Showing papers in "Inorganic Chemistry in 1992"

Bond valence sum analysis of metal-ligand bond lengths in metalloenzymes and model complexes

Abstract: Bond valence sums (BVS's) have been calculated for a series of model complexes for important metalloenzymes. Values calculated from crystallographic distances predict the correct oxidation state of the metal center in a wide range of structural types. Many of the selected complexes have previously been studied by X-ray absorption spectroscopy, and first-shell metal-ligand bond distances have been determined by analysis of extended X-ray absorption fine structure (EXAFS)

NMR study of solution structures and dynamics of lanthanide(III) complexes of DOTA

Abstract: The low-temperature limiting NMR spectra ( 1 H and 13 C) of 12 LnDOTA - complexes (Ln=La, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu) support the presence in solution of two isomeric forms. The relative abundance of the two isomers changes markedly along the lanthanide series with no apparent trend; NMR data suggest that the structure of the major isomer of LaDOTA - corresponds to that one of the minor isomer of the corresponding Lu 3+ complex

Aqueous uranium complexes. 2. Raman spectroscopic study of the complex formation of the dioxouranium(VI) ion with a variety of inorganic and organic ligands

Abstract: The Raman spectra of the aqueous dioxouranium(VI) ion have been measured as a function of ligand and uranyl concentrations at various constant pH values. The ligands investigated were F[sup [minus]], Cl[sup [minus]], Br[sup [minus]], SO[sub 4][sup 2[minus]], HSO[sub 4][sup [minus]], NO[sub 3][sup [minus]], ClO[sub 4][sup [minus]], CH[sub 3]CO[sub 2][sup [minus]], and C[sub 2]O[sub 4][sup 2[minus]]. A linear correlation between the frequency of the O=U=O symmetrical stretching vibration ([nu][sub 1], cm[sup [minus]1]) and the average number [bar n] of ligand coordinated equatorially to the central uranium atom in the given species has been established for the above-mentioned ligands according to the following equation: [nu][sub 1] (cm[sup [minus]1]) = -A[bar n] + 870, where A is a characteristic coefficient (cm[sup [minus]1]) representing the shift in the [nu][sub 1] band for the addition of each ligand to the uranyl(VI) center relative to 870 cm[sup [minus]1] for UO[sub 2][sup 2+](aq). Except for the case of ClO[sub 4][sup [minus]] (A = -15 cm[sup [minus]1]), the values of A are positive and vary in the range 0-15. The preceding equation was derived earlier for OH[sup [minus]] anions with A = 21.5 [+-] 1.0 cm[sup [minus]1]. Results obtained elsewhere for CO[sub 3][sup 2[minus]] also fit this equationmore » with A = 19.0 [+-] 1.0 cm[sup [minus]1]. This linear correlation provides a convenient, nondestructive method of identifying the possible stoichiometry of uranyl(VI) complexes in solution and a means for estimating their stability fields with respect to ligand concentration and pH.« less

Activation of the trans geometry in platinum antitumor complexes. Synthesis, characterization, and biological activity of complexes with the planar ligands pyridine, N-methylimidazole, thiazole and quinoline. Crystal and molecular structure of trans-dichlorobis (thiazole)platinum(II)

Abstract: The presence of planar ligands in trans-[PtCl 2 (py) 2 ] (py=pyridine) greatly enhances the cytotoxicity of such species, with respect both to their corresponding cis isomer and also to trans-[PtCl 2 (NH 3 ) 2 ]. The cytotoxicity of trans-[PtCl 2 (py) 2 ] in murine tumor cell lines is equivalent to the anticancer drug cisplatin, cis-[PtCl 2 (NH 3 ) 2 ] (J. Med. Chem. 1989, 32, 2240)

Electronic absorption spectra of the iron(II) complexes of 2,2'-bipyridine, 2,2'-bipyrimidine, 1,10-phenanthroline, and 2,2':6',2''-terpyridine and their reduction products

