Two- and three-dimensional cadmium-organic frameworks with trimesic acid and 4,4′-trimethylenedipyridine

Three novel cadmium-organic frameworks built-up from 1,3,5-benzenetricarboxylate anions (HxBTCx-3) and 4,4'-trimethylenedipyridine (TMD) have been hydrothermally synthesized, and characterized using single-crystal X-ray diffraction, thermoanalytical measurements, elemental analysis, and IR and Raman spectroscopies: [Cd(HBTC)(TMD)(2)](.)8.5H(2)O (1), [Cd(HBTC)(TMD)(H2O)](.)4.5H(2)O (II), and [Cd-2(BTC)(TMD)(2)(NO3)](.)3H(2)O (III), with structures I and II being isolated as a mixture of crystals. Structure I contains an undulating infinite two-dimensional [Cd(HBTC)(TMD)(2)] framework, with a (4,4) topology and rectangular pores, ca. 3.4 x 11.0 Angstrom in cross-section, distributed in a herringbone manner. The crystal structure of I is obtained by parallel packing of this 2D framework in an [ABAB(...)] fashion. Compound II has a porous 3D diamondoid framework with channels running in several directions of the unit cell, which allows 2-fold interpenetration to occur. The most prominent channels are distributed in a brick-wall fashion along the c axis and have a cross-section of ca. 3.2 x 13.2 Angstrom. Structure III can be seen as the three-dimensional assembly of binuclear secondary building units (SBU), which leads to a compact, neutral, and coordinatively bonded eight-connected framework, [Cd-2(BTC)(TMD)(2)(NO3)], exhibiting an unusual 3(6)4(22) topology. The increased flexibility of the TMD ligands (brought about by the three methylene groups between the two 4-pyridyl rings) can lead, for the same reactive system, to a large variety of crystal architectures.