Discrete and extended architectures based on the association of lanthanide ions with two derivatives of cinnamic acid (2-methoxycinnamic acid and 3-methoxycinnamic acid) have been synthesized and characterized by IR spectroscopy, elemental analyses, X-ray diffraction and magnetic measurements. The use of the 2-methoxycinnamic ligand enables the synthesis of a series of dinuclear complexes (Ce3+ (1), Nd3+ (2), Gd3+ (3), Dy3+ (4)), while the presence of 3-methoxycinnamic acid induces the formation of one-dimensional coordination polymers (Ce3+ (5), Nd3+ (6), Dy3+ (7)). Investigations of the magnetic properties of the complexes reveal that they all exhibit field-induced slow relaxation of the magnetisation, mainly induced by Raman and direct relaxation processes.