Trigonal pyramidal complexes

To date all the symmetries adopted by transition metal ions in melts are very simply related to the octahedron and tetrahedron. The T and O centers discussed in detail in Section 4.4 have not had specific geometries assigned to them but they are probably distorted versions of and Oh, respectively. In the same way that the dodecahedral symmetry can arise from double of flattened tetrahedra (Section 4.3 and Ref. 196), so a T Oh transformation through a trigonal pyramid (Cgy) and a trigonal bipyramid ( >3 ) is easily visualized (Fig. 48). One might then expect O-center spectra to resemble those of Ni(II) in D h symmetry and indeed a considerable likeness is apparent between the spectrum of a known complex (Fig. 49D),(27d that of the proposed NiCla (Fig. 34), and the O-center spectra depicted in Fig. 33. Unfortunately, no trigonal pyramidal complexes of Ni(II) appear to be known. 

Tin(II) chlorides are similarly complex (Fig. 10.5). In the gas phase, SnCh forms bent molecules, but the crystalline material (mp 246°, bp 623°) has a layer structure with chains of comer-shared trigonal pyramidal SnClsl groups. The dihydrate also has a 3-coordinated structure with only I of the H2O molecules directly bonded to the Sn (Fig. I0.5c) the neutral aquo complexes are arranged in double layers with the second H2O molecules interleaved between them to form a two-dimensional H-bonded network... 

X-ray crystallographic analysis of Fe[0Si(0 Bu)3]3THF revealed a distorted tetrahedral geometry (toward a trigonal pyramid) at the Fe center. Related alkyl siloxide complexes of Fe(III) with dimeric structures, [Fe(OSiMe3)3]2 and [Fe(OSiEt3)3]2, have been reported by Schmidbaur and Richter [98]. 

In (362), the cation is distorted trigonal pyramidal with the axial positions occupied by one S atom and the central P atom of the P3 ligand. In the anion the nickel center is bonded to six S-donors of three xanthate ligands. Upon reaction with dppe an approximately square planar NiS2P2 complex results.938 A similar coordination geometry is found for the two complexes (361a,b) 939,940... 

In their pursuit of modeling Type I copper proteins, Kitajima et al. reported112 a rare, tetrahedrally coordinated complex (105), which displayed an EPR spectrum consistent with the presence of the unpaired electron in the dz2 orbital.1 They also isolated a square-pyramidal DMF adduct (complex (106)). They were successful in providing structural proof of a copper(II) complex (trigonal pyramidal) with C6F5S -coordinated complex (107), with CuN3S chromo-phore.113 The X-ray analysis (poor data set) of a closely similar complex with Ph3CS as the... 

The structure of a copper(I) complex [Cu(L)][BPh4] (trigonal pyramidal three pyridyl groups in the trigonal plane and tertiary amine at the apex ligand as that in complex (4)) was also determined.29 The structure of complex [Cu2(L)(MeCN)2][BF4]2 (ligand as that in complex (179))169 and complex [Cu(L)][BPh]4 (ligand as that in complex (220)) 09 were also reported. 

Tolman and co-workers investigated the oxygenation behavior of a copper(I) complex (790) (trigonal pyramidal) and demonstrated the formation of end-on peroxo-dicopper(II) species.58... 

In the bifunctional radiopharmaceuticals, Tc and Re complexes that are suitable for coupling to antibodies are almost square-pyramidal oxo complexes of tetradentate ligands, as mentioned earlier. Spies et al. [65] recently studied the syntheses and structures of rhenium complexes with a tetradentate NS3 tripod ligand 2, 2,, 2"-nitrilotris(ethanethiol) (l in Fig. 9) as an interesting alternative to the oxo complex. Such ligands could lead to weakly polar, trigonal-bipyramidal complexes in which the metal atom is more strongly shielded than in the square-pyramidal oxo complexes. Schemes for the syntheses... 

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