Synthesis and metal ion complexation of acyclic Schiff base podands with lipophilic amide and ester end groups

A series of acyclic Schiff base podands 14?C19 with lipophilic amide and ester end groups were synthesized in good yield and in a simple way. Their transition metal ions complexation was studied using conductometric method in acetonitrile (AN) at 25 °C. Schiff base podands 14?C16 showed a continuous decrease in the molar conductances in their complexation with Hg²⁺, Pb²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ which begins to level off at a mole ratio of 1:1 crown-to-metal indicating the formation of a stable 1:1 complexes. The order of the stability constants of the metal ions studied with the Schiff base podands 14, 15 and 16 is: Hg²⁺ > Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ > Ag⁺. Metal ion complexation by acyclic diamide or diester podands involves presumably the oxygen atoms of the carbonyl groups in addition to the nitrogen atoms of the imino groups.     

A convenient synthesis of new thiaazacrown ethers and study of their complexation reactions with some transition metal cations in binary acetonitrile–chloroform mixture using the conductometric method

Three novel thiaazacrown ethers 1, 2 and 3 were synthesized in a simple way and in high yield. The complex formation between Ag⁺, Cu²⁺, Zn²⁺, Pb²⁺, Hg²⁺ and Cd²⁺ metal cations with thiaazacrown ethers 1, 2 and 3 have been studied in acetonitrile:chloroform (1:1) binary solvent system using conductometric technique. The conductance data show that the stochiometry of the complexes with Ag⁺, Cu²⁺ and Zn²⁺ cations is 1:1 (L:M), but in the case of Pb²⁺ and Hg²⁺ cations, a 1:2 (L:M) complex is formed in solutions. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data at 25 °C. It was found that the stability constants of 1-Ag²⁺, 2-Ag⁺ and 3-Ag⁺ complexes are higher than those of their corresponding Zn²⁺ and Cu²⁺ complexes and found to vary in order 3 > 1 > 2 for Ag⁺.     

How do phosphoramides compete with phosphine oxides in lanthanide complexation? Structural, electronic and energy aspects at ab initio and DFT levels

Novel comparison of the structural, electronic and energy aspects of lanthanide complexes of model phosphoramides (PAs) with those of phosphine oxides (POs), phosphate esters (PEs) and phosphoryl trihalides (PHs) has been carried out by ab initio and DFT calculations. Atoms in Molecules (AIM) and Natural Bonding Orbital (NBO) analyses were performed to understand the electronic structure of ligands L and related complexes, L–Ln³⁺. NBO analysis indicates that the negative charge on phosphoryl oxygen (O_P) and the p character of the phosphoryl lone pair, Lp(O_P), increase in the order PH < PE < PO < PA. Positive charge of the lanthanide cation in PA complexes is less than those of PH, PE and PO complexes, due to the more intense ligand to metal charge transfer (LMCT). The metal–ligand distance decreases in the order PH > PE > PO > PA, which is confirmed by the results of AIM analysis. Charge density at the bond critical point of L–Ln³⁺ follows the sequence PH < PE < PO < PA. The results of the Energy Decomposition Analysis (EDA) indicate that the donative interaction and LMCT increases in order PH < PO < PE < PA. The effect of basis set superposition error (BSSE) on the L···Ln³⁺ interaction energies was also studied in detail at DFT, MP2 and CCSD(T) levels using the counterpoise (CP) method. Trends in the CP-corrected L–Ln³⁺ bond energies are in good accordance with the optimized O_P···Ln³⁺ distances. The results show that the difference between CP-corrected and uncorrected interaction energies in PA complexes is larger than those in the others, because PAs are more deformable. It is depicted that PAs are comparable with POs in lanthanide complexation.     

Complexation and thermodynamic studies of oxathiadibenzocrown ethers with Cu2+, Pb2+, Zn2+ and Cd2+ ions

A thermodynamic study of the complexation of Cu²⁺, Pb²⁺, Zn²⁺ and Cd²⁺ ions with 1 and 2 in acetonitrile has been carried out. The study was conducted in the temperature range 283–308 K using a conductometric technique. The observed molar conductivity, Λ, was found to decrease significantly for mole ratios [L]_t/[M]_t less than unity in all cases. A model involving 1:1 stoichiometry has been used to analyze the conductivity data. The stability constant, K, for each 1:1 complex was determined from the conductivity data by using a nonlinear least-squares curve fitting procedure. The results show that compound 1 has no peak selectivity for any of the metal cations, while compound 2 selectively associates with Cu²⁺ and Pb²⁺. Complexes of 1 have the following stability order Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺  and Pb²⁺ > Cu²⁺ for the complexes of 2. The ?H° and ?S° values for the complexation process were obtained from the slope and intercept of the Van’t Hoff plots respectively. All ?G° values were negative and were determined from the Gibbs–Helmholtz equation and the significance of these values is discussed.     

