Crystalline compounds of trivalent Eu, Tb formed with Al(OH) 6 Mo 6 O 1 8 3 - and Cr(OH) 6 Mo 6 O 1 8 3 - anions were prepared from solutions containing lanthanide(III) and (NH 4 ) 3 M(OH) 6 Mo 6 O 1 8 (M=Al,Cr). Stoichiometric compounds containing both Eu and Gd were also prepared. The calculated mean value of hydration numbers of lanthanide ions, n=7.6+/-1.4, is consistent with the X-ray diffraction data leading to n=7. Luminescence of Tb 3 + in complex with Al(OH) 6 Mo 6 O 1 8 3 - is surprisingly intense, in spite of a strong quenching effect by energy transfer to the Tb 4 + -Mo 5 + charge transfer state which one could expect. The Eu 3 + compound formed with Cr(OH) 6 Mo 6 O 1 8 3 - represents the system where two different metal ions could emit light and a very effective energy transfer from Eu 3 + to Cr(III) could occur.