Azulene-moiety-based ligand for the efficient sensitization of four near-infrared luminescent lanthanide cations: Nd3+, Er3+, Tm3+, and Yb3+

The ML(4) complexes formed by reaction between the bidentate azulene-based ligand diethyl 2-hydroxyazulene-1,3-dicarboxylate (HAz) and several lanthanide cations (Pr(3+), Nd(3+), Gd(3+), Ho(3+), Er(3+), Tm(3+), Yb(3+), and Lu(3+)) have been synthesized and characterized by elemental analysis, FT-IR vibrational spectroscopy and electrospray ionization mass spectroscopy. Spectrophotometric titrations have revealed that four Az(-) ligands react with one lanthanide cation to form the ML(4) complex in solution. Studies of the luminescence properties of these ML(4) complexes demonstrated that Az(-) is an efficient sensitizer for four different near-infrared emitting lanthanide cations (Nd(3+), Er(3+), Tm(3+), and Yb(3+)); the resulting complexes have high quantum yield values in CH(3)CN. The near-infrared emission arising from Tm(3+) is especially interesting for biologic imaging and bioanalytical applications since biological systems have minimal interaction with photons at this wavelength. Hydration numbers, representing the number of water molecules bound to the lanthanide cations, were obtained through luminescence lifetime measurements and indicated that no molecules of water/solvent are bound to the lanthanide cation in the ML(4) complex in solution. The four coordinated ligands protect well the central luminescent lanthanide cation against non-radiative deactivation from solvent molecules.     

Structural and electronic characterization of the complexes obtained by the interaction between bare and hydrated first-row transition-metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) and glycine

The complexes formed by the simplest amino acid, glycine, with different bare and hydrated metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) were studied in the gas phase and in solvent in order to give better insight into the field of the metal ion-biological ligand interactions. The effects of the size and charge of each cation on the organization of the surrounding water molecules were analyzed. Results in the gas phase showed that the zwitterion of glycine is the form present in the most stable complexes of all ions and that it usually gives rise to an eta(2)O,O coordination type. After the addition of solvation sphere, a resulting octahedral arrangement was found around Ni(2+), Co(2+), and Fe(2+), ions in their high-spin states, whereas the bipyramidal-trigonal (Mn(2+) and Zn(2+)) or square-pyramidal (Cu(2+)) geometries were observed for the other metal species, according to glycine behaves as bi- or monodentate ligand. Despite the fact that the zwitterionic structure is in the ground conformation in solution, its complexes in water are less stable than those obtained from the canonical form. Binding energy values decrease in the order Cu(2+) > Ni(2+) > Zn(2+) approximately Co(2+) > Fe(2+) > Mn(2+) and Cu(2+) > Ni(2+) > Mn(2+) approximately Zn(2+) > Fe(2+) > Co(2+) for M(2+)-Gly and Gly-M(2+) (H(2)O)(n) complexes, respectively. The nature of the metal ion-ligand bonds was examined by using natural bond order and charge decomposition analyses.     

Silver(I) Complexes with Nitrogen-Containing Noncyclic, Macrocyclic, and Macrobicyclic Ligands in Propylene Carbonate

Stability constants and thermodynamic data for complex formation of silver(I) with noncyclic, macrocyclic, and macrobicyclic ligands have been measured in propylene carbonate using potentiometric and calorimetric methods. All ligands containing two nitrogen donor atoms form extremely stable complexes. Only if substituents reduce the basicity of the nitrogen donor atoms, the stability of the complexes decreases drastically. However, the cryptand (221) forms the most stable complex of all ligands examined. In this case, the dimensions of the ligand cavity and of the cation are nearly identical.     

Novel CdCl2 and HgCl2 complexes with 3-monosubstituted and 3,3-disubstituted 1-furoylthioureas: IR and Raman spectra

Two series of coordination complexes of CdCl(2) and HgCl(2) with 3-monosubstituted and 3,3-disubstituted 1-furoylthioureas were prepared and characterized. These complexes were obtained with a medium to high yield from ethanolic solutions of both ligand and salt. The formed complex results from the salt-ligand interaction with participation of both the salt anion and cation. Information on the coordination chemistry of these complexes was derived from thermal stability data, and IR, Raman and (13)C CPMAS NMR spectra. On coordination the electronic structure of these ligands changes as a whole, affecting practically all their vibrational pattern, however, within that complex pattern some vibrations provide valuable information on the nature of the studied complexes. These thiourea derivatives behave as neutral ligands, which coordinate the metal ion through the sulfur atom of the thiocarbonyl group. This fact is supported by the observed frequency shift, to lower values, in the nu(CS) vibration on the coordination and the appearance of a low frequency Raman line which was assigned to the metal-sulfur stretching, nu(M-S), in the formed complex. The frequency of the nu(CO) vibration always increases on complex formation, which discards the participation of the carbonyl group in the coordination process. The complexation takes place preserving the free ligand conformation, established from intra-molecular interactions, particularly in 3-monosubstituted ligands. Such features of the studied ligands and their complexes are also supported by (13)C CPMAS NMR spectra. This spectroscopic information correlates with the reported behavior of the ligands in ion selective electrodes.     