Theoretical investigation on conformational preferences and structural properties of 2-lithio-1,3-diphosphinane and 2-lithio-1,3-dimethyl-1,3-diphosphinane

A new family of dialphosphacyclohexane is introduced which has three nucleophilic centers. The conformational stabilities and structural properties of 2-lithio-1,3-diphosphinane and 2-lithio-1,3-dimethyl-1,3-diphosphinane were investigated computationally by DFT calculations and NBO analyses at B3LYP/6-31+G(d,p). Relative energy trend in 1,3-diphosphinane and 1,3-dimethyl-1,3-diphosphinane conformations explored from steric and hyperconjugative point of view. The stability trend of 2-lithio derivatives based on calculated relative energies in 1,3-diphosphinane is 1d > 1f > 1b > 1a > 1c > 1e and for 1,3-dimethyl-1,3-diphosphinane derivatives is 2f > 2d > 2b > 2a > 2c > 2e. Calculated NBO atomic charges indicate that high positive charge at lithium and small C–Li Wiberg bond indexes in these derivatives are demonstrators of ionic nature of the C–Li bonds. Stereoelectronic interactions, polarizability of phosphorus, and chelate formation between each of phosphorous and lithium are determining factors in stability trend observed in these derivatives. Ease of lithiation in bis(dimethylphosphino)methane, 1,3-diphosphinane, and 1,3-dimethyl-1,3-diphosphinane derivatives was estimated and compared by isodesmic reaction.     

Solvent extraction of europium trifluoromethanesulfonate into nitrobenzene by using three electroneutral receptors

From extraction experiments and $ \gamma $ -activity measurements, the extraction constants corresponding to the general equilibrium Eu³⁺(aq) + 3 A^?(aq) + L(nb) $ \Leftrightarrow $ EuL³⁺(nb) + 3A^?(nb) taking place in the two-phase water–nitrobenzene system ( $ {\text{A}}^{ - } = {\text{CF}}_{ 3} {\text{SO}}_{3}^{ - } $ ; L = electroneutral receptors denoted by 1, 2, and 3 – see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the EuL³⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the series of 3 < 2 < 1.

Paramagnetic properties and molecular structure of coordination saturated inclusive lanthanide complexes with 18-crown-6 using NMR

Earlier NMR spectra of lanthanide complexes [Ln(18-crown-6)(NO₃)₃] have been analyzed by us (Babailov in Inorg Chem 51(3):1427–1433, 2012), where Ln³⁺ = La³⁺ (I), Ce³⁺ (II), Pr³⁺ (III) and Nd³⁺ (IV). The NMR signal assignment and conformational molecular dynamic have been found by 1D NOE and relaxation spectroscopy as well as on 2D NOESY and EXSY experiments at 170 K. In the present paper the ¹H NMR method is used to study the features of paramagnetic properties of complexes I–IV and [Eu(18-crown-6)(NO₃)₃] (V) at ambient temperature. The investigation was carried out by special method based on analysis of Δδ/z> on k(Ln)/z> (where k(Ln) is Bleaney’s constant, Δδ is paramagnetic contribution to the lanthanide-induced shifts). The obtained results indicate that the structure of the complexes (in CDCl₃ and CD₂Cl₂) are very similar.     

Synthesis,characterization, spectrophotometric and electrochemistry studies,and DNA cleavage of copper(II) complexes of a new azacrown bis-macrocycle and its mono-cyclic analogue

A new azacrown bis-macrocycle (5) and its mono–cyclic analogue (7) were synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, DEPT ¹³C NMR, MS, and elemental analysis. The reaction with copper(II) nitrate yielded the corresponding complexes, formulated as Cu(5)(NO₃)₂·3H₂O (8), and Cu(7)(NO₃)₂·2.5H₂O (9). Also the stoichiometries of the complexes were determined in alcoholic solution and the results show that for both complexes the ratio of ligand to metal was 1:1 in methanol. The redox behavior of both complexes has been studied by cyclic voltammetry in DMF. Cyclic voltamogram of 8 shows quasi-reversible Cu^II/Cu^I redox couple whereas 9 shows a reversible Cu^II/Cu^I redox couple. Mono- and bis-macrocycle copper(II) complexes (8 and 9 respectively) cleaved plasmid pGS2 DNA by using an oxidative mechanism with 3- mercaptopropionic acid (MPA) as the reductant under aerobic conditions. The bis-macrocycle copper(II) complex 8 showed higher cleavage efficiency than their mono-macrocycle analogue 9 at the same Cu²⁺ concentration.     

