Strain alleviation in an isomorphous series of lanthanide 2-nitroterephthalates [Ln2(TPNO2)3(H2O)2]·2H2O (Ln = Pr – Lu, except Pm)

Abstract An extended series of trivalent lanthanide 2-nitroterephthalates, [Ln 2 (TPNO 2 ) 3 (H 2 O) 2 ]·2H 2 O, (Ln = Pr through Lu, except Pm) were synthesized hydrothermally from Ln 2 O 3 and 2-nitroterephthalic acid (H 2 TPNO 2 ) at 170 °C in Teflon lined Parr steel autoclaves, and were characterized via single crystal X-ray diffraction, powder X-ray diffraction, FT-IR spectroscopy, elemental analyses, and thermogravimetric analyses. All [Ln 2 (TPNO 2 ) 3 (H 2 O) 2 ]·2H 2 O coordination polymers are isomorphous, crystallizing in the monoclinic crystal system with space group C 2/c. The metal centers in all networks possess the coordination number 8, while forming a three-dimensional extended lattice. Two metal centers form Ln 2 O 14 entities, comprising crystallographically identical LnO 8 polyhedra, connected via edge-sharing, utilizing two carboxylate O-atoms. These Ln 2 O 14 units are separated along the a - and b -axes by individual 2-nitroterephthalate linkers, while being closely connected along the c -axis via two carboxylate groups on each side. Compared to small inorganic anions, the rather flexible 2-nitroterephthalate seems to allow for the unobstructed decrease in size of the LnO 8 polyhedra as Ln 3+ ionic radii decrease towards the heavier Ln elements. Hence, the structural parameters of the crystal lattice adjust gradually without noticeable strain buildup along the series resulting in isomorphous arrangements for all networks. The thermogravimetric and FT-IR measurements seem to confirm the structural features.