Metal rotations about

Templeton demonstrated that the two isomers of [W(CO)(dppe)(dtc) (T7 -MeOC=C=CHPh)] interconvert (Tc —120°) on the NMR time scale. Molecular orbital (MO) calculations on the model complex [WH4(CO)(i7 -H0C=C=CH2)] provided the rotational profile shown in Fig. 2 characterized by a low barrier to rotation of the allenyl fragment with respect to the metal (rotation about the z axis) and a higher barrier for rotation about the Cp-Cy double bond. The former process possesses two energy minima... 

C. Intertriangular Metal Rotations About Pseudo Threefold Axes... 

Studies have been made on the rate of growth of oxide films on different crystal faces of a metal using ellipsometric methods. The rate was indeed different for (100), (101), (110), and (311) faces of copper [162] moreover, the film on a (311) surface was anisotropic in that its apparent thickness varied with the angle of rotation about the film normal. 

Drilhng. Glass is dtiUed with carbide or bonded-diamond dtiUs under a suitable coolant such as water or kerosene. Other drilling processes include a metal tube rotating about its axis (core drilling), an ultrasonic tool in combination with an abrasive slurry, or an electron beam. Tolerances less than 0.1 mm are readily obtained with diamond-core drilling and, if required, holes smaller than 25 )J.m-dia can be made with the electron-beam method. 

The fdr studies reveal that the alkyl chains in SAMs of thiolates on Au(lll) usually are tilted 26-28° from the surface normal, and display 52-55° rotation about the molecular axis. This tilt is a result of the chains reestabUshing VDW contact in an assembly with - 0.5 nm S—S distance, larger than the distance of - 0.46 nm, usually quoted for perpendicular alkyl chains in a close-packed layer. On the other hand, thiolate monolayers on Ag(lll) are more densely packed owing to the shorter S—S distance. There were a number of different reports on chain tilt in SAMs on Ag(lll), probably owing to different amounts of oxide, formed on the clean metallic surface (229,230,296,297). In carefully prepared SAMs of alkanethiolates on a clean Ag(lll) surface, the alkyl chains are practically perpendicular to the surface. 

NMR spectra show the ethene molecules to undergo a propeller type rotation about the metal-alkene axis the fluxionality is removed on cooling such rotation is not observed with coordinated C2F4, indicating a higher barrier to rotation, in keeping with the stronger Rh—C bonds [66]. 

H-NMR studies of oligocarbene Ru(II) complexes indicate a substantial barrier to rotation about the metal-carbene carbon and nitrogen-R bonds. This restricted rotation is thought to arise as a consequence of intramolecular non-bonding cis interactions of the carbene nitrogen-R substituents, and not because of any significant double bond character in ruthenium-carbene carbon (76). 

Inversion at sulfur (also selenium and, occasionally, tellurium) coordinated to Pt(II), and indeed to a number of other transition metal centers, e.g., W(0), Re(I), Rh(III), and especially Pt(IV), has been studied extensively over several decades (246). Observation of the kinetics of such processes is often complicated by concurrent changes elsewhere in the complex, for example by hindered rotation about C-S in the square-planar complexes [(XS)2Pt(p-SX)2Pt(SX)2]2 with X = C6F4H, CgF5, C6F4(4-CF3). Resolution of the observed kinetics here indicated barriers (AG ) of between 54 and 59kJmol-1 for inversion at coordinated sulfur, between 40 and 60 kJ mol-1 for the hindered rotation (247). 

Rotating-Disk Electrode, Study of the kinetics and mechanism of electrode processes under well-defined mass transport conditions is possible through use of methods of the rotating-disk electrode (RDE). The RDE consists of a disk of metal embedded in a cylindrical insulator (e.g., Teflon) holder (see Fig. 6.24). It is rotated about its center. Only the bottom end of the metal disk is exposed to the solution. 

Haymore (4) has pointed out that the noncyclic ligand has many degrees of freedom with respect to rotations about single bonds, whereas the cyclic analog has fewer since the ends are connected. Thus, the cyclic chelate should be greatly favored from an entropy consideration. If correct, this explanation allows one to postulate that the poor metal complexing properties observed for non-cyclic ethers is a result of small... 

A metal cylinder is mounted to rotate about a horizontal axis. This is called the drum. The end-to-end dimension is the width of print to be produced plus a generous tolerance. The drum in the copiers originally developed by Xerox Corporation was manufactured with a surface coating of amorphous selenium (more recently, ceramic or organic... 

The facility of 1H-azepines to form transition metal carbonyl complexes was realized soon after they were first synthesized. Variable temperature HNMR studies on the tricarbonyliron complex formed either by photolysis of 1-ethoxycarbonyl-l//-azepine with tricarbonyliron in THF, or by heating the azepine with nonacarbonyldiiron in hexane, demonstrated that it undergoes rapid reversible valence tautomerism and that there is considerable restricted rotation about the N—CO bond (B-69MI51600). The molecular geometry of the complex has been determined by X-ray analysis (see Section 5.16.2.2). 

These molecules are flexible because rotation about single bonds is free, so they can wrap themselves around a metal ion to obtain four comfortable donor-atom-to-metal links within five-membered rings. Nitrilotriacetic acid is easily synthesized industrially from ammonia, formaldehyde, and hydrocyanic acid (the Strecker synthesis) and therefore is potentially an inexpensive but effective chelating agent. 

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