Synergistic extraction of some divalent metal cations into nitrobenzene by using strontium dicarbollylcobaltate and electroneutral macrocyclic lactam receptor

From extraction experiments and $ \gamma $ -activity measurements, the exchange extraction constants corresponding to the general equilibrium M²⁺(aq) + 1·Sr²⁺(nb) $ \Leftrightarrow $ 1·M²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (M²⁺ = Mg²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Cu²⁺, Zn²⁺, Cd²⁺, $ {\hbox{UO}}_{2}^{2 + } $ , Mn²⁺, Co²⁺, Ni²⁺; 1 = macrocyclic lactam receptor–see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1·M²⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: Mg²⁺ < Co²⁺ < Cu²⁺, Mn²⁺, Ni²⁺ < Cd²⁺ < Ca²⁺ < Ba²⁺, Zn²⁺ < Pb²⁺ <  $ {\hbox{UO}}_{2}^{2 + } $ .

Mononuclear copper(II) complexes of bis-triazole-based macrocyclic Schiff base hydrazones: direct synthesis,EPR studies,magnetic and thermal properties

Mononuclear copper(II) complexes of 1,2,4-triazole-based Schiff base macrocyclic hydrazones, III and IV, have been reported. The prepared amorphous complexes have been characterized by spectroscopic methods, electron spray ionization mass spectrometry, and elemental analysis data. Electrochemical studies of the complexes in DMSO show only one quasi-reversible reduction wave at +0.43 V (ΔE = 70 mV) and +0.42 V (ΔE = 310 mV) for III and IV, respectively, which is assigned to the Cu(II) → Cu(I) reduction process. Temperature dependence of magnetic susceptibilities of III and IV has been measured within an interval of 2–290 K. The values of χ_M at 290 K are 1.72 × 10^?3 cm³ mol^?1 and 1.71 × 10^?3 for III and IV, respectively, which increases continuously upon cooling to 2 K. EPR spectra of III and IV in frozen DMSO and DMF were also reported. The trend g_|| > g⊥ > g_e suggests the presence of an unpaired electron in the d_x2?y2 orbital of the Cu(II) in both complexes. Furthermore, spectral and antimicrobial properties of the prepared complexes were also investigated.     

Synthesis, spectroscopic studies of new water-soluble Co(II) and Cu(II) macrocyclic complexes of 4,15-bis(2-hydroxyethyl)-2,4,6,13,15,17-hexaazatricyclodocosane: their interaction studies with calf thymus DNA and guanosine 5′ monophosphate

New water soluble Co(II) 1, Ni(II) 2 and Cu(II) 3 complexes of 4,15-bis(2-hydroxyethyl)-2,4,6,13,15,17-hexaazatricyclodocosane Co(II) were synthesized and characterized by various techniques, viz. elemental analysis, conductivity measurements, infrared, electronic, ESI-MS, ¹H and ¹³C NMR spectroscopy. Molar conductance measurements in aqueous solution showed that complexes 1, 2 and 3 are ionic in nature. On the basis of spectroscopic data, a square planar geometry was assigned to the complexes involving four N-atoms of the two cyclohexane moieties. Interaction studies of 1 and 3 with CT-DNA were carried using UV/Visible absorption spectroscopy, fluorescence spectrophotometry, cyclic voltammetry and viscosity measurements. Absorption spectral traces reveal 27.7 and 23.3% hyperchromism for complexes 1 and 3, respectively indicative of strong binding to CT-DNA. These results were authenticated by fluorescence quenching experiments and viscosity measurements. The intrinsic binding constants K _b of 1 and 3 are 2.94 × 10⁴ and 2.71 × 10⁴ M^?1, respectively. Early transition metals show preference for O6 position while later ones copper and cobalt prefer N7 position of DNA base guanine. To validate this hypothesis, interaction studies of copper (II) and cobalt (II) complexes were carried out with 5′GMP, which revealed electrostatic interactions are more favored along with hydrogen bonding than coordinate covalent interaction to N7 position of guanine.     

