14-membered Tetraaza Macrocycles Research Articles

Rhodium(III) and Platinum(II) Complexes of Azamacrocycle: Synthesis, Characterization and Antimicrobial Evaluation

A dihydroperchlorate salt of octamethyl derivative of 14-membered tetraazamacrocycle, Me8[14]diene·2HClO4 (L·2HClO4), was formed by the condensation of 1,2-diamino propane with acetone in the presence of a quantitative amount of perchloric acid, which on extraction with chloroform at pH above 12 yielded free ligand (L). The interaction of rhodium(III) trichloride trihydrate and platinum(II) chloride with free ligand L produced six-coordinated octahedral orange-red complex, cis-[RhLCl2]Cl and four-coordinated square-planar yellow complex, [PtL]Cl2, respectively. Axial substitution reactions on [RhLCl2]Cl with KX (X = NO3, Br or I) and NaNO2 afforded six-coordinated deep brown products [RhLY2]Y (Y= NO3, Br, I or NO2). The ligand and metal complexes were characterized based on analytical, molar conductivity, spectroscopic and magnetochemical data. The antimicrobial activities of the concerned ligand and its complexes have been explored against some selected bacteria and fungi.

Syntheses, characterization, and antimicrobial studies of Ni(II), Cu(II), and Co(III) complexes with an N-pendant azamacrocyclic chelator

Condensation of 1,2-diamino propane with acetone in the presence of perchloric acid furnished a 14-membered octamethyl tetraazamacrocycle, Me8[14]diene⋅2HClO4, which further produced a mixture of isomeric ligands, Me8[14]anes (LA, LB, and LC), on reduction with NaBH4 and subsequent extraction with CHCl3 (pH > 12). The isomers were separated by fractional crystallization from xylene. Interaction of LC with excess acrylonitrile afforded an N-pendant derivative, LCX, in which two cyanoethyl groups were attached to less crowded nitrogen atoms (N4 and N11). Upon the interaction of LCX with Ni(CH3COO)2⋅4H2O, Cu(ClO4)₂⋅6H2O, and Co(CH3COO)₂⋅4H₂O, square planar [Ni(LCX)](ClO4)2 and [Cu(LCX)](ClO4)2 and octahedral trans-[Co(LCX)Cl2](ClO4), respectively, were produced. Axial substitution reactions of trans-[Co(LCX)Cl2](ClO4) with KCNS, KM (M = NO3, Br, or I), and NaNO2 afforded substituted trans-[Co(LCX)(NCS)2](SCN), trans-[CoLCX(X)2](ClO4), and trans-[Co(LCX)(NO2)2](ClO4), respectively. The ligand and corresponding metal complexes were characterized based on the analytical, spectroscopic, magnetic moment, and molar conductivity data. Gram-positive and gram-negative bacteria and different fungi were used to evaluate the antibacterial and antifungal activities of the ligand and its metal complexes.

Measurements of thermodynamic parameters for complexation between a tetra-aza macrocycle ligand and some metal cations based on conductometric method

Thermodynamic aspects of complexation process between 14-membered tetra-aza macrocycle ligand and four metal cations were studied in ethanol–water (EtOH–H2O) binary mixtures at different temperatures by applying conductometric method. In all the cases, the stability constants (logKf) of 1:1 formed complexes between ligand and cations were obtained by fitting the molar conductivity curves using the Genplot computer program and the formation constant values (logKf) were generally in the range of 1.41–2.70. The values of thermodynamic parameters, standard enthalpy (ΔHC∘) and standard entropy (ΔSC∘) were obtained from the temperature dependence of the stability constants using the Van’t Hoff plots. Complexes in every cases were found to be entropy stabilized, and the selectivity order of all the complexes changes as well as the changes in composition of the solvent mixtures. The experimental data was tested by using artificial neural network (ANN) technique and was in a good agreement with estimated data.

