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

Reaction in aqueous solution of cadmium
nitrate, succinic acid
(H2suc), 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 446108 mab topology, while {[Cd­(suc)­(3-pna)]·2.5H2O}n (2, 3-pna = 3-pyridylnicotinamide)
has a simple 3-D non-interpenetrated 41263 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 {Cd2O2} rhomboid dimers that serve
as the 6-connected nodes. {[Cd­(suc)­(4-pna)­(H2O)]·2H2O}n (3, 4-pna = 4-pyridylnicotinamide)
manifests an extremely rare 2-D 4-connected 66 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)­(H2O)]·3.5H2O}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.