η-Allyl-cobalt (II) complexes

(η³-Cyclooctenyl)Co(bisphosphine) compounds react with HBF₄ in the presence of alkenes with oxidation of the metal to give the novel, paramagnetic organocobalt(II) species [(η³-cyclooctenyl)Co(bisphosphine)]⁺BF₄⁻, (η³-2-RC₃H₄)Co(bisphosphine) complexes react similarly. The Co(II) compounds form adducts with CO and NO (the latter being diamagnetic) and undergo facile chemical and electrochemical reduction.     

Synthesis and characterization of two novel cobalt (II) phosphine complexes: crystal structures of [CoCl3(Cy2PCH2PCy2H)] and [Co(NO3)2(Cy2PCH2PCy2O)]. Cy = cyclohexyl, C6H11

The complexes [(Cy₂PCH₂PCy₂H)CoCl₃] (1) and [(Cy₂PCH₂PCy₂O)Co(NO₃)₂] (2), Cy = cyclohexyl (C₆H₁₁), have been prepared and characterized by EPR, UV-Vis, microanalysis and X-ray crystallography. The reaction CoCl₂ · 6H₂O and dcpm, dcpm = bis(dicyclohexylphosphino)methane, was found to form the monomeric, four coordinate, thermochromic and paramagnetic complex [(Cy₂PCH₂PCy₂H)CoCl₃] (1). Of particular interest is the formation of a zwitterion, or inner salt, in which the dangling phosphine adds a hydrogen atom, giving the phosphorus a +1 formal charge. The molecule adopts a pseudo-tetrahedral geometry around the central cobalt atom to which the cyclohexyl groups bind in an equatorial fashion to the phosphine. The reaction of Co(NO₃)₂ · 6H₂O and dcpm in a toluene/methanol/methylene chloride mixture yields the pseudo-octahedral complex [(Cy₂PCH₂PCy₂O)Co(NO₃)₂] (2). The cobalt is in the +2 oxidation state with one of the phosphorus atoms again having a +1 formal charge. The complex adopts a pseudo-octahedral geometry around the central cobalt atom with the cyclohexyl groups binding in an equatorial fashion to the phosphine similar to [(Cy₂PCH₂PCy₂H)CoCl₃].     

Electrophoretic study of cationic cobalt(III) complexes with [N2O] and [N2O2] Schiff base ligands

The electrophoretic migration behavior of acid-sensitive cationic alkylcobalt(III) complexes with tridentate Schiff bases and amines as well as that of related ‘inorganic’ cobalt(III) chelates with tridentate and tetradentate Schiff bases was studied. A correlation of the electrophoretic mobility of the organocobalt complexes in question with their structure was established. An attempt to optimize the analytical procedures for capillary electrophoretic separation of these rather labile complex cations is outlined. Their decomposition in solutions under ambient conditions was surveyed using this technique.     

Synthesis and characterisation of copper(II), zinc(II) and cobalt(II) complexes of salicylglycine, a metabolite of aspirin

Copper(II), nickel(II) and cobalt(II) complexes of the aspirin metabolite salicylglycine (H₂L), of stoichiometry M(HL)₂·solvate, have been prepared and characterised. In these complexes salicylglycinate is coordinated to the metal via its carboxylato group and possibly also its amide oxygen in the copper(II) complex. Under basic conditions copper(II) forms the complex Cu(LH₋₁)·2H₂O·MeOH, in which the ligand is coordinated to the metal via its carboxylate and phenolate oxygen atoms and the deprotonated peptide nitrogen atom.     