A new 14-membered tetraazamacrocycle-bonded silica stationary phase for reversed-phase high-performance liquid chromatography

A new high-performance liquid chromatography stationary phase has been prepared by covalently bonding 14-membered tetraazamacrocycle to silica gel using γ-chloropropyltrimethoxylsilane as coupling agent. The structure of the new material was characterized by infrared spectroscopy and elemental analysis. With 32 solutes including aromatic and aliphatic compounds, the linear solvation energy relationship method was successfully used to chromatographically evaluate the new phase in reversed phase mode. The retention property of the new phase shows evident similarity with that of ODS stationary phase, as well as distinctive, unique retention characteristics. The separations of n-alkylbenzene, carbamate and organophosphorus pesticides with diversified functional groups as well as phenolic compounds demonstrate that in addition to hydrophobic interaction, dipole–dipole interaction and hydrogen bonding interaction plus acid–base equilibrium could also be simultaneously offered by this new stationary phase, as a result excellent chromatographic performances are guaranteed.

Axial Interactions of Nitrate Ions to a Silver(II) Ion Supported by C-H…O Hydrogen Bonds in a Silver(II) Tetraazamacrocyclic Complex

show similar coordination tendencies to metal ions and form corres-ponding metal complexes, the chemical and structural properties of metal complexes are greatly influenced by the stereochemistry of cyclohexane rings fused on the 14-membered tetraazamacro-cycle. Thus, the axial coordination of solvent molecules to the nickel(II) ion in [Ni(

Synthesis of two configurational isomers of a 14-membered tetraaza macrocycle bearing N-CH 2CH 2CONH 2 pendent arms and their copper(II) complexes: Crystal structures of the complexes

Two isomers of 1,8-bis( N-carbamoylethyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 2) bearing two N-CH 2CH 2CONH 2 groups, C- meso-L 2 and C- racemic-L 2, have been prepared and characterized. Each isomer reacts with Cu(II) ion to form a five-coordinate complex, [Cu( C- meso-L 2)](ClO 4) 2 ( 1) or [Cu( C- racemic-L 2)](ClO 4) 2 ( 2), in which only one pendent amide group is coordinated to the metal ion. The crystal structure of 1 · CH 3CN shows that the complex possesses trans-III-type N-configuration and has a slightly distorted square-pyramidal coordination geometry with a relatively long axial Cu–O ( N-CH 2CH 2CONH 2) bond (2.207(3) Å). On the other hand, 2 exhibits trans-V configuration and has a slightly distorted trigonal bipyramidal coordination geometry with a very short equatorial Cu–O ( N-CH 2CH 2CONH 2) bond (2.007(3) Å); the Cu–O distance is distinctly shorter than the Cu–N distances (2.062(4)–2.090(4) Å). The complex 1 exhibits a d–d transition band at approximately 565 nm, whereas the band for 2 is observed at approximately 770 nm.

Biological evaluation of 153Sm and 166Ho complexes with tetraazamacrocycles containing methylcarboxylate and/or methylphosphonate pendant arms

153Sm and 166Ho complexes with two series of tetraazamacrocyclic ligands containing methylcarboxylate and/or methylphosphonate pendant arms were synthesized and their charge, lipophilicity, protein binding and in vitro and in vivo behaviour evaluated. The first series has the same backbone, a 14-membered tetraazamacrocycle containing a pyridine unit with different pendant arms, namely methylcarboxylates (ac3py14) or methylphosphonates (MeP2py14 and P3py14). The second series comprises 12- to 14-membered tetraazamacrocycles having methylcarboxylates and/or methylphosphonates as pendant arms (trans-DO2A2P, TRITA, TRITP, TETA and TETP). The 153Sm/166Ho complexes with the 14-membered tetraazamacrocycles containing the pyridine unit are neutral, hydrophilic, have a significant plasmatic protein binding, are unstable in vivo and present a slow rate of radioactivity excretion and high hepatic retention. 153Sm/166Ho complexes with the 12- to 14-membered tetraazamacrocycles are quantitatively prepared, except those with TETP. These complexes are hydrophilic, have an overall negative charge and present a medium to low plasmatic protein binding. The 153Sm/166Ho- trans-DO2A2P, 153Sm/166Ho-TRITA and 166Ho-TRITP complexes are stable in vitro and in vivo, presenting a rapid clearance from main organs and a high rate of whole body radioactivity excretion. Biological profile of 153Sm/166Ho-TRITA complexes makes them promising candidates for therapy when conjugated to a biomolecule, while 166Ho-TRITP is potentially useful for bone targeting due to its considerable uptake by bone.