Synthesis and characterization of heterodinuclear Ln(3+)-Fe3+ and Ln(3+)-Co3+ complexes,bridged by cyanide ligand (Ln3+ = lanthanide ions). Nature of the magnetic interaction in the Ln(3+)-Fe3+ complexes

The reaction of Ln(NO3)3.aq with K3[Fe(CN)6] or K3[Co(CN)6] in N,N'-dimethylformamide (DMF) led to 25 heterodinuclear [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O and [Ln(DMF)4(H2O)3(mu-CN)Co(CN)5].nH2O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr(3+)-Fe3+), (Tm(3+)-Fe3+), (Ce(3+)-Co3+), (Sm(3+)-Co3+), and (Yb(3+)-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P21/c or P21/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.     

Carbamoylphosphine oxide complexes of trivalent lanthanide cations: role of counterions, ligand binding mode, and protonation investigated by quantum mechanical calculations

We present a quantum mechanical study of carbamoylphosphine oxide (CMPO) complexes of MX(3) (M(3+) = La(3+), Eu(3+), Yb(3+); X(-) = Cl(-), NO(3)(-)) with a systematic comparison of monodentate vs bidentate binding modes of CMPO. The per ligand interaction energies Delta E increase from La(3+) to Yb(3+) and are higher with Cl(-) than with NO(3)(-) as counterions, as a result of steric strain in the first coordination sphere with the bidentate anions. The energy difference between monodentate (via phosphoryl oxygen) and bidentate CMPO complexes is surprisingly small, compared to Delta E or to the binding energy of one solvent molecule. Protonation of uncomplexed CMPO takes place preferably at the phosphoryl oxygen O(P), while in the Eu(NO(3))(3)CMPOH(+) complex carbonyl (O(C)) protonation is preferred and O(P) is bonded to the metal. A comparison of uranyl and lanthanide nitrate complexes of CMPO shows that the interaction energies Delta E of the former are lower. Finally, the effect of grafting CMPO arms at the wide rim of a calix[4]arene platform is described. The results are important for our understanding of cation binding and extraction by potentially bidentate CMPO, diamide, and diphosphoryl types of ligands.     

cis-Bis(bipyridine)ruthenium Imidazole Derivatives: A Spectroscopic, Kinetic, and Structural Study

The ruthenium bis(bipyridine) complexes cis-[Ru(bpy)(2)Im(OH(2))](2+), cis-[Ru(bpy)(2)(Im)(2)](2+), cis-[Ru(bpy)(2)(N-Im)(2)](2+), cis-[Ru(dmbpy)(2)Im(OH(2))](2+), cis-[Ru(dmbpy)(2)(N-Im)(OH(2))](2+)(bpy = 2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, Im = imidazole, N-Im = N-methylimidazole), have been synthesized under ambient conditions in aqueous solution (pH 7). Their electrochemical and spectroscopic properties, absorption, emission, and lifetimes were determined and compared. The substitution kinetics of the cis-[Ru(bpy)(2)Im(OH(2))](2+) complexes show slower rates and have lower affinities for imidazole ligands than the corresponding cis-[Ru(NH(3))(4)Im(OH(2))](2+) complexes. The crystal structures of the monoclinic cis-[Ru(bpy)(2)(Im)(2)](BF(4))(2), space group = P2(1)/a, Z = 4, a = 11.344(1) ?, b = 17.499(3) ?, c = 15.114(3) ?, and beta = 100.17(1) degrees, and triclinic cis-[Ru(bpy)(2)(N-Im)(H(2)O)](CF(3)COO)(2).H(2)O, space group = P&onemacr;, Z = 2, a = 10.432(4) ?, b = 11.995(3) ?, c = 13.912(5) ?, alpha = 87.03(3) degrees, beta = 70.28(3) degrees, and gamma = 71.57(2) degrees, complexes show that these molecules crystallize as complexes of octahedral Ru(II) to two bidentate bipyridine ligands with two imidazole ligands or a water and an N-methylimidazole ligand cis to each other. The importance of these molecules is associated with their frequent use in the modification of proteins at histidine residues and in comparisons of the modified protein derivatives with these small molecule analogs.     