Steric control in the formation of Co2(CO)6-alkyne complexes from Group 14 tetraalkynes and their reactions with acid

A series of tetrakis(trimethylsilylethyne) derivatives of Group 14 metals (2–4) was prepared. Co₂(CO)₆ complexes 5–10 were synthesised by the reaction of 2–4 with Co₂(CO)₈. From the silyl and germyl based compounds 2 and 3, either one or two alkynes could be complexed with Co₂(CO)₆. In contrast, the tin derived compound 4 could accommodate up to four Co₂(CO)₆ complexes. The longest wavelength UV-Vis absorbances of the silicon and germanium-based complexes were consistent with multiple, non-conjugated Co₂(CO)₆ chromophores. The tetrakis Co₂(CO)₆ complex 10, however, absorbs at a much longer wavelength suggesting conjugation of Co₂(CO)₆ complexes through the tin. The reactivity towards protonolysis of the uncomplexed alkynes 2–4 is a consequence of the hyperconjugative stabilisation of the intermediate β-vinyl cation (the β-effect): Sn(CCSiMe₃)₃>SnOTf(CCSiMe₃)₂>SiMe₃>Ge(CCSiMe₃)₃. The reactivity of the Co₂(CO)₆ complexes, however, was quite different from the reactions of 2–4 and from analogous all-carbon systems. Treatment of 5–10 with strong acid led neither to protiodemetallation of the complexed or non-complexed alkynes but to decomplexation of the cobalt. Similarly, ligand metathesis reactions between 10 and Ph₂SiCl₂ were not observed. The normal reactivity of silylalkynes towards electrophiles, which was expected to be enhanced by the presence of the cobalt complex, was diminished by the particular steric environment of the molecules under examination (5–10). As a result, the favoured reaction under these conditions was decomplexation of the cobalt.     

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

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

Cobalt(II) and cadmium(II) chelates with nitrogen donors and O2 bonding to Co(II) derivatives

The formation of Cd(II) and Co(II) complexes with N-methylethylenediamine (men) has been studied at 298 K in dimethylsulfoxide (dmso) in an ionic medium set to 0.1 mol dm⁻³ with Et₄NClO₄ in anaerobic conditions by means of potentiometric, UV-Vis, calorimetric and FT-IR technique. Mononuclear ML_j (M=Cd, Co; j=1-3) complexes are formed in exothermic reactions, whereas the entropy changes oppose the complexes formation. The results are discussed in terms of different basicities and steric requirements and the whole of the thermodynamic data reported till now for the two ions with a number of diamines are summarized to visualize the selectivity of the ligands. The dioxygen uptake of Co(men)₂ species has also been studied by means of UV-Vis and EPR techniques. The kinetic parameters and stability constants obtained for the formation of the superoxo and μ-peroxo species are discussed in terms of solvent effect and steric hindrance due to methyl group.Cyclic voltammetry was used to confirm the stability constant for the Co(dmen)₂ (dmen=N,N^′-dimethylethylenediamine) superoxo adduct formation but was not successful to investigate this Co(men)₂-O₂ system.     

Nickel(II) and copper(II) complexes of mixed benzene-triazolehemiporphyrazines

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Kinetics and mechanism of the axial substitution reactions of (ligand)bis(4,5-dichloro-1,2-benzo semiquinonediiminato)cobalt(III) complexes

Square-pyramidal (Ph₃X)bis(4,5-dichloro-1,2-benzosemiquinonediiminato)cobalt(III) complexes (X = As, Sb or P) have been synthesized. The kinetics of axial substitution for the triphenylantimony complex have been studied for 10 entering ligands (L*). The reaction is of reversible second-order in both directions for all complexes. Labile behavior is indicated by the rate constants in the range from 6.33 × 10³ (for L* = Ph₃P in MeOH) to 5.4 (L* = py in CH₂Cl₂) M⁻¹ s⁻¹. The kinetics is consistent with an I_a mechanism. The log of the second-order rate constant for axial substitution is a linear function of nucleophilic reactivity n_Pt°, which is due to the trans-labilizing effect of the entering ligand in the six-coordinate transition state.     

Imidazole-based nickel(II) and cobalt(II) coordination complexes for potential use as models for histidine containing metalloproteins

