Quinquedentate Ligand Research Articles

Cover Feature: Scorpiands: Quinquedentate Ligands that Couple the Rigidity of Cyclam and the Flexibility of a Coordinating Side Chain (Eur. J. Inorg. Chem. 1/2023)

Cover Feature: Scorpiands: Quinquedentate Ligands that Couple the Rigidity of Cyclam and the Flexibility of a Coordinating Side Chain (Eur. J. Inorg. Chem. 1/2023)

Scorpiands: Quinquedentate Ligands that Couple the Rigidity of Cyclam and the Flexibility of a Coordinating Side Chain

AbstractThis review tells the story of scorpiands, polyamine ligands which, when specifically stimulated, act as scorpions, and of their metal complexes, scorpiates. Scorpiands consist of a tetramine macrocycle (typically cyclam) capable of firmly including a transition metal and of a side chain ending with a nitrogen containing coordinating group: under unperturbed conditions the coordinating group is bound to the metal (ON), but on addition of acid the nitrogen is protonated and comes off the metal (OFF). Alternating acid/base addition makes the side chain move imitating the tail of a scorpion that bites a prey firmly immobilized by the claws. Occurrence of the ON‐OFF motion is monitored by the colour change of the scorpiate complexes associated to the change of coordination or by fluorescence quenching/restoring when a light‐emitting substituent is linked to the side arm. Scorpiate complexes can be considered optical molecular switches and, from a different standpoint, molecular machines able to convert chemical energy into mechanical work.

Mono-, di- and tri-nuclear manganese(II) complexes derived from a quinquedentate ligand: Superoxide dismutase and catalase mimetic studies

In this study, three manganese complexes [Mn(H2L)Cl2]·MeOH, [Mn3(L)2(OAc)2(MeOH)2]·2MeOH and [Mn2Ca(L)2(OAc)2(MeOH)2]·2MeOH derived from a quinquedentate Schiff base ligand (H2L) were synthesised and characterised by the spectroscopic and analytic methods. Molecular structures of the complexes were determined by single crystal X-ray diffraction studies. In mononuclear complex [Mn(H2L)Cl2]·MeOH, the Mn(II) ions are seven-coordinate pentagonal bipyramidal geometry with two chloride ions at the axial positions. The trinuclear complex [Mn3(L)2(OAc)2(MeOH)2]·2MeOH consists of two mononuclear units linked by a central Mn(II) ion. The calcium containing complex [Mn2Ca(L)2(OAc)2(MeOH)2]·2MeOH contains two mononuclear units bridged by a six-coordinate Ca(II) ion. The superoxide dismutase (SOD activities of the structurally complexes were evaluated and the mononuclear complex [Mn(H2L)Cl2]·MeOH showed the greatest SOD activity with an IC50 value of 0.95μM which gives a calculated kcat value of 1.67×106M−1s−1. Finally, the ability of the complexes to disproportionate H2O2 in the presence of base was tested by measuring the rate of oxygen evolution at room temperature. The trinuclear [Mn3(L)2(OAc)2(MeOH)2]·2MeOH complex is the most efficient complex catalase mimic of the tested complexes with the fastest rate 5.33ml/s.

Antifungal and Spectral Studies of Cr(III) and Mn(II) Complexes Derived from 3,3′-Thiodipropionic Acid Derivative

The Cr(III) and Mn(II) complexes with a ligand derived from 3,3′-thiodipropionic acid have been synthesized and characterized by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, IR, UV, and EPR spectral studies. The complexes are found to have [Cr(L)X]X2 and [Mn(L)X]X, compositions, where L = quinquedentate ligand and X=NO3−, Cl− and OAc−. The complexes possess the six coordinated octahedral geometry with monomeric compositions. The evaluated bonding parameters, Aiso and β, account for the covalent type metal-ligand bonding. The fungicidal activity of the compounds was evaluated in vitro by employing Food Poison Technique.