Self-assembly,characterisation, and crystal structure of multinuclear metal complexes of the [2 x 3] and [3 x 3] grid-type

The self-assembly of new multimetallic complexes of grid-type architecture is described. The binding of a set of tris-terdentate ligands, 1 a-1 d, based on terpyridine-like subunits, with different octahedrally coordinated metal ions leads to the formation of species whose structure depends strongly on the ligand, the metal ion, the counterion, the solvent, and the reaction conditions. Under suitable conditions, the [3 x 3] grid was obtained from the reaction of ligand 1 a with zinc tetrafluoroborate and from ligand 1 b with mercury triflate. The other ligands led to the formation of mainly one compound of composition [M(6)L(5)](12+), which has the structure of an incomplete [2 x 3] grid. The crystal structure of such a [2 x 3] grid, [Co(6)(1 d)(5)](12+), has been determined. In this complex, the three central pyrimidine-pyridine-pyrimidine non-coordinating sites adopt transoid NCbond;CN conformations. The much less stable cisoid conformations, the "pinching" of the coordination sites in the complex, the weaker donor strength of the central binding site, and the steric demand of the substituents are all factors contributing to the reluctance to produce the [3 x 3] structure. A subtle interplay between the nature of the metal, the steric demand of the ligand, the reaction conditions, and the type of counterion determine the product of self-assembly. The results obtained show that by tuning the parameters, complexes containing six or nine octahedrally coordinated metal ions in a well-defined grid-type arrangement are accessible. Both types of arrays, [2 x 3] and [3 x 3 ], are of interest as self-assembled inorganic architectures of well-defined structure and nuclearity that may be suitable prototypes for selective information storage media.     

A comparison of the acidity and the complexing ability of (o-hydroxyphenyl) bis- and (o-hydroxyphenyl) mono-methylenephosphonic acids towards lanthanide(III) ions

The characterization of the acid-base properties of a family of three phenoldimethylenephosphonic acids differently substituted by auxo- or chromophoric groups was studied. These ligands may be considered as pentaacids. Their pK(a) were determined in aqueous solution at 25 degrees C and constant ionic strength 0.1 mol dm(-3) by potentiometry and UV-visible spectrophotometry. Eventually, the complexing power of these molecules with lanthanide cations, Ce(3+), Pr(3+), Nd(3+), Sm(3+) and Eu(3+), was studied keeping in view the possible application to the treatment of radioactive liquid waste. The number, the nature of the species in solution, their stability constants and their individual electronic spectra as restored by computation have been determined. In all cases, complexes of 1:1 stoichiometry accompanied by hydroxy and protonated species are postulated. The comparison of tri- and pentaacids confirms that the acids having the methyl group at the para position with respect to the phenolic OH, have the highest complexing power.     

Fe(II), Ru(II) and Re(I) complexes of endotopic, sterically non-hindering, U-shaped 8,8'-disubstituted-3,3'-biisoquinoline ligands: syntheses and spectroscopic properties

The redox behaviour, optical-absorption spectra and emission properties of U-shaped and elongated disubstituted biisoquinoline ligands and of derived octahedral Fe(ii), Ru(ii), and Re(i) complexes are reported. The ligands are 8,8'-dichloro-3,3'-biisoquinoline (1), 8,8'-dianisyl-3,3'-biisoquinoline (2), and 8,8'-di(phenylanisyl)-3,3'-biisoquinoline (3), and the complexes are [Fe(3)(3)](2+), [Fe(2)(3)](2+), [Ru(1)(phen)(2)](2+), [Ru(2)(3)](2+), [Ru(3)(3)](2+), [Re(2)(py)(CO)(3)](+), and [Re()(py)(CO)(3)](+). For the ligands, the optical properties as observed in dichloromethane are in line with expectations based on the predominant (1)pipi* nature of the involved excited states, with contributions at lower energies from (1)npi* and (1)ILCT (intraligand charge transfer) transitions. For all of the Fe(ii), Ru(ii), and Re(i) complexes, studied in acetonitrile, the transitions associated with the lowest-energy absorption band are of (1)MLCT (metal-to-ligand charge transfer) nature. The emission properties, as observed at room temperature and at 77 K, can be described as follows: (i) the Fe(ii) complexes do not emit, either at room temperature or at 77 K; (ii) the room-temperature emission of the Ru(ii) complexes (phi(em) > 10(-3), tau in the micros range) is of mixed (3)MLCT/(3)LC character (and similarly at 77 K); and (iii) the room-temperature emission of the Re(i) complexes (phi(em) approximately 3 x 10(-3), tau < 1 ns) is of (3)MLCT character and becomes of (3)LC (ligand-centered) character (tau in the ms time scale) at 77 K. The interplay of the involved excited states in determining the luminescence output is examined.     