Hydrogen Peroxide Decomposition by a Non‐Heme Iron(III) Catalase Mimic: A DFT Study

Non-heme iron(III) complexes of 14-membered tetraaza macrocycles have previously been found to catalytically decompose hydrogen peroxide to water and molecular oxygen, like the native enzyme catalase. Here the mechanism of this reaction is theoretically investigated by DFT calculations at the (U)B3LYP/6-31G* level, with focus on the reactivity of the possible spin states of the FeIII complexes. The computations suggest that H2O2 decomposition follows a homolytic route with intermediate formation of an iron(IV) oxo radical cation species (L.+FeIV==O) that resembles Compound I of natural iron porphyrin systems. Along the whole catalytic cycle, no significant energetic differences were found for the reaction proceeding on the doublet (S=1/2) or on the quartet (S=3/2) hypersurface, with the single exception of the rate-determining O--O bond cleavage of the first associated hydrogen peroxide molecule, for which reaction via the doublet state is preferred. The sextet (S=5/2) state of the FeIII complexes appears to be unreactive in catalase-like reactions.

Microwave-assisted synthesis and characterization of novel metal-free and metallophthalocyanines containing four 14-membered tetraaza macrocycles

The novel tetrasubstituted metal-free phthalocyanine ( 6) and metallophthalocyanines ( 7, 8) bearing four 14-membered tetraaza macrocycles moieties on peripheral positions have been synthesized by cyclotetramerization reaction of phthalonitrile derivative ( 5) in a multi-step reaction sequence. The new compounds were characterized by a combination of IR, 1H NMR, 13C NMR, UV–vis, elemental analysis and MS spectral data.

Properties of a new 4-imidazolyl derivative of a 14-membered tetraazamacrocyclic chelating agent

A new bis-N,N'-(5-methylimidazol-4-ylmethyl) derivative of a 14-membered tetraazamacrocycle, L1, has been synthesized. The protonation constants of this compound and the stability constants of its complexes with divalent first-row transition metal ions and Fe3+ were determined at 298.2 K in aqueous 0.10 mol dm(-3) KNO3. Compound L1 exhibits high overall basicity, which is mainly conferred by the imidazolyl groups. The complexes of the divalent first row-transition metal ions of L1 follow the Irving-Williams order of stability with the maximum for Cu2+ as expected, but a steep fall of constants is verified for the Mn2+, Fe2+ and Co2+, in one side, and for the Zn2+ complexes, in the other side. Additionally, L1 shows a large affinity for Fe3+, and the relative stability constants for its Cd2+ and Pb2+ complexes indicate that L1 may be useful for the complexometric determination of these two toxic metal ions in solutions containing both metal ions. These studies together with NMR, UV-vis and EPR spectroscopic data indicated the presence of mononuclear complexes, which adopt distorted pyramidal or octahedral geometries depending on the metal centre. The X-ray crystal structure of [Cu(HL1)](PF6)2(NO3).H2O showed that the coordination sphere of the copper centre can be described as a distorted square pyramid with the basal plane defined by three nitrogen donors of the macrocycle backbone and one nitrogen atom from one imidazolyl pendant arm. The apical position is occupied by the nitrogen atom of the macrocycle trans to the pyridine ring. To achieve this coordination environment, the macrocycle is folded along the axis defined by the two N atoms contiguous to the pyridine ring. The free methylimidazolyl arm points away from the metal centre leading to an intramolecular Cu[dot dot dot]N distance of 5.155(1) A.

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 (L 2) bearing two N-CH 2CH 2COOMe 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 (L 3) containing one N-CH 2CH 2COOMe group have also been prepared. The crystal structure of [NiL 2](ClO 4) 2 shows that the complex has a slightly distorted trans-octahedral coordination geometry with two relatively short axial Ni–O ( N-CH 2CH 2COOMe group) bonds (2.136(3) Å). In various solvents, however, a considerable proportion of [NiL 2] 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 < H 2O < DMF ⩽ DMSO. In the case of [CuL 2](ClO 4) 2, only one N-CH 2CH 2COOMe group is involved in coordination. The N-CH 2CH 2COOMe group of [NiL 3](ClO 4) 2 is not directly involved in coordination even in the solid state, though the functional group of [CuL 3](ClO 4) 2 is coordinated to the metal ion.

