Showing papers in "Inorganic Chemistry in 1993"

Bond valence sum analysis of metal-ligand bond lengths in metalloenzymes and model complexes. 2. Refined distances and other enzymes

Abstract: The bond valence sum (BVS) method is further applied to metalloenzyme active sites. When a particular coordination model is assumed, the BVS method allows for oxidation states of metal ions in metalloproteins to be determined from metal-ligand bond distances measured using extended X-ray absorption fine structure (EXAFS) analysis. Thus, the BVS can be used to determine the compatibility between a given coordination model and a particular oxidation state. A new procedure for calculating r 0 values on which BVS's are based is presented. This procedure allows for calculation of r 0 values on heteroleptic complexes and was used to determine a new set of r 0 distances using complexes that more closely model the active sites of interest

Application of a universal force field to metal complexes

Abstract: The ability of a universal force field (UFF) to reproduce the structures of a variety of metal-containing molecules is examined. M-C bond distances are well reproduced, and errors in M-Y polar covalent bond distances are generally less than 0.05 A. Use of half-integer bond orders to take into account π back-bonding and the trans influence leads to errors of less than 0.05 A in bond distances for these complexes. Errors on the order of 0.15 A remain for high-valent-metal to halogen bond distances

NMR study on the coordination behavior of dissymmetric terdentate trinitrogen ligands on methylpalladium(II) compounds

Abstract: Neutral compounds of the type [(6-RC 5 H 3 N-2-C=NCH 2 CH 2 -2-C 5 H 4 N)Pd(CH 3 )(Cl)] (R=H (MAP), CH 3 (6'-CH 3 -MAP)) have been synthesized starting from [(cyclooctadiene)Pd(CH 3 )(Cl)], while ionic compounds of the type [(6-RC 5 H 3 N-2-C=NCH 2 CH 2 -2-C 5 H 4 N)Pd(CH 3 )] + °(Y)] - (Y=Cl, CF 3 SO 3 , NO 3 ; R=H, CH 3 ) wore formed by reacting the chlorides in a polar solvent with silver triflate and silver nitrate, respectively

Anion-exchange reactions of hydroxy double salts

Abstract: Hydroxy double salts (HDS's) comprise a class of layered materials which are similar to layered double hydroxides (LDH's) and show a comparable intracrystalline reactivity. All samples described in this paper were prepared by reacting a solid oxide MeO with various solutions.

Evidence for strong mixing between the LC and MLCT excited states in bis(2-phenylpyridinato-C2,N')(2,2'-bipyridine)iridium(III)

Abstract: The well-resolved absorption, excitation, and luminescence spectra of [Ir(ppy)2bpy]+ (ppyH = 2-phenylpyridine, bpy = 2,2'-bipyridine) in different media at cryogenic temperatures are presented. In solutions and glasses at ambient temperature the lowest energy excited state corresponds to an Ir - bpy charge-transfer excitation whereas in the crystalline host lattice [Rh(ppy)2bpy]PF6 the lowest excited state at 21 450 cm-1 is assigned to a 37r-r* excitation localized on the cyclometalating ppy- ligands. The next higher excited Ir - bpy charge-transfer state has shifted to 21 820 cm-', only 300 cm-I above the 3LC excited state. The close proximity of the 3LC and 3MLCT excited states and the large spin-orbit coupling constant of Ir3+ induce a strong mixing of charge-transfer character into the 3LC lowest excited states, resulting in increased oscillator strengths, reduced lifetimes, short axis polarized transitions, and a large zero-field splitting of 10-15 cm-1.

Electronic spectra and photophysics of platinum(II) complexes with α-diimine ligands. Mixed complexes with halide ligands

