Abstract: A relationship is established between the structural and thermoanalytical characteristics of the decomposition of hydrogen maleates and phthalates of Fe(II), Co(II), Ni(II), Cu(II). The temperatures of the onset of the first and second stages of decomposition grow in the series of both hydrogen maleates Cu ≤ Fe < Co < Ni and phthalates Fe ≤ Co < Ni < Cu, while the lengths of (Formula Presented.) and M–Oanion bonds shrink in these structures. At the third stage, the temperature of the onset of the decarboxylation of hydrogen maleates and phthalates falls in the order Fe > Co > Ni > Cu. The size of metal nanoparticles additionally contained in a polymer or graphene shell grows from 3.5 to 5 nm (Co) and from 4.5 to 7 nm (Ni) upon moving from composites obtained through the decomposition of hydrogen maleates to hydrogen phthalates. Polymeric conglomerates containing shell-less copper nanoparticles, the average size of which ranges from 7.5 to 50 nm, are incorporated into a polymer matrix of composites obtained via the thermolysis of Cu(II) hydrogen maleate and phthalate.