Terminal Coordination Research Articles

A general method for assembling (.mu.-oxo)bis(.mu.-carboxylato)diiron(III) complexes with labile terminal sites using a bridging dicarboxylate ligand

Structural and spectroscopic models of the (μ-oxo)bis(μ-carboxylato)diiron(III) center found in the marine invertebrate respiratory protein hemerythrin have been synthesized with a variety of facially coordinating tridentate ligands. In order to mimic the functions and the related diiron proteins ribonucleotide reductase and methane monooxygenase new model complexes are required having vacant or labile terminal coordination sites

Adsorption and electrooxidation of some simple organic molecules on rhodium(111) as probed by real-time FTIR spectroscopy: comparisons with platinum (111)

The electrooxidation pathways of seven simple organic molecules in 0.1 M HClO{sub 4} on ordered Rh(111) were examined by means of real-time sequences of FTIR spectra obtained during slow (2 mV s{sup {minus}1}) voltammetric sweeps. The reactants studied are formic acid, methanol, ethanol, acetaldehyde, ethylene glycol, glyoxal, and oxalic acid for concentrations between 0.05 and 0.5 M. High coverages ({theta} {ge} 0.4) of adsorbed CO are formed in most cases, as detected from a band at about 1880-1890 cm{sup {minus}1} at the most negative potentials ({minus}0.25 to +0.05 V vs SCE), which is replaced by a band at 2030-2040 cm{sup {minus}1} at more positive potentials. These two features are assigned to C-O vibrations, {nu}{sub CO}, associated with CO adsorbed in bridging and terminal coordination geometries, respectively. The former configuration is apparently engendered by hydrogen coadsorption. For cyclic voltammograms between {minus}0.25 and +0.6 V, the adsorbed CO formed by dissociative reactant chemisorption only undergoes complete electrooxidation during the reverse portion of the potential sweep, at ca. 0.4V. This inability to remove adsorbed CO on ordered Rh(111) appears to be at least partly responsible for the observed weakly electrocatalytic properties of this surface for organic electrooxidations. The production of CO{sub 2} evenmore » from formic acid, which occurs readily on Pt(111), does not commence in earnest on Rh(111) until CO is removed during the reverse scan. The electrooxidation of the other reactants on ordered Rh(111) is largely limited to the production of small amounts of CO{sub 2}, although some electrooxidation of acetaldehyde (but not ethanol) to acetic acid is detected. These results are compared with corresponding reactions on ordered Pt(111) and for the electrooxidation of solution CO.« less

Approximating the Steiner Tree in the Placement Process

By simulating the movement of a node in a tree, an iso-distance error graph (IDEG) which contains connection errors generated by replacing a Steiner tree with its equivalent non-Steiner tree is developed. The IDEG is used to estimate how well various types of non-Steiner trees function as a Steiner tree in the placement of components on a printed wiring board (PWB). To reduce connection errors in the IDEG and pursue computational efficiency, a row-based tree family in which the tree length is primarily dependent on the terminal coordinates of each row, is constructed. Then, based on the analysis of the error distribution on the IDEG, the row-based trees and the spanning tree are compared in terms of their approximation to the Steiner tree.

Guanidine ligands in transition metal complexes. Terminal and bridging coordination of arginine, canavanine, and methylguanidine to platinum (II)

Guanidine ligands in transition metal complexes. Terminal and bridging coordination of arginine, canavanine, and methylguanidine to platinum (II)

Potential multifunctional anti-cancer metal complexes. I. Synthesis and x-ray structural studies of some dinuclear rhodium(II) carboxylate complexes with diamine-substituted acridine ligands in terminal coordination positions

The preparations are reported of [Rh(RCO 2) 2L] 2 [where R = CH 3, C 2H 5, and CH 3OCH 2; L = 6-chloro-2-methoxy-9-[2(NR′ 2)ethyl]aminoacridine (R′ = H, CH 3)]. X-ray structural studies have been carried out on two of the compounds [ R = C 2H 5, R′ = H, (1); R = CH 3, R′ = CH 3, ( 2)]. Compound 1 is monoclinic, space group C2/ c, with a = 20.864(11), b = 15.736(4), c = 14.402(4) Å, β = 93.14(4)°, V = 4721 Å 3, and Z = 4; 2 is monoclinic, space group P2 1/ n, a = 8.861(2), b = 23.089(10), c = 12.014(2) Å, β = 105.84(2)°, V = 2365 Å 3, and Z = 2. Both compounds comprise the standard dinuclear rhodium(II) carboxylate unit with the substituted acridine ligands coordinated to rhodium in the axial positions, via the NH 2 group nitrogen in 1 and the N(CH 3) 2 nitrogen in 2. The dimethyl substitution on the tertiary amine group in 2, and an associated conformational change in the diamine chain, result in an increased separation of the acridine ligand from the metal centre. There is a pronounced acridine base stacking in 1 but not in 2.

