Bond lengths of metals

A potentially important probe of the bonding in alkynyl complexes, and, in particular, the extent of M—> CCR 7r-backbonding, is to determine how the M—C=C—R fragment is structurally perturbed by the oxidation or reduction of the complex. The M—C=0 bond lengths of metal-carbonyl complexes are extremely sensitive to oxidation state, with M-C bonds lengthening and C=0 bonds contracting as the oxidation state of the metal increases (and, concomitantly, M - CO rr-backbonding decreases) (154). 

Of course, this simple picture constitutes only a crude approximation and should be valued only for showing that the completion of a metal layer around C o with 32 Ba-atoms is, indeed, plausible. More precise predictions would have to rely on ab initio calculations, including a possible change in bond lengths of Qo> such as an expansion of the double bonds of C o due to electron transfer to the antibonding LUMO (as was found in the case of QoLii2[I2,131T... 

Transition-metal complexes of the thionylimide anion exhibit characteristic vibrations in the regions 1260-1120, 1090-1010 and 630-515 cm , which are assigned to Oas(NSO), Os(NSO) and <5(NSO), respectively. X-ray structural data for several M-NSO complexes reveal N-S and S-O bond lengths of ca. 1.46 0.04 A indicative of double bond character in both of these bonds. 

White tin, on the other hand, has metallic properties. Each atom in the crystal forms six bonds, four with length 3.016 A and two with length 3.175 A. When I first made a thorough study of bond lengths in metals (9) I interpreted these values as showing the valence to be 2.44 later (5) the value was recalculated to be 2.50, and then 10) to be 2.56. This value is explained by use of the metallic orbital. The atoms Sn+, Sn, and Sn- have the structures... 

If the thiomalate ligand is not present in excess, it is completely displaced. When gold binds, the M ions are displaced in the gold metal ratio of 3 2, which suggests bidentate coordination. EXAFS data shows AuS2 coordination with Au—S bond lengths of 229 pm [20, 103]. In the presence of both cadmium and zinc, zinc is preferentially displaced which is possibly a consequence of thermodynamics as Zn7MT and CdyMT react at comparable rates. 

The structural information on the alkaline earth metal derivatives of the heavier group 14 elements is markedly limited. The first silyhnagnesium compound to be structurally characterized was (Me3Si)2Mg (DME), which is monomeric with distorted tetrahedral geometry of the Mg atom and Si-Mg bond length of 2.630(2)... 

Fig. 20. The variation in strain energy, V, for various conformations of [M(18-crown-6)]n+ complex, as a function of strain-free M-0 bond length. The M—O bond lengths of various metal ions are indicated on the M-0 bond length axis. The curves are for the planar D3d (+-+-+-), half-buckled (+-+--), and buckled (++-+ +-) conformers shown in Fig. 21, and for the complex of the open chain complex of pentaethylene glycol. The calculations were carried as described in the text, and in Refs. (4 and 60). Redrawn after Ref. (60). 

Fig. 25. The effect of metal ion size on porphyrin ruffling. Very small metal ions [P(V) with an ideal P-N bond length of 1.84 A and low-spin Ni(II) with an ideal Ni-N length of 1.90 A in (a) and (b)) cause extensive S4 ruffling. Metal ions close to the right size (M-N = 2.035 A) give planar structures [Zn(II) in (c)]. Metal ions that are too large [Pb(II) at (d) with ideal Pb-N of 2.39 A] are extruded from the plane of the porphyrin and cause it to dome. For clarity, substituents on the porphyrins such as phenyl or ethyl groups have been omitted. Modified after Ref. (77).

The carbides with the NaCl structure may be considered to consist of alternating layers of metal atoms and layers of semiconductor atoms where the planes are octahedral ones of the cubic symmetry system. (Figure 10.1). In TiC, for example, the carbon atoms lie 3.06A apart which is about twice the covalent bond length of 1.54 A, so the carbon atoms are not covalently bonded, but they may transfer some charge to the metal layers, and they do increase the valence electron density. 

TaCl2(PMe3)2]2(U-Cl)2 (13). The short metal-metal bond length of 2.710(2)A has been interpreted as a formal metal-metal double bond on the basis of molecular orbital arguments (13,14). An unusual feature of this complex is that it reacts with molecular... 

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