Tetradentate Macrocyclic Ligand Research Articles

Bimetallic MV2CuII3 (M = Mo, W) Coordination Complexes Based on Octacyanometalates: Structures and Magnetic Variations Tuned by Chelated Tetradentate Macrocyclic Ligands

Four octacyanometalate-based bimetallic Cu-M (M = Mo, W) assemblies coordinated by tetradentate macrocyclic ligands were prepared via self-assembly process in a stoichiometric ratio of [M(CN)8]3- and Cu(macrocycle)2+ and characterized in terms of structures and magnetic properties. The crystal structures are varied depending on the macrocycles used. The employment of cyclam with no pendant groups produced a one-dimensional chain (1) with a rope-ladder pattern, whereas macrocycles with side groups allowed for the formation of two-dimensional honeycomb-like architectures (2-4). From the crystal structures, the variations in apical Cu-Nax lengths and Cu-Nax-Cax angles on the bridging pathways are observed, which arises from the existence of side groups on macrocyclic ligands. The magnetic results reveal that all of the prepared compounds show ferromagnetic couplings between magnetic centers transimitted through CN bridges under the present structural parameters. Comparing the magnetic strength of the Cu-Mo (3d-4d; 2) and Cu-W (3d-5d; 3) complexes supports that 3d-5d magnetic coupling is stronger than 3d-4d because the 5d orbital is more diffuse than 4d. The magnetic analyses for 1-4 and related complexes tentatively suggest that, when the Cu-Nax distances are long enough, the axial Cu-Nax bond length in the bridging route may be one of the major structural parameters to determine the magnitude of the ferromagnetic exchange coupling.

EPR, IR and electronic spectral studies on Ni(II) and Cu(II) complexes with N-donor tetradentate [N 4] macrocyclic ligand

Nickel(II) and copper(II) complexes are synthesized with a novel tetradentate macrocyclic ligand, i.e. 2,6,12,16,21,22-hexaaza;3,5,13,15-tetraphenyltricyclo[15,3,1,1 7–11] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) and characterized by the elemental analysis, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic and EPR spectral studies. All the complexes are non-electrolytic in nature. Thus, these may be formulated as [M(L)X 2] [M = Ni(II), Cu(II) and X = Cl −, NO 3 − and (1/2)SO 4 2−]. Ni(II) and Cu(II) complexes show magnetic moments corresponding to two and one unpaired electron, respectively. On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Ni(II) and tetragonal geometry for Cu(II) complexes.

Solvent Effects on the Oxidation of RuIVO to ORuVIO by MnO4-. Hydrogen-Atom versus Oxygen-Atom Transfer

The kinetics of the oxidation of trans-[RuIV(tmc)(O)(solv)]2+ to trans-[RuVI(tmc)(O)2]2+ (tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, a tetradentate macrocyclic tertiary amine ligand; solv = H2O or CH3CN) by MnO4- have been studied in aqueous solutions and in acetonitrile. In aqueous solutions the rate law is -d[MnO4]/dt = kH2O[RuIV][MnO4-] = (kx + (ky)/(Ka)[H+])[RuIV][MnO4-], kx = (1.49 +/- 0.09) x 101 M-1 s-1 and ky = (5.72 +/- 0.29) x 104 M-1 s-1 at 298.0 K and I = 0.1 M. The terms kx and ky are proposed to be the rate constants for the oxidation of RuIV by MnO4- and HMnO4, respectively, and Ka is the acid dissociation constant of HMnO4. At [H+] = I = 0.1 M, DeltaH and DeltaS are (9.6 +/- 0.6) kcal mol-1 and -(18 +/- 2) cal mol-1 K-1, respectively. The reaction is much slower in D2O, and the deuterium isotope effects are kx/kxD = 3.5 +/- 0.1 and ky/kyD = 5.0 +/- 0.3. The reaction is also noticeably slower in H218O, and the oxygen isotope effect is kH216O/kH218O = 1.30 +/- 0.07. 18O-labeled studies indicate that the oxygen atom gained by RuIV comes from water and not from KMnO4. These results are consistent with a mechanism that involves initial rate-limiting hydrogen-atom abstraction by MnO4- from coordinated water on RuIV. In acetonitrile the rate law is -d[MnO4-]/dt = kCH3CN[RuIV][MnO4-], kCH3CN = 1.95 +/- 0.08 M-1 s-1 at 298.0 K and I = 0.1 M. DeltaH and DeltaS are (12.0 +/- 0.3) kcal mol-1 and -(17 +/- 1) cal mol-1 K-1, respectively. 18O-labeled studies show that in this case the oxygen atom gained by RuIV comes from MnO4-, consistent with an oxygen-atom transfer mechanism.