Iron-sulphur dimers with bidentate phenolate-thiolate terminal ligands

[Fe 2S 2L 2] 2− complexes 1– 4 having phenolate—thiolate terminal coordination by the ligands L1– L4 have been prepared and studied by a range of physical methods. Their electronic spectra show strong absorption in the region 390–420 nm attributable to 0 → Fe charge-transfer. 1H NMR for 1– 4 demonstrates the diagnostic pattern of dipolar broadened resonances with negative isotropic shifts for α-methylene and meta protons and positive shifts for ortho and para protons. 57Fe Mössbauer spectra of the solid complexes display quadrupole doublets with large splittings (0.68–0.99 mm s −1) typical of chelated [2Fe2S] 2+ and isomer shifts (0.28–0.31 mm s −1) only slightly raised from those for [Fe 2S 2(SR) 4] 2−. First reduction processes occur at potentials in the range −1.35 to −1.47 V and are more reversible than those for [Fe 2S 2(OAr) 4] 2−. On chemical reduction, 1 and 3 give EPR signals having g av = 1.929 and 1.928, respectively, attributable to the corresponding trianions. Reduced 2 and 4, however, more readily give the g av, ⋍ 1.92 type signals characteristic of solvent-induced modification of the coordination. The effectiveness of phenolate coordination in decreasing g 2 and g 3 for [2Fe2S] + suggests that the low g values of the Rieske proteins result from oxygenous ligation.

New non-molecular poly-adamantanoid crystal structures of Cd(SAr)2. Zeolitic Cd4(SC6H4Me-4)8, and solvated Cd8(SC6H4Br-4)16(DMF)3(DMF = dimethylformamide), in relation to the molecular structures of aggregates in solution

Crystalline Cd4(SC6H4Me-4)8 contains a three-dimensionally non-molecular zeolitic lattice of vertex-linked adamantanoid cages, while crystalline Cd8(SC6H4Br-4)16(DMF)3(DMF = dimethylformamide) contains a derived two-dimensionally non-molecular lattice with linkages interrupted by CdSAr and Cd(DMF)3 terminal co-ordination: Cd n.m.r. spectra of Cd(SC6H4X-4)2(X = H, F, Cl, Br, Me) in DMF solution indicate the existence of temperature-dependent equilibria between large and small molecular aggregates.

Substituted osmium clusters containing labile ligands. The preparation, characterisation, and some reactions of [Os3H(OR)(CO)9(MeCN)](R = H, Me, Et, or Ph) and the isomers of [Os3H(SR)(CO)9(MeCN)](R = Me, Et, or Ph); the crystal and molecular structure of [Os3H(SPh)(CO)9(PEt3)

The compounds [Os3H(ER)(CO)10](E = O, R = H, Me, Et, or Ph; E = S, R = Me, Et, or Ph) react with Me3NO in MeCN to produce the acetonitrile derivatives [Os3H(ER)(CO)9(MeCN)]. For ER = OR there is only one such compound formed which has the acetonitrile ligand attached to one of the bridgehead osmium atoms. These clusters react with P(OMe)3 to form two isomers of the compounds [Os3H(OR)(CO)9{P(OMe)3}], both of which have the phosphite ligands co-ordinated to one of the bridgehead osmium atoms. For the case ER = SR three isomers of the acetonitrile derivative are formed, two with the acetonitrile ligand attached to the unique osmium atom and one as in the alkoxy case. These isomers react with phosphorus donor ligands to produce isomers of the compounds [Os3H(SR)(CO)9(PR′3)], where the phosphorus donor ligand is bound to the same osmium atom as the acetonitrile in the starting material. The compounds [Os3H(OR)(CO)8-{P(OMe)3}2] were prepared from reaction of [Os3H(OR)(CO)10] with 2.2 equivalents of Me3NO followed by P(OMe)3. All the products have been characterised by i.r. and 1H n.m.r. spectroscopy and structural assignments made. The structure of [Os3H(SPh)(CO)9(PEt3)] was confirmed by X-ray analysis and shown to consist of a riangle of Os atoms with one edge bridged by both a hydride and a phenylthiolato ligand. The triethylphosphine ligand occupies a ‘pseudo’ axial site on one of the Os atoms involved in bridge bonds. The nine carbonyl groups all occupy terminal co-ordination sites.

Synthesis and characterization of [Fe 2OX 6] 2tau; (X = Cl, Br, I) complexes. Crystal and molecular structure of (BzPh 3P) 2 [Fe 2OCl 6

Improved and simple methods for the preparation of [Fe 2OX 6] 2tau; (X = Cl Br I) complexes are described. The complexes were obtained in high and purified yields as the BzPh 3P + or R 4N + salts. An X-ray crystallographic study of (BzPh 3P) 2 [Fe 2OCl 6] revealed a structure for the complex anion in which the two iron atoms are linked by gdot; -oxo bridge and the terminal coordination sites are occupied by the chloride ligands. Mcolon; ssbauer and infrared spectra for the complexes are reported.