Abstract: Emission properties have been studied for a series of compounds of the formula (L_2)PtC1_2, where L_2 is N,N,N',N'-tetramethylethylenediamine, 2,2'-bipyridine (bpy), 4,4'-Me_2bpy, 5,5'-Me_2bpy, 4,4'-(t-Bu)_2bpy, 3,3'-(CH_3OCO)_2bpy, and 1,10-phenanthroline, and also for the compound Pt(bpy)I_2. Most of them exhibit orange to red luminescence from a triplet ligand-field (^3LF) state, both as solids and in glassy solution. These emissions are very broad (fwhm 2300-3400 cm^(-1) at 10 K) and structureless and are strongly Stokes-shifted from absorption. The two exceptions are the solid "red" form of Pt(bpy)Cl_2, which exhibits a relatively narrow (fwhm 1050 cm^(-1) at 10 K), vibronically structured (Δν ~ 1500 cm^-1)) red emission, and Pt(3,3'-(CH_3OCO)_2bpy)Cl_2, which exhibits a broad (fwhm 2500 cm^(-1) at 10 K) but structured (Δν ~1300 cm^(-1)) orange emission. Both of these emissions are assigned to triplet metal-to-ligand charge-transfer (^3MLCT) excited states. For the former compound, a linear-chain structure has destabilized a dσ*(d_(z^2)) level, yielding a dσ* → π*(bpy) state as the lowest energy excited state, while for the latter, the strongly electron-withdrawing substituents have stabilized a bpy π* level, yielding a dσ* → π*(bpy) state as the lowest energy excited state. The relative energies of the various types of excited states, including ligand 3_(ππ*) states, are discussed in detail. The crystal structures of Pt(5,5'-Me_2bpy)Cl_2 (monoclinic Cc, Z = 4, a = 13.413(7) A, b = 9.063(4) A, c = 12.261(9) A, 0 = 121.71(6)') and Pt(3,3'-(CH_3OCO)_2bpy)Cl_2 (triclinic P1, Z = 2, a = 7.288(2) A, b = 9.932(3) A, c = 11.881(5) A, α = 98.04(3)°, β = 103.56(3)°, γ = 106.54(3)°) are reported.

Characterization of calcium aluminate phases in cements by aluminum-27 MAS NMR spectroscopy

Abstract: 27 Al magic-angle spinning (MAS) NMR spectroscopy of the central and satellite transitions is shown to be a powerful technique for the characterization of calcium aluminates and aluminate hydrates, which are of importance in the chemistry of high alumina and Portland cements. Synthetic samples of CaO.2Al 2 O 3 , CaO.Al 2 O 3 , 12CaO.7Al 2 O 3 , 3CaO.Al 2 O 3 , CaO.Al 2 O 3 .10H 2 O, γ-Al(OH) 3 , 6CaO.Al 2 O 3 .3SO 3 .32H 2 O (ettringite), 4CaO.Al 2 O 3 .13H 2 O, 4CaO.Al 2 O 3 .SO 3 .12H 2 O (monosulfate) and hydrated samples of high alumina and Portland cements are investigated. For the synthetic samples 27 Al quadrupole coupling constants (C Q ), asymmetry parameters (η) of the electric field gradient (EFG) tensors, and isotropic chemical shifts (γ( 27 Al)) are determined with high accuracies from computer simulations of the complete manifolds of spinning sidebands (ssb's) for the satellite transitions or of the central transition (centerband and ssb's). Simulations of the ssb manifolds show that some of the samples cannot be characterized by a single set of C Q and η values, but rather by a distribution of these values. The ranges of the distribution in C Q and η are estimated by summation of simulated ssb patterns for the satellite transitions employing sets of slightly different C Q and η values. The quadrupole coupling parameters are shown to be an important supplement to γ( 27 Al) in the characterization of structurally different Al sites and for identification of the individual aluminates in 27 Al MAS NMR spectra of hydrated cement samples. Linear correlations between C Q and the mean bond angle deviations from ideal tetrahedry symmetry, as well as between C Q and a calculated estimate for the geometrical dependency of the EEG tensor are reported, for the anhydrous calcium aluminates. These correlations allow assignment of the C Q values for CaO.2Al 2 O 3 , 12CaO.7Al 2 O 3 , and 3CaO.Al 2 O 3 , all of which contain two nonequivalent AlO 4 tetrahedra in the asymmetric unit

Oxygen-17 NMR study of water exchange on gadolinium polyaminopolyacetates [Gd(DTPA)(H2O)]2- and [Gd(DOTA)(H2O)]- related to NMR imaging