Abstract: The iron(II) complexes [Fe(bpy) 3 ] 2+ (I), [Fe(phen) 3 ] 2+ (II), [Fe(phen) 3 ] 2+ (III), and [Fe(terpy) 2 ] 2+ (IV) (bpy, 2,2'-bipyrimidine; bpym, 2,2'-bipyrimidine; phen, 1,10-phenanthroline; terpy, 2,2':6'2''-terpyridine) were subjected to two (for IV) or three (for I-III) stepwise one-electron electrochemical reductions; the products were studied in situ by solution UV-vis-near-IR spectroscopy

Oxidation of ferrous ions by ozone in acidic solutions

Abstract: The oxidation of ferrous ions by ozone in acidic solutions of pD 0-2 was studied using a stopped-flow spectro-photometer. The reaction can be characterized as an oxygen atom transfer from O 3 to Fe 2+ . An intermediate product assigned to be the ferryl ion, FeO 2+ , was found and its UV-vis spectrum measured.

A kinetic investigation of the lanthanide DOTA chelates. Stability and rates of formation and of dissociation of a macrocyclic gadolinium(III) polyaza polycarboxylic MRI contrast agent

Abstract: The complexation of the gadolinium(III) ion by DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-teiracarboxylic acid) through the formation of an intermediate complex (stability constant K * =6.9×10 3 M -1 ) in which the metal ion is incompletely coordinated as shown by NMR spectroscopy. Dyes were used to measure the pH changes that take place during process. Between pH 4 and 6, the HDOTA 3- form is the kinetically active species (k f,HL =1.0×10 6 M -1 s -1 ) despite its low concentration

Chemical bonding in rutile-type compounds

Abstract: We present an ab initio study of the bonding in the rutile (TiO 2 ) structure, where the five members TiO 2 , VO 2 , CrO 2 , RuO 2 , and ZnF 2 are investigated by means of band structure calculations, from which we derive electron densities, densities of states, total energies, and structure factors. We present simple molecular orbital schemes in order to interpret the main features of the calculated densities of states. Our results show that a MX 6 cluster model (with M=Ti, Zn, V, Cr, or Ru and X=O or F) accounts only for part of the bonding mechanism

Electrocatalytic reduction of nitrite and nitrosyl by iron(III) protoporphyrin IX dimethyl ester immobilized in an electropolymerized film

Abstract: Thin polymeric films formed by anodic electropolymerization of an iron(III) protoporphyrin IX dimethyl ester complex, [Fe III (PP)Cl], on glassy-carbon or optically transparent SnO 2 electrodes are effective catalysts for the electroreduction of HONO/NO 2 - or NO to N 2 O, N 2 , NH 2 OH, and NH 3 . The yield of N 2 is enhanced in the compact environment of the redox polymer.

Synthesis, crystal structures, and coordination intercalation behavior of two copper phosphonates

Abstract: Two copper phosphonates, Cu(O 3 PCH 3 ).H 2 O and Cu(O 3 PC 6 H 5 ).H 2 O, have been synthesized and their structures determined. Cu(O 3 PCH 3 ).H 2 O is monoclinic: space group P2 1 /c, a=8.495 (4) A, b=7.580 (4) A, c=7.289 (4) A, β=90.08 (4) o , Z=4, V=469.4 (7) A 3 . Refinement with 683 observed reflections for which 1 ≥3σ(I) gave R=0.030 and R w =0.041

Water-soluble tris(hydroxymethyl)phosphine complexes with nickel, palladium, and platinum. Crystal structure of [Pd{P(CH2OH)3}4].cntdot.CH3

Abstract: The large-scale synthesis of the water-soluble phosphine P(CH 2 OH) 3 (1) from either PH 3 or [P(CH 2 OH) 4 ]Cl is described. Treatment of [MX 2 (COD)] (M=Pt or Pd; X=Cl, Br, or I; COD=cycloocta-1,5-diene) with 1 gives the corresponding [MX 2 {P(CH 2 OH) 3 } 2 ] (2-7) complexes which are soluble in water, methanol, or dmso but insoluble in most common organic solvents