Linear trinuclear coordination compounds with 4-ethyl-1,2,4-triazole. Structure and magnetic properties

The synthesis and characterisation of a series of linear trinuclear coordination compounds containing 4-ethyl-1,2,4-triazole (Ettrz) are presented. The crystal structure of the first linear trinuclear Mn(II) compound [Mn 3(Ettrz) 6(H 2O 6](CF 3SO 3) 6 was determined at room temperature. The compound crystallizes in the space group P 3 1 c, with lattice constants a = b = 14.545(2) Å and c = 20.072(3) Å. In the linear trimer the metal ions are linked by three 1,2-bidentate coordinating triazole ligands. The manganese ions are coordinated octahedrally. For the terminal metal ions the octahedral coordination is completed by H 2O molecules. The coordination distances are: MnN 2.24 Å and MnO 2.19 Å. The Co(II), Ni(II) and Zn(II) compounds are X-ray isomorphous with the Mn(II) compound. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J values of −0.6 cm −1, −14.7 cm −1 (Ising approximation) and −9.4 cm −1, respectively. An expression for the magnetisation and magnetic susceptibility of a linear Mn(II) trimer is presented. The Cu(II) and Cd(II) compounds, with composition [M 3(Ettrz) 9(H 2O) 3](CF 3SO 3) 6(H 2O) x, are also likely to be trinuclear. The terminal coordination sites in these compounds appear to be occupied by three monodentate coordinating triazole ligands and three water molecules. Surprisingly, the magnetic exchange in the Cu compound appears to be ferromagnetic.

Effect of oxide and sulfide bridging ligands on the structure and magnetic properties of tetranuclear cyclopentadienyl chromium clusters

The indicated framework has Cr-Cr single bonds ~average 2.830(3) A) and Cr--Fe single bonds (average 2.758(3) A). Cr--S (average 2.270(5) A) and Fe--S (average 2.218(4) ~) ~3_ sulfide bridges are found above each face of the tetrahedron and each chromium atom is bound to a C5H5 ligand while the iron atom is bound to the OOCCMe~ group. The monodentate terminal coordination of this group was unexpected (Fe-~, 1.896(10) A; C-O, 1.32(1) and 1.25(1) ~) and leads to a 16-electron environment for Fe and the paramagnetism of (V) (~ef = 2.81 BM).

An optimal solution to a wire-routing problem

A wire-routing problem which arises commonly in the layout of circuits for very large scale integration is discussed. Given the coordinates of terminals u 1, u 2,…, u n of one component and ν 1, α 2, …, ν n of another, the problem is to lay out n wires so that the ith wire connects ν i to ν i , and adjacent wires are separated at least by some fixed distance. The solution with minimum wire length is characterized, and an optimal algorithm which constructs it is presented.

Spectroscopic study of the structures of [M2(η-C5H5)2(CO)n(CNR)4 –n] complexes (n= 1 or 2; M = Fe or Ru) in solution. The structure of cis-[(η-C5H5)(OC)Fe(µ-CO)(µ-CNPri)Fe(CNPri)(η-C5H5)] in the solid state

Various [M2(η-C5H5)2(CO)n(CNR)4 –n] complexes have been prepared [n= 2, M = Fe, R = Ph, p-ClC6H4CH2, PhCH2, p-MeC6H4CH2, p-MeOC6H4CH2, D(+)-Ph(Me) CH, Me, Et, Prn, Bun, Prl, C6H11, or But; M = Ru, R = Pri; n= 1, M = Fe, R = Me, Et, or Pri]. In solution, they exist as rapidly interconverting equilibrium mixtures of isomers; where n= 2, the RNC ligands are less likely to adopt bridged as opposed to terminal co-ordination as R is varied along the above series. The isomer distribution is a consequence of electron-withdrawing R favouring µ-CNR co-ordination and, less importantly, the more bulky R favouring terminal CNR. Where n= 1, only one predominant isomer is observed in solution. The crystal and molecular structure of cis-[Fe2(η-C5H5)2(COt)-(CNRt)(COµ)(CNRµ)](R = Pri) has been determined by an X-ray diffraction study. It has been solved by the heavy-atom method from photographic data and refined by full-matrix least squares to R= 0.103 for 807 non-zero unique reflections. Crystals are monoclinic with space group P21/c(no. 14), Z= 4, a= 13.881 ± 0.015, b= 10.755 ± 0.010, c= 15.262 ± 0.015 A, and β= 112.5 ± 0.1°.