystal structure obtained for (1) and (2) indicates that they are new class of tetralactone type macrocyclic Cu(II) chelate complexes with paddle wheel Cu₂-acetate cage structure. The 1:1, Cu(II) and ligand ratio leads into formation of a novel binuclear Cu(II) tetracarboxylate complexes. The macrocyclic chelate ring size in compounds 1 and 2 was altered from [15] membered to [19] membered by introducing phthalyl and diphenyl head groups as discussed in detail. The single crystal X-ray structure shows the Cu(II)?Cu(II) distance 2.613(13) Å for 1 and 2.626(13) Å for 2, the corresponding room temperature EPR spectra recorded for powdered polycrystalline samples indicate the existence of Cu(II)?Cu(II) dimeric system.