High-Pressure Study of Oxo-bridged Mixed-Valent Mn-III/Mn-IV Dimers

A combination of high-pressure single crystal X-ray diffraction and high-pressure SQUID magnetometry has been used to study two oxo-bridged mixed-valent Mn-III/Mn-IV dimers. [Mn2O2(bpy)(4)](ClO4)(3)center dot 3CH(3)CN, (1.3CH(3)CN; bpy = 2,2'-bipyridine) has been compressed to 2.0 GPa whilst [Mn2O2(bpy)(4)](PF6)(3)center dot 2CH(3)CN center dot 1H(2)O, (2.2CH(3)CN center dot 1H(2)O) could be measured crystallographically up to 4.55 GPa. The PF6 salt of [Mn2O2(bpy)(4)](3+) has never been reported before while 1 has been reported as a hydrate and in a different crystallographic space group. The application of hydrostatic pressure imposes significant distortions and modifications in the structures of both complexes. In particular, in complex 1.3CH(3)CN the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond lengths, whilst in 2.2CH(3)CN center dot 1H(2)O the Mn-O Mn bridging angles and the Mn-O bond lengths are substantially unchanged. Interestingly 2.2CH(3)CN center dot 1H(2)O also shows a constant contraction in nearly all the Mn-N bonds. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 1.3CH(3)CN and 0.84 GPa for 2.2CH(3)CN center dot 1H(2)O.