Octahedral complexes distortion

Fig. 3.12 An octahedral complex. Distorted octahedral complexes are usually described by an axis along which a compression, elongation or other change may be regarded as occurring. Possibilities are a tetragonal distortion (along a C4 axis), a trigonal distortion (along a C3) and, more rare, a digonal distortion (along a Cj).

In fact the vast majority of 6-coordinate complexes are indeed octahedral or distorted octahedral. In addition to the twist distortion just considered distortions can be of two other types trigonal and tetragonal distortions which mean compression or elongation along a threefold and a fourfold axis of the octahedron respectively (Fig. 19.8). 

The compound Ag(TaF6)2 crystallizes in triclinic syngony with cell parameters (A, grad.) as follows a = 9.061, b = 5.607, c = 5.207, a = 118.7, p = 91.61, y = 102.3. Ag(TaF6)2 is composed of two separate layers made up of octahedral ions AgF64 and distorted octahedral complexes NbFe that are linked through the planes. 

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

The series of 3d elements from scandium to iron as well as nickel preferably form octahedral complexes in the oxidation states I, II, III, and IV. Octahedra and tetrahe-dra are known for cobalt, and tetrahedra for zinc and copper . Copper(II) (d9) forms Jahn-Teller distorted octahedra and tetrahedra. With higher oxidation states (= smaller ionic radii) and larger ligands the tendency to form tetrahedra increases. For vanadium(V), chromium(VI) and manganese(VII) almost only tetrahedral coordination is known (VF5 is an exception). Nickel(II) low-spin complexes (d8) can be either octahedral or square. 

Quinazoline-2-thione-4-one (522) and its 3-phenyl derivative coordinate to Ni11 after deprotonation via the S and the NI donor resulting in a square planar complex.1372 The related 2-isopropylquinoline-8-thiolate (523) forms a distorted tetrahedral complex.1 73 For deprotonated 2-thiocarbamyl-thiazoline (HL = (524)) the octahedral complex [NiL(H20)4]+ is favored over the square planar [NiL2] complex.1374... 

Methyl pyruvate thiosemicarbazone in the presence of zinc chloride or acetate resulted in the formation of complexes with the ligand hydrolyzed or transesterified. The complexes with pyruvate thiosemicarbazone, ZnL2, or ethyl pyruvate thiosemicarbazone, ZnLCl2 were structurally characterized by single-crystal X-ray crystallography showing respectively a distorted octahedral and distorted square pyramidal geometry.874... 

Would Jahn-Teller distortion be as significant for tetrahedral complexes as it is for octahedral complexes For which of the electron configurations would Jahn-Teller distortion occur ... 

Most of these comments also apply to octahedral complexes, which tend to show longer bonds also. Again, there are examples ranging from near-regular to shapes better described as distorted tetrahedral with two long interactions. 

---