Synthesis and studies on metal coordination with a novel carboxyamide ligand

Novel complexes of Co(II), Ni(II), Cu(II) and Pd(II) with the new ligand [N,N'-bis(2-carboxy-1-oxo-phenelenyl)ethylenediamine] (H2L) have been synthesized and characterized on the basis of elemental analyses, magnetic susceptibility, thermal, infrared, electronic, 1H NMR and EPR spectral studies. Infrared and 1H NMR spectra show that H2L acts as a binegative tetradentate ligand. Coordination occurs through deprotonated carboxylate oxygens and nondeprotonated amido nitrogens in all the complexes. Electronic spectral studies and magnetic moment values suggest N2O2 coordination around each metal centre with strong field square planar chromophores. The probable structures of the complexes have been assigned on the basis of spectral studies. The complex formation between M(II) [M(II) = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] and (L2-) has also been studied potentiometrically in 75% aqueous DMF at 25 degrees C in 0.1 M NaClO4. The stability constants were found to follow the order: Mn(II) < Co(II) < Ni(II) < Cu(II) > Zn(II).     

Spin crossover studies in tris(N,N′-dialkyldithiocarbamato)iron(III) complexes

A series of fifteen complexes of the type [Fe(RRNCS₂)₃] with symmetric (R=R=n- C₆H₁₃, n-C₈H₁₇, CH₂–CH=;CH₂, C₆H₅, C₆H₁₁ and C₆H₅CH₂), unsymmetric (R = CH₃; R = n-C₄H₉, C₆H₁₁, C₆H₅ and R = C₂H₅; R = n-C₄H₉, C₆H₁₁, C₆H₅ and i-C₃H₇) and ring substituents (RNR=pyrrolidyl and piperidyl) have been synthesized and their magnetic moments and Mössbauer spectra recorded from room temperature (RT) to liquid nitrogen temperature (LNT). Room temperature Mössbauer spectra of all the complexes exhibit an asymmetric doublet, which could be resolved into two doublets, each corresponding to low and high spin states in equilibrium. The crystal structure of tris(N, N-diallyldithiocarbamato)iron(III) shows it to be monoclinic with trigonally distorted octahedral geometry and space group C2/c. Fe–S stretching vibrations in the far i.r. region also show equilibria, HS LS. Depending on the nature of the alkyl group substituent, variable temperature magnetic moment and Mössbauer spectral studies, all the complexes may be divided into three groups; high spin complexes exhibiting spin-crossover (⁶A_1g ²T_2g), high spin complexes exhibiting spin transition (⁶A_1g ⁴T_1g) and intermediate spin complexes showing spin transition (⁴A_1g ²T_2g). On the basis of areas of the two doublets corresponding to high and low spin states, their percent contributions were calculated. Furthermore, magnetic moments of the equilibrium mixture calculated on the basis of respective areas compare well with the experimentally determined _eff values. E_Q values for both high and low spin states show linear decrease with increasing temperature.     

Synthesis of bipyridine and terpyridine based ruthenium metallosynthons for grafting of multiple pyrene auxiliaries

The synthesis of novel ruthenium(II) bipyridine or terpyridine complexes bearing an increasing number of pyrene or toluyl moieties is described. The ruthenium complexes are constructed in a first step with ligands bearing the required bromine functions, followed in a second step by stepwise grafting of 1-ethynylpyrene or 4-ethynyltoluene promoted by Pd(0). A complex bearing a protected triethylsilylacetylene function was also prepared. In situ deprotection of this function with K₂CO₃ and cross-coupling with 1-bromopyrene afforded a soluble complex in which two pyrene moieties are linearly linked via ethynyl spacers to one of the bipyridine ligands. These highly coloured complexes exhibit well defined absorption and emission properties in solution at both rt and 77 K.     

Correlating axial and equatorial ligand field effects to the single-molecule magnet performances of a family of dysprosium bis-methanediide complexes

Treatment of the new methanediide–methanide complex [Dy(SCS)(SCSH)(THF)] (1Dy, SCS = {C(PPh₂S)₂}²⁻) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS)₂][Dy(SCS)₂(K(DME)₂)₂] (2Dy), [Dy(SCS)₂][Na(DME)₃] (3Dy) and [Dy(SCS)₂][K(2,2,2-cryptand)] (4Dy). For further comparisons, the bis-methanediide complex [Dy(NCN)₂][K(DB18C6)(THF)(toluene)] (5Dy, NCN = {C(PPh₂NSiMe₃)₂}²⁻, DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for 2Dy–5Dy, with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s⁻¹). Fitting the alternating current magnetic susceptibility data for 2Dy–5Dy gives energy barriers to magnetic relaxation (U_eff) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus 2Dy–4Dy join a privileged group of SMMs with U_eff values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For 2Dy–4Dy, the Dy-components can be grouped into 2Dy–cation/4Dy and 2Dy–anion/3Dy, where the former have almost linear C Dy C units with short average Dy C distances, and the latter have more bent C Dy C units with longer average Dy C bonds. Both U_eff and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M–L distances produces enhanced SMM properties. Comparison with 5Dy demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between U_eff barrier and axial linearity in structurally comparable systems.

Studies on equatorial donor and C Dy C angle variation effects on energy barriers to the slow relaxation of magnetisation are reported.     

Lipophilic Diamides as Ionophores for Alkali and Alkaline Earth Metal Cations

A series of lipophilic N, N, N′,N′-tetrasubstituted diamides were prepared and their selectivity in solvent polymeric membranes was studied, cis-N, N, N′, N′-Tetraisobutylcyclohexane-1,2-dicarboxamide induces a selectivity in membranes for Li⁺over alkaline earth metal cations and other alkali metal cations by a factor of about 1000 and 100 respectively. The ionophore N, N′-diheptyl-N,N′-dimethylethylmalonamide is an attractive candidate for the use in microelectrodes for the determination of intracellular Mg²⁺-activities.     