Trivalent metal ion directed synthesis and characterization of macrocyclic complexes

A novel series of complexes of the type [M(TML)X]X2, where TML is a tetradentate macrocyclic ligand, M = Cr(III), Mn(III) or Fe(III), X = Cl-, CH3COO- or ? NO3, were synthesized by template condensation of dibenzoyl and thiocarbohydrazide in the presence of trivalent metal salts in a methanolic medium. The complexes were characterized with the help of elemental analyses, conductance measurements, molecular weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. The electronic spectra together with the magnetic moments suggest five coordinate square pyramidal geometry for these complexes. The molar conductance indicates them to be 1:2 electrolytes.

Template synthesis, spectroscopic studies and biological activities of macrocyclic complexes derived from thiocarbohydrazide and glyoxal

A novel series of complexes of the type [M(TML)X2]; where TML is Tetradentate Macrocyclic Ligand; M = Co(II), Ni(II), Cu(II), Zn(II)or Cd(II); X = Cl− , CH3COO− or have been synthesized by template condensation of glyoxal and thiocarbohydrazide in the presence of divalent metal salts in methanolic medium. The complexes have been characterized by elemental analyses, conductance measurements, molecular weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. Electronic spectra along with magnetic moments suggest a six coordinate octahedral geometry for these complexes. The low molar conductance values indicates them to be non-electrolytes. The biological activities of the metal complexes have been tested in vitro against a number of pathogenic bacteria to assess their inhibitory potential.

Crystal Structure of [1,4,8,11-Tetraazacyclotetradecanenickel(II)]bis-(dihydrogenphosphate)bis(phosphoric acid) [Ni(C10H24N4)](H2PO4)2 2(H3PO4)

In the title compound, [Ni(C10H24N4)](H2PO4)2·2(H3PO4), the Ni atom lies at the center of inversion, and is coordinated in a slightly distorted square coordination geometry by four N atoms of the tetradentate macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane. The structure consists of infinite two-dimensional cationic [Ni(C10H24N4)]2+ layers alternating with sheets containing H2PO4- anions and H3PO4 molecules connected by hydrogen bonds and stacked along the bc planes. The latter are interconnected to the framework through hydrogen bonds.

Synthesis and Characterization of trans-[Co((BA)2en)(amine)(CN)] and trans-K[Co((BA)2en)(CN)2] Complexes:Indication of Cobalt-cyanid π -Back Bonding Interaction

