Square planar structures complex ions with

Ni" forms square-planar bis-complexes with the amidate anions of L-Val, L-Phe, and L-Pro. The structure of bis(Gly)-bis(imidazole)nickel(ii) has been reported and the configuration around the metal atom is cis-O(carboxyl), cis-N(amine), cis-N(imidazole). Tetra- and penta-peptide complexes of nickel(ii) consume oxygen in neutral solutions as the metal ion catalyses peptide oxidation to give a number of products, including amides of amino-acids and peptides, oxo-acids, and C02- ... 

The other example is the chloro complexes of platinum(II) and palla-dium(II), which also have square-planar structures (13). The PtCl42-and the PdCl42 complexes have identical structures, with the same bond lengths, and form isostructural solutions. By using the difference between their normalized diffraction curves contributions from interactions not involving the metal atoms can be eliminated and precise structures can be derived, not only for the complex but also for the structure beyond the first coordination sphere of the metal ion. 

The VSEPR model for predicting structure does not work for complex ions. However, we can safely assume that a complex ion with a coordination number of 6 has an octahedral arrangement of ligands, and that complexes with two ligands are linear. On the other hand, complex ions with a coordination number of 4 can be either tetrahedral or square planar there is no reliable way to predict which will occur in a particular case. 

Electron spin resonance spectroscopy (ESR) has been used by several research groups to characterize the local structure of CTB-Cu (iO, 11, 13). For the neat Ionomer, both Isolated and dimeric copper complexes, as shown In Fig. 9, have been reported. Fig. 10 compares the ESR spectra for CTB-Cu and Blend 1, PSVP/ CTB-Cu (1 1). The strong signal near 3160 G was due to Isolated copper Ions with a square planar structure as In Fig. 9a. The measured g-Lande factor and hyperflne Interaction parameters were gy" 2.320, g = 2.059, A = 145 6, and 30 + 5 G, which agreed with those reported for Isolated Cu(II) Ions In model compounds (14). 

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