Tripodal Ligand Tris Research Articles

Dioxo-bridged dinuclear manganese(III) and -(IV) complexes of pyridyl donor tripod ligands: combined effects of steric substitution and chelate ring size variations on structural, spectroscopic, and electrochemical properties.

The syntheses and structural, spectral, and electrochemical characterization of the dioxo-bridged dinuclear Mn(III) complexes [LMn(mo-O)(2)MnL](ClO(4))(2), of the tripodal ligands tris(6-methyl-2-pyridylmethyl)amine (L(1)) and bis(6-methyl-2-pyridylmethyl)(2-(2-pyridyl)ethyl)amine (L(2)), and the Mn(II) complex of bis(2-(2-pyridyl)ethyl)(6-methyl-2-pyridylmethyl)amine (L(3)) are described. Addition of aqueous H(2)O(2) to methanol solutions of the Mn(II) complexes of L(1) and L(2) produced green solutions in a fast reaction from which subsequently precipitated brown solids of the dioxo-bridged dinuclear complexes 1 and 2, respectively, which have the general formula [LMn(III)(mu-O)(2)Mn(III)L](ClO(4))(2). Addition of 30% aqueous H(2)O(2) to the methanol solution of the Mn(II) complex of L(3) ([Mn(II)L(3)(CH(3)CN)(H(2)O)](ClO(4))(2) (3)) showed a very sluggish change gradually precipitating an insoluble black gummy solid, but no dioxo-bridged manganese complex is produced. By contrast, the Mn(II) complex of the ligand bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine (L(3a)) has been reported to react with aqueous H(2)O(2) to form the dioxo-bridged Mn(III)Mn(IV) complex. In cyclic voltammetric experiments in acetonitrile solution, complex 1 shows two reversible peaks at E(1/2) = 0.87 and 1.70 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and the Mn(III)Mn(IV) <--> Mn(IV)(2) processes, respectively. Complex 2 also shows two reversible peaks, one at E(1/2) = 0.78 V and a second peak at E(1/2) = 1.58 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and Mn(III)Mn(IV) <--> Mn(IV)(2) redox processes, respectively. These potentials are the highest so far observed for the dioxo-bridged dinuclear manganese complexes of the type of tripodal ligands used here. The bulk electrolytic oxidation of complexes 1 and 2, at a controlled anodic potential of 1.98 V (vs Ag/AgCl), produced the green Mn(IV)(2) complexes that have been spectrally characterized. The Mn(II) complex of L(3) shows a quasi reversible peak at an anodic potential of E(p,a) of 1.96 V (vs Ag/AgCl) assigned to the oxidation Mn(II) to Mn(III) complex. It is about 0.17 V higher than the E(p,a) of the Mn(II) complex of L(3a). The higher oxidation potential is attributable to the steric effect of the methyl substituent at the 6-position of the pyridyl donor of L(3).

Caging the mercurous ion: a tetradentate tripodal nitrogen ligand enhances stability and J(1H199Hg)

The dimeric mercurous ion has been encapsulated by a pair of the tetradentate tripodal nitrogen ligands tris[(2-(6-methylpyridyl))methyl]amine (TLA). The complex [Hg2(TLA)2](ClO4)2 (1) was isolated directly from an acetonitrile solution of Hg(ClO4)2 ⋅ 3H2O and TLA. Complex 1 crystallizes in the triclinic space group \(\bar P1\) with a = 10.537(2) A, b = 10.751(2) A, c = 10.907(2) A, α = 75.20(3)○, β = 73.73(3)○, γ = 75.73(3)○, and Z = 1. The cation is located an inversion center. The Hg–Hg and Hg–Namine bond distances are 2.5469(8) and 2.297(6) A, respectively, and the average Hg–Npyridyl bond length is 2.75(7) A. Complex 1 was stable indefinitely in acetonitrile-d3 solution, permitting detection of 13 and 22 Hz heteronuclear couplings between the Hg(I) ions and the methylene protons of the ligand. Comparisons with the structures and spectroscopic properties of related mercuric and mercurous complexes are made.