Abstract: The water-exchange rate constants for the [Gd(DTPA)(H[sub 2]O)][sup 2[minus]] and [Gd(DOTA)(H[sub 2]O)][sup [minus]] complexes as determined by variable-temperature [sup 17]O NMR are respectively k[sub ex[sup 298]] = (4.1 [+-] 0.3) x 10[sup 6] and (4.8 [+-] 0.4) x 10[sup 6] s[sup [minus]1]. The activation volumes ([Delta]V[sup [double dagger]]), measured up to 200 MPa, are 12.5 [+-] 0.2 and 10.5 [+-] 0.2 cm[sup 3] mol[sup [minus]1], indicating an extreme dissociative activation mode for the water-exchange mechanism. The mechanism (D) is further supported by the large activation enthalpies ([Delta]H[sup [double dagger]] = +52.0 [+-] 1.4 and +48.8 [+-] 1.6 kJ mol[sup [minus]1]) and positive entropies ([Delta]S[sup [double dagger]] = +56.2 [+-] 5 and +46.6 [+-] 6 kJ mol[sup [minus]1] K[sup [minus]1]) obtained for the [Gd(DTPA)(H[sub 2]O)][sup 2[minus]] and [Gd(DOTA)(H[sub 2]O)][sup [minus]] complexes, respectively, In the first coordination sphere of these two monoaqua complexes there is only space for one water molecule, and thus the bond breaking of the coordinated water should be the rate-determining step. The [sup 17]O relaxation contribution of the second coordination sphere. All these considerations lead to the conclusion that the effectiveness of [Gd(DTPA)(H[sub 2]O)][sup 2[minus]] and [Gd(DOTA)(H[sub 2]O)][sup [minus]] as contrast agents in MRI is not limited bymore » the relatively low water-exchange rates but by T[sub 1m], the longitudinal relaxation time of water protons in the first coordination sphere.« less

Photochemical synthesis and structure of a 3-dimensional anionic polymeric network of an iron(II) oxalato complex with tris(2,2'-bipyridine)iron(II) cations

Abstract: The structures of single crystals of [bipyH] + °Fe III (ox) 2 (H 2 O) 2 ] - .H 2 O (1) and of a photoreaction product of 1, namely of single crystals of a 3-dimensional polymeric compound [Fe II (bipy) 3 ] 2+ n °Fe II 2 (ox) 3 ] n 2n- (2), where ox is oxalate and bipy is 2,2'-bipyridine, have been determined by X-ray diffraction. Crystal data: 1, monoclinic, I1a1.

Photophysical properties of rhenium(I) tricarbonyl complexes containing alkyl- and aryl-substituted phenanthrolines as ligands

Abstract: A number of complexes of the type Re(L-L)(CO)[sub 3py][sup +] have been prepared, where L-L is 1,10-phenanthroline or a phenanthroline derivative containing methyl or phenyl groups and py is pyridine. All of the complexes are highly emissive at room temperature in solution or at 77 K in a glass, and the room-temperature luminescence data are consistent with emission from a [sup 3]MLCT state. The emission maximum ranges from 510 to 548 nm in CH[sub 2]Cl[sub 2], depending on L-L, and a linear relationship between [lambda][sub max] and the electrode potentials for oxidation and reduction is evident. Lifetimes in acetonitrile are of the order of several microseconds at room temperature (1.6-13 [mu]s), and emission quantum yields are very high (0.17-0.29). Results of photophysical measurements performed at low temperature indicate the presence of two unequilibrated emitting states, a [sup 3]MLCT and a [sup 3]LC (ligand-centered) state. Time-resolved spectra have established that the [sup 3]LC state is the longer-lived of the two and gives a structured spectrum similar to that of the uncoordinated ligand L-L. Both states show a dependence on the substitution pattern, and the contribution of each is uncoordinated ligand L-L. Both states shown a dependence on the substitution pattern, andmore » the contribution of each is determined by the particular L-L. Trends in the room-temperature data may also be accounted for by invoking a multistate model: however, the states are in thermal equilibrium under these conditions.« less

A dimeric calcium siloxide lightly stabilized by ammonia ligands

Abstract: The reaction of calcium granules with Ph 3 SiOH in an ammoniacal-toluene solution at 40 o C produces the complex [Ca 2 (OSiPh 3 ) 4 (NH 3 ) 4 ].0.5C 7 H 8 (1), and reaction of compound 1 with thf at room temperature yields [Ca(OSiPh 3 ) 2 -(thf)] n (2). These two compounds were characterized by IR and 1 H, 13 C, and 29 Si NMR spectroscopy, DSC, and TGA, and the structure of complex 1 was determined by single-crystal X-ray crystallography. The molecule consist of a dimeric calcium motif with one terminal and three μ 2 -bridging triphenylsiloxide ligands

