A New Family of 4f-3d Heterometallic Metal–Organic Frameworks with 2,2′-Bipyridine-3,3′-dicarboxylic Acid: Syntheses, Structures and Magnetic Properties

Eight isostructural lanthanide­(III)-cobalt­(II) heterometallic metal–organic frameworks (MOFs), {[Ln₂Co­(BPDC)₄(H₂O)₆]·xH₂O}_n (Ln = La (1-La, x = 9), Pr (2-Pr, x = 11), Nd (3-Nd, x = 8), Sm (4-Sm, x = 9), Eu (5-Eu, x = 6), Gd (6-Gd, x = 6.5), Tb (7-Tb, x = 7), Dy (8-Dy, x = 8); H₂BPDC = 2,2′-bipyridine-3,3′-dicarboxylic acid), have been prepared and characterized. In these complexes, two crystallographically independent Ln³⁺ ions are connected via carboxyl groups into binuclear units, which are further linked into a lanthanide chain through bridging BPDC^2–. Each Co²⁺ ion is chelated by the bipyridine groups of three BPDC^2– and further links the lanthanide chain to form a three-dimensional framework. The framework with one-dimensional channels occupied by water molecules possesses a new topology with the short (Schläfli) vertex symbol {3·6²}­{3²·6⁶·7³·8³·9}­{6²·7}. The magnetic properties of the eight heterometallic MOFs have been studied, in which only 8-Dy displays slow relaxation of the magnetization at low temperature.