Synthesis and Characterization of the First (1, 2‐Benzenedithiolato)iron(III) Complexes with Tripodal Ligands

AbstractThe reaction of iron(III) perchlorate nonahydrate with the tripodal tetradentate ligand tris[(2‐pyridyl)methyl]amine (tpa) or bis[(2‐pyridyl)methyl][(1‐methylimidazol‐2‐yl)methyl]amine (bpia) and 1, 2‐benzenedithiolate (dtc) yields the iron(III) coordination compounds [Fe(tpa)(dtc)]ClO4·0.25 MeOH (1) and [Fe(bpia)(dtc)]ClO4 (2), respectively. These are the first iron(III) complexes with tripodal ligands and dtc, resulting in a N4S2 coordination environment. The new compounds were isolated and characterized by single crystal X‐ray crystallography as well as spectroscopic methods. Compound 1 crystallizes in the monoclinic space group P21/c (No. 14) with a = 29.636(6), b = 12.502(3), c = 14.390(3)Å, β = 102.19(3)°, V = 5211(2)Å3, Z = 8. Compound 2 crystallizes in the orthorhombic space group P212121 (No. 19) with a = 8.881(2), b = 16.155(3), c = 17.895(4)Å, V = 2567.4(9)Å3, Z = 4. Furthermore the new compound [Fe(tpa)(tcc)](ClO4)·0.25 H2O (3) (where tcc = tetrachlorocatecholate dianion) is presented and compared to the dithiolato complexes. 3 crystallizes in the monoclinic space group P21/c (No. 14) with a = 8.982(1)Å, b = 34.329(6)Å, c = 8.648(1)Å, β = 94.22(1)°, V = 2659.3(6)Å3, Z = 4.

A comparison of the gas, solution, and solid state coordination environments for the copper(II) complexes of a series of aminopyridine ligands of varying coordination number

The synthesis and characterization of the copper(II) complexes of a series of aminopyridine ligands that range from tri- to heptadentate is described. The ligands include the tripod ligand tris(2-((2-pyridylmethyl)amino)ethyl)amine, TREN-pyr, and the following linear ligands: (2-pyridylmethyl)(2-(2-(2-((2-pyridylmethyl)amino)ethyl)amino)ethyl)amine, TRIEN-pyr; bis(2-((2-pyridylmethyl)amino)ethyl)amine, DIEN-pyr; (2-pyridylmethyl)(2-((2-pyridylmethyl)amino)ethyl)amine, EN-pyr; bis(2-pyridylmethyl)amine, AM-pyr; and methyl(2-((-pyridylmethyl)amino)ethyl)amine, MeEN-pyr. The following methods were used to determine the binding geometries of the Cu(II) complexes in the solid, solution, and gas phases: magnetic susceptibility measurements, absorption spectroscopy, EPR spectroscopy, electrochemistry, and analyzing the gas phase ion-molecule reactions in a mass spectrometer. The solid state structures for the TRIEN-pyr and DIEN-pyr complexes were determined by X-ray crystallography. [Cu(TRIEN-pyr)](BF 4) 2 crystallized in the octahedral system, space group Pbca, with a=9.4107(7), b=17.536(13), c=30.132(6) Å, and Z=8 ( R=0.064, R w=0.060). [Cu(DIEN-pyr)](BF 4) 2 crystallized in the octahedral system, space group Pbca, with a=29.137(5), b=14.829(3), c=9.850(1) Å, and Z=8 ( R=0.071, R w=0.066). The coordination numbers of the Cu(II) complexes in this study are dependent on the denticity of the ligand. The complexes with AM-pyr, MeEN-pyr and TRIEN-pyr appear to be six-coordinate, DIEN-pyr to be five-coordinate and the EN-pyr to be four-coordinate in the solid state. The TREN-pyr complex was isolated as a dimer in the solid state but appears to be a tetragonally distorted monomeric complex in the solution and gas phases. For all of the complexes except DIEN-pyr, the coordination sphere appears to be independent of the phase of the complex. The Cu(II) DIEN-pyr complex appears to be five-coordinate in the solid phase, a mixture of four- and five-coordinate in the solution phase, and predominately four-coordinate in the gas phase.

Formation of racemate and mesocate complexes from an achiral tripodal ligand containing three benzimidazole groups.