It has been established that small molecule model complexes have been useful in studying more complex biological systems of metalloproteins. Because many metalloproteins have active sites that contain multiple histidine residues bound to a metal center, a series of imidazole-containing scorpionate ligands and the associated Co and Ni complexes have been developed to investigate the bonding parameters of histidine containing active sites. The tris(2-imidazolyl) carbinol (2-TIC, 6) and tris[2-(N-methylimidazolyl)] carbinol (2-^MeTIC, 7) complexes of Ni²⁺ and Co²⁺, namely [Co(2-^MeTIC)₂]Cl₂ (8), [Co(2-^MeTIC)₂](NO₃)₂ (9), [Ni(2-^MeTIC)₂]Cl₂ (10), [Ni(2-^MeTIC)₂](NO₃)₂ (11), [Co(2-TIC)₂](NO₃)₂ (12), and [Ni(2-TIC)₂](NO₃)₂ (13), have been prepared from the reaction of the appropriate ligand and appropriate metal salt in polar solvent. These complexes have been characterized by single crystal X-ray diffraction, spectroscopic techniques, and magnetic susceptibility. In each solid-state structure the metal center in the cation coordinates to three N atoms from two ligands and adopts a pseudo-octahedral coordination geometry. The X-ray characterization of tris[2-(N-methylimidazolyl)] carbinol is also reported.     

Synthesis, characterization and biological properties of cobalt(II) complexes of 1,10-phenanthroline and maltol

The synthesis and characterization of two cobalt(II) complexes, Co(phen)(ma)Cl 1 and Co(ma)₂(phen) 2, (phen = 1,10-phenanthroline, ma⁻ = maltolate or 2-methyl-4-oxo-4H-pyran-3-olate) are reported herein. The complexes have been characterized by FTIR, CHN analysis, fluorescence spectroscopy, UV-visible spectroscopy, conductivity measurement and X-ray crystallography. The number of chelated maltolate ligands seems to influence their DNA recognition, topoisomerase I inhibition and antiproliferative properties.     

A new mixed-valence hexanuclear cobalt complex, [Co4Co2(dea)2(Hdea)4)(piv)4](ClO4)2·H2O: Synthesis, crystal structure and magnetic properties

A new Co^II/Co^III hexanuclear complex, [Co₄^IICo₂^III(dea)₂(Hdea)₄)(piv)₄](ClO₄)₂·H₂O 1, has been obtained by reacting cobalt(II) perchlorate, diethanolamine, and pivalic acid (H₂dea = diethanolamine and piv = pivalato anion). The cobalt ions are held together by four μ₃ and four μ₂ alkoxo bridges as well as by four syn-syn carboxylato groups. The hexanuclear motif contains four Co(II) and two Co(III) ions. The {Co^II₄Co^III₂(μ₂-O)₄(μ₃-O)₄} core can be described as a four face-sharing monovacant and bivacant distorted heterocubane units. The cobalt(III) ions are hexacoordinated. Two of the cobalt(II) are hexacoordinated, while the two others are pentacoordinated with a bipyramidal stereochemistry. The magnetic properties of 1 have been investigated in the temperature range 1.9-300 K. Compound 1 exhibits an overall antiferromagnetic behaviour with a ground singlet spin state.     

Cobalt(II) complexes of the antibiotic sulfadiazine, the X-ray single crystal structure of [Co(C10H9N4O2S)2(CH3OH)2]

Cobalt(II) complexes of sulfadiazine formulated as [Co(C₁₀H₉N₄O₂S)₂(CH₃OH)₂] and [Co(C₁₀H₉N₄S)₂(H₂O)₂] have been synthesized and characterized by elemental analysis, infrared and UV-Vis spectroscopy and magnetic susceptibility measurements. The crystal structures of the complex [Co(C₁₀H₉N₄O₂S)₂(CH₃OH)₂] and of free sulfadiazine are also reported. The cobalt complex and the sulfadiazine ligand both crystallize in the monoclinic space group, P21/c, with sulfadiazine acting as a bidentate ligand. Cobalt is coordinated to two-sulfonamide nitrogen and the pyrimidine nitrogen of the sulfadiazine. Two molecules of methanol complete the octahedral geometry around the cobalt, with interligand hydrogen bonding between methanol and sulfadiazine. Infrared spectroscopy confirmed the presence of water molecule in the coordination sphere of [Co(C₁₀H₉N₄S)₂(H₂O)₂]. The electronic spectra and magnetic moments of both complexes were similar, indicating that both complexes have similar structure.     

