SYNTHESIS AND X-RAY CRYSTAL-STRUCTURE OF THE TRIETHYLAMMONIUM MAGNESIUM BETA-OCTAMOLYBDATE(IV) SALT [ET(3)NHC](2)[MG(H2O)(6)MO8O26]CENTER-DOT-2H(2)O

[Et(3)NH](4)[Mo8O26] reacted with MgCl2 and CaCl2 giving the triethyla mmonium magnesium beta-octamolybdate(VI) salt [Et(3)NH](2)[Mg(H2O)(6)M o8O26]. 2H(2)O (3) and the triethylammonium hydronium beta-octamolybda te(VI) salt [Et(3)NH](3)[(H3O)Mo8O26]. 2H(2)O (4), respectively. A sma ll amount of [Et(3)NH](2)[Mo6O19] was formed as a by-product. The salt s 3 and 4 were characterized by X-ray crystallography. The [Mg(H2O)(6) Mo8O26](2-) moiety in 3 is polymeric, with each octahedral [Mg(H2O)(6) ](2+) ion sandwiched between two beta[Mo8O26](4-) ions, being hydrogen bonded to three terminal Mo=n oxygen atoms on one face of each beta[M o8O26](4-) ion. The X-ray crystal structure of 4 corresponds to that r eported previously. IR and conductivity data are given for 3 and 4.