Two complexes of the achiral tripodal ligand tris(1-benzimidazolylethyl)amine (nteb), viz., [Mn(nteb)(2)(H(2)O)(2)](ClO(4))(2).CH(3)OH, 1, and [Ag(2)(nteb)(2)](CF(3)CO(2))(2).2H(2)O, 2, have been synthesized and characterized by IR, (1)H NMR, and EPR spectroscopy (1), electrospray mass spectrometry, thermogravimetric analysis, and X-ray crystallography. Compound 1 contains chiral complex cations due to the same handedness of two nteb ligands (deltadelta or lambdalambda) but crystallizes as a racemate, while 2 contains a dinuclear mesocate because of the opposite handedness (deltalambda) of two nteb ligands. Crystal data for 1: space group P(-)1 with a = 9.471(4) A, b = 16.884(7) A, c = 19.906(8) A, alpha = 77.930(7) degrees, beta = 88.063(7) degrees, gamma = 89.706(7) degrees, V = 3111(2) A(3), and Z = 2. Crystal data for 2: space group P(-)1 with a = 9.3390(12) A, b = 10.2168(13) A, c = 16.382(2) A, alpha = 75.721(3) degrees, beta = 87.857(3) degrees, gamma = 71.738(3) degrees, V = 1437.2(3) A(3), and Z = 1. In 1, water serves as an auxiliary ligand, connected to one imidazole N atom of each nteb ligand through a H-bridge; the cationic complexes are associated intermolecularly via pi.pi interactions. In contrast to 1, the coordination to the Ag(+) ions in 2 occurs in a heterochiral manner and produces a dinuclear mesocate.

The effect of ligand charge on the coordination geometry of an Fe(III)ion: five- and six-coordinate Fe(III) complexes of tris(2-benzimidazolylmethyl)amine.

By using the tripodal tetradentate ligand tris(2-benzimidazolylmethyl)amine (H(3)ntb), which can have several charge states depending on the number of secondary amine protons, mononuclear octahedral and dinuclear trigonal bipyramidal Fe(III) complexes were prepared. The reaction of mononuclear octahedral [Fe(III)(H(3)ntb)Cl(2)]ClO(4), 1, with 3 equiv of sec-butylamine in methanol led to the formation of mononuclear cis-dimethoxo octahedral Fe(III)(H(2)ntb)(OMe)(2), 2. One equivalent of the sec-butylamine was used to generate the monoanionic H(2)ntb(-) ligand where one of the three amines in the benzimidazolyl groups was deprotonated. The remaining 2 equiv were used to generate two methoxides that were coordinated to the octahedral Fe(III) ion in a cis fashion as demonstrated by the chlorides in 1. Reaction of 1 with excess (7 equiv) sec-butylamine generated the doubly deprotonated dianionic Hntb(2-) that stabilized the dinuclear mu-oxo Fe(III)(2)O(Hntb)(2), 3, adopting a five-coordinate trigonal bipyramidal geometry. The magnetic data for 3 are consistent with the antiferromagnetically coupled Fe(III) (S = 5/2) sites with the coupling constant J = -127 cm(-1).

Unequivocal synthetic pathway to heterodinuclear (4f,4f') complexes: magnetic study of relevant (Ln(III), Gd(III)) and (Gd(III), Ln(III)) complexes.

The tripodal ligand tris[4-(2-hydroxy-3-methoxyphenyl)-3-aza-3-buten]amine (LH(3)) is capable of coordinating to two different lanthanide ions to give complexes formulated as [LLnLn'(NO(3))(3)].x H(2)O. The stepwise synthetic procedure consists of introducing first a Ln(III) ion in the inner N(4)O(3) coordination site. The isolated neutral complex LLn is then allowed to react with a second and different Ln' ion that occupies the outer O(6) site, thus yielding a [LLnLn'(NO(3))(3)].x H(2)O complex. A FAB(+) study has confirmed the existence of (Ln, Ln') entities as genuine, when the Ln' ion in the outer site has a larger ionic radius than the Ln ion in the inner site. The qualitative magnetic study of the (Gd, Ln) and (Ln, Gd) complexes, based on the comparison of the magnetic properties of (Gd, Ln) (or (Ln, Gd)) pairs and (Y, Ln) (or (Ln, La)) pairs, is very informative. Indeed, these former complexes are governed by the thermal population of the Ln(III) Stark levels and the Ln-Gd interaction, while the latter are influenced by the thermal population of the Ln(III) Stark levels. We have been able to show that a ferromagnetic interaction exists at low temperature in the (Gd, Nd), (Gd, Ce), and (Yb, Gd) complexes. In contrast, an antiferromagnetic interaction occurs in the (Dy, Gd) and (Er, Gd) complexes. Although we cannot give a quantitative value to these interactions, we can affirm that their magnitudes are weak since they are only perceptible at very low temperature.

Isolation of monomeric Mn(III/II)-H and Mn(III)-complexes from water: evaluation of O-H bond dissociation energies.