Synthesis and thermal behavior study of complexes of the type [Pd(μ-X)(4-eb-p-phen)]2 (X = Cl,Br, I,N3, NCO,SCN) and 4-eb-p-phen [bis(4-ethylbenzyl)p-phenylenediimine]

The Schiff base bis(4-ethylbenzyl) p-phenylenediimine, 4-eb-p-phen (1), and six new dimeric Pd(II) complexes of the type [Pd(μ-X)(4-eb-p-phen)]₂ {X = Cl (2), Br (3), I (4), N₃ (5), NCO (6), SCN (7)} have been synthesized and characterized by elemental analysis, IR spectroscopy, and ¹H and ¹³C{¹H}-NMR experiments. The thermal behavior of the complexes 2–7 has been investigated by means of thermogravimetry and differential thermal analysis. From the final decomposition temperatures, the thermal stability of the complexes can be ordered in the following sequence: 3 > 4 > 7 > 2 ≈ 5 > 6. The final products of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction (XRD).     

Synthesis of p-tert-butylcalix[4]arene semitubes and their binding studies with C60

The synthesis of p-tert-butylcalix[4]arene semitubes in one step reaction with fairly good yields is described. The structures of these compounds were confirmed by ¹H NMR, ¹³CNMR and mass spectrometry. The complexation ability of these compounds with C₆₀ was investigated and found that they are able to form 1:1 complexes. The stability constants of these complexes were determined and found to be 15, 203 and 525 dm³ mol^?1 for the semitubes 3a, 3b, 3c respectively. The binding energies of each of C₆₀, the semitubes and the complexes are calculated using PM6 (Semiempirical quantum chemical) and DFT (Density Functional Theory) methods and found in the order m > p > o. On the other hand, the calculated binding energies using DFT method showed that the stabilities of both centered and side complexes are in the order p > m > o.     

Synthesis and catalytic activity of novel Ni-N complexes

A series of nickel complexes with 1,3-xylylenediamine, 1,2-diaminobenzene and 1,2-aminobenzylamine were first synthesized and characterized. The reaction of these amines with Ni(OAc)₂ · 4H₂O and NiCl₂ · 6H₂O in methanol or tetrahydrofuran resulted in the production of four novel nickel complexes I, II, III, and IV. The structure of each complex was determined by X-ray diffraction analysis. Each complex was also characterized using elemental analysis, ¹H NMR and IR. The complexes were then used to catalyze the Henry reaction, and good catalytic results (65?C99%) were achieved. The catalytic activity of the complexes was determined by ¹H NMR.     

Click synthesis of triazole-linked calix[4]arene ionophores. Potentiometric and ESI-MS screening of ion-selectivity

A series of 1,2,3-triazole-linked calix[4]arene ionophores comprised of different O-donor groups (OH, COOEt, CONEt₂) attached either to the lower rim of calix or to the triazole moieties were synthesized to explore their ion-selectivity for the first time in potentiometric transduction. Plasticized PVC membrane electrodes (ISEs) were fabricated, and their potentiometric selectivities were measured toward a series of mono- and divalent metal ions. Structure-ion-selectivity relationship and the structural requirements of the coordination sphere for selective binding were established. ISEs made of calix[4]arene-bis-triazoles were found generally to exhibit distinct Ag⁺ selectivity in the order 3 ≈ 4 > 2 > 1, indicating the beneficial effect of the carboxamide or ester groups in the complexing site. In contrast, calix[4]arene-tetratriazole 5 comprised only sp ² N-donor atoms displayed excellent Cu²⁺ selectivity over a series of alkali-, alkaline earth- and transition metal ions. A unique feature of the outstanding Ag⁺ selective electrodes made of 3 and 4 was recognized and suggested their potential application as Na⁺ ISEs in systems not containing silver ions. Further, the potential use of competitive ESI-MS experiments for screening the binding affinities of ionophores 3–6 to different metal ions was also demonstrated.     

Experimental and theoretical study on the complexation of Ca2+ with beauvericin

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ca²⁺(aq) + 1·Sr²⁺(nb) ? 1·Ca²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex(Ca²⁺, 1·Sr²⁺) = 1.1 ± 0.1. Further, the stability constant of the 1·Ca²⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb(1·Ca²⁺) = 10.1 ± 0.2. Finally, by using quantum mechanical density functional level of theory calculations, the most probable structures of the non-hydrated 1·Ca²⁺ and hydrated 1·Ca²⁺·H₂O complex species were predicted.     