The structure of vitamin B12 (cyano cobalamine) was determined in the laboratory of Hodgkin and co-workers in the mid-1960s. In the equatorial plane the central six coordinate cobalt (III) ion is surrounded by four pyrole nitrogen atoms of a corrin ligand. While one of the axial sites is occupied by a 5,6-dimethyl benzimidazol-α-Dribofuranose-3-phosphate, the second axial ligand position is occupied by a cyanide group. The vitamin can be converted in vivo to active alkylcobalamin coenzymes. These alkylcobalamin are know naturally occurring compounds with a biologically active carbon-metal bond. The macrocyclic tetradentate ligands with four nitrogen donor or Schiff base ligands (N2O2) which coordinated to four equatorial position octahedral structure of cobalt (III) center are considered as models for vitamin B12. 6-10 The effect of axial ligation (amine) on properties of cyano group with an organic monoanion ligand has played an important role in our knowledge of the properties of vitamin B12 and of model compounds. The coordination of the amine ligand in trans position can lead to cyano activation barrier of dissociation. A variety of physical methods such as infrared and NMR have been used to study of π-back bonding from the cobalt (III) metal center into cyano ligand. Infrared and NMR spectroscopy allows one to investigation of the effect amines on the cyano ligand π-back bonding in complexes. These results were indicative of the existence of dπ-pπ back bonding in cyano cobalt species (Scheme 1). The effect of trans axial ligands on the cyanide chemical shifts and stretching properties can influence the relative stabilization of I and II species by the axial ligand. In this paper, we report result of H NMR and IR study of a series of trans-(Schiff base)CN(amine)cobalt(III) complexes with different axial ligands (Scheme 2), which permits a more detailed analysis of these properties.

Template synthesis, spectroscopic studies and biological screening of macrocyclic complexes derived from thiocarbohydrazide and benzil

A novel series of complexes of the type [M(TML)X2]; where TML is a tetradentate macrocyclic ligand; M = Co(II), Ni(II), Cu(II) or Zn(II); X = Cl−, CH3COO− or NO3− have been synthesized by template condensation of benzil and thiocarbohydrazide in the presence of divalent metal salts in methanolic medium. The complexes have been characterized with the help of elemental analyses, conductance measurements, molecular weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. Electronic spectra along with magnetic moments suggest the six coordinate octahedral geometry for these complexes. The low value of molar conductance indicates them to be non-electrolytes. The biological activities of metal complexes have been tested in vitro against a number of pathogenic bacteria to assess their inhibiting potential.

Structural and Magnetic Properties of a Complete Halide Series of NiIIComplexes with a Pyridine-Containing 14-Membered Macrocycle

The complete halide series of Ni(II) complexes containing the tetradentate macrocyclic ligand 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L), was fully characterized by X-ray diffraction. The fluoro, chloro, and bromo complexes are dinuclear species with formula [{Ni(L)}2(mu-X)2]2+ (X = halide), whereas only mononuclear species with formula [Ni(Y)(solv)(L)]n+ (Y = halide or solvent molecule), were obtained with I. To date, the fluoro derivative is the first nonorganometallic coordination compound containing the Ni(mu-F)2Ni core. The magnetic properties of these halo complexes have been studied. Intramolecular interactions were observed in the three dinuclear complexes, being antiferromagnetic in the fluoro derivative and ferromagnetic in both the chloro and bromo ones. The two iodo derivatives are paramagnetic species, as would be expected for mononuclear octahedral Ni(II) complexes. Density functional theory calculations led us to relate the magnetic behaviors of these compounds to the values of the corresponding Ni-X-Ni(i) angle. The analysis of the singly occupied molecular orbitals gave a clear comprehension of the different magnetic exchange interactions found in these Ni(II) complexes.

Spectroscopic characterization and EPR spectral studies on transition metal complexes with a novel tetradentate, 12-membered macrocyclic ligand

Complexes of Cr(III), Mn(II), Co(II), Ni(II) and Cu(II) containing a tetradentate macrocyclic N-donor ligand have been prepared via template reaction of 2,3-pentanedione, ethylene-di-ammine and transition metal ions. The complexes have been characterized on the basis of the elemental analysis, molar conductance, magnetic moment susceptibility, IR, electronic and EPR spectral studies. The complexes are of high spin type and possess four coordinate tetrahedral five coordinate square pyramidal and six coordinated octahedral/tetragonal geometry.