The syntheses and properties of the monomeric [MnIII/IIH31(OH)]-/2- and [MnIIIH31(O)]2- complexes are reported, where [H31]3- is the tripodal ligand tris[(N'-tert-butylureaylato)-N-ethyl)]aminato. Isotope-labeling studies with H218O confirmed that water is the source of the terminal oxo and oxygen in the hydroxo ligand. The molecular structures of the [MnIIH31(OH)]2- and [MnIIIH31(O)]2- complexes were determined by X-ray diffraction methods and show that each complex has trigonal bipyramidal coordination geometry. The MnIII-O distance in [MnIIIH31(O)]2- is 1.771(4) A, which is lengthened to 2.059(2) A in [MnIIH31(OH)]2-. Structural studies also show that [H31]3- provides a hydrogen-bond cavity that surrounds the MnIII-O(H) units. Using a thermodynamic approach, which requires pKa and redox potentials, bond dissociation energies of 77(4) and 110(4) kcal/mol were calculated for [MnIIH31(O-H)]2- and [MnIIIH31(O-H)]-, respectively. The calculated value of 77 kcal/mol for the [MnIIH31(O-H)]2- complex is supported by the ability of [MnIIIH31(O)]2- complex to cleave C-H bonds with bond energies of <80 kcal/mol.

Synthesis and characterisation of zinc(ii) complexes of tripodal N7 ligands involving pyridine and amine or amide nitrogen donors. Crystal structure of a zinc(ii) complex

Two tripodal heptadentate ligands tris[2-(2-pyridylmethyl)aminoethyl]amine (tpaa), and tris[2-picolinamidoethyl]amine (trenpicam) were synthesized as their hydrochloride salts and their protonation constants determined by potentiometry; variable pH 1H NMR spectroscopy allows the determination of the order of protonation of their different basic nitrogen atoms. The stability constants of the zinc(II) chelates with these ligands, determined by potentiometry and UV spectrometry, show the formation of [Zn(LH2)]4+, [Zn(LH)]3+ and [ZnL]2+ species with tpaa, whereas amide group deprotonation of trenpicam permits the detection of the variable stoichiometry species [ZnL]2+, [ZnL2]2+, [Zn(L2H−1)]+, [Zn(L2H−3)]−, [Zn2(LH−2)2] and [Zn2(L2H−5)]−, where LH−x is an amide-deprotonated ligand. The zinc(II) complexes [ZnL](ClO4)2 (L = tpaa or trenpicam), and the dinuclear complex [Zn2(LH−2)Cl2] (L = trenpicam) have been prepared and characterized by IR and mass spectroscopy. The crystal structure of the protonated ligand [Htrenpicam](ClO4) and the complex [Zn(tpaa)](ClO4)2 are reported. [Htrenpicam]+ contains one intra-molecular H-bond and in the cation [Zn(tpaa)]2+ the geometry around the Zn2+ ion is distorted octahedral with one pyridyl nitrogen uncoordinated.

Copper complexes of the functionalised tripodal ligand tris(2-pyridyl)methylamine and its derivatives †

The coordination chemistry of the new tripodal ligand tris(2-pyridyl)methylamine (tpm) with copper(I), copper(II) and zinc(II) has been investigated. The synthesis of tpm can readily be modified to access a variety of related tripodal ligands such as 2-(methylsulfanyl)-1,1-di(2-pyridyl)ethylamine (mde); in addition, the primary amine function can be derivatised to extend further the range of complexes obtained. tpm itself is a versatile ligand, showing three distinct coordination modes: bidentate (py, NH2), tridentate (2py, NH2) and tridentate (3py). Complexes of stoichiometries Cu(tpm)n (n = 1–3) have been obtained. The (2py, NH2) coordination mode is illustrated by the crystal structure of [Cu(tpm)2][BF4]2·Me2CO, whilst (3py) coordination is found in the crystal structures of [Cu(SO4)(tpm)(H2O)]·3H2O, [{Cu(tpm)}2Br3]Br·3MeOH and also the zinc complex [Zn(tpm)(H2O)3]2[Zn(H2O)6][SO4]3·3H2O. Amide derivatives of tpm give complexes of stoichiometry CuL2, and the crystal structures of [Cu(tpma)2][BF4]2 [tpma = tris(2-pyridyl)methylacetamide] and [Cu(tpms)2]·8H2O {tpmsH = 4-oxo-4-[tris(2-pyridyl)methylamino]butanoic acid} have been determined. The crystal structure of the sulfate-bridged dimeric complex [{Cu(SO4)(mde)}2]·3H2O shows the mde ligand to be tridentate, with (2py, NH2) coordination.