Synthesis, characterization, and crystal structures of M(DO3A) (M = Fe, Gd) and Na[M(DOTA)] (M = Fe, Y, Gd)

Abstract: Macrocyclic amino carboxylate (DOTA and DO3A, where DOTA is 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane and DO3A is 1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane) complexes of Gd(III) and Fe(III) have been synthesized, characterized, and evaluated for use as potential contrast agents for magnetic resonance imaging (MRI). X-ray single-crystal analyses reveal four nitrogens and three oxygens coordinated to the iron in both Na[Fe(DOTA)][center dot]5H[sub 2]O and Fe(DO3A)[center dot]3H[sub 2]O. None of the waters are coordinated to iron atoms; the former iron complex has an uncoordinated carboxylate arm. Magnetic susceptibility and Moessbauer data confirm that both of the Fe(III) complexes are high spin (S = 5/2) compounds. Enneacoordination about the metal in the crystallographically isostructural series Na[M(DOTA)(H[sub 2]O)][center dot]4H[sub 2]O (M = Gd, Y, Eu) involves the four nitrogen atoms, an oxygen from each carboxyl arm, and one water molecule. Gd(DO3A) has been crystallized as a novel hydrated complex [(Gd(DO3A))Na[sub 2]CO[sub 3]][sub 3][center dot]17H[sub 2]O in which each enneacoordinate Gd atom is coordinated to the four nitrogens and an oxygen from each carboxyl arm of the ligand, as well as two oxygens of the carbonate ion. No water molecule is coordinated to the Gd atoms in the crystal structure. The Gd(DO3A) and Gd(DOTA)-species are more effective water proton relaxation agents than themore » Fe(III) chelates.« less

Magnetic properties of an octanuclear iron(III) cation

Abstract: The magnetic properties of {[(tacn) 6 Fe 8 (μ 3 -O) 2 (μ 2 -OH) 12 ]Br 7 (H 2 O)}Br.H 2 O, Feg, tacn=1,4,7-triazacyclononane, a moleculecomprising eight iron(III) ions bridged by oxo and hydroxogroups, are reported. The magnetic susceptibility, both dc and ac, and the magnetization indicate that at low-temperature spin levels with 8

Ligand variation and metal ion binding specificity in zinc finger peptides

Abstract: Three metal binding peptides with coordination sites Cys 2 His 2 , Cys 3 His, and Cys 4 have been prepared and their metal binding properties characterized. The peptides are based on a zinc finger consensus sequence and have the sequences ProTyrLysCys 4 ProGluCys 7 GlyLysSerPheSerGlnLysSerAspLeuValLysXaa 20 GlnArgThrYaa 24 ThrGly (Xaa=Yaa=His; Xaa=His, Yaa=Cys; Xaa=Yaa=Cyn).

Structure, spectroscopic and magnetic properties of rare earth metal(III) derivatives with the 2-formyl-4-methyl-6-(N-(2-pyridylethyl)formimidoyl)phenol ligand

