for aqueous solutions of MnBr, and MnCI2 at a variety of concentrations were analysed by least-squares curie fittingcalculations.Thedata,obtained at ambient temperature,werefoundto beconsistent with equilibria between species of the type [Mn)4,..,(H,0).]'"-+lt (where X = CI, Brand n = 4,5,6) for which it was possible to determine the average value of n (i.e. nav) at each concentration. To fit the data, a third distance, in addition to Mn-X and Mn-0 in the complexes, was shown to be significant in the least-squares calculations; this third distance at 4.4A represents the radius of the first hydration sphere around the complexes and is reasonably interpreted as Mn to solvent water molecules hydrogen bonded to the water molecules in the complexes. By carefully parameterising the calculations using EXAS data for solid reference compounds, the dependence of nar on concentration was determined; calculations werecarriedout both wilhdatasetsforsingle concentrationsand also with data sets for four different concentrations simultaneously. The latter calculations enabled the direct refinement of the slope k and the intercept MO for the concentration dependence represented as n, = M Okc/mol dm-', where c is the concentration. For both MnC12 and MnBr, solutions, MO, the number of water ligands in the complex at infinite dilution, was found to be 6, as expected. The slopes k were found to be 0.18(1) and 0.25(1), respectively. The greater slope in the case of MnBr2 shows that its solutions have a smaller value of n,, than foundincomparable MnCl,solutions; in neithercase doesn,reach4 beforesaturation OCCUIS.

Abstract:The electrochemical investigation of a number of polyarene-iron complexes ([3]"-[915+) containing etheric, sulphide, and sulphone bridges indicated that there were various degrees of interaction based on the nature of the bridging heteroatoms. While the electrochemical investigation of all etheric complexes showed that the metallic moieties behaved as isolated redox centers, it was found that there was electronic communication (ca. 70-80 mV) for the isomeric sulphide complexes [412+ and [612+. The rate constant of the following chemical reaction (k,) was calculated for some of these complexes and it was found that these rates were affected by the nature of the solvent, the bridging ligand, and the temperature. At various temperatures, kfindicated a higher degree of stability for complexes containing sulphide bridges than for those containing etheric bridges, especially at room temperature. The effect of a strong coordinating solvent, such as acetonitrile, on the k, of complex [3]'+ indicated that the substitution of the arene ligand with acetonitrile molecules proceeded as a dissociative mechanism. Controlled potential coulometry was also used to verify the transfer of two electrons in the first reduction process of the di-iron complexes.Key words: cyclopentadienyliron, cyclic voltammetry, arene complexes, isolated and interacting redox centers.

Surprisingly, in the course of an X-Ray study of [TiCl2(CsH6)]206 we found definite evidence of colinearity of titanium and oxygen atoms. In fact, the crystals of (I), having^t hese unit cell constants: a = 7.47 Á.; b = 9.86 A.; c = 12.58 A.; 3 = 127°56', space group P21/c, have only two molecules per unit cell, so that the molecule must be centrosymmetrical.The colinearity of titanium and oxygen atoms is further confirmed by the Patterson and Fourier syntheses on the ac and be planes. At the present stage of refinement of the structure (R = 0.20), the fractional coordinates (x, y, z) of the heavy atoms have been assumed to be: Ti: 0.454, 0.132, 0.393; CF: 0.767, 0.132, 0.403; CW 0.178,0.047, 0.187.It results that: 1, as above said, the Ti-O-Ti atoms are colinear. 2, All the carbon atoms of the cyclopentadiene ring are at the same distance (2.35 ± 0.05 A.