Syntheses and relaxation properties of mixed gadolinium hydroxypyridinonate MRI contrast agents.

The tripodal ligand tris[(3-hydroxy-1-methyl-2-oxo-1,2- didehydropyridine-4-carboxamido)ethyl]amine (TREN-Me-3,2-HOPO) forms a stable Gd3+ complex that is a promising candidate as a magnetic resonance imaging (MRI) contrast agent. However, its low water solubility prevents detailed magnetic characterization and practical applicability. Presented here are a series of novel mixed ligand systems that are based on the TREN-Me-3,2-HOPO platform. These new ligands possess two hydroxypyridinone (HOPO) chelators and one other chelator, the latter of which can be easily functionalized. The ligands described use salicylamide, 2-hydroxyisophthalamide, 2,3-dihydroxyterephthalamide, and bis(acetate) as the derivatizable chelators. The solution thermodynamics and relaxivity properties of these new systems are presented. Three of the four complexes (salicylamide-, 2-hydroxyisophthalamide-, and 2,3-dihydroxyterephthalamide-based ligands) possess sufficient thermodynamic stability for in vivo applications. The relaxivities of the three corresponding Gd3+ complexes range from 7.2 to 8.8 mM-1 s-1 at 20 MHz, 25 degrees C, and pH 8.5, significantly higher than the values for the clinically employed polyaminocarboxylate complexes (3.5-4.8 mM-1 s-1). The high relaxivities of these complexes are consistent with their faster rates of water exchange (< 100 ns), higher molecular weights (> 700), and greater numbers of inner-sphere coordinated water molecules (q = 2) relative to those of polyaminocarboxylate complexes. A mechanism for the rapid rates of water exchange is proposed involving a low energy barrier between the 8- and 9-coordinate geometries for lanthanide complexes of HOPO-based ligands. The pathway is supported by the crystal structure of La[TREN-Me-3,2-HOPO] (triclinic P1: Z = 4, a = 15.6963(2) A, b = 16.9978(1) A, c = 17.1578(2) A, alpha = 61.981(1) degrees, beta = 75.680(1) degrees, gamma = 71.600(1) degrees), which shows both 8- and 9-coordinate metal centers in the asymmetric unit, demonstrating that these structures are very close in energy. These properties make heteropodate Gd3+ complexes promising candidates for use in macromolecular contrast media, particularly at higher magnetic field strengths.

Formation of mono-, bi-, tri-, and tetranuclear Ag(I) complexes of C3-symmetric tripodal benzimidazole ligands.

The C3-symmetric tripodal ligand tris(2-benzimidazolylmethyl)amine (ntb) and its alkyl-substituted derivatives tris(N-R-benzimidazol-2-ylmethyl)amine (R = methyl, Mentb; R = ethyl, Etntb; R = propyl, Prntb) react with various silver(I) salts to afford mononuclear [Ag(Prntb)(CF3SO3)].0.25H2O, 1, binuclear [Ag2(Mentb)2](CF3SO3)2.H2O, 2, trinuclear [Ag3(Etntb)2](ClO4)3.CH3OH, 3, and tetranuclear [Ag4(ntb)2(CH3CN)2(CF3CO2)2](CF3CO2)2.2H2O, 4. All four complexes have been characterized by elemental analyses, IR spectroscopy, and X-ray crystallography. The Ag(I) ion in 1 is coordinated to the three imine nitrogen atoms of the Prntb ligand and one oxygen atom of the trifluoromethanesulfonate anion in a distorted tetrahedral environment. Dinuclear 2 has C2 symmetry with each Ag(I) atom trigonally coordinated by two arms of one Mentb and one arm of another. Trinuclear 3 has C3 symmetry with a Ag3 regular triangle sandwiched between a pair of Etntb ligands such that one arm of each ligand is involved in linear coordination about an Ag(I) atom. In the tetranuclear complex 4, two linearly coordinated Ag(I) atoms lying on the molecular C2 axis are bridged by a pair of ntb ligands and the remaining pendant arm of each ntb ligand is attached to another Ag(I) atom whose tetrahedral coordination sphere is completed by an acetonitrile molecule and a chelating trifluoroacetate anion. Complexes 2 and 3 may be regarded as an aggregation of two tridentate ligands by a silver dimer and a trinuclear cluster with weak Ag...Ag interactions, respectively, while in 4 the aggregation of two tripodal ligands by four Ag(I) ions affords a multicomponent internal cavity. The packing modes of complexes 1-3 are dominated by weak supramolecular pi...pi and CH...pi interactions. Hexagonal or square channels are generated in 1 and 2, and a honeycomb layer structure is formed in 3 with solvate molecules and counteranions occupying the voids. The crystal structure of 4 consists of a three-dimensional network consolidated by NH...O and OH...O hydrogen bonds.

