Twenty seven new rare earth (Ln) compounds CuLn2 Ge2O8, CuLn2Ge4O12 and CuLn2Si4O12 have been synthesized. The powder diagrams were indexed and solid solutions of silicates and germanates were investigated. Structural variations with temperature, lanthanide contraction and Ge/Si substitution are described. Indications for second order phase transitions were found.