Synthesis, Characterization of an Unusual Crystalline Material with Hydroxycarboxylate Ligand

A new porous coordination polymer with the general formula [Zn(Hmal)(H2O)2]n·nH2O (1) (H3mal = malic acid) has been designed and synthesized via solvothermal routine. In the polymer, the malate dianion acts as the unique quinquedentate ligand with five oxygen atoms participating in the coordination. The Zn(II) ions are interconnected via hydroxyl and carboxyl groups from the malate ligands to form a big loop. Further, the loops were linked by the bidentate β-carboxyl group to shape 2-D porous framework, which exhibits a classical brick-like topology.

A novel three-dimensional heterometallic coordination polymer: poly[[hexaaquabis[μ3-3,5-dicarboxylatopyrazolato-κ5O3,N2:N1,O5:O5′](μ2-oxalato-κ4O1,O2:O1′,O2′)copper(II)dierbium(III)] trihydrate

The title novel heterometallic 3d-4f coordination polymer, {[CuEr(2)(C(5)HN(2)O(4))(2)(C(2)O(4))(H(2)O)(6)].3H(2)O}(n), has a three-dimensional metal-organic framework composed of two types of metal atoms (one Cu(II) and two Er(III)) and two types of bridging anionic ligands [3,5-dicarboxylatopyrazolate(3-) (ptc(3-)) and oxalate]. The Cu(II) atom is four-coordinated in a square geometry. The Er(III) atoms are both eight-coordinated, but the geometries at the two atoms appear different, viz. triangular dodecahedral and bicapped trigonal prismatic. One of the oxalate anions is located on a twofold axis and the other lies about an inversion centre. Both oxalate anions act as bis-bidentate ligands bridging the latter type of Er atoms in parallel zigzag chains. The pdc(3-) anions act as quinquedentate ligands not only chelating the Cu(II) and the triangular dodecahedral Er(III) centres in a bis-bidentate bridging mode, but also connecting to Er(III) centres of both types in a monodentate bridging mode. Thus, a three-dimensional metal-organic framework is generated, and hydrogen bonds link the metal-organic framework with the uncoordinated water molecules. This study describes the first example of a three-dimensional 3d-4f coordination polymer based on pyrazole-3,5-dicarboxylate and oxalate, and therefore demonstrates further the usefulness of pyrazoledicarboxylate as a versatile multidentate ligand for constructing heterometallic 3d-4f coordination polymers with interesting architectures.

{2,2′-[1,1′-(4-Azaheptane-1,7-diyldinitrilo)diethylidyne]diphenolato}copper(II)

The quinquedentate ligand 2,2'-[1,1'-(4-azaheptane-1,7-diyldinitrilo)diethylidyne]diphenol in the title compound, [Cu(C22H27N3O2)], furnishes an N3O2 donor set, which results in a distorted square-pyramidal coordination; the two O and two imine N atoms lie in the basal plane, while the secondary amine N atom of the ligand occupies the axial position. The axial Cu-N bond is 0.33 A longer than the average of the equatorial bonds, and the O atoms are trans. The symmetry of the molecule is lowered by the twist-boat and chair conformations adopted by the two CuNN chelate rings. The complex contains two intramolecular C-H...O interactions, and two molecules of the complex are linked into a dimer by means of moderate N-H...O hydrogen bonds. Spectroscopic evidence supports the presence of hydrogen bonds.

3,11,19‐Trithia[3.3.3]pyridinophane: Structural Diversity in Its Transition Metal Complexes

AbstractThe pyridine‐containing aza‐thia macrocycle 3,11,19‐trithia[3.3.3]pyridinophane (10) and its complexes with NiII, PdII, CuI, AgI and HgII were synthesised and their crystal structures were determined. The NiII and HgII complexes (11, 12) are mononuclear with 10 serving as an unusual quinquedentate ligand. The CuI complex 13 is also mononuclear with 10 being tetra‐coordinated to a tetrahedral CuI. Palladium(II) forms a binuclear complex 14 which exists as an inorganic zwitterion and both PdII metal ions adopt the expected square‐planar geometry with facial coordination. Silver(I) forms one‐dimensional coordination polymers (15 and 16) with 10 and these exhibit two different coordination modes, namely tetrahedral and trigonal planar. It was found that the macrocycle 10 did not show any selectivity among a series of metal ions. The electronic and redox properties of several complexes were studied. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Influence of Coordination Geometry upon Copper(II/I) Redox Potentials. Physical Parameters for Twelve Copper Tripodal Ligand Complexes