Abstract: The compounds [ML[sub 2](H[sub 2]O)[sub 4]](ClO[sub 4])[sub 3][center dot]4H[sub 2]O ((1)M), where M is a trivalent rare earth metal and L the bidentate liquid 2-formyl-4-methyl-6-(N-(2-pyridylethyl)formimidoyl)phenol, have been synthesized. Single crystals of [GdL[sub 2](H[sub 2]O)[sub 4]](ClO[sub 4])[sub 2]Cl[center dot]2.75H[sub 2]O have been obtained, and its crystal structure has been solved. This compound crystallizes in the monoclinic system, space group P2[sub 1]/c. The structure consists of [GdL[sub 2](H[sub 2]O)[sub 4]][sup 3+] cations, perchlorate and chloride anions and noncoordinated water molecules. The Gd atom is surrounded by eight oxygen atoms, four belonging to water molecules and the other four to the carbonyl and phenolic functions of two L ligands. The coordination sphere of Gd is very close to a perfect square antiprism. (1)Eu exhibits a strong luminescence in the solid state. The transition energies of the luminescence spectrum have been determined. The temperature dependences of the molar magnetic susceptibility [chi][sub M] for (1)M (M = Gd, Nd, Eu, Sm) have been measured. A perfect Curie law is observed for (1)Gd. The EPR spectrum reveals a zero-field splitting within the [sup 8]S[sub 7/2] ground state characterized by an axial parameter [vert bar]D[vert bar] = 4.0 [times] 10[sup [minus]2] cm[sup [minus]1]. [chi][sub M]T for (1)Ndmore » decreases from 1.64 cm[sup 3] K mol[sup [minus]1] at 300 K down to 0.8 cm[sup 3] K mol[sup [minus]1] at 4.2 K as the temperature T is lowered, due to the crystal-field splitting of the [sup 4]I[sub 9/2] free-ion state. For both (1)Eu and (1)Sm compound, the first free-ion excited states are thermally populated at 300 K; hence, their magnetic behaviors significantly deviate from the Curie law. The magnetic data have been satisfactorily interpreted in the free-ion approximation. For (1)Eu, an excellent agreement between optical and magnetic properties has been obtained. 29 refs., 7 figs., 3 tabs.« less

Synthesis, structure, and electronic spectroscopy of neutral, dinuclear gold(I) complexes. Gold(I)-gold(I) interactions in solution and in the solid state

Abstract: A series of neutral, dinuclear gold(I) complexes containing phosphine and thiolate ligands have been synthesized and characterized by elemental analysis and by 1 H and 31 P NMR and UV-visible spectroscopy. Crystal structures of two of the complexes are reported. [Au 2 (p-tc) 2 (dppb)] (4) crystallizes in the triclinic space group P1 (Z=2) with unit cell dimensions a=10.757(2) A, b=13.177(2) A, c=14.630(3) A, α=82.23(1) o , β=83.16(1) o , and γ=75.42(1) o ; R=0.0286. [Au 2 (p-tc) 2 (dpppn)] (5) crystallizes in the monoclinic space group P2 1 /n (Z=4) with unit cell dimensions a=12.007(1) A, b=25.292(5) A, c=13.421(2) A, andβ=94.92(1) o ; R=0.0432

Ring-opening reactions of the anticancer drug carboplatin : NMR characterization of cis-[Pt(NH3)2(CBDCA-O)(5'-GMP-N7) in solution

Abstract: We have studied reactions of the anticancer drug (Pt(NH 3 ) 2 (CBDCA-O,O'] (carboplatin, «Paraplatin», where H 2 CBDCA is cyclobutane-1,1-dicarboxylic acid) with nitrate, phosphate, chloride, and 5'-guanosine monophosphate (5'-GMP) in aqueous solution at 310 K using 1 H, 15 N, ( 1 H, 15 N], and 31 P NMR spectroscopy. A structure for cis-(Pt(NH 3 ) 2 (CBDCA-O)(5'-GMP)] is proposed which accounts for the inequivalence of all six cyclobutane ring protons in this complex.

Biomimics of vanadium bromoperoxidase : vanadium(V)-schiff base catalyzed oxidation of bromide by hydrogen peroxide

Abstract: A six-coordinatc vanadium(V) complex, LVO(OEt)(EtOH), where H 2 L=N-(2-hydroxyphenyl)salicylideneamine, is shown to be a catalyst precursor in the oxidation of bromide by hydrogen peroxide in DMF solution. The oxidized bromine specie is trapped by organic substrate and, by product analysis, is shown to be a two-electron-oxidized species, rather than a bromine radical. The bromination reaction is quantitative with respect to hydrogen peroxide. The acid dependence of the stoichiometry of the bromination reaction is etablished. Using UV/vis spectrophotometry, 51 V NMR spectroscopy, and kinetic data

Rigid nonlabile polyoxometalate cryptates [ZP5W30O110](15-n)- that exhibit unprecedented selectivity for certain lanthanide and other multivalent cations

