Silver square planar complexes

Phthalocyanine is a divalent ligand with a geometry appropriate for forming a four-coordinated square-planar complex and was thought ideal for generating an Au(II) species. The action of AuBr on molten 1,3-diiminoisoindoline in the absence of solvent indeed yields a neutral gold phthalocyanine (63). The EPR spectra of the complex in 1-chloronaphthalene at 77 K clearly showed the presence of Au(II), a d9 ion. The g value is 2.065, comparable to 2.042 for copper and 2.093 for silver phthalocyanine (64, 80). 

Having seen that structural predictions are very difficult, we will now turn to the choice of transition metal. We have already seen the dependence of the coordination mode in square planar complexes on various factors and noticed the preference for polymeric chains with the silver(I) complexes owing to the linearly coordinated silver centre. Chiu et al. [325] reported on a series of arylmethylene and methyl wingtipped bis-carbene complexes of silver(I) (polymeric bridging) and palladium(II) (monomeric chelating). Carbene transfer to palladium was achieved in DMSO since solubility in CHjCfj was very poor. 

In terms of its coordination chemistry, the silver(I) ion is typically characterized as soft . Although originally believed to only bind ligands in a linear arrangement, it was soon shown that it can adopt a variety of coordination environments, the most common one being a four-coordinate tetrahedral geometry. Square-planar complexes are not rare, and various silver(I) cluster complexes also contain three-and five-coordinate sUver(I) ions. 

As in the case of the ammonia complexes the number of amine molecules which can be coordinated depends on the electronic configuration of the metal concerned. With the Ag+ ion two groups are coordinated to give a linear structure about the silver atom which apparently uses jj hybrid orbitals. On the other hand Pd and Pt ions show a coordination number of four and their bonding orbitals are of the dsp -hyhnd type, so they yield square-planar complexes with amines. The Ni +, Cr +, and Co ions, along with many others, have a coordination number of six and so form octahedral complexes with amines. 

Further work has been reported on the synthesis of complex phosphine-based ligand systems via the coordination-promoted self-assembly of simpler phosphines bearing appropriate functional groups. A series of ligands bearing one to four mem-substituted diphosphinoarene groups attached to a central core has been prepared and self-assembled via coordination to silver. Also reported is a route to the pyrene-appended phosphine (122), which, when coordinated to rhodium in a square-planar complex via the P and S centres, forms a self-assembled tweezer system in which two nearby pyrenyl... 

Silver has square planar coordination in Ag[meso-Me6[14]ane](N03)2 (Ag-N 2.16 A) with distant axial oxygens (Ag-O 2.81 A) the complex has... 

Fluoride complexes of silver(III) are exemplified by the purple-red Cs2KAgF6 (elpasolite structure, octahedral Ag3+ paramagnetic with /x = 2.6/ub). Yellow MAgF4 (M = Na, Rb, K) and XeF AgF4 are diamagnetic and probably square planar [65],... 

The longest established silver(III) complexes are the red to brown bi-guanides, like the ethylene bis(biguanide) shown in Figure 4.14 persulphate oxidation of Ag+ in the presence of this ligand gives a silver(III) complex with essentially square planar coordination. 

A review on this oxidation state includes some kinetic data. One of the simplest examples is the diamagnetic square planar ion Ag(OH)4, easily prepared in less than millimolar concentrations by electrochemical oxidation of a silver anode in strong base. It is stable for a few hours in 1 M NaOH, and forms orange complexes with tri- and tetrapeptides which resemble... 

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