Ligands square pyramidal

Figure 7.8 The structure of InCls " showing square-pyramidal (C4 ) geometry. The In-Clapex distance is significantly shorter than the In-Clbase distances and In is 59 pm above the basal plane this leads to a Clapex-In-Clbase angle of 103.9° which is very close to the theoretical value required to minimize Cl Cl repulsions whilst still retaining C4, symmetry (103.6°) calculated on the basis of a simple inverse square law for repulsion between ligands. [NEt4]2[TlCl5] is isomoiphous with [NEt4]2[InCl5] and presumably has a similar structure for the ardon.

Figure 19.5 The interconversion of trigonal bipyra-midal configurations via a square-pyramidal intermediate. Notice that the Li ligands, which in the left-hand tbp are axial, become equatorial in the right-hand tbp and simultaneously 2 of the L2 ligands change from equatorial to axial.

Complexes with mixed 0-and A -donor ligands such as edta and Schiff bases are well known and [Fe(edta)(H20)] and [Fe(salen)Cl] are examples of 7-coordinate (pentagonal bipyramidal) and 5-coordinate (square-pyramidal) stereochemistries respectively. 

The coordination number of Ni rarely exceeds 6 and its principal stereochemistries are octahedral and square planar (4-coordinalc) with rather fewer examples of trigonal bipyramidal (5), square pyramidal (5), and tetrahedral (4). Octahedral complexes of Ni arc obtained (often from aqueous solution by replacement of coordinated water) especially with neutral N-donor ligands such as NH3, en, bipy and phen, but also with NCS, N02 and the 0-donor dimethylsulfoxide. dmso (Me2SO). 

Mixed 6),Af-donor ligands such as Schiff bases are of interest in that they provide examples not only of square-planar coordination but also, in the solid state, examples of square-pyramidal coordination by dimerization (Fig. 28.6(b)). A similar situation occurs in the bis-dimethylglyoximato complex, which dimerizes by sharing oxygen atoms, though the 4 coplanar donor atoms are all nitrogen atoms. Copper(II) carboxylates are easily obtained by crystallization from aqueous solution or, in the case of the higher carboxylates, by precipitation with the appropriate acid from ethanolic solutions... 

The structures of several adducts can be rationalized on the basis [128] that in a 5-coordinate low-spin d8 tbp system, the acceptor ligands prefer to occupy an equatorial site (IrCl(CO)2(PPh3)2) whereas a 7r-donor prefers an axial site. In a square pyramidal situation, it is weakly bonded acceptors that prefer the apical position, e.g. (IrCl(S02)(C0)(PPh3)2. 

The anionic pentafluorophenyls have square pyramidal structures but are evidently non-rigid in solution (19F NMR shows all ligands equivalent). The neutral adducts are also square pyramidal (apical C6F5, trans-L) [192],... 

A number of tertiary phosphine complexes with bulky ligands (Figure 3.80) have modified square pyramidal structures, examples being M(I)3Br2, Pt(II)3Br2 and Pd(III)3Br2 (all X-ray) [136]. 

With a tridentate ligand Au(terpy)Cl3.H20 has, in fact, AuCl(terpy)2"1" with weakly coordinated chloride and water while Au(terpy)Br(CN)2 has square pyramidal gold(III) the terpyridyl ligand is bidentate, occupying the axial and one basal position [124]. Macrocyclic complexes include the porphyrin complex Au(TPP)Cl (section 4.12.5) cyclam-type macrocyclic ligands have a very high affinity for gold(III) [125],... 

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