Synthesis, characterization, and spontaneous resolution of chiral nickel(II) complexes with the tripod ligand tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine.

The chiral nickel(II) complexes of a tripod-type ligand with the chemical formulas [Ni(H3L)](NO3)2.MeOH (1), [Ni(H3L)](ClO4)2.MeOH (2), and [Ni(H3L)](C6H5COO)2.6H2O (3) were synthesized and characterized (H3L = tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine). The crystal structures of 1-3 were determined by their single-crystal X-ray analyses. 1, C37H40N12O7Ni: orthorhombic, P2(1)2(1)2(1); a = 14.198(2) A, b = 22.422(2) A, c = 12.019(2) A, Z = 4. 2, C37H40N10O9Cl2Ni: orthorhombic, P2(1)2(1)2(1); a = 14.206(2) A, b = 22.735(3) A, c = 12.696(3) A, Z = 4. 3, C50H58N10O10Ni: triclinic, P1; a = 14.191(5) A, b = 16.048(4) A, c = 13.692(4) A, alpha = 115.25(2) degrees, beta = 111.07(3) degrees, gamma = 64.75(2) degrees, Z = 2. Each complex has an octahedral coordination environment for the nickel(II) ion, formed by the six nitrogen donor atoms, and is either a delta (clockwise) or a lambda (anticlockwise) enantiomorph, depending on the screw arrangement of the tripod-type ligand around the nickel(II) ion. The circular dichroism (CD) spectrum of a powdered sample of a crystal of 1 showed a positive and a negative peak at 915 and 630 nm, respectively, and that of another crystal showed an enantiomeric pattern. The observation of the Cotton effect and the crystal structure provided evidence for spontaneous resolution of the chiral complex molecule.

Kinetics and mechanism of copper(II) complex formation with tripodal aminopolythiaether and aminopolypyridyl ligands in aqueous solution.

The complex formation kinetics of aquated copper(II) ion reacting with 12 related tripodal ligands have been studied in aqueous solution at 25 degrees C, mu = 0.10 M (NaClO4). For most of the ligands studied, specific formation rate constants have been resolved for both the unprotonated and monoprotonated ligand species. All of the tripodal ligands included in this study contain a bridgehead amine nitrogen with the three legs consisting of 2-methylthioethyl or 2-ethylthioethyl and/or 2-pyridylethyl or 2-pyridylmethyl. Since the bridgehead nitrogen is too sterically hindered to participate in initial coordinate bond formation, the first bond must involve a thiaether sulfur or a pyridine nitrogen on one of the pendant legs followed by coordination to the bridgehead nitrogen to complete the first chelate ring. All kinetic data are interpreted in terms of this presumed sequence in the bond formation steps. For the two ligands in which all three pendant legs contain thiaether sulfur donor atoms, the rate-determining step appears to be at the point of second bond formation (chelate ring closure), although the distinction is not well defined. For all other unprotonated ligands, the kinetic behavior is consistent with the first-bond formation being rate-determining. Upon protonation, the rate-determining step appears to shift to the point of proton loss associated with second-bond formation in several cases. A particularly interesting observation is that the tripodal ligand tris(ethylthioethyl)amine (TEMEA) exhibits specific Cu(II) complex formation rate constants that are virtually identical to those for a closely related macrocyclic ligand, 1,4,8-trithia-11-azacyclotetradecane ([14]aneNS3), but the calculated CuIIL dissociation rate constants differ by a factor of 1000. A further comparison of the calculated dissociation rate constants for Cu(II)-tripodal ligand complexes indicates that a Cu(II)-N(pyridine) bond is approximately 10(4) times stronger than a Cu(II)-SR2 bond. This leads to the conclusion that a 1:1 Cu(II)-SR2 complex would have a predicted stability constant of about 0.04 M-1 in aqueous solution--the first estimate obtained for the strength of a single Cu(II)-S(thiaether) bond.