Abstract: Reaction of aqueous solutions of the heteropolytungstate [NaP[sub 5]W[sub 30]O[sub 110]][sup 14[minus]] with various cations Z[sup n+] in a sealed container at 120-180[degrees]C for several hours leads to cation exchange and the formation of [ZP[sub 5]W[sub 30]O[sub 110]][sup (15-n-)] when Z = Ca[sup 2+], trivalent Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, or Bi, or tetravalent Ce or U. No exchange occurred for Z = Cd[sup 2+], Sn[sup 2+], Tl[sup 3+], Ce[sup 3+], Pr[sup 3+], or Th[sup 4+] at temperatures up to 180[degrees]C. The lanthanide selectivity appears to be determined by ionic radius. The new complexes, which are hydrolytically stable from pH 0 to pH 9--10, are characterized by cyclic voltammetry, IR spectra, and [sup 31]P NMR spectra (single line in all cases except when Z = Y[sup 3+] which shows [sup 2]J([sup 31]P-O-[sup 89]Y) = 1.6 Hz); [delta] = [minus]68.1 to +17.6 ppM. The lanthanide-induced shifts of the [sup 31]P nucleus are predominantly pseudocontact in origin. The [sup 183]W NMR spectrum of the Eu[sup 3+] derivative has four doublets at +62.5, [minus]201.7, [minus]209.5, and [minus]297.5 ppM (1:2:1:1) consistent with the C[sub 5v] structure found for the Na derivative. The emission spectrum of the Eumore » derivative and the ESR spectrum of the Gd derivative are reported. The low proton relaxivity of the latter complex (ca. 1.0 mM s[sup [minus]1] at 300 MHz) is consistent with the presumed structure in which Gd[sup 3+] is inaccessible to solvent water. 25 refs., 7 figs., 3 tabs.« less

Electronic structure of the "molecular light switch" bis(bipyridine)dipyrido[3,2-a:2',3'-c]phenazineruthenium(2+). Cyclic voltammetric, UV/visible and EPR/ENDOR study of multiply reduced complexes and ligands

Abstract: The chelate ligand dipyrido[3,2-a:2',3'-c]phenazine (dppz), its 11,12-dimethylderivative dmdppz, and corresponding complexes with [Ru(bpy) 2 ] 2+ were studied in multiply reduced states by low-temperature cyclic voltammetry and UV/vis and EPR spectroscopy. The (dm)dppz ligands are reduced in two reversible steps. Higly resolved EPR and 1 H-ENDOR spectra of the intermediate anion radicals were obtained and analyzed.

Synthesis and high-resolution optical spectroscopy of bis[2-(2-thienyl)pyridinato-C3,N'](2,2'-bipyridine)iridium(III)

Abstract: The synthesis and high-resolution absorption and luminescence spectra at cryogenic temperatures of [Ir(thpy)[sub 2]bpy][sup +](thpyH = 2-(2-thienyl)pyridine, bpy = 2, 2'-bipyridine) are reported. In the crystalline host lattices [Rh(ppy)[sub 2]bpy]-PF[sub 6] and [Ir(ppy)[sub 2]bpy]PF[sub 6](ppyH = 2-phenylpyridine) the lowest excited states around 18,900 cm[sup [minus]1] correspond to spin-forbidden [sup 3][pi]-[pi]* transitions on the thpy[minus], whereas the next higher excited state is assigned to an Ir [yields] bpy charge-transfer transition at 21,700 cm[sup [minus]1]. This metal to ligand charge-transfer ([sup 3]MLCT) state is found to be strongly dependent on the surroundings. In liquid environments it can shift below the [sup 3][pi]-[pi]* state, which remains at about the same energy. Evidence for a mixing of charge-transfer character into the [sup 3][pi]-[pi]* excited states is provided by the measured oscillator strengths, the luminescence lifetimes, the vibronic structure, and by a comparison with the properties of analogous cyclometalated Rh[sup 3+] complexes.

Synthesis, crystal structure, and magnetic properties of (.mu.-bipyrimidine)(cyanato)copper(II) and -(thiocyanato)copper(II) complexes

Abstract: The synthesis, structure, and spectroscopic and magnetic properties of three 2,2'-bipyrimidine (C 8 H 6 N 4 , bpm)-containing copper(II) complexes of formula [Cu 2 (bpm)(NCO) 4 ] n (1), (Cu(bpm)(NCS) 2 ] n (2) and [Cu 2 (bpm)-(NCS) 4 ] n (3) are reported. Compounds 1 et 2 crystallize in the monoclinic system, space group C2/c and Z=4, with a=19.486, b=7.527, c=15.252A, β=137.8° for 1 and a=11.543, b=13.948, c=7.818A, β=93.26° for 2, whereas compound 3 is orthorhombic, space group Fddd, with a=12.811, b=22.473, c=24.259A, Z=16