Bis- and tris-(3-aminopropyl) derivatives of 14-membered tetraazamacrocycles containing pyridine: synthesis, protonation and complexation studies

New N-(3-aminopropyl) (L1, L2) and (2-cyanoethyl) (L3, L4) derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized. The protonation constants of L1 and L2 and the stability constants of their complexes with Ni2+, Cu2+, Zn2+ and Cd2+ metal ions were determined in aqueous solutions by potentiometry, at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO3. Both compounds have high overall basicity due to the presence of the aminopropyl arms. Their copper(II) complexes exhibit very high stability constants, which sharply decrease for the complexes of the other studied metal ions, as usually happens with polyamine ligands. Mono- and dinuclear complexes are formed with L2 as well as with L1, but the latter exhibits mononuclear complexes with slightly higher K(ML) values while the dinuclear complexes of L2 are thermodynamically more stable. The presence of these species in solution was supported by UV-VIS-NIR and EPR spectroscopic data. The single crystal structures of [Cu(H2L2)(ClO4)]3+ and [CoL3Cl]+ revealed that the metal centres are surrounded by the four nitrogen atoms of the macrocycle and one monodentate ligand, adopting distorted square pyramidal geometries. In the [CoL3Cl]+ complex, the macrocycle adopts a folded arrangement with the nitrogen atom opposite to the pyridine at the axial position while in the [Cu(H2L2)(ClO4)]3+ complex, the macrocycle adopts a planar conformation with the three aminopropyl arms located at the same side of the macrocyclic plane.

Intra- vs Intermolecular Photoinduced Electron Transfer Reactions of a Macrocyclic Donor−Acceptor Dyad

The synthesis, structural characterization, and photophysical behavior of a 14-membered tetraazamacrocycle with pendant 4-dimethylaminobenzyl (DMAB) and 9-anthracenylmethyl groups is reported (L3, 6-((9-anthracenylmethyl)amino)-trans-6,13-dimethyl-13-((4-dimethylaminobenzyl)amino)-1,4,8,11-tetraazacyclotetradecane). In its free base form, this compound displays rapid intramolecular photoinduced electron transfer (PET) quenching of the anthracene emission, with both the secondary amines and the DMAB group capable of acting as electron donors. When complexed with Zn(II), the characteristic fluorescence of the anthracene chromophore is restored as the former of these pathways is deactivated by coordination. Importantly, it is shown that the DMAB group, which remains uncoordinated and PET active, acts only very weakly to quench emission, by comparison to the behavior of a model Zn complex lacking the pendant DMAB group, [ZnL2]2+ (Chart 1). By contrast, Stern-Volmer analysis of intermolecular quenching of [ZnL2]2+ by N,N-dimethylaniline (DMA) has shown that this reaction is diffusion limited. Hence, the pivotal role of the bridge in influencing intramolecular PET is highlighted.

Metal Ion Directed Synthesis of 12 and 14-Membered Tetraaza Macrocyclic Complexes and their Physico-Chemical Studies

The template condensation reaction of o-phenylenediamine with 2,3-butanedione or 2,4-pentanedione resulted in the formation of new series of 12 and 14-membered tetraaza macrocyclic complexes: [ML1Cl2], [ML2Cl2] [M=Co(II), Ni(II) and Zn(II)]; [CuL1]Cl2 and [CuL2]Cl2. The formation of the macrocyclic framework and the overall geometry of the complexes have been characterized by elemental analyses, FT-IR, 1HNMR, UV-Visible, magnetic susceptibility and conductivity measurements. The copper(II) complexes exhibit square planar geometry, whereas an octahedral geometry is suggested for all other complexes.