Ab initio study of superalkalis. First ionization potentials and thermodynamic stability

Abstract: The equilibrium geometries and fundamental frequencies of the Li 2 F + , Li 2 F, Na 2 Cl + , Na 2 Cl, Li 2 O, Li 3 O + , Li 3 O, Li 2 S, Li 3 S + , Li 3 S, Na 2 O, Na 3 O + , Na 3 O, Li 3 N, Li 4 N + , Li 4 N, Li 3 P, Li 4 P + , and Li 4 P species were calculated at MP2-FULL/6-31+G *

Electronic coupling in cyano-bridged ruthenium polypyridine complexes and role of electronic effects on cyanide stretching frequencies

Abstract: The spectroscopic and electrochemical properties of a series of polynuclear complexes containing cyano-bridged ruthenium polypyridine units are consistent with a valence-localized model. In all the Ru(II) forms, the lowest metal-to-ligand charge-transfer (MLCT) states are localized on N-bonded moieties. The photophysical properties at 298 and 77 K indicate that efficient intercomponent energy-transfer processes from C-bonded to N-bonded chromophoric units take place. The mixed-valence forms of these complexes show low-energy absorption bands which are assigned to metal-to-metal charge-transfer transitions involving C-bonded Ru(II) and N-bonded Ru(III) centers. The resonance Raman spectrum of [NC-Ru[sup II](bpy)[sub 2]-CN-Ru[sup III](bpy)[sub 2]-CN][sup 2+] under near-resonance conditions with the Ru(II) [yields] Ru(III) charge-transfer band shows enhancement of the bridging cyanide stretching as expected for this type of electronic transition. In the infrared spectra the number of cyanide stretching bands supports the valence-localized model. For the representative [NC-Ru[sup II](bpy)[sub 2]-CN-Ru[sup III](bpy)[sub 2]-CN][sup 2+] complex, three CN stretches (one bridging, two terminal) are observed. Time-resolved infrared measurements for the MLCT excited state of [NC-Ru[sup II](bpy)[sub 2]-CN-Ru[sup II](bpy)[sub 2]-CN][sup +] are reported. The excited-state IR spectrum shows features similar to those of the chemically prepared mixed-valence dimer, [NC-Ru[sup II](bpy)[sub 2]-CN-Ru[sup III](bpy)[sub 2]-CN][sup 2+], strongly suggesting that valence delocalization is not significant inmore » the excited state. The electronic factors affecting the frequency of the bridging cyanide are analyzed by examining the behavior of the mixed-valence ions [M-NC-M[prime](bpy)[sub 2]-CN-M][sup 6+/4+] and [NC-M[prime](bpy)[sub 2]-CN-M][sup 3+/2+] (M = [Ru(NH[sub 3])[sub 5]][sup 2+/3+]; M[prime] = Ru[sup II], Os[sup II], Re[sup I]).« less

Photophysical properties of hexanuclear copper(I) and silver(I) clusters

Abstract: The spectroscopic properties, including emission spectra and lifetimes, absorption and diffuse reflectance spectra and excitation spectra, of the hexanuclear copper(I) and silver(I) clusters Cu6(mtc)6 (1), Ag6(mtc) (2), and Ag6(dtc)6 (3) (mtc = di-n-propylmonothiocarbamate, dtc = di-n-propyldithiocarbamate) are reported. At room temperature 1 exhibits a strong single emission (e.g., in toluene λem max = 725 nm, τ = 1.0 μs) , while at 77 K each of these is a bright emitter (spectral properties: 1 in toluene, λem max = 762 nm, τ = 20 μs; 2 in toluene, λem max = 607 nm, τ = 131 μs; 3 in toluene, λem max = 550 nm, τ = 21 μs). In analogy to previous assignments in tetranuclear Cu(I) clusters, the emission bands in the octahedral (MI)6 clusters are assigned to spin-forbidden transitions from triplet excited states which are mixed d -> s and LMCT (ligand to metal charge transfer) in character modified by metal-metal interactions.

