Square-planar configuration

Gold Compounds. The chemistry of nonmetallic gold is predominandy that of Au(I) and Au(III) compounds and complexes. In the former, coordination number two and linear stereochemistry are most common. The majority of known Au(III) compounds are four coordinate and have square planar configurations. In both of these common oxidation states, gold preferably bonds to large polarizable ligands and, therefore, is termed a class b metal or soft acid. 

The preparation and structural characterization were successful for the complexes (L)Au(C=C)3, with L = PMe3 or Me2PhPCH2 and R = Ph. The two compounds are colorless and diamagnetic, and have the expected square-planar configuration of the gold(m) center.120... 

The three Pt(II) atoms have a square planar configuration and are each coordinated through bridging diphenylphosphido ligands, without any metal-metal bonding interaction. 

This class of compounds, which includes 1,4,8,11-tetraazacyclotetradecane (otherwise known as cyclam), consists of a cyclic macrostructure containing four central nitrogen atoms. These nitrogens form a complex with a transition metal, holding it in the center of a square-planar configuration. Often, the cavity size formed by the macrocycle will stabilize one oxidation state of the transition metal over others due to the size of the metal center... 

A Photodehydro- We have seer in Chapter 11 that the [Pg.895]

Based on the similarity of the spectra it was proposed that oxidation had not occurred at the porphyrin ring but rather at the silver ion. The sample was found to be diamagnetic, as expected for a ds square planar configuration. Cyclic voltametry with AgnOEP also confirmed that the oxidation occurred at the central metal and the measured AgmOEP/Ag1IOEP couple was 0.44 V.574... 

In 1893 a third important regularity was observed by Nikolai Semenovich Kumakov (1860—1941).107 While investigating the substitution of ligands by thiourea and thioacetamide, Kumakov found that replacement occurs with all the ligands of the cis compound but only with the acid radicals of the trans compound (Scheme 2). Since the two isomers yield different products, this reaction, known as Kumakov s reaction or Kumakov s test, may be used to differentiate cis from trans isomers of dipositive platinum or palladium. Kumakov s classic reaction played a crucial role in Werner s proof of the square planar configuration of Pt11 and in Chemyaev s formulation of the trans effect. 

Bis(propylenediamine) complexes with the four nitrogen atoms in the square planar configuration usually adopt the tram methyl (equatorial) configuration253-255 (15), but in Pt(.R-pn) + one methyl group is axial (16).256... 

Although square-planar configuration is customarily considered classical for v/c-dioximate of nickel(II), attempts have been made repeatedly over the years for preparing the above complexes in other configurations also. By employing weakly polar solvents and some other variations, success has been claimed in the preparation of mono(dioxime) complexes of nickel(II).42,43 The dichloro-bis(l,2-cyclohexanedione dioximato)nickel(II) has been shown to have an octahedral vie structure.44 Examples of tris(dioxime) complexes of transition metals in general45"18 and of bivalent atoms40,47 in particular are rare and structural details of only a tris(dioxime) complex of cobalt(III) are known.48 In a more recent publication,49 the crystal structure of tris(l,2-cyclohexanedione dioximo)nickel(II) sulfate dihydrate has been elucidated. 

Proton NMR spectra of some V1" and Cr1" complexes indicated a facial octahedral configuration with all three sulfur atoms cis.234 More recent 13C and 19F NMR data on a wide range of transition metal complexes of fluorinated monothio-/ -diketones support the assignment of cis square-planar and facial octahedral geometries.235,236 X-Ray structural data have established the cis square-planar configuration for a Pd" and a Pt" complex237 and four Ni" complexes,238,239 the tetrahedral configura-... 

Configurations intermediate between a square and a tetrahedron are known. An important example is Wilkinson s catalyst, Rh(PPh3)3Cl. Four-coordinate rhodium(I) would normally adopt a square planar configuration, but the bulk of the phosphine ligands causes a distortion from coplanarity of the four donor atoms, increasing the distances between the PPh3 groups. The conflict of interest between the central... 

As part of a search for other ligands capable of adopting a square-planar configuration about a metal atom and thus potentially able to form stacked units our attention was drawn to the ligand H2P2052- (diphosphonate), usually abbreviated pop. Platinum complexes of this ligand - in particular [Pt2 (pop) i,] l - have already been subject to interesting studies of their luminescence, electronic, Raman and infrared spectra (12-161. Our initial objectives were to try to incorporate [Pt v(en)2X2]2+ (en =... 

Figure 17.5.7(e) shows the structure of the Z-shaped binuclear [Xe-Au-F-Au-Xe]3+ ion and its immediate anion environment in [Au2Xe2F] [SbF6]3. The Au atom is coordinated by one Xe atom and three F atoms in a square-planar configuration, with Au-Xe bond length 264.7 pm. 

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