Metal complexes of tetrapodal ligands: synthesis, spectroscopic and thermal studies, and X-ray crystal structure studies of Na(I), Ca(II), Sr(II), and Ba(II) complexes of tetrapodal ligands N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine and N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine

Twelve complexes 1-12 of general category [M(ligand)(anion)(x)(water)(y)], where ligand = N,N,N',N'-tetrakis(2-hydroxypropyl/ethyl)ethylenediamine (HPEN/HEEN), anion = anions of picric acid (PIC), 3,5-dinitrobenzoic acid (DNB), 2,4-dinitrophenol (DNP), and o-nitrobenzoic acid (ONB), M = Ca(2+), Sr(2+), Ba(2+), or Na(+), x = 1 and 2, and y = 0-4, were synthesized. All of these complexes were characterized by elemental analysis, IR, (1)H and (13)C NMR, and thermal studies. X-ray crystal studies of these complexes 1-12, [Ca(HPEN)(H(2)O)(2)](PIC)(2).H(2)O (1), [Ca(HEEN)(PIC)](PIC) (2), Ba(HPEN)(PIC)(2) (3), [Na(HPEN)(PIC)](2) (4), Ca(HPEN)(H(2)O)(2)](DNB)(2).H(2)O (5),Ca(HEEN)(H(2)O)](DNB)(2).H(2)O (6), [Sr(HPEN)(H(2)O)(3)](DNB)(2) (7), [Ba(HPEN)(H(2)O)(2)](DNB)(2).H(2)O](2) (8), [[Ba(HEEN)(H(2)O)(2)](ONB)(2)](2) (9), [[Sr(HPEN)(H(2)O)(2)](DNP)(2)](2) (10), [[Ba(HPEN)(H(2)O)(2)](DNP)(2)](2) (11), and [Ca(HEEN)(DNP)](DNP) (H(2)O) (12), have been carried out at room temperature. Factors which influence the stability and the type of complex formed have been recognized as H-bonding interactions, presence/absence of solvent, nature of the anion, and nature of the cation. Both the ligands coordinate the metal ion through all the six available donor atoms. The complexes 1 and 5-11 have water molecules in the coordination sphere, and their crystal structures show that water is playing a dual character. It coordinates to the metal ion on one hand and strongly hydrogen bonds to the anion on the other. These strong hydrogen bonds stabilize the anion and decrease the cation-anion interactions by many times to an extent that the anions are completely excluded out of the coordination sphere and produce totally charge-separated complexes. In the absence of water molecules as in 2 and 3 the number of hydrogen bonds is reduced considerably. In both the complexes the anions case interact more strongly with the metal ion to give rise to a partially charge-separated 2 or tightly ion-paired 3 complex. High charge density Ca(2+) forms only monomeric complexes. It has more affinity toward stronger nucleophiles such as DNP and PIC with which it gives partially charge-separated eight-coordinated complexes. But with relatively weaker nucleophile like DNB, water replaces the anion and produces a seven coordinated totally charge-separated complex. Sr(2+) with lesser charge/radius ratio forms only charge-separated monomeric as well as dimeric complexes. Higher coordination number of Sr(2+) is achieved with coordinated water molecules which may be bridging or nonbridging in nature. All charge-separated complexes of the largest Ba(2+) are dimeric with bridging water molecules. Only one monomeric ion-paired complex was obtained with Ba(PIC)(2). Na(+) forms a unique dinuclear cryptand-like complex with HPEN behaving as a heptadentate chelating-cum-bridging ligand.     

N,N'-ethylenebis(pyridoxylideneiminato) and N,N'-ethylenebis(pyridoxylaminato): synthesis, characterization, potentiometric, spectroscopic, and DFT studies of their vanadium(IV) and vanadium(V) complexes

The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds.     