Twelve related tripodal ligands have been synthesized in which the three legs linked to a bridgehead nitrogen are 2-methyl- or 2-ethylthioethyl and/or 2-pyridylethyl or -methyl. Utilization of both terminal methyl and ethyl groups on the thiaether legs was designed to determine whether slight differences in solvation or steric effects might cause detectable changes in properties. Inclusion of both methyl and ethyl linkages of the pyridines to the bridgehead nitrogen provides a comparison of the effect of five- versus six-membered chelate rings, respectively. For each of the tripodal ligands included in this work, the protonation constants and Cu(II) complex stability constants were carefully determined in aqueous solution at 25 °C, μ = 0.10 M (ClO4-). The CuII/IL redox potentials were also determined using slow-scan cyclic voltammetry, thereby permitting the stability of the Cu(I) complexes to be calculated. The stability constants for the twelve Cu(II) complexes range from 106 to 1017, increasing by 104−105 as the first and second alkylthioethyl substituents are replaced by 2-pyridylmethyl groupswith only a slight increase upon the introduction of a third pyridyl leg. When 2-pyridylethyl groups are introduced, much smaller trends are noted. For the corresponding Cu(I) complexes, the calculated stability constants are relatively constant (at ∼1015) regardless of the donor set or the length of the pyridyl linkages to the bridgehead. Combination of these data with previous measurements on related macrocyclic and acyclic ligands containing both thiaether sulfur and amine nitrogen donor atoms reveals that, for 35 different uncharged terdentate, quadridentate and quinquedentate ligands, the stabilities of the CuIL complexes lie within the narrow range of about 1012−1016, with few exceptions, regardless of large differences in coordination geometry and donor strength. For these same 35 ligands, the CuIIL stability constants span 26 orders of magnitude. Thus, the Cu(II/I) potentials, which cover a range of 1.5 V, are shown to be inversely related to the logarithmic values of the CuIIL stability constants for a wide range of ligand types. Future strategies for manipulating the redox behavior of Cu(II/I) systems should recognize that alteration of the ligand coordination geometry primarily impacts the properties of the Cu(II) complex with almost no effect upon the Cu(I) properties.

The syntheses, spectra and structures of five-coordinate cobalt(II) complexes of pyrazolyl-containing ligands

Cobalt(II) chloride complexes of 2,6-bis(1-(pyridin-2-yl)pyrazol-3-yl)pyridine ( L 1 ) and 2,6-bis(pyrazol-3-yl)pyridine ( L 2 ) have been prepared and characterised by electronic spectroscopy and single-crystal X-ray diffractometry. The spectra are normal for five-coordinate cobalt(II) complexes. [Co( L 1 )Cl 2] is triclinic, crystallising in space group P1̄ with a = 9.530(4), b = 10.642(6), c = 12.675(5) Å, α = 65.97(4), β = 70.34(4), γ = 67.65(4)°. The structure was refined by least-squares techniques to convergence at R = 0.036 for 2342 observed reflections. In this complex the potentially quinquedentate ligand functions as a tridentate ligand. [Co( L 2 )Cl 2] is monoclinic, crystallising in space group C2/ c with a = 10.255(4), b = 17.138(4), c = 7.988(3) Å, β = 104.62(2)°. The structure was refined by least-squares techniques to convergence at R = 0.026 for 999 observed reflections. The structure of this complex is extremely similar to that of dichloro(2,2′:6′,2″-terpyridine)cobalt(II), with the tridentate ligand spanning the two axial sites and one equatorial site of an approximate trigonal bipyramid with the chloro ligands bound in the equatorial plane.