Ferromagnetically coupled gadolinium(III)copper(II) molecular material

Abstract: The compound Gd 2 (ox) [Cu(pba)] 3 [Cu(H 2 O) 5 ]-20H 2 O (1), where ox stands for oxalato and pba for 1,3-propylenebis(oxamato), has been synthesized. 1 crystallizes in the monoclinic system, space group C2/m. The lattice parameters are a=21.18(7) A, b=21.098 (2) A, c=15.079 (1) A, and β=92.06 (2) o , with Z=4. The crystal structure consists of layers of double-sheet polymers separated by water molecules

Comparison of the crystal structures of tris heterocyclic ligand complexes of ruthenium(II)

Abstract: The structures of [Ru(bpy)[sub 3]](PF[sub 6])[sub 2] (bpy = 2,2[prime]-bipyridine) and [Ru(bpm)[sub 3]](PF[sub 6])[sub 2][center dot]CH[sub 3]CN (bpm = 2,2[prime]-bipyrimidine) have been determined by single-crystal X-ray diffraction. [Ru(bpy)[sub 3]](PF[sub 6])[sub 2] crystallized in the hexagonal space group. [Ru(bpm)[sub 3]](PF[sub 6])[sub 2][center dot]CH[sub 3]CN crystallized in the triclinic space group. Ru-N bond distances in [Ru(bpy)[sub 3]][sup 2+] were 2.056 (2) [angstrom] and average 2.067 (4) [angstrom] in [Ru(bpm)[sub 3]][sup 2+]. Other bond distances and angles lead to the conclusion that the structures of the [Ru(bpy)[sub 3]][sup 2+] and [Ru(bpm)[sub 3]][sup 2+] cations are basically the same.

A new nickel(II) cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) complex covalently attached to tris(1,10-phenanthroline)ruthenium(2+). A new candidate for the catalytic photoreduction of carbon dioxide

Abstract: A bifunctional supramolecular complex Ru(phen) 2 (phen-cyclam-Ni)(ClO 4 ) 4 (6) (phen-cyclam=1-(1,10- phenanthrolin-5-ylmethyl)-1,4,8,11-tetraazacyclotetradecane) has been newly synthesized, and its spectropic, redox properties, and catalytic behavior in the photoreduction of CO 2 have been examined.

.beta.-Halogenated-pyrrole porphyrins. Molecular structures of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetramesitylporphyrin, nickel(II) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetramesitylporphyrin, and nickel(II) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin

Abstract: The X-ray structures of the β-substituted-pyrrole, its nickel(II) complex (NiTMOBP), and the nickel(II) derivative are reported. The synthesis of the free base H 2 TPFPOBP is also described. All these molecules are nonplanar, displaying saddle-shaped conformations

Hypochlorous acid decomposition in the pH 5-8 region

Abstract: The decomposition of hypochlorous acid in the neutral pH region was studied in 1.0 M NaClO 4 from 15 to 50 o C. The pK a of HOCl was also determined under these conditions. Hypochlorous acid has a maximum decomposition rate at pH 6.89. A mechanism for the decomposition of HOCl is proposed involving Cl 2 O.H 2 O and ClO 2 - as intermediates

Copper(II)-catalyzed oxidation of catechol by molecular oxygen in aqueous solution

Abstract: The oxidation of catechol by molecular oxygen in the presence of catalytic amounts of copper(II) ions has been followed by use of a Clark-type oxygen electrode and spectrophotometric methods at 25.0 o C and with the ionic strength maintained at 1.0 M (KNO 3 )

Molecular mechanics calculations of transition-metal complexes

Abstract: A molecular mechanics force field appropriate for the modeling of Cu(II), Ni(II) (S = 1), Co(III), Fe(III), Cr(III), Zn(II), and Rh(III) complexes with amine, carboxylate, pyridine, and thia ether ligands is presented in its entirety. The parameters comprising the force field were determined by matching a large number of strain-minimized structures with their corresponding crystal structures. Within the force field, the only parameters that were altered from one system to another were the strain-free bond length and the force constant of the metal-ligand bond. The calculations indicate that some corrections for electronic effects have to be applied in order to obtain a consistent force field.