Ternary complexes of zinc(II) with nitrilotriacetic acid and some selected thiol amino-acids and related molecules

Solution equilibria of the system zinc(II)-nitrilotriacetic acid (NTA)-secondary ligand (L) have been studied. The secondary ligands investigated are thiol amino-acids and related molecules. Potentiometric titrations of reaction mixtures containing equimolar Zn(2+), NTA and secondary ligand have shown the formation of 1 : 1 : 1 ternary complexes. The formation constants of these complexes have been determined at 25 degrees (mu = 0.1M, KNO(3)). The mode of chelation is discussed.     

Direct measurements of rate constants and activation volumes for the binding of H2, D2, N2, C2H4, and CH3CN to W(CO)3(PCy3)2: theoretical and experimental studies with time-resolved step-scan FTIR and UV-vis spectroscopy

Pulsed 355 nm laser excitation of toluene or hexane solutions containing W-L (W = mer,trans-W(CO)3(PCy3)2; PCy3 = tricyclohexylphosphine; L = H2, D2, N2, C2H4, or CH3CN) resulted in the photoejection of ligand L and the formation of W. A combination of nanosecond UV-vis flash photolysis and time-resolved step-scan FTIR (s2-FTIR) spectroscopy was used to spectroscopically characterize the photoproduct, W, and directly measure the rate constants for binding of the ligands L to W to reform W-L under pseudo-first-order conditions. From these data, equilibrium constants for the binding of L to W were estimated. The UV-vis flash photolysis experiments were also performed as a function of pressure in order to determine the activation volumes, DeltaV thermodynamic, for the reaction of W with L. Small activation volumes ranging from -7 to +3 cm3 mol(-1) were obtained, suggesting that despite the crowded W center an interchange mechanism between L and the agostic W...H-C interaction of one of the PCy3 ligands (or a weak interaction with a solvent molecule) at the W center takes place in the transition state. Density functional theory (DFT) calculations were performed at the B3LYP level of theory on W with/without the agostic C-H interaction of the PCy3 ligand and also on the series of model complexes, mer,trans-W(CO)3(PH3)2L (W'-L, where L = H2, N2, C2H4, CO, or n-hexane) in an effort to confirm the infrared spectroscopic assignment of the W-L complexes, to simulate and assign the electronic transitions in the UV-vis spectra, to determine the nature of the HOMO and LUMO of W-L, and to understand the agostic C-H interaction of the ligand vs solvent interaction. Our DFT calculations indicate an entropy effect that favors agostic W...H-C interaction over a solvent sigma C-H interaction by 8-10 kcal mol(-1).     

Unusual complexing properties of 2-(2'-pyridyl)- and 2-hydrazino-8-hydroxyquinoline

The ligands 2-(2'-pyridyl)- and 2-hydrazino-8-hydroxyquinoline form terdentate complexes with a 5,5-bicyclic ring system, the stabilities being greater than those of the corresponding 8-hydroxyquinolinates. This study affords a more complete picture of the behaviour of terdentate 2-substituted 8-hydroxyquinolines. Solutions of these ligands and metal ions are complicated by formation of the protonated species MHL(2+), M(HL)(2+)(2) and MLHL(+). The existence of the protonated species is dependent not only on pH and ligand:metal-ion molar ratio but also on the nature of the metal ion itself.     

Derivatives of phosphate Schiff base transition metal complexes: synthesis, studies and biological activity

We report the synthesis and structural characterization of series of tetra- and hexacoordinate metal chelate complexes of phosphate Schiff base ligands having the general composition LMX(n).H(2)O and L(2)MX(n) (L=phosphate Schiff base ligand; M=Ag(+), Mn(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), or Fe(3+) and X=NO(3)(-), Br(-) or Cl(-)). The structure of the prepared compounds was investigated using elemental analysis, IR, 1H and 31P NMR, UV-vis, mass spectra, solid reflectance, magnetic susceptibility and conductance measurements as well as conductometric titration. In all the complexes studied, the ligands act as a chelate ligand with coordination involving the phosphate-O-atom and the azomethine-N-atom. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordination capacity of ligand. IR spectra show the presence of coordinated nitrate and water molecule, the magnetic moments of all complexes show normal magnetic behavior and the electronic spectra of the metal complexes indicate a tetra- and octahedral structure for Mn(2+), octahedral structure of Fe(3+) and both square-planar and distorted octahedral structure for Cu(2+) complexes. Antimicrobial activity of the ligands and their complexes were tested using the disc diffusion method and the chosen strains include Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Microsporum canis, Trichophyton mentagrophyte and Trichophyton rubrum. Some known antibiotics are included for the sake of comparison and the chosen antibiotic are Amikacin, Doxycllin, Augmantin, Sulperazon, Unasyn, Septrin, Cefobid, Ampicillin, Nitrofurantion, Traivid and Erythromycin.     

