AbstractBy reaction of hydrated rare earths chlorides (M = La, Nd, Sm, Gd, Dy, Er, Yb, Y) with orthoformates, the following adducts have been prepared: MCl3· 4MeOH, MCl3·3EtOH (M = La, Nd, Sm, Gd, Yb), MCl4· 4 EtOH (M = Dy, Er, Y); adducts MCl3· 3iso‐PrOH have been prepared by successive action of methyl orthoformate and of 2‐propanol. The solubilities of these adducts in the corresponding alcohols at 25° (for the lanthanum adducts equally at 0 and 50°) are given. Two examples of the transsolvatation of these compounds, yielding adducts with weakligands, are