Comparative study on the coordination chemistry of cobalt(II), nickel(II), and copper(II) with derivatives of salen and tetrahydrosalen: metal-catalyzed oxidative dehydrogenation of the carbon-nitrogen bond in coordinated tetrahydrosalen

Abstract: The salen complexes ML (M II =Cu, Ni, Co) and the corresponding tetrahydrosalen complexes M[H 4 ]L (M II =Cu, Ni) were prepared and characterized by their vis absorption and EPR spectra, by their magnetic moments, and by cyclic voltammetry in acetonitrile

Equilibrium and Kinetic Studies of Lanthanide Complexes of Macrocyclic Polyamino Carboxylates

Abstract: The stability constants (log K[sub LnL]) of lanthanide complexes of macrocyclic polyamino carboxylates, LnL (where Ln is Ce[sup 3+], Gd[sup 3+], and Lu[sup 3+] and L is DO3A = 1,4,7,10-tetraazacyclododecane-1,3,7-triacetic acid and HP-DO3A = 10-(hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid), have been determined at 25.0 [plus minus] 0.1[degree]C and [mu] = 0.1 ((CH[sub 3])[sub 4]NCl). The stability constants of lanthanide complexes of DO3A increase with the decreasing ionic radii or increasing charge density of Ln[sup 3+]. For L = HP-DO3A, the stability constant of GdL is greater than that of CeL; however the stability constants of GdL and LuL are similar. The protonation constants, K[sub H] (M[sup [minus]1]), of the LnL complexes have been determined at 25.0 [plus minus] 0.1[degree]C and [mu] = 1.0 (NaCl), and the values are 18 [plus minus] 3 for Ce(DO3A), 115 [plus minus] 8 for Gd(DO3A), 11 [plus minus] 1 for Ce(HP-DO3A), and 240 [plus minus] 25 for Gd(HP-DO3A). The rates of acid-assisted dissociation of the protonated complexes, ML(H), have been measured at 25.0 [plus minus] 0.1[degree]C and [mu] = 1.0 (NaCl). Direct, k[sub d] (s[sup [minus]1]), and acid-assisted, k[sub 1] (M[sup [minus]1] s[sup [minus]1]), dissociation rate constants are k[sub d] = (1.8 [plus minus] 0.8) [times] 10[sup [minus]3]more » and k[sub 1] = (1.12 [plus minus] 0.04) [times] 10[sup [minus]1] for Ce(DO3A) and k[sub d] = (1.4 [plus minus] 0.2) [times] 10[sup [minus]4] and k[sub 1] = (2.00 [plus minus] 0.04) [times] 10[sup [minus]3] for Ce(HP-DO3A). The rates of dissociation of the other complexes are first order in acid at low [H[sup +]], but the rates saturate at high [H[sup +]]. 40 refs., 5 figs., 3 tabs.« less

Synthesis and structural characterization of lanthanide(III) texaphyrins

Abstract: The synthesis and characterization of several lanthanide(III) texaphyrin complexes of 4, 5, 9, 24-tetraethyl-16, 17-dimethoxy-10, 23-dimethyl-13, 20, 25, 26, 27-pentaazapentacyclo[20.2.1.1 heptacosa]-1, 3, 5, 7, 9, 11(27),-12, 14, 16, 18, 20, 22(25), 23-tridecaene (2), 4, 5, 9, 24-tetraethyl-16, 17-bis((3-hydroxypropyl)oxy)-10, 23-dimethyl-13, 20, 25, 26, 27-pentaazapentacyclo-[20.2.1.1] heptacosa-1,3, 5, 7, 9, 11(27), 12, 14(19), 15, 17, 20, 22(25),-20, 25, 26, 27-pentaazapentacyclo[20.2.1.1] heptacosa-1,3, 5, 7, 9, 11(27), 12, 14, 16, 18, 20, 22(25), 23-tridecaene (30), respectively, are reported. Single crystals suitable for X-ray diffraction were obtained for the La(III) complex 3, the Gd(III) complexes 9 and 37, the Eu(III) complex 36, and the Lu(III) complex 22, by dissolving the respective complex in MeOH/CHCl[sub 3] and layering with diethyl ether. The five lanthanide(III) texaphyrin complexes all crystallize in the triclinic space group, P[bar 1] (No. 2), with Z = 2. The complexes are characterized by five-coordination from the texaphyrin, a coordinated methanol molecule on one side and at least one symmetrically bidenate NO[sub 3][sup [minus]] ion opposite the methanol. The 10-coordinate La(III) complex 3 has two bidentate NO[sub 3][sup [minus]] ions on the same side of the macrocycle. The europium(III) and gadolinium(III) texaphyrins 36 and 37 are structurally isomorphous and are 9-coordinate species with a bidentatemore » NO[sub 3][sup [minus]] ion and a methanol molecule on the top side of the macrocycle. On the other hand, the lutetium(III) texaphyrin is 8-coordinate with only a single bidentate NO[sub 3][sup [minus]] ion chelated on the [open quotes]top[close quotes] side of complex. In an unusual case of disorder, the gadolinium(III) texaphyrin 9 has both 9- and 10-coordinate species present in the solid state. The geometry of the 9-coordinate species is like that found in 36 and 37, while the 10-coordinate Gd(III) species similar to the La(III) species 3.« less