Exploring Mycobacterium avium inhibition by macrocyclic compounds

Derivatives of synthetic macrocyclic compounds, MCC, 12- and 14-membered tetraazamacrocycles with N-pendant arms, such as N-methyl (Mepy14), N-acetate (DOTA, TETA and ac 3py14) and N-methylphosphonate (DOTP) groups, were investigated in terms of their in vitro activity against Mycobacterium avium and for intracellular clearance, using the murine macrophage cell line J-774. Perspective results on a laboratory strain, of opaque morphology, showed in vitro activity with varying inhibitory patterns from one compound to another. The most active compounds, such as TETA, presented N-acetate pendant arms. Inhibition levels of 90% and above were obtained at 50 mg/l. Inhibition was confirmed with both the free compound and its iron(III) complex for DOTP, Mepy14, ac 3py14, and TETA. However, with DOTA, no inhibitory effect was observed for the iron(III) complex, suggesting that chelation was at the origin of the inhibitory effect or that the donor atoms of the ligand were strongly involved. Nevertheless, simple experiments indicated that ferric ion might not be responsible for this reversed activity. Intracellular activity using 50 mg/l of TETA confirmed in vitro results with the laboratory strain. Results expressed as relative growth (%), of the drug-containing samples compared to control samples ranged from 2 to 123% (growth promotion) with no apparent relationship between inhibitory activity and the colony morphology of the strains. These studies showed that the evaluation of synthetic macrocycles may be relevant in development of a new family of compounds for use against M. avium infections.

Synthesis and coordination behaviors of 14-membered tetraaza macrocyclic copper(II) complexes bearing two N-propionic acid or N-propionic methyl ester groups

A di- N-functionalized 14-membered tetraaza macrocycle, [H 4L 3](ClO 4) 2 (L 3 = 1,8-bis(2-carboxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane), has been synthesized by acid hydrolysis of 1,8-bis(2-cyanoethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L 2). The copper(II) complexes [CuL 2](ClO 4) 2 and [Cu(H 2L 3)](ClO 4) 2 were prepared and characterized. The complex [Cu(H 2L 3)] 2+ readily reacts with methanol to yield [CuL 4] 2+ (L 4 = 1,8-bis(2-carbomethoxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane). The N-CH 2CH 2COOH groups of [Cu(H 2L 3)](ClO 4) 2 are not coordinated to the metal ion in the solid state but are involved in coordination in various non-aqueous solvents or in aqueous solutions of pH ⩽ 1.0. Interestingly, [CuL 4](ClO 4) 2 exists as two stable structural isomers, 1 (the pendant ester groups are not involved in coordination) and 2 (one of the two ester groups is coordinated to the metal ion), in the solid state; the two isomers can be prepared selectively by controlling ionic strength of a methanol solution of the complex. Crystal structures and coordination behaviors of the two isomers are described. The di- N-cyanoethylated macrocyclic complex [CuL 2](ClO 4) 2 is rapidly decomposed in 0.1 M NaOH solution even at room temperature. On the other hand, [Cu(H 2L 3)](ClO 4) 2 and [CuL 4](ClO 4) 2 are quite inert against decomposition under similar basic conditions. In acidic or basic aqueous solutions, [CuL 4] 2+ is hydrolyzed to [Cu(H 2L 3)] 2+ or [CuL 3].

Solution 1H n.m.r. of paramagnetic Co2+complexes with dioxobis(carboxymethyl)tetraazamacrocycles

Paramagnetic shifts in the 1H n.m.r. spectra were observed for high-spin Co2+ complexes with 12--14-membered tetraazamacrocycles incorporating two amide groups and two pendant carboxymethyl groups. The pseudocontact term due to the dipolar interaction between the metal ion and the resonant protons was calculated on the basis of X-ray structures, and the Fermi contact term due to spin delocalization was determined. The ethylenediamine moiety of the ligand molecule is coordinated in an unsymmetric manner, even in solution, and internal motion (involving conformational change of the macrocyclic frame and exchange of coordinate bonds) is much slower than the n.m.r. observation frequency. In the 12-membered macrocyclic complex Co(L12), three of the eight CH2 groups fix their orientation in the n.m.r. time scale; in Co(L13) only one CH2 group fixes its orientation; in Co(L14) all CH2 groups undergo a rapid reorientation. The facility in internal motion increases with the ring size, and shows a correlation with the chemical stabilities of these Co2+ complexes against oxidation; to atmospheric oxygen, Co2+(L12) is the most resistant and Co2+(L14) is the most susceptible.