Lewis adducts of the side-on end-on dinitrogen-bridged complex [{(NPN)Ta}2(mu-H)2(mu-eta 1:eta 2-N2)] with AlMe3, GaMe3, and B(C6F5)3: synthesis, structure, and spectroscopic properties

Reaction of the side-on end-on dinitrogen complex [{(NPN)Ta}(2)(mu-H)(2)(mu-eta(1):eta(2)-N(2))] (1; in which NPN=(PhNSiMe(2)CH(2))(2)PPh), with the Lewis acids XR(3) results in the adducts [{(NPN)Ta}(2)(mu-H)(2)(mu-eta(1):eta(2)-NNXR(3))], XR(3)=GaMe(3) (2), AlMe(3) (3), and B(C(6)F(5))(3) (4). The solid-state molecular structures of 2, 3, and 4 demonstrate that the N-N bond length increases relative to those found in 1 by 0.036, 0.043, and 0.073 A, respectively. In solution complexes 2-4 are fluxional as evidenced by variable-temperature (1)H NMR spectroscopy. The (15)N{(1)H} NMR spectra of 2-4 are reported; furthermore, their vibrational properties and electronic structures are evaluated. The vibrational structures are found to be closely related to that of the parent complex 1. Detailed spectroscopic analysis on 2-4 leads to the identification of the theoretically expected six normal modes of the Ta(2)N(2) core. On the basis of experimental frequencies and the QCB-NCA procedure, the force constants are determined. Importantly, the N-N force constant decreases from 2.430 mdyn A(-1) in 1 to 1.876 (2), 1.729 (3), and 1.515 mdyn A(-1) (4), in line with the sequence of N-N bond lengths determined crystallographically. DFT calculations on a generic model of the Lewis acid adducts 2-4 reveal that the major donor interaction between the terminal nitrogen atom and the Lewis acid is mediated by a sigma/pi hybrid molecular orbital of N(2), corresponding to a sigma bond. Charge analysis performed for the adducts indicates that the negative charge on the terminal nitrogen atom of the dinitrogen ligand increases with respect to 1. The lengthening of the N-N bond observed for the Lewis adducts is therefore explained by the fact that charge donation from the complex fragment into the pi* orbitals of dinitrogen is increased, while electron density from the N-N bonding orbitals p(sigma) and pi(h) is withdrawn due to the sigma interaction with the Lewis acid.     

Palladium salicylaldimine complexes containing boronate esters

Reactions of salicylaldehydes with boronate ester derivatives of aniline have been examined. Addition of these Schiff base ligands to palladium acetate or Na₂PdCl₄ afforded novel boron-containing trans-bis(N-arylsalicylaldiminato) palladium complexes.Condensation of salicylaldehyde (2-HOC₆H₄C(O)H) with H₂NC₆H₄Bpin (pin=1,2-O₂C₂Me₄) afforded the boron-containing Schiff bases, 2-HOC₆H₄C(H)=NC₆H₄Bpin (1–3a). Similar reactivity with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde gave the corresponding Schiff bases (1-3b) and (1-3c), respectively. Reaction of Schiff bases (2) and (3) with palladium acetate or Na₂PdCl₄ afforded complexes of the type PdL₂ (4,5), where L=deprotonated Schiff base. The molecular structure of the nitro-salicylaldehyde 4-Bpin palladium complex (5b) was characterized by an X-ray diffraction study. All new palladium compounds have been characterized fully and tested for their antifungal activity against Aspergillus niger and Aspergillus flavus.     

Evaluation of the contribution to hydration of nonelectrolytes from the hydrophobic effect

A new method was suggested for estimating the hydrophobic effect of contributions to the Gibbs energies and enthalpies of hydration of hydrocarbons, inorganic gases and rare gases. In accordance with this method the hydrophobic effect contribution to the Gibbs energy was evaluated from the difference between the hydration Gibbs energy of a solute and the non hydrophobic contribution. To estimate the latter value, the known dependence connecting the Gibbs energies of solvation of a solute in a number of aprotic solvents to the Hildebrand solubility parameter for these solvents was used. The non hydrophobic contribution to the Gibbs energy of hydration was calculated for various solutes from such dependences extended to water as solvent. The Hildebrand solubility parameter for water used in the calculation was corrected for the effect of association through hydrogen bonding. This correction was made by subtraction of the water self-association enthalpy from the enthalpy of vaporization of water. The evaluated Gibbs energies of the hydrophobic effect are positive for saturated hydrocarbons, inorganic gases and rare gases and linearly depend on the solute molecular refraction. The hydrophobic contribution to the hydration enthalpies of the solutes was calculated in the same manner as was made to calculate the hydrophobic contribution to Gibbs energies of hydration. Enthalpies of the hydrophobic effect for the solutes under study are negative.     

M?ssbauer and other spectral studies of Fe(III) complexes of benzothiazolines

Different molar reactions of Fe(OPr¹)₃, and FeCl₃ with benzothiazolines having an NSH donor system. derived by the condensation ofo-aminothiophenol with heterocyclic aldehydes. viz. pyridine-2-aldehyde. furfuraldehyde and thiophene-2-aldehyde. lead to the formation of [Fe.Pr¹(NS)₂]₂, [Fc(NS)₃] and [Fe(NS)₂Cl| type of complexes. The resulting derivatives have been characterized by elemental analysis, conductivity measurements, molecular weight determinations and magnetic studies. IR, electronic, M?ssbauer and ESR spectral data have been used to deduce the structures of the resulting derivatives.