A number of complex malonates of the general formulae Rz[MII(C3Hz04)z] * x H,O [where R = K, Na, and Tl(1); M(II) = Zn, Cd, Hg and Be] have been prepared by treating the freshly precipitated heavy metal hydroxide with a solution of alkali or thallous hydrogen malonate and submitting the resulting solution to crystallisation. The general behaviour of these compounds has been studied.