Spectral, physicochemical and biological characterization of 2,5,11,14,19,20-hexaaza-3,12-dimethyl-4,13-dipropyl-tricyclo [13.3.1.1(6-10)]cosane-1(19),2,4,6(20),7,9,11,13,15,17-decaene and its transition metal complexes

The synthesis of a tetradentate nitrogen donor macrocyclic ligand i.e. 2,5,11,14,19,20-hexaaza-3,12-dimethyl-4,13-dipropyl-tricyclo[13.3.1.1(6-10)]cosane-1(19),2,4,6(20),7,9,11,13,15,17-decaene and its complexes with manganese(II), cobalt(II), nickel(II) and copper(II) have been reported. The complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, mass, 1H-n.m.r. (Ligand), i.r., electronic, and e.p.r. spectral studies. On the basis of molar conductance the complexes may be formulated as [M(L)X2] [where M = Mn(II), Co(II), Ni(II) and Cu(II), and X = Cl− & NO 3 − ] due to their nonelectrolytic nature in dimethylformamide (DMF). All the complexes are of the high spin type and are six coordinated. On the basis of i.r., electronic and e.p.r. spectral studies an octahedral geometry has been deduced for Mn(II), Co(II) and Ni(II) complexes, and tetragonal geometry for Cu(II) complexes. The antimicrobial activities of the ligand and its complexes, as growth inhibiting agents, have been screened in vitro against several species of bacteria and plant pathogenic fungi.

Spectroscopic studies on Co(II), Ni(II) and Cu(II) complexes with a new macrocyclic ligand: 2,9-dipropyl-3,10-dimethyl-1,4,8,11-tetraaza-5,7:12,14-dibenzocyclotetradeca-1,3,8,10-tetraene

Cobalt(II), nickel(II) and copper(II) complexes containing a tetradentate macrocyclic nitrogen donor ligand i.e. 2,9-dipropyl-3,10-dimethyl-1,4,8,11-tetraaza-5,7:12,14-dibenzocyclotetradeca-1,3,8,10-tetraene have been synthesized and characterized by elemental analysis, molar conductance, magnetic moments, mass, 1H NMR, IR, electronic and EPR spectral studies. All the complexes are of high spin type and posses four-coordinated tetrahedral, five-coordinated square pyramidal and six-coordinated octahedral/tetragonal geometry. The ligand and its metal complexes were also screened against the growth of some bacteria and plant pathogenic fungi in vitro.

Quantum-Chemical Calculations of Ruthenium Nitrosyl Complexes with Tetradentate Macrocyclic Ligands

The geometric structure of the ground state and of metastable isomers of nitrosyl complexes trans-[Ru(P)(NO)(Cl)] (P = porphinate dianion) and trans-[Ru(NO)(salen)(X)]q [salen = N,N'-ethylenebis(salicylideniminate) dianion; X = Cl- (q = 0), H2O (q = +1)] was optimized within the framework of the density functional method (SVWN/LanL2DZ+6-31G). The local minima corresponding to metastable isomers with a linear NO coordination through the oxygen atom and with a side η2 NO coordination were found on the potential energy surfaces of these compounds. The second metastable states of all the three complexes have a lower energy. The difference in energies between the stable and metastable isomers is the least in the case of the complex trans-[Ru(NO)(salen)(Cl)].

Spectroscopic studies on Mn(II), Co(II), Ni(II), and Cu(II) complexes with N-donor tetradentate (N 4) macrocyclic ligand derived from ethylcinnamate moiety

Manganese(II), cobalt(II), nickel(II), and copper(II) complexes are synthesized with a novel tetradentate ligand, viz. 1,5,9,13-tetraaza-6,14-dioxo-8,16-diphenylcyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic, and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolyte nature for Mn(II), Co(II), and Cu(II) whereas 1:2 electrolytes for Ni(II) complexes. Thus, these complexes may be formulated as [M(L)X 2] and [Ni(L)]X 2, respectively (where M=Mn(II), Co(II), and Cu(II) and X=Cl − and NO 3 −). On the basis of IR, electronic, and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.