USING TWO DIMENSIONAL NMR TECHNIQUES TO ASSIGN PROTON AND CARBON SPECTRA FOR COBALT(III) COMPLEXES DERIVED FROM LINEAR QUINQUEDENTATE LIGANDS CONTAINING NITROGEN AND SULFUR DONOR ATOMS

High resolution NMR spectroscopy was used to study the structure of a cobalt(III) complex derived from the linear quinquedentate ligand, 7-methyl-4, 10-dithia-l, 7, 13-tria-zatridecane, NH2-CH2CH2-S-CH2CH2-N(CH3)-CH2CH2-S-CH2CH2-NH2. The flexibility of this ligand allows it theoretically to form four distinct structural isomers with metal ions. The one dimensional proton spectrum exhibited by [Co(NSNSN)Cl]Cl2, is complicated and does not provide structural insight. A combined utilization of proton, carbon, DEPT, COSY, NOESY and HETCOR spectra was employed to establish geometric structure type, make individual proton assignments, identify proton-proton connectivities that result from scalar coupling, and distinguish interactions occurring as a result of through-space interactions. Information about the five-membered chelate ring orientations was also obtained. Two groups of signals were shown to correlate with each carbon signal, exhibiting a definite nonequivalence between geminal protons. Geminal protons were found to have coupling constants of 14 Hz. In contrast, the vicinal protons were found to have coupling constants of 5-7 Hz.

Copper(II) Complexes of N,N'-Bis((2-substituted-imidazol-4-yl)methylene)-3,3'-diaminodi- propylamine (2-Substituent = H, Me): Delta and Lambda Enantiomorphs of the Protonated Complex and Helical Structure of the Deprotonated Complex Formed by Hydrogen Bonds.

Copper(II) complexes with the quinquedentate ligands H(2)L(n)() (n = 1, 2) of the 1:2 condensation products of 3,3'-diaminodipropylamine and each of 4-formylimidazole and 4-formyl-2-methylimidazole have been synthesized and characterized, where the complexes have the general formula of [Cu(H(2)L(n)())]X(2) and are abbreviated as 1X(2), and 2X(2) (n = 1, 2 for 2-substituent = H, Me; X = ClO(4), NO(3), Cl). X-ray crystal structures of 1(NO(3))(2), and 2(Cl)(2) were determined: 1(NO(3))(2), monoclinic, space group P2(1)/c (No. 14), a = 9.610(4) Å, b = 13.463(5) Å, c = 15.568(5) Å, beta = 98.12(3) degrees, and Z = 4; 2(Cl)(2), monoclinic, space group P2(1)/n (No. 14), a = 9.884(2) Å, b = 15.073(3) Å, c = 15.295(2) Å, beta = 98.57(2) degrees, and Z = 4. The complex assumes Delta or Lambda enantiomorphs due to the spiral arrangement of the quinquedentate ligand around the copper(II) ion, and these Delta and Lambda enantiomorphs of the cation for 1(NO(3))(2) and 2(Cl)(2) coexist as the racemic form in the crystals. When the protonated complexes were treated with NaOH, the mono-deprotonated complexes with the formula [CuHL(n)()]ClO(4), 1'ClO(4) (n = 1) and 2'ClO(4) (n = 2), were obtained. Crystal data for 1'ClO(4): Pbca (No. 61) with a = 13.211(3) Å, b = 25.387(3) Å, c = 10.939(3) Å, and Z = 8.; 2'.ClO(4), Pbca (No. 61) with a = 16.554(4) Å, b = 20.609(4) Å, c = 12.423(3) Å, and Z = 8. The structures consist of an electronically monopositive copper(II) complex involving a deprotonated imidazole moiety and a protonated imidazole moiety per molecular unit and a mononegative anion ClO(4)(-), where an imidazolate nitrogen atom N(2) of the copper(II) complex is hydrogen bonded to the imidazole nitrogen atom N(6) ( denotes the symmetry operation of (1)/(2) + x, (1)/(2) - y, -z) of the adjacent unit with the hydrogen bond distance of N(2).N(6) of 2.842(6) for 1'ClO(4) and 2.815(4) Å for 2'ClO(4) to give a one-dimensional helical structure running along the a-axis. Through the hydrogen bonds, the Delta isomer only aggregates with the Delta isomer and the Lambda isomer only aggregates with the Lambda isomer to give an extended helical chain structure described as DeltaDeltaDeltaDeltaDelta. or LambdaLambdaLambdaLambdaLambda., respectively.