Mono- and dinuclear zinc(II) complexes of biological relevance. Crystal structures of [L2Zn](PF6)2, [L'Zn(O2CPh)2(H2O)], [L'2Zn2(.mu.-OH)2](ClO4)2, and [L'2Zn2(.mu.-OH)(.mu.-CH3CO2)2](ClO4).cntdot.H2O (L = 1,4,7-triazacyclononane, L' = 1,4,7-trimethyl-1,4,7-triazacyclononane)

Abstract: The macrocycle 1,4,7-triazacyclononane (C 6 H 15 N 3 ; L) reacts with Zn(II) ions in methanolic solution forming the 2:1 species [L 2 Zn] 2+ . The crystal structure of [L 2 Zn](PF 6 ) 2 (1) has been determined. Crystal data: space group C2/c, a=9.719 (2) A, b=16.312 (3) A, c=15.017 (3) A, β=92.04 (3) o , V=2379.3 (8) A 3 , and Z=4.

Toward artificial metallopeptidases: mechanisms by which platinum(II) and palladium(II) complexes promote selective, fast hydrolysis of unactivated amide bonds in peptides

Abstract: Certain platinum(II) and palladium(II) complexes attached to the sulfur atom of cysteine, S-methylcysteinc, and methionine in peptides and in other amino-acid derivatives promote, under relatively mild conditions, selective hydrolysis of the unactivated amide hond involving the carhoxylic group of the amino acid anchoring the metal complex.

Iron octaethyltetraazaporphyrins: synthesis, characterization, coordination chemistry, and comparisons to related iron porphyrins and phthalocyanines

Abstract: This paper describes the synthesis and characterization of a series of iron octaethyltetraazaporphyrin complexes and a comparison of these substances to related iron porphyrins and phthalocyanines. Experimental evidence provided by magnetic susceptibility measurements, 1 H NMR, EPR, and Mossbauer spectroscopies, cyclic voltammetry, and/or X-ray crystallography indicates the tetraazaporphyrin ligand is a stronger a donor and π acceptor than is a porphyrin ligand

Olefin epoxidation and alkane hydroxylation catalyzed by robust sulfonated manganese and iron porphyrins supported on cationic ion-exchange resins

Abstract: Robust sulfonated manganese and iron porphyrin supported on poly(vinylpyridinium) polymers have been used as catalysts in olefin epoxidation and alkane hydroxylation by iodosylbenzene. The metalloporphyrins are attached to protonated or methylated poly(vinylpyridine) polymers by the coordination of one pyridine unit, thus providing a proximal effect, and by additional interactions of the porphyrin sulfonato groups with the polymer pyridinium units. The best catalysts are the complexes containing halogen atoms at the pyrrole [beta]-positions. In all these oxygenation reactions manganese porphyrins are better catalysts than the corresponding iron complexes. From comparative studies with another ion-exchange resin without a potential axial ligand, it can be noted that the concept of the proximal effect is a key factor in metalloporphyrin-catalyzed reactions, not only for soluble complexes but also for supported catalysts.

Hexakis(acetato)oxotetrazinc, a well-tailored molecular model of zinc oxide. An experimental and theoretical investigation of the electronic structure of Zn4O(acetate)6 and ZnO by means of UV and x-ray photoelectron spectroscopies and first principle local density molecular cluster calculations

Abstract: A thorough investigation of the electronic structure of Zn 4 O(acetate)a and ZnO has been used to test the hypothesis that the former compound is a well-tailored molecular model of the latter solid. First principle local density molecular cluster calculations relative to Zn 4 O(acetate) 6 and ZnO indicate that the tetrahedral arrangement of four Zn atoms around the central oxygen present in the title compound is a very good model of the oxygen chemical environment in ZnO