Zinc and Cadmium Complexes of Pyridinemethanol Carboxylates: Metal Carboxylate Zwitterions and Metal-Organic Frameworks.

The heterofunctional lactone furo[3,4-b]pyridin-5(7H)-one (L1 ) undergoes a coordination-induced ring-opening reaction with Zn(NO3 )2  ⋅ 6H2 O to yield the zwitterionic [Zn(L1 ')2 (H2 O)2 ] (1, L1 '=2-(hydroxymethyl)nicotinate) with an uncoordinated carboxylate. The same reaction with Cd(NO3 )2  ⋅ 4H2 O provides a two-dimensional (2D) network of [Cd(L1 ')2 ]n (3) with the carboxylates coordinated to cadmium(II) propagating the assembly. The corresponding reactions of Zn(NO3 )2  ⋅ 6H2 O and Cd(NO3 )2  ⋅ 4H2 O with 2-(hydroxymethyl)isonicotinic acid (HL2 ) generated zwitterionic [Zn(L2 )2 (H2 O)2 ] (2) and a 2D network [Cd(L2 )2 ]n ⋅nDMF (4, DMF=N,N'-dimethylformamide), respectively. Complexes 1-4 are weakly emissive, giving ligand-centered emissions at 409 nm (1), 412/436 nm (2), 404 nm (3), and 412/436 nm (4) in CHCl3 solutions upon excitation at 330 nm. This work points to the potential of using 'hidden' functionalities widely found in small organic molecules and natural products for the construction of coordination complexes with new functionality and potential applications.