Ligand-controlled dimensionality: 1D, 2D and 3D Gd(iii) coordination polymers based on SO42− and pyridine carboxylate N-oxide ligands

Abstract

Three Gd(III)-sulfate polymers [Gd(PNO)(H₂O)₂(SO₄)]_n (1), [Gd(NNO)(H₂O)₂(SO₄)]_n (2), and [Gd(INO)(H₂O)(SO₄)]_n (3) exhibiting a systematic variation in framework dimensionality have been hydrothermally synthesized by using three isomeric pyridine carboxylate N-oxides, PNO = picolinate N-oxide, NNO = nicotinate N-oxide, and INO = isonicotinate N-oxide, as organic components. Compound 1 comprises 1D coordination chains that are unable to propagate to higher dimensionalities due to the convergent endo PNO ligand. The structure of compound 2 consists of hydrogen-bonded layers. The formation of the 2D layer is attributed to the more divergent NNO than PNO. Compound 3 consists of a 2-fold interpenetrating “3D herringbone” framework, in which the most divergent exo ligands of INO connect the individual Gd-sulfate inorganic chains to produce the 3D coordination network. It is demonstrated that the convergence or divergence of the three isomeric ligands of the pyridine carboxylate N-oxide can be used to engineer the dimensionality of the coordination polymers.