Metal carbonyls of telluroether formed by the oxygen atom transfer reaction to M(CO)6 (M = Mo, W) in the presence of (p-CH3OC6H4)2TeO and relative kinetic investigation

A new synthetic process is reported for the preparation of two substituted metal carbonyls, (p-CH₃OC₆H₄)₂TeM(CO)₅ (M = Mo, W). In the presence of (p-CH₃OC₆H₄)₂TeO as O atom transfer reagent in tetrahydrofuran solvent, a CO ligand is replaced by telluroether when M(CO)₆ (M = Mo, W) is reacted with (p-CH₃OC₆H₄)₂TeO under very mild experimental conditions (r.t.). The products were characterized by elemental analysis, mass, IR and ¹H NMR spectroscopies. The spectra suggest that the coordination geometry is distorted from a regular octahedral structure due to an asymmetrical bulky telluroether ligand on the metal atom. Kinetics of these reactions of M(CO)₆ with (p-CH₃OC₆H₄)₂TeO show the reactions are first order in the concentration of M(CO)₆ and of Te oxide. The rates of reaction decrease in the order W(CO)₆>Mo(CO)₆>Cr(CO)₆, and the results obtained are discussed in term of a presumed mechanism.     

Reactivity of palladium(II) methyl complexes towards CO2: formation of carbonate complexes

Treatment of a benzene solution of (tmeda)PdMe₂ or (dppe)PdMe₂ with carbon dioxide gives the corresponding methyl bicarbonate complex, (L-L)PdMe(O₂COH). These were characterised by NMR spectroscopy and elemental analysis. Under strictly dry conditions no reaction was observed. Recrystallisation of the tmeda bicarbonate complex from acetone yields the corresponding η²-carbonate complex, which was characterised by X-ray crystallography. The reaction probably proceeds through attack by free carbonic acid on the dimethyl complex.     

DNA photocleavage activity of cobalt(III) polypyridyl complexes containing dpq ligand

Four cobalt(III) polypyridyl complexes, [Co(phen)_3−n(dpq)_n]³⁺ (phen = 1,10-phenanthroline, dpq = dipyrido[3,2-f:2′,3′-h]-quinoxaline) (n = 0, 1, 2, and 3) were synthesized and the influences of the dpq ligand on the photophysical properties, electrochemical properties, DNA binding affinities, as well as photonuclease activities of the complexes, were examined in detail. The presence of dpq ligand increases the DNA binding affinities of the corresponding complexes remarkably with respect to [Co(phen)₃]³⁺. With the sequential substitution of phen ligand by dpq ligand, the ¹O₂ quantum yields of the corresponding complexes are enhanced greatly. As a result, the photonuclease activities follow the order of [Co(dpq)₃]³⁺ > [Co(phen)(dpq)₂]³⁺ > [Co(phen)₂(dpq)]³⁺ ? [Co(phen)₃]³⁺. It was found all the examined complexes can generate OH upon UV irradiation, and OH is also involved in DNA photocleavage as reactive oxygen species.     

Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO₄ (1), [Co(TPA)Br]ClO₄ (2), [Co(TPA)(H₂O)]Cl(ClO₄) (3) and [Co₂(TPA)₂(μ-tp)](ClO₄)₂ · 2H₂O (4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV-vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2-300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl⁻ ion in 1, Br⁻ ion in 2, coordinated oxygen atom from H₂O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1-3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣D∣ = 7.3 cm⁻¹, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm⁻¹. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique - the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.     

Electrochemical and spectroscopic characterization of new cobalt(II) complexes. Catalytic activity in oxidation reactions by molecular oxygen

The synthesis and characterization of some new complexes with tetradentate Schiff bases derived from bis(salicylaldehyde)etylenediimine, H₂Salen are reported in this paper. The Co(II) Schiff bases complexes investigated are: (bis(5-nitro-salicylaldehyde) ethylenediiminato)cobalt(II), (CoNSalen); (bis(-ethyl-salicylaldehyde) ethylenediiminato)cobalt(II) (CoEtSalen); (bis(-ethyl-3,5-diiode-salicylaldehyde) ethylenediiminato) cobalt(II),(CoDIEtSalen); (bis(,5-dimethyl-3-iode-salicylaldehyde)ethylenediiminato)cobalt(II) (CoDMISalen) and (bis(salicylaldehyde)methylene-p,p′-diphenylene)cobalt(II), (CoSalmbfn). The characterization of the complexes was performed by elemental analysis, UV–Vis, FTIR spectroscopy, powder X-ray diffraction and cyclic voltammetry. Pyridine (py), present in the solution of complexes in DMF, coordinates to the metal ion in axial position, inducing a significant decrease of the redox potentials. Significant influences have the substituents grafted on ligands’ molecules. The separated complexes evince catalytic activity in the oxidation reaction of 2,6-di-t-butylphenol with molecular oxygen. These complexes seem capable of forming reversible adducts with molecular oxygen.     

