Organotin (IV) complexes formed between 0 01 M dimethyltin dichloride solutions prepared at pH 2 6 and 4 0, and trimethyltin chloride prepared at pH 3 4, with Na- 119 montmori 1lonite clay have been characterised using Sn Mflssbauer spectroscopy, X-ray diffraction, thermogravimetric analysis and water sorption isotherms Following cation exchange, Mttssbauer spectroscopy identified two tin species in the dimethyltin (IV)-exchanged clay prepared at pH 2 6 A cis species was characterised by an isomer shift, Q , of “1. 1 11 mms , and quadrupole splitting,A , of 3 12 mms , and a trans species, characterised by an isomer shift, 6 of 1 27 -1 -1 mms , and quadrupole splitting of 4 24 mms In the dimethyltin (IV)-exchanged clay prepared at pH 4 0, a cis_1 species, characterised by an isomer shift, 6 of 1 12 mms and quadrupole splitting,A of 2 89 mms , along with a trans species, characterised by an isomer shift, 6 , of 1 26 mms , and quadrupole splitting,A , of 3 66 mms were also identified However, a single tin species, characterised by an isomer shift, 6 , of 1 32 mms and quadrupole splitting of 3 79 mms , was identified in the trimethyltin (IV)-exchanged clay prepared at pH 3 4 Within the temperature range 20-450°C, the intercalated species of each of the three thermally pretreated organotin (IV)-exchanged clays were found to be unstable with respect to increasing pretreatment temperature For each of the dimethyltin (IV)-exchanged clays prepared at pH 2 6 and 4 0, the thermolysis pattern of the intercalated species, as characterised using MOssbauer spectroscopy, was quite similar, with cis and trans species being converted to lV^SnO between 20 and 230°C At temperatures greater than 200°C, Me2SnO and remaining trans species were converted to oxides of tin The trimethyltin (IV)-exchanged clay behaved in almost identical way, where a low isomer shift component was formed, albeit at a somewhat higher pretreatment temperature than the dimethyltin (IV)-exchanged systems However, at temperatures greater than 200°C, any remaining methylated components were similarly converted to oxides of tin. The temperatures at which these inorganic oxides of tin appeared in the dimethyltin (IV) exchanged clays were seen to coinside with a collapse in the basal spacing from 13 8A in the clay preapred at pH 2 6, and 15 9A in the clay prepared at pH 4 0, to 9 6A A similar collapse in the basal spacing from 13 8A to 9 6A was seen for the trimethyltin (IV)-exchanged clay. Following thermal pretreatment at 120°C, both dimethyltin (IV)-exchanged clays displayed type IV isotherms in the B E T classification for the adsorption of water However, the clay prepared at pH 4 0 had a lower sorption capacity and exhibited a less marked hysteresis which closed sooner than that of the exchanged clay prepared at pH 2 6.