Structure and bonding of bisaquamercury(ii) and trisaquathallium(iii) trifluoromethanesulfonateElectronic supplementary information (ESI) available: symmetry coordinates for 1 and 2; observed and calculated frequencies and potential energy distribution for CF3SO3???, 1 and 2; X-ray absorption edge structure for 1, [Hg(OH2)6](ClO4)2, [Hg(NH3)4](ClO4)2, 2 and [Tl(OH2)6]3+. See http://www.rsc.org/suppdata/dt/b2/b206021n/