Silver metal-ligand bonding

Crystal structures of 1-methylcytosine and 1-methylthymine complexes have been determined as aids to the understanding of Ag binding to polynucleotides. In (1-methylcytosine)silver(I) nitrate, a centrosymmetric dimer was present in which the N heterocycles were bridged by two Ag" ions. Within these dimers, there were two strong metal-ligand bonds, (Ag—N = 222.5, Ag—O = 236.7 pm) and an eight-membered ring (8) resulted. 

Metal-ligand bond lengths in [Ag(9S3)2] show the danger of reasoning too closely from ionic radii. Silver-sulfur distances (average 2.72 A Table 1) fall well short of those expected from the sum of ionic radii (2.99 A) [104]. This difference reflects appreciable covalency in the Ag-S interaction as well as (to a lesser extent) conformational constraints imposed by 9S3. Clearly arguments from ionic radii... 

The chloride ions that appear outside the brackets represent chloride anions that balance the positive charge on the coordination compound. When a coordination compound dissolves in water, the ligands (inside the brackets) remain bound to the metal cation, but the nonligands (outside the brackets) exist as individual ions. These chloride ions precipitate in the presence of silver ions. The chloride ions inside the brackets, which are ligands bonded to the cobalt center, do not precipitate as AgCl. 

Substituted tris(pyrazolyl)borates were recently employed as silver(l) ligands due to their ability to yield heat and air stable metal complexes. Two research groups have prepared very similar sUver(l)-tris(pyrazolyl)borate compounds for catalyzing carbene insertion chemistry. Both systems require electron-withdrawing groups on the tris(pyrazolyl)borate ligands to stabilize the sUver(l) complexes and enhance the electrophilicity of the putative silver-carbenoids (129,130). Dias et al. (129) found that, with CF3 substitutes, a complex of [HB(3,5-(Cp3)2pz)3] Ag(thf) could activate ethyl diazoacetate (EDA) to react with different C X (X = Cl, Br, 1) bonds to afford either C—X bond insertion products or 1,1-hydrochlorination products. At the time of this writing, this unique reactivity was reported only with a silver catalyst (Fig. 27). 

Complexes of S(XSO)2 with silver(I) and zinc(II) where the ligand bonds to the metal through either oxygen or nitrogen atoms have been sttucturally characterized. 

Ten /13-TePh ligands adopt an unsymmetrical pattern of one shorter , one longer and one intermediate Cu-Te bonding distances. These distances (2.552(3)-2.708(3) A) are, expectedly, shorter than their Ag-Te counterparts, and reflect the difference between the ionic radii of the two metals.This contraction of the metal-tellurium bonding distances is reflected in the overall size of the cluster frame. Thus, for comparison, the Te4 - Te7 distance is 12.29 A in 5 and 12.95 A in 3a similarly the telluride ligands Tel5-- Tel6 are 7.72 A apart in the copper complex whereas they are separated by 8.81 A in the silver cluster 3a. 

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