A novel (CF3SO3−)6 cluster with multiple F · · · F interactions: crystal structure of a self-assembled trinuclear Ag(I) complex with the tripodal ligand tris(2-benzimidazolylmethyl)amine

Self-assembly of silver(I) trifluoromethanesulfonate with the tripodal ligand tris(2-benzimidazolylmethyl)amine (ntb) affords the trinuclear complex [Ag3(ntb)2](CF3SO3)3, which exhibits a rhombohedral network formed from N–H⋯O hydrogen bonds and weak Ag⋯O interactions linking [Ag3(ntb)2]3+ cations with a novel S6-symmetric (CF3SO3−)6 cluster consolidated by multiple F⋯F interactions.

Solution and solid state structures of uranium(III) and lanthanum(III) iodide complexes of tetradentate tripodal neutral N-donor ligands †

The solid state structure of the isostructural complexes [M(tpa)I3(py)] (M = LaIII or UIII) containing the tripodal ligand tris[(2-pyridyl)methyl]amine (tpa) has been determined. The metal ions are eight-co-ordinated by the tetradentate tpa, three iodide ions and a pyridine molecule. The [U(Mentb)2]I3 complex was prepared by treating [UI3(thf)4] with two equivalents of tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb). Crystallographic studies show that the UIII is eight-co-ordinated by two tetradentate Mentb with the ligand arms wrapped around the metal in a pseudo-D3 symmetric arrangement. Solution NMR studies in pyridine show a large difference in the behaviour of ntb and tpa towards complexation, and a greater stability of the bis(ligand) complexes for ntb than for tpa. At a ntb∶metal ratio of 0.5∶1 the bis(ligand) complex is already present in solution in greater quantity than the mono(ligand) complex for both La and U and at a ratio of 2∶1 only the bis(ligand) species exists in solution. On the other hand the bis(tpa) complexes of La and U appear in pyridine solution only at tpa∶metal ratios larger than 1∶1, and even at ratios larger than 3∶1 both the bis(tpa) and the mono(tpa) species are still present in solution. The preferential formation of the bis(ntb) complexes with respect to the mono(ntb) complexes (K2/K1 = 8 ± 1 for U and =35 ± 4 for La) has been related to the presence in solution, as well as in the solid state, of strong π–π interaction between benzimidazole rings. The absence of such interactions in the bis(tpa) complexes can explain their lower stability with respect to the bis(ntb) complexes.

Structures and Properties of Novel Mononuclear Iron(III) Complexes with Benzimidazole Containing Tripodal Tetradentate Ligands

The iron(III) complexes of the tripodal benzimidazole-containing ligands tris(2-benzimidazolylmethyl)amine (ntb), bis(2-benzimidazolylmethyl)(2-hydroxyethyl)-amine (bbimae) and tris(5,6-dimethyl-2-benzimidazolylmethyl)amine (me2ntb) are structural and functional models for intradiol cleaving catechol dioxygenases. The complexes [Fe(ntb)Cl2]Cl · 3 CH3OH (1; P 1, a = 9.830(2) Å, b = 12.542(3) Å, c = 13.139(3) Å, α = 82.88(3)°, β = 73.45(3)°, γ = 85.53(3)°, V = 1539.2(6) Å3; Z = 2) and [Fe(bbimae)Cl2]Cl (2; P21/n, a = 7.461(2) Å, b = 18.994(5) Å, c = 14.515(4) Å, β = 98.22(2)°, V = 2035.8(9) Å3, Z = 4) have been characterized by X-ray crystallography and spectroscopic methods. In the octahedrally coordinated complexes two cis coordination sites – essential for catechol binding – are occupied by chloride ligands. The significant intradiol cleaving catechol dioxygenase activity of the model complexes was examined using 3,5-di-tert-butylcatechol as a substrate. Die Strukturen und Eigenschaften neuer mononuklearer Eisen(III)-Komplexe mit benzimidazolhaltigen vierzähnigen Tripod-Liganden Die Eisen(III)-Komplexe der benzimidazolhaltigen vierzähnigen Tripod-Liganden Tris(2-benzimidazolylmethyl)amin (ntb), Bis(2-benzimidazolylmethyl)(2-hydroxyethyl)amin (bbimae) und Tris(5,6-dimethyl-2-benzimidazolylmethyl)amin (me2ntb) sind strukturelle und funktionelle Modellverbindungen für die intradiol spaltenden Catecholdioxygenasen. Die Komplexe [Fe(ntb)Cl2]Cl · 3 CH3OH (1; P 1, a = 9.830(2) Å, b = 12.542(3) Å, c = 13.139(3) Å, α = 82.88(3)°, β = 73.45(3)°, γ = 85.53(3)°, V = 1539.2(6) Å3; Z = 2) und [Fe(bbimae)Cl2]Cl (2; P21/n, a = 7.461(2) Å, b = 18.994(5) Å, c = 14.515(4) Å, β = 98.22(2)°, V = 2035.8(9) Å3, Z = 4) wurden mit röntgenographischen und spektroskopischen Methoden charakterisiert. In den oktaedrisch koordinierten Komplexen sind zwei cis-ständige Koordinationsstellen, die essentiell für die Anbindung von Catechol sind, durch Chloroliganden besetzt. Die Komplexe der drei Liganden zeigen signifikante intradiolspaltende Catecholdioxygenase-Aktivitäten bei Verwendung von 3,5-Di-tert-butylcatechol als Substrat.