Noncovalent interactions of Cu+ with N-donor ligands (pyridine, 4,4-dipyridyl, 2,2-dipyridyl, and 1,10-phenanthroline): collision-induced dissociation and theoretical studies

Collision-induced dissociation of complexes of Cu+ bound to a variety of N-donor ligands (N-L) with Xe is studied using guided ion beam tandem mass spectrometry. The N-L ligands examined include pyridine, 4,4-dipyridyl, 2,2-dipyridyl, and 1,10-phenanthroline. In all cases, the primary and lowest-energy dissociation channel observed corresponds to the endothermic loss of a single intact N-L ligand. Sequential dissociation of additional N-L ligands is observed at elevated energies for the pyridine and 4,4-dipyridyl complexes containing more than one ligand. Ligand exchange processes to produce Cu+Xe are also observed as minor reaction pathways in several systems. The primary cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level are performed to obtain model structures, vibrational frequencies, and rotational constants for the neutral N-L ligands and the Cu+(N-L)x complexes. The relative stabilities of the various conformations of these N-L ligands and Cu+(N-L)x complexes as well as theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using B3LYP/6-31G* optimized geometries. Excellent agreement between theory and experiment is observed for all complexes containing one or two N-L ligands, while theory systematically underestimates the strength of binding for complexes containing more than two N-L ligands. The ground-state structures of these complexes and the trends in the sequential BDEs are explained in terms of stabilization gained from sd-hybridization and repulsive ligand-ligand interactions. The nature of the binding interactions in the Cu+(N-L)x complexes are examined via natural bond orbital analyses.     

Synthesis of triple-stranded complexes using bis(dipyrromethene) ligands

The reaction of an α-free, β,β'-linked bis(dipyrromethene) ligand with Fe(3+) or Co(3+) led to noninterconvertible triple-stranded helicates and mesocates. In the present context, a stable α-free ligand 2 has been developed and complexation of ligands 1 and 2 with diamagnetic Co(3+), Ga(3+), and In(3+) has been studied. The triple-stranded M(2)1(3) (M = Ga, In) and M(2)2(3) (M = Co, Ga, In) complexes were characterized using matrix-assisted laser desorption ionization time-of-flight spectrometry, (1)H NMR and UV-vis spectroscopy, and X-ray crystallography. Again, the (1)H NMR analysis showed that both the triple-stranded helicates and mesocates were generated in this metal-directed assembly. Consistent with our previous finding on coordinatively inert Co(3+) complexes, variable-temperature NMR spectroscopy indicated that the triple-stranded helicate and mesocate of labile In(3+) did not interconvert in solution, either. However, the diastereoselectivity of the M(2)2(3) complexes was found to improve with an increase in the reaction temperature. Taken together, this study complements the coordination chemistry of poly(dipyrromethene) ligands and provides further insight into the formation of helicates versus mesocates.     

Ligands Based on Phosphine-Stabilized Aluminum(I), Boron(I), and Carbon(0)

A systematic quantum chemical study of the bonding in d⁶-transition-metal complexes, containing phosphine-stabilized, main-group-element fragments, (R₃P)₂E, as ligands (E=AlH, BH, CH⁺, C), is reported. By using energy decomposition analysis, it is demonstrated that a strong M−E bond is accompanied by weak P−E bonds, and vice versa. Although the Al−M bond is, for example, found to be very strong, the weak Al−P bond suggests that the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower, but still higher than those for two-carbon-based ligands. For neutral ligands, electrostatic interactions are the dominating contributions to metal–ligand bonding, whereas for the cationic ligand a significant destabilization, with weak orbital and even weaker electrostatic metal–ligand interactions, is observed. Finally, for iron(II) complexes, it is demonstrated that different reactivity patterns are expected for the four donor groups: the experimentally observed reversible E−H reductive elimination of the borylene-based ligand (E=BH) exhibits significantly higher barriers for the protonated carbodiphosphorane (CDP) ligand (E=CH) and would proceed through different intermediates and transition states. For aluminum, such reaction pathways are not feasible (E=AlH). Moreover, it is demonstrated that the metal hydrido complexes with CDP ligands might not be stable towards reduction and isomerization to a protonated CDP ligand and a reduced metal center.