Control of Self-Penetration and Dimensionality in Luminescent Cadmium Succinate Coordination Polymers via Isomeric Dipyridylamide Ligands

Abstract

Reaction in aqueous solution of cadmium nitrate, succinic acid (H 2 suc), and one of four possible isomeric dipyridylamide coligands has afforded a series of two-dimensional (2-D) and three-dimensional (3-D) coordination polymers. All were structurally characterized by single-crystal X-ray diffraction. [Cd(suc)(4-pina)] n ( 1, 4-pina = 4-pyridylisonicotinamide) displays a 3-D 6-connected self-penetrated 4 4 6 10 8 mab topology, while {[Cd(suc)(3-pna)]·2.5H 2 O} n ( 2, 3-pna = 3-pyridylnicotinamide) has a simple 3-D non-interpenetrated 4 12 6 3 pcu network. The supramolecular isomer 2′ has exactly the same stoichiometry and overall pcu topology as 2 but shows a difference in succinate binding mode. Compounds 1, 2, and 2′ all show similar [Cd(suc)] n layers with embedded {Cd 2 O 2 } rhomboid dimers that serve as the 6-connected nodes. {[Cd(suc)(4-pna)(H 2 O)]·2H 2 O} n ( 3, 4-pna = 4-pyridylnicotinamide) manifests an extremely rare 2-D 4-connected 6 6 layer self-penetrated topology based on cross-pillared [Cd(suc)] n helical chains. Slight adjustment of the donor disposition resulted in the formation of the 2-D (4,4) grid coordination polymer {[Cd(suc)(3-pina)(H 2 O)]·3.5H 2 O} n ( 4, 3-pina = 3-pyridylisonicotinamide), which has [Cd(suc)] n helical chains similar to those in 3 but avoids cross-pillaring. Luminescent and thermal properties of these four new materials are discussed.