Trivalent transition metal ion directed macrocycles

Trivalent chromium, manganese and iron salts react in situ with 2,6-diacetylpyridine and 1,2-diantinobenzene to form complexes containing a 18-membered N 6 tetradentate macrocyclic ligand. The complexes are of distorted octahedral type [M(TML)]X 3 , where M = Cr I I I , Mn I I I or Fe I I I and X = Cl, Br, NO 3 or NCS for Cr I I I and Fe I I I ; and X = OAc for Mn I I I , TML = tetradentate macrocyclic ligand. The iigand coordinates through all the six nitrogen atoms. The complexes behave as 1 : 3 electrolytes and the test for anions are positive, indicate their presence outside the coordination sphere.

Crystal structure of (1,10-phenanthroline-N,N')(1,4,7,10-tetraazacyclododecane-N,N',N",N"')nickel(II) diperchlorate.

The crystal structure of the title compound, [Ni(C8H20N4)(C12H8N2)](ClO4)2, has been determined by X-ray diffraction. The Ni(II) ion is six coordinated with four nitrogen atoms of the tetradentate macrocyclic ligand and two nitrogen atoms of the bidentate ligand in a distorted octahedron geometry. The folded tetradentate macrocyclic ligand adopts a configuration having four five-membered chelate rings in distorted eclipsed conformations. The four hydrogen atoms of the amine groups of the macrocyclic ligand are on the same side towards the bidentate ligand.

Divalent cobalt, nickel and copper chelates of macrocycle derived from 2,3-butanedione and its dihydrazide

Divalent cobalt, nickel and copper salts reacts in situ with 2,3-butanedione and its dihydrazide to form complexes containing a 16-membered tetradentate macrocyclic ligand. The complexes derived from 2,3-butanedione and its dihydrazide may be represented as [M(C 1 6 H 2 4 N 8 )X 2 ], where M = Co I I , Ni I I and Cull and X = Cl, Br, NO 3 , NCS.

Biomimetic Catalysis of Catechol Cleavage by O2 in Organic Solvents − Role of Accessibility of O2 to FeIII in 2,11-Diaza[3,3](2,6)pyridinophane-Type Catalysts

Three new complexes, [Fe(LN4H2)Cl2]+, [Fe(LN4H2)(Cat)]+, and [Fe(LN4H2)(DBC)]+, were synthesized by using the tetradentate macrocyclic ligand LN4H2 (where LN4H2, Cat, and DBC stand for 2,11-diaza[3,3](2,6) pyridinophane, catecholate, and 3,5-di-tert-butylcatecholate, respectively). The structure of [Fe(LN4H2)Cl2]+ was determined by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with a = 9.613(1), b = 11.589(1), c = 14.063(2) Å, β=110.20(2)°, V = 1541.9(3) Å3, and Z = 4. These complexes were found to catalyze the oxidation of catechol groups using O2. This was performed in various organic solvents at 20 °C. The reaction rates were measured for the stoichiometric complexes [Fe(LN4H2)(Cat)]+ and [Fe(LN4H2)(DBC)]+. It was found that despite the relatively high energy of the ligand-to-metal charge transfer O(DBC or Cat)→FeIII, their activity was comparable to that of the fast TPA systems [TPA indicates tris(2-pyridylmethyl)amine]. The oxidation products of DBCH2 have been studied. It has then been shown that the LN4H2 systems catalyse by means of both intra- and extradiol cleavage of catechol groups. The existence of multiple reactive pathways can account for the fast reactivity observed.

Copper(II) complexes of pyridyl-appended diazacycloalkanes: synthesis, characterization, and application to catalytic olefin aziridination.

