Piano stool structures

The structure of these complexes is not regular and has been described as 4 3 (C ) piano stool , which is obtained by slight distortion of a capped trigonal prism (C2d). 

The synthesis of (80) from [Ircp Cl2]2 and 2,2 -biimidazole has been detailed.119 The X-ray structure of (80) shows the expected three-legged piano-stool arrangement round the Ir center. 

The complex [(cp )IrCl(2,2 -bpy-4,4 -COO(CH2)3-pyrrole)]C104 has a typical three-legged piano-stool structure, with short Ir-cp distances due to the strong 7r-acceptor properties of the bpy ligands.540... 

General Structural Features. The general structure of halfsandwich ruthenium(II)-arene complexes is shown in Fig. 12. The structural, stereochemical and electronic features of metal-arene complexes have been discussed (63). A typical piano-stool geometry consists of an rj6-arene occupying three coordination sites of the pseudo-octahedral complex, leaving the three legs X, Y, and Z available for coordination. The sites X and Y can be taken up by two monodentate ligands, but are more commonly... 

Fig. 12. (a) General structure of the half-sandwich, piano-stool ruthenium—arene complexes (b) X and Y are commonly occupied by a bidentate ligand L giving a monofunctional complex (c) tethering of a monodentate ligand to the arene results in a bifunctional complex. 

Compounds of the type [MoXCp(NO)2] (Cp = rj5 - C5H5 or Tj5-C5Me5) and [MoX(Rpzb)(NO)2] are also known (Rpzb- = anion tris(2-pyrazolyl)(R)borate)18,22 and are monomeric in solution, the Cp derivatives having the three-legged piano stool structure (see 5).18,19... 

The pentabenzyl derivative KC5(CH2Ph)5.3THF84 has the same piano stool structure as NaC5Me5.3py. The bond distances from potassium to the rf-C5(CH2Ph)5 ring are in the range 296.8(5)-309.5(5) pm. 

The ruthenium compound in entry 11 has a piano-stool structure (LXIII), and hindered rotation about the Ru-aromatic ring bond may... 

A family of molecular rotors (e.g., compound 4 in Fig. 17.4 a) has been designed to perform rotation under electrochemical stimulation.59 60 The molecules have a piano-stool structure with a stator meant to be grafted on an oxide surface and a rotor bearing redox-active groups, so that addressing the molecule with nanoelectrodes would trigger rotation (Fig. 17.4 b). To avoid intramolecular electron transfer between two electroactive units, which would compete with rotation, insulating... 

Chart 2 General structure of Ru11 and Os11 piano-stool arene complexes... 

Bonding in sandwich compounds such as ferrocene arises through interaction of the delocalised p MOs of the ring with orbitals of the metal, and cannot be treated in a localised fashion. As in alkenes, both donor and acceptor interactions are involved. Other ligands such as CO can be present, as in the piano-stool structure 5 or the metal-metal bonded dimer 6. 

Fig. 2. The molecular structure of [WI2(CO)2(CNBu ),], oriented to show the 4 3 piano-stool structure. Only the coordinated carbon atoms of the /er/-butyl isocyanide ligands are shown. [Reprinted with permission from Inorg. Chem. 1979, 18, 1907. Copyright 1979 American Chemical Society.)...

Treatment of [Mo(CO)3Tp] with X2 (X = Br, I) affords the seven-coordinate complexes [MoX(CO)3Tp], which has been characterized crystallographically for X = Br. The structure can either be viewed as a distorted capped trigonal prism with Br capping a quadrilateral face or as a 3 4 piano stool.73... 

---