Gas, solution, and solid state coordination environments for the nickel(II) complexes of a series of aminopyridine ligands of varying coordination number

The synthesis and characterization of the nickel(II) complexes from a series of aminopyridine ligands that range from tri- to heptadentate is described. The ligands include the tripod ligand tris(2-((2-pyridylmethyl)amino)ethyl)amine, TREN-pyr, and the following linear ligands: (2-pyridylmethyl)(2-(2-((2-((2-pyridylmethyl)amino)ethyl)amino)ethyl)amine, TRIEN-pyr; bis(2-((2-pyridylmethyl)amino)ethyl)amine, DIEN-pyr; (2-pyridylmethyl)(2-((2-pyridylmethyl)amino)ethyl)amine, EN-pyr; bis(2-pyridylmethyl)amine, AM-pyr; and methyl(2-((-pyridylmethyl)amino)ethyl)amine, MeEN-pyr. The following methods were used to determine the binding geometries of the nickel(II) complexes in the solid, solution, and gas phases: magnetic susceptibility measurements, absorption spectroscopy, electrochemistry, and analyzing the gas phase ion-molecule reactions in a mass spectrometer. The linked five-membered chelate character of the linear ligands appear to have imposed high-spin, octahedral geometry on the complexes in the condensed phases. The tripod ligand TREN-pyr and the two tridentate ligands, AM-pyr and MeEN-pyr, form six-coordinate complexes in the gas phase. In contrast, the rest of the complexes (TRIEN-pyr, DIEN-pyr, and EN-pyr) were found to have lower coordination numbers in the gas phase (five-, five-, and four-coordinate, respectively). The potentially heptadentate tripod ligand TREN-pyr does not appear to confer any unusual properties on the Ni(II) ion in the solution or solid phases, but does appear to be more effective than the hexadentate ligand TRIEN-pyr at maintaining the six-coordinate geometry in the gas phase.

Synthesis and characterization of a ferric complex of the tripodal ligand tris(2-benzimidazolylmethyl)amine—a superoxide dismutase mimic

The mononuclear iron complex 1 was synthesized using a tripodal ligand, tris(2-benzimidazolylmethyl)amine (ntb), where ntb served as a neutral tetradentate chelating ligand for the distorted octahedral ferric ion. Three benzimidazole groups of ntb and one chloride anion formed a base of octahedral geometry. One of the two axial positions was occupied by an apical nitrogen atom of ntb and the other site was occupied by another chloride anion. Two of the chloride anions in complex 1 are in a cis arrangement. The decay of the electrochemically generated superoxide radical (O 2 −) by complex 1 was observed using cyclic voltammetry. The superoxide dismutase (SOD) activity of complex 1 was also examined using a modified method of the light- and riboflavin-driven hydroxylaminenitrate assay. Reaction of complex 1 with an O 2 − radical in methanol gave the μ-oxo dinuclear iron complex 2. The μ-oxo group was substituted for the basal chloride anion of complex 1 in complex 2. Complex 2 could also be synthesized using weak bases instead of the O 2 − radical.

Luminescent Lanthanide Complexes with Encapsulating Polybenzimidazole Tripodal Ligands

Reaction of the tripodal ligands tris(N-alkylbenzimidazol-2-ylmethyl)amine with europium perchlorate affords the luminescent complexes [Eu(Rntb)2](ClO4)3·nCH3CN·0.5H2O (R = methyl, npropyl; n = 1, 2) in which the central Eu3+ ion is well encapsulated in a cubic coordination environment. Right- or left-handed screw arrangement of the three arms of the ligand causes the cation [Eu(Rntb)2]3+ to be chiral, and two enantiomers crystallize together in complex [Eu(nPrntb)2](ClO4)3·2CH3CN·0.5H2O to give a racemer, but only one enantiomer is found in complex [Eu(Mentb)2](ClO4)3·CH3CN·0.5H2O.