Lanthanide complexes of macrocyclic derivatives useful for medical applications

Abstract The protonation constants of two series of tetraazamacrocyclic ligands with acetate and methylphosphonate pendant arms, as well as their stability constants with Cu2+, La3+, Sm3+, and Ho3+, were determined. All the values were determined in aqueous solution at 298.0 K and 0.10 mol dm–3 in N(CH3)4NO3. In the first series, the effect of both types of pendant arms was observed by appending them in the same macrocyclic backbone, a 14-membered tetraazamacrocycle containing pyridine (ac3py14, p2py14, and p3py14). In the second series, two effects were taken into account, the increase of the cavity size of the macrocycle, from 12- to 14-membered, and the appending of acetate (dota, trita, and teta) or methylphosphonate (dotp, tritp, and tetp) arms. The ligands containing methylphosphonate arms have higher thermodynamic stability compared to the corresponding ones with acetate arms, especially in the series of compounds containing pyridine, even upon correction of the different basicity values of the ligands. On the other hand, the ligands with smaller macrocyclic cavity size, namely, dota and dotp, exhibit the largest values of stability constants. In contrast, ac3py14 presents low stability constants with lanthanides. An interpretation of these features based on the known adopted arrangement of dota and teta when free or coordinated with lanthanides is evaluated.

Kinetic studies of the on/off reaction of the amino group in the side chain of Cu(ii), Ni(ii), and Co(ii) complexes with 14-membered tetraazamacrocycles

The kinetics of the on/off reaction of the amino group in the side chain of tetraazamacrocyclic Cu2+, Ni2+ and Co2+ complexes has been measured. The rate law k(obs)=k(0)+k(H)[H+]+k(OH)/[H+], the sum of the forward and reverse reaction, gives rise to u-shaped pH dependences from which the three rate constants can be determined. k(H) describes the proton assisted dissociation of the amino group bound to the metal ion and is roughly correlated to the equilibrium constant of the reaction. k(OH) is determined by the protonation constant of the free amino group and the rate constant describing the binding of the amino group to the metal ion. k(0) is composed of the rate constant for the opening of the chelate ring without proton assistance and the rate for the reactivity of the ammonium group in the formation of the chelate ring. Our results show that the rates of the opening and closing of the chelate ring are very little dependent on the nature of the metal ion.

Bis- and tris-(methylphosphonic) acid derivatives of a 14-membered tetraazamacrocycle containing pyridine: synthesis, protonation and complexation studies.

Two N-methylphosphonic acid derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized, H(4)L(1) and H(6)L(2). The protonation constants of these compounds and the stability constants of complexes of both ligands with Ni(2+), Cu(2+) and Zn(2+) were determined by potentiometric methods at 298 K and ionic strength 0.10 mol dm(-3) in NMe(4)NO(3). The high overall basicity of both compounds is ascribed to the presence of the phosphonate arms. (1)H and (31)P NMR spectroscopic titrations were performed to elucidate the sequence of protonation, which were complemented by conformational analysis studies. The complexes of these ligands have stability constants of the order of or higher than those formed with ligands having the same macrocyclic backbone but acetate arms. At pH = 7 the highest pM values were found for solutions containing the compound with three acetate groups, followed immediately by those of H(6)L(2), however, as expected, the increasing pH favours the complexes of ligands containing phosphonate groups. The single-crystal structure of Na(2)[Cu(HL(1))]NO(3)x8H(2)O has shown that the coordination geometry around the copper atom is a distorted square pyramid. Three nitrogen atoms of the macrocyclic backbone and one oxygen atom from one methylphosphonate arm define the basal plane, and the apical coordination is accomplished via the nitrogen atom trans to the pyridine ring of the macrocycle. To achieve this geometric arrangement, the macrocycle adopts a folded conformation. This structure seems consistent with Uv-vis-NIR spectroscopy for the Ni(2+) and the Cu(2+) complexes and with the EPR for the latter.