New butane-1,2,3,4-tetracarboxylato bridged cobalt(II) complexes

Four butane-1,2,3,4-tetracarboxylato bridged supramolecular complexes [Co₂(H₂O)₅(BTC)]·2H₂O 1, [Co₂(H₂O)₅(BTC)]·2H₂O 2, [Co₂(H₂O)₆(bpy)₂(BTC)]·4H₂O 3 and [Co₂(H₂O)₂(bpy)₂(BTC)] 4, (H₄BTC = butane-1,2,3,4-tetracarboxylic acid, 2,2-bpy = 2,2-bipydine) are synthesized and characterized by single-crystal X-ray diffraction. IR spectroscopy, TG-DTA analyses, elemental analyses, powder X-ray diffraction and magnetic measurements for 3 and 4 are carried out. The dinuclear Co unit in 2 is bridged by BTC⁴⁻ anions into 2D layers, which are assembled via interlayer hydrogen bonds into a 3D (4⁴·6²)(4⁵·6⁵)₂(4⁶·6⁸·8) topological supramolecular architecture. In 3, the [Co₂(H₂O)₆(bpy)₂(BTC)] molecules are aggregated to 2D layers via π-π stacking interactions, the resulting layers are engaged in hydrogen bonding leading to a novel 3D supramolecular architecture with the schläfli symbol of (10².12)₂(4.10²)₂(4².10².12²). The Co atoms in 4 are linked by BTC⁴⁻ anions into a 1D chain, then the hydrogen bonding and π-π stacking interactions result in formation of a 3D novel (4³.6².8)₂(4⁶.6⁶.8³)(6³)₂ topological networks. The variable temperature magnetic characterizations on 3 and 4 suggest weak antiferromagnetic or ferromagnetic coupling exchange via π···π stacking interactions (J = -0.03 cm⁻¹ for 3, J = 0.11 cm⁻¹ for 4).     

Novel cobalt(II) complexes with pyridyl/ether or pyridyl/thioether ligands. The conversion of pyridyl/thioether cobalt(II) complex to pyridyl/sulfinato cobalt(III) compound

Two new cobalt(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesized as perchlorate salts. The crystal structures show that [Co(pydado)](ClO₄)₂ · H₂O (1) crystallizes in the triclinic space group and [Co(pydadt)](ClO₄)₂ (2) crystallizes in the monoclinic space group P2_1/c. The cation [Co(pydado)]²⁺ is pseudo-octahedral with the two pyridyl groups in trans position. However, in [Co(pydadt)]²⁺ complex, the size of thioether sulfur atoms imposes a distorted octahedral geometry; the pyridyl groups and the sulfur atoms are in trans position. The reaction of the complex 2 and hydrogen peroxide resulted to the oxidation of Co^II into Co^III and the thioether groups of the ligand to sulfinate groups with elimination of the central ethylenic group of pydadt. Thus, complex 2 was converted to bis[3-(2-pyridylmethylamino)ethanesulfinate] cobalt(III) complex (3) {[Co(pynso)₂](ClO₄) · 0.5H₂O}. The X-ray crystal structure reveals that the compound 3 crystallizes in the triclinic space group with the same donor atoms (N_pyridyl, N_amine and S) belonging to the two ligands in cis-position. In aqueous solution, the stability constants of the Co(II) chelates with these two ligands, determined by potentiometry, show the formation of [Co(LH)]³⁺ and [CoL]²⁺ species in all cases. The chelating power of pydadt ligand is slightly greater than that of pydado.