Methane vs benzene activation via transient tantalum amido-imido complex tert-Bu3SiNHTa(:NSiBu3-tert)2: structure of (py)2MeTa(:NSiBu3-tert)2

Abstract: Addition of Me 3 TaCl 2 to 20 equiv to LiNHSi t Bu 3 in hexanes resulted in CH 4 and ( t Bu 3 SiNH)Me 2 Ta=NSi t Bu 3 (1, 63%) Thermolysis of 1 in benzene resulted in disproportionation, but in pyridine and THF, L 2 MeTa(=SSi t Bu 3 ) 2 (L=py, 2(py) 2 , 68%; THF 2 13%) and MeH were produced

Insulin mimetic peroxovanadium complexes: preparation and structure of potassium oxodiperoxo(pyridine-2-carboxylato)vanadate(V), K2[VO(O2)2(C5H4NCOO)].2H2O, and potassium oxodiperoxo(3-hydroxypyridine-2-carboxylato)vanadate(V), K2[VO(O2)2(OHC5H3NCOO)].3H2O, and their reactions with cysteine

Abstract: The complexes potassium oxodiperoxo(pyridine-2-carboxylato)vanadate(V), K 2 [VO(O 2 ) 2 (C 5 H 4 NCOO)].2H 2 O (1), and potassium oxodiperoxo(3-hydroxypyridine-2-carboxylato)vanadate(V), K 2 [VO(O 2 ) 2 (OHC 5 H 3 NCOO)].3H 2 O (2), were prepared, and their structures were determined: 1, Cc

Alkane oxidation catalyzed by .mu.-oxo-bridged diferric complexes: a structure/reactivity correlation study

Abstract: A series of μ-oxo-bridged diferric complexes, Fe 2 OL 4 X n (ClO 4 ) m , containing two bidentate nitrogen ligandes (L=2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine, and 1,10-phenanthroline) and one exchangeable coordination site (X=H 2 O, Cl, CH 3 CO 2 , CF 3 CO 2 ) per iron were synthenized and characterized by their 1 H NMR, electronic, and Raman spectra and by their magnetic properties. 1 H NMR data showed that X=H 2 O or X=bridging CH 3 CO 2 were labile ligands while X=Cl was much less exchangeable. Complex 3D (L=4,4'-dimethyl-2,2'-bipyridine, X=CF 3 CO 2 , n=2, m=2) was characterized crystallographically

Crystal structure and magnetic properties of two nitronyl nitroxide biradicals and of their copper(II) complexes

Abstract: The crystal structures and the magnetic properties of two nitronyl nitroxide biradicals, NITPh(4-NIT)=1,4-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-dihydro-1H-3-imidazol-2'-yl)benzene (I) and NITPh(3-NIT)=1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-dihydro-1H-imidazol-2-yl)benzene (II), and of two novel adducts with Cu(hfac) 2 , [Cu(hfac) 2 ] 4 NITPh(4-NIT) (III) and [Cu(hfac) 2 ] 3 NITPh(3-NIT) (IV), where hfac=hexafluoroacetylacetonate, are reported