Synthesis and characterization of glycol ether and oxime modified precursors of niobium(V) for soft transformation to niobia

A glycol ether modified precursor, [Nb{O(CH₂CH₂O)₂}(OPrⁱ)₃] (A) was prepared by the reaction of Nb(OPrⁱ)₅ with O(CH₂CH₂OH)₂ in 1:1 molar ratio in anhydrous benzene. Further reactions of A with a variety of internally functionalized oximes in different molar ratios, yielded heteroleptic complexes of the type, [Nb{O(CH₂CH₂O)₂}(OPrⁱ)_3?n{ON = C(CH₃)(Ar)}_n] (1–9) {where Ar = C₄H₃O-2, n = 1 [1], n = 2 [2], n = 3 [3]; C₄H₃S-2, n = 1 [4], n = 2 [5], n = 3 [6]; C₅H₄N-2, n = 1 [7], n = 2 [8], n = 3 [9]}. All the above derivatives have been characterized by elemental analyses, FT-IR, NMR (¹H, ¹³C {¹H}) and FAB mass studies. Spectral studies of 1–9 suggest the presence of mono- and bi-dentate mode of oxime moieties, in the solution and in the solid states, respectively. FAB mass studies indicate monomeric nature for 3 and dimeric nature for A. TG curves of A and 6 show their low thermal stability. Soft transformation of A and 3 to pure niobia, a and b, respectively have been carried out by sol–gel technique. The XRD patterns of niobia a and b suggest the formation of nano-size crystallites of average size of 10.8 and 19.5 nm, respectively. The XRD patterns also indicate the formation of monoclinic phase of the niobia in both the cases. Absorption spectra of a and b suggest energy band gaps of 4.95 and 4.39 eV, respectively.     

Synthesis, crystal structures, and DNA-binding properties of zinc(II) and nickel(II) complexes with tris[2-(N-ethyl)benzimidazylmethyl]amine and cinnamate ligands

Tris[2-(N-ethyl)benzimidazylmethyl]amine (Etntb) and two of its complexes, [Zn(Etntb)(cinnamate)]NO₃·2DMF (1) and [Ni(Etntb)(cinnamate)·(H₂O)]NO₃ (2) have been synthesized and characterized by physico-chemical and spectroscopic methods. Single-crystal X-ray diffraction revealed that the complexes have different structures. In complex 1, the coordination sphere around Zn(II) is distorted trigonal bipyramidal, whereas the coordination sphere around Ni(II) is distorted octahedral in complex 2. The DNA-binding properties of the free ligand and its complexes have been investigated by electronic absorption, fluorescence, and viscosity measurements. The results suggest that the ligand and both complexes bind to DNA via an intercalative mode, and their binding affinity for DNA follows the order 1 > 2> ligand.     

Synthesis and biological activity of Magnesium(II) complexes of heptaaza Schiff base macrocyclic ligands; 1H and 13C chemical shifts computed by the GIAO-DFT and CSGT-DFT methodologies

Two new pendant armed Schiff base macrocyclic complexes, [MgL¹](ClO₄)₂ (1), and [MgL²](ClO₄)₂ (2), have been prepared via cyclocondensation of 2,6-diformylpyridine and 2,6-diacetylpyridine with two hexadentate hexaamines, ten and tmen, in the presence of Mg(II) ion. The ligands are 15-membered pentaaza macrocycles having two 2-aminoethyl pendant arms. The newly prepared complexes are investigated by IR, ¹H NMR, ¹³C{¹H} NMR, DEPT(135), COSY(H, H) and HMQC spectroscopic methods. The antimicrobial screening of newly prepared complexes, 1 and 2, as well as previously prepared similar complexes, [MgL³](ClO₄)₂ (3) and [MgL⁴](ClO₄)₂ (4), against Escherichia coli, Staphylococcus aureus and candidia albicans showed that the macrocyclic complexes of Mg(II) containing 15-membered pentaaza ring (1, 2 and 3) have no activity. Where as the compound 4, which contain 16-membered pentaaza ring, had remarkable inhibition zone on the culture of S. aureus and E. coli as compared with standard drugs. The ¹H and ¹³C chemical shieldings of gas phase complexes were also studied by the gauge independent atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods at the level of density functional theory (DFT). The computed ¹³C chemical shifts are in reasonably good agreement with the experimental data.     

Experimental and DFT study on the complexation of Ba2+ with beauvericin

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ba²⁺(aq) + 1·Sr²⁺(nb) ?1·Ba²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (Ba²⁺, 1·Sr²⁺) = 1.2 ± 0.1. Further, the stability constant of the beauvericin–barium complex (abbrev. 1·Ba²⁺) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Ba²⁺) = 9.5 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1·Ba²⁺ complex species was predicted.