[en] Carried out is X-ray investigation of the crystal structure of the compounds M₃AnO₂(CO₃)₂xnH₂O(1) and Msub(4)AnOsub(2)(COsub(3))sub(2,5)xnHsub(2)O(2), where M=Na, K and Rb, An=Np(5), Pu(5) and Am(5). Determined is a general structural scheme of carbonate compounds of pentavalent actinides, in the basis of which is mutual substitution of actinide atoms and atoms of alkaline metals. It is shown, that the main structural elements of different carbonate compounds are anion layers of [Msub(x)(AnOsub(2))sub(1-x)COsub(3)] variable composition, where x can have the values from 0 to 1. It is shown, that as far as the structure is concerned, the compounds (1) and (2) are recorded in the form of Msub(2)[MAnOsub(2)(COsub(3))sub(2)]xnHsub(2)O(1) Msub(2)[Msub(1,2)(AnOsub(2))sub(0.8)x(COsub(3))sub(2)]xnHsub(2)O(2) and they are the edge members of the continuous lin of Msub(2)[Msub(1+x)(AnOsub(2))sub(1-x)(COsub(3))sub(2)]xnHsub(2)O compounds, where 0 < or approximately X < or approximately 0.2. On the basis of the obtained peculiarity of carbonate crystal structure considered is the possibility of corbonate compounds formation of different composition