Preparation and electrochemical study of a silver(I) complex of a heptaaza quinquedentate macrocyclic ligand

The quinquedentate ligand L, prepared by template condensation of bis-6,6″-(α-methylhydrazino)-4′-phenyl-2,2′:6″,2′-terpyridine with glyoxal, forms a stable crystalline complex of silver(I) [Ag(L)(H 2O) 2][PF 6]. Oxidative cyclic voltammetry of this complex in acetonitrile shows a reversible one-electron oxidation wave at +0.75 V, vs a Ag/AgBF 4 reference electrode. Electrochemical oxidation by controlled potential electrolysis of such a solution and investigation of the oxidized product by EPR and IR spectroscopy, elemental analysis and conductivity, shows that the oxidation wave could correspond to the formation of a ligand-radical cation.

Crystal structures and Mössbauer spectra of spin-crossover iron(III) complexes of quinquedentate ligands

Magnetic properties, Mossbauer spectra and crystal structures of spin-crossover iron(III) complexes with a quinquedentate ligand [FeLX]BPh4 are reported. X and L denote a unidentate ligand and a quinquedentate ligand, respectively. [Fe(mbpN)(im)]BPh4 shows spin-crossover behavior in an appropriate organic solvent, and [Fe(mbpN)(lut)]BPh4, [Fe(bpN)(py)]BPh4 and [Fe(salten)X]BPh4 (X=4me-py or 2me-im) show spin-crossover behavior in a solid and in an organic solvent. It was found that the ligand field strength of salten was stronger than that of mbpN. The rates of spin-state interexchange in the complexes are as fast as the inverse of the lifetime (1×10−7 s) of the Mossbauer nuclear level. The Mossbauer spectroscopic behavior of [Fe(mbpN)(lut)]BPh4 and [Fe(bpN)(py)]BPh4 is different to that of [Fe(salten)X]BPh4 (X=4me-py or 2me-im). The difference was ascribed to the different geometrical positions of the corresponding anions.

Quinquedentate Coordination of 3-[(2'-Amino-ethyl)amino]-2-[(2″-aminoethyl)aminomethyl]propionic Acid (LH). Crystal Structure of trans-[Co(L)Cl][ClO4].H2O And Molecular Mechanics Examination of Isomers

The anion (1c) of the branched polyamino acid 3-[(2′-aminoethyl)amino]-2-[(2″-aminoethyl)- aminomethyl ] propionic acid (1b) binds as a quinquedentate ligand to cobalt(III). Reaction with cobalt(II) chloride, followed by oxidation and acidification, yields exclusively one isomer of [Co(1c) Cl ]+. The complex was crystallized readily as a perchlorate monohydrate salt, in the monoclinic space group P 21/n, a 7.921(2), b 17.357(4), c 11.852(4) Ǻ, β 107.25(2)°, Z = 4; a single-crystal X-ray structure determination was refined to R 0.033 for 2099 `observed' reflections. The carboxylate and two adjacent secondary amines occupy an octahedral face, with the chloro ligand trans to the carboxylate , and the secondary amines adopt R,S stereochemistries. The Co-O distance [1.901(2) Ǻ] is at the short end of the range of cobalt- carboxylate bonds, and Co-N distances [average 1.944 Ǻ (primary amines), average 1.950 Ǻ (secondary amines)] are slightly shorter than average for Co-N bonds. The Co- Cl distance is 2.255(1) Ǻ. Molecular mechanics examination of all possible isomers and conformers of [Co(1c) Cl ]+ and of the related pentaamine 1,5,9-triamino-5-methyl-3,7-diazanonane (2) indicate a greater variation in strain energy across the range of isomers and conformers in the latter more strained system.

Chlorometal(III) complexes of a new chiral quinquedentate polyamino acid based on (SS)-trans-cyclohexane-1,2-diamine