As part of an ongoing effort to rationally design new copper catalysts for olefin aziridination, a family of copper(II) complexes derived from new tetradentate macrocyclic ligands are synthesized, characterized both in the solid state and in solution, and screened for catalytic nitrene transfer reactivity with a representative set of olefins. The pyridylmethyl-appended diazacycloalkane ligands L6(py)2, L7(py)2, and L8(py)2 are prepared by alkylation of the appropriate diazacycloalkane (piperazine, homopiperazine, or diazacyclooctane) with picolyl chloride in the presence of triethylamine. The ligands are metalated with Cu(ClO4)(2).6H2O to provide the complexes [(L6(py)2)Cu(OClO3)]ClO4 (1), [(L7(py)2)Cu(OClO3)]ClO4 (2), and [(L8(py)2)Cu](ClO4)2 (3), which, after metathesis with NH4PF6 in CH3CN, afford [(L6(py)2)Cu(CH3CN)](PF6)2 (4), [(L7(py)2)Cu(CH3CN)](PF6)2 (5), and [(L8(py)2)Cu](PF6)2 (6). All six complexes are characterized by X-ray crystallography, which reveals that complexes supported by L6(py)2 and L7(py)2 (1, 2, 4, 5) adopt square-pyramidal geometries, while complexes 3 and 6, ligated by L8(py)2 feature tetracoordinate, distorted-square-planar copper ions. Tetragonal geometries in solution and d(x2 - y2), ground states are confirmed for the complexes by a combination of UV-visible and EPR spectroscopies. The divergent flexibility of the three supporting ligands influences the Cu(II)/Cu(I) redox potentials within the family, such that the complexes supported by the larger ligands L7(py)2 and L8(py)2 (5 and 6) exhibit quasi-reversible electron transfer processes (E1/2 approximately -0.2 V vs Ag/AgCl), while the complex supported by L6(py)2 (4), which imposes a rigid tetragonal geometry upon the central copper(II) ion, is irreversibly reduced in CH3CN solution. Complexes 4-6 are efficient catalysts (in 5 mol % amounts) for the aziridination of styrene with the iodinane PhINTs (in 80-90% yields vs PhINTs), while only 4 exhibits significant catalytic nitrene transfer reactivity with 1-hexene and cyclooctene.

Ligand binding inside the cavities of lacunar and saddle-shaped cyclidene complexes: molecular mechanics and molecular dynamics studies.

Cobalt(II) complexes with tetradentate macrocyclic cyclidene ligands are known to coordinate one additional axial base molecule, leaving the sixth vacant coordination site at the metal ion available for small ligand (e.g., O2) binding. Molecular mechanics and molecular dynamics simulations provide a microscopic view of 1-methylimidazole (MeIm) binding within the cavities of several lacunar (bridged) and saddle-shaped (unbridged) cyclidenes and uncover the roles of the bridges and the walls of the clefts in steric protection of the cobalt(II) coordination site. Short bridges (C3 and C6) prevent inside-the-cavity MeIm binding because of severe ligand distortions leading to high-energy penalties (58 and 25 kcal/mol, respectively), while long bridges (C8 and C12) flip away from the MeIm binding site, allowing for penalty-free MeIm inclusion. In the unbridged saddle-shaped complex, there is no energy difference between inside- and outside-the-cavity MeIm binding. The preferential existence of the coordinatively unsaturated, five-coordinate species Co(unbrCyc)(MeIm)2+ should therefore be explained by electronic, rather than steric, factors. Molecular dynamics and free energy simulations reveal the presence of a weak (ca. 4 kcal/mol in the gas phase and ca. 2 kcal/mol in methanol solution) noncovalent MeIm binding site at the entrance of the cleft of cobalt(II) unbridged cyclidene, at a distance of about 4 A from the metal ion. The macrocycle geometry remains undistorted at such large Co-N(MeIm) separations, while the cavity opens up by 0.9 A upon covalent MeIm binding (Co-N(MeIm) distance of 2 A). An increase in macrocycle strain energy upon MeIm inclusion is compensated by favorable nonbonded interactions between the incoming base and the walls of the unbridged cyclidene.