Two examples of transition metal molyb dates were studied with the use of X-ray di raction and DC mag- netometry techniques. First comp ound, copp er dimolyb date trihydrate CuMo 2 O 7

3H 2 O contains 2D layers. The second one is brillar cobalt trimolyb date o ctahydrate CoMo 3 O 10

8H 2 O. Both comp ounds exhibit paramagnetic b ehaviour at ro om temp erature. However, in the rst one copp er ions form dimers linked by oxygen bridges, in which exchange interactions b etween two lo calized spin states o ccur. The second comp ound consists of isolated cobalt ions in the o ctahedral surroundings, resulting in magnetic prop erties deviating from the Curie law.