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The proton magnetic resonance spectra of tetraamminecobalt(III) complexes with a series of amino alcohols have been analysed and the coupling constant data utilized to calculate the conformational populations for the various complexes. When substitution occurred at the carbon adjacent to the amine group, the equatorial orientation of the substituent was not markedly preferred over the axial. However, when substitution occurred adjacent to the alcohol group, the substituent was found to be exclusively in the equatorial orientation.

The conformations adopted by six-membered diamine chelate rings in complexes of the types [Co(NH3),L]3+, [Co(CN)4L]-, [Pt(bpy)L]2+, [Pt(NH3)2L]2+ and [CoL3]3+ have been studied by n.m.r. techniques. The ligands (L) used in the study were meso- and (+)-pentane-2,4-diamine, butane-1,3-diamine, propane-1,3-diamine and 2-methylpentane-2,4-diamine. It has been found that for most complexes of meso-pentane-2,4-diamineth e diequatorial chair conformation predominates, although for the bipyridineplatinum(II) complex it is unclear whether the skew-boat conformation is significantly populated or the chair structure is unusually distorted. For (+)-pentane-2,4-diamine chelates, which normally adopt the skew-boat conformation in octahedral complexes, the chair conformation with an axial and an equatorial methyl group has a mole fraction of 0.5 and 0.7 for the bipyridine- and diammine-platinum(II) complexes, respectively. In tetraammine(butane-1,3- diamine)cobalt(III) the chelate ring is in the chair conformation with the methyl equatorial.

The circular dichroism spectra are reported for tetraamminecobalt(III) complexes with the chiral amino alcohols 2-aminopropan-1-ol, 2- aminobutan-1-ol, 1-aminopropan-2-ol, 2-amino-1-phenyl-ethanol, ψ- ephedrine and ephedrine with the alcohol groups protonated (OH) and deprotonated (O-). The solvent dependence of the chemical shifts of the NH protons was investigated to determine the effects of stereoselective solvation on the circular dichroism, but, in contrast to some other related systems, the chemical shift difference between the two NH2 protons was relatively insensitive to solvent. Consistent with this, the circular dichroism spectra of the tetraphenylborate salts of the deprotonated complexes were found not to be markedly dependent on solvent. Tetraammine-{(-)-ψ-ephedrine)cobalt(III) and tetraammine{(-)- ephedrine}cobalt(III) were found to have the same signs of Cotton effects for the various d-d transitions, whereas bis{(-)-ψ- ephedrine}copper(II) and bis{(-)-ephedrine}copper(II) had opposite signs. This has been explained in terms of different conformer populations in the cobalt(III) and copper(II) systems.

The crystal structures of tetraammine{()-2-methylpentane-2,4-diamine} cobalt(III) tetrachlorozincate chloride and 2,2'-bipyridine{()-2-methylpentane-2,4-diamine)platinum(II) nitrate semihydrate have been determined by X-ray structure analysis. The former crystals are orthorhombic with the space group P212121, with a 12.49, b 20.16 and c 7.68 . The latter crystals are also orthorhombic but with the space group Pbca with a 14.96, b 28.69 and c 19.45 . Both structures have been refined by least-squares methods to weighted R values of 0.034 (1407 reflections) and 0.055 (2301 reflections), respectively. The six-membered diamine chelate ring has a flattened chair conformation in the cobalt complex, and an unsymmetric boat conformation in the platinum complex. Strain-energy-minimization calculations show these structures correspond to energy minima and the calculated geometrical parameters are in good agreement with those observed for the chelate ring. Proton n.m.r. spectra are consistent with the chair conformation being almost exclusively populated in the ammine complex and in the tetracyanocobaltate(III) complex in aqueous solution, but the and 13C n.m.r. spectra of the platinum(II) complex show that, although the chair conformer predominates, the boat conformation is significantly populated in solution.

An analysis of the 3JH,H coupling constants for the CH2CH2 segment in the chelate rings formed by N-methylethane-1,2-diamine, and a crystal structure analysis of [Co(NH3)4{(±)-pn}] (S2O6)1.5,H2 (pn, propane-1,2-diamine) have shown that in cobalt(III) five-membered diamine chelate rings the NCCN torsional angle is approximately 51°. For platinum(II) complexes of N-methylethane-1,2- diamine, the 3JH,H technique yielded a value of 52.5° for the NCCN torsional angle. Problems involved with the refinement of the structure prevented the determination of a reliable value of this torsional angle in the crystal structure analysis of [Co(NH3),{(-)-dmbn}] (NO3)3,1.5H2O where dmbn is 3,3-dimethylbutane-1,2-diamine. However, this analysis showed that (-)-dmbn has the (R)-absolute configuration. The 3J H,H values for the CH2CH segment in complexes of dmbn show that the NCCN torsional angle for the dmbn chelates in solution is significantly greater than for the other diamines. The conformer populations for the N-methylethane-1,2-diamine complexes were also determined by the 3JH,H technique. For the tetraamminecobalt(III) and tetracyanocobaltate(III) complexes the mole fractions of the conformer with the methyl group equatorial were found to be 0.92 and 0.78, respectively. For the bipyridineplatinum(II) complex, one conformation was found to be populated exclusively. This was assumed to be the axial conformer because of the unfavourable interaction of the equatorial N-methyl group with the proton on C6 of the 2,2'-bipyridine group. The Jpt, H values for an equatorial C-H proton in square-planar platinum(II) complexes of dmbn show that the t-butyl group is restricted to the equatorial orientation even in this stereochemistry. The conformational-energy minimization technique was applied to the two complexes studied by crystal structure analysis.

The crystal structure of tetraammine{()-pentane-2,4-diamine}cobalt(III) dithionate dihydrate [Co{()-ptn}(NH3)4] (S2O6)1.5,2H2O has been determined by X-ray structure analysis. The crystals are triclinic with the space group Pī, with a 11.43, b 11.65, c 7.78 , α 100.48, β 105.95, and γ 75.95. The structure has been refined by least-squares methods with anisotropic temperature factors to an R value of 0.043 for 2654 reflections. The six-membered diamine chelate ring has a skew-boat conformation in which the two methyl groups are in equatorial orientations. A strain- energy-minimization calculation for the complex reveals an energy difference of 8.3 kJ mol-l between the preferred skew-boat conformation and the chair conformation. The calculated minimum-energy geometry for the skew-boat conformation is in good agreement with the observed structure for the chelate ring in the dithionate salt. The lH N.M.R. spectra of this complex and other complexes of the chiral isomer of pentane-2,4-diamine are discussed in terms of the observed structures and the conformational analysis.

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