The potentially quinquedentate ligand (SS,SS)-3-(2-aminocyclohexylamino)-2-(2-aminocyclohexylaminomethyl)propionic acid (HL1), prepared via a metal-directed condensation reaction, readily formed a (carboxylatotetraamine)chlorocobalt(III) complex cation as well as the rhodium(III) and chromium(III) analogues. The compound SS,SS-[CoL1(Cl)][ClO4]·0.75HClO4·2H2O crystallizes in the orthorhombic space group P212121, a= 7.825(2), b= 16.566(6), c= 19.737(11)Å, and the crystal structure determined by X-ray diffraction methods refined to a residual of 0.066 for 1475 independent observed reflections. The co-ordinated chloride has a trans disposition relative to the carboxylate group of the ligand, the two pairs of nitrogen donors from the cyclohexane-1,2-diamine residues being coplanar with the cobalt ion. The NHCH2CH(CO2–)CH2NH core of the ligand necessarily occupies an octahedral face. Metal–nitrogen distances [Co–N 1.920(11)–1.982(11)Å] are slightly longer than in the 3-(2-aminoethylamino)-2-(2-aminoethylaminomethyl)propionic acid analogue although the metal–oxygen distance [1.916(10)Å] is comparable to that in the analogue, as is the Co–Cl distance [2.223(4)Å]. Comparisons of structures and kinetics of base hydrolysis with related systems are drawn.

Tridentate coordination of dioxomolybdenum(VI) with some potentially quinquedentate (N 2O 3) Schiff base ligands

Three complexes of molybdenum(VI) 4–6 have been prepared and characterised using potentially quinquedentate ligands derived from Schiff base condensations using 1,3-diamino-2- hydroxypropane. From NMR spectroscopic evidence it is clear that the ligands bind to the metal ion in a terdentate manner, leaving two of the possible ligand donor atoms uncoordinated. This represents a new coordination mode for monomeric complexes of these ligands with a transition metal ion. In solution, the sixth coordination site of the MoO 2 2+ ion is occupied by a solvent molecule while in the solid state, the 13C NMR spectrum of 4 suggests that the sixth coordination site of MoO 2 2+ is occupied by a phenolic oxygen, probably via an intermolecular interaction between the complexes.

57Fe Mössbauer spectra and spin-crossover behavior of [Fe(mbpN)(lut)]BPh4

New spin-crossover complexes [Fe(III)L(lut)]BPh4 (L = mbpN or bpN) with N4O2 moiety are reported. The structure of the mbpN (N3O2 quinquedentate ligand) complex is determined at 293 K, and the temperature dependences of the57Fe Mossbauer spectra and magnetic susceptibilities for both complexes have been examined.

Synthesis, spectroscopic and redox behaviour of copper(II) complexes with quinquedentate thiaaza ligands

Three potentially quinquedentate ligands, 1,11-diamino-6-oxa-3,9-dithiaundecane (LO), 1,6,11-triaza-3,9-dithiaundecane (LN), 1,11-diamino-3,6,9-trithiaundecane (LS) and their quadridentate analogue 1,11-diamine-3,9-dithiaundecane (LC) were prepared. Their copper(II) complexes of composition CuL(ClO 4) 2 have been isolated for the quinquedentate ligands, whereas for LC the dimeric complex Cu 2(LC) 3(ClO 4) 2 was the main product. ESR spectroscopy showed that the copper(II) complex with LO has rhombic symmetry, whereas the complexes with LN and LS are tetragonal, and the dimeric LC complex exhibits a weak Cu(II)-Cu(II) interaction. The cyclic voltammograms of the complexes with the quinquedentate ligands show a negative potential shift in comparison with the complex with the tetradentate ligand LC. Under CO, the E 1/2 value for Cu(LS)(ClO 4) 2 shifts anodically by 50 mV due to formation of [Cu(LS)(CO)] +.

Nickel(II) and cobalt(II) complexes of potentially quinquedentate macrobicyclic ligands. Reversible binding of dioxygen to a cobalt(II) complex

Two new macrobicyclic ligands which are potentially quinquedentate have been prepared and characterised. Variable-temperature NMR studies show that the nickel(II) complex of one of these ligands exists as a mixture of two conformers at low temperature which take part in two independent exchange processes as the temperature is raised. In the first, one conformer undergoes a form of self exchange and in the second, the two conformers interconvert. The ESR spectrum of the cobalt(II) complex of one of the new ligands indicates that it exists as a mixture of four- and five-co-ordinate species, with the five-co-ordinate material arising from intermolecular binding of the ligand secondary amine group to the cobalt(II) ion. This complex binds dioxygen reversibly and the O2 adduct has reasonable stability with respect to autoxidation.