Synthesis of novel chiral and acentric coordination polymers by the reaction of zinc or cadmium salts with racemic 3-pyridyl-3-aminopropionic acid

Under hydrothermal (solvothermal) reaction conditions chiral compounds 1, 2, and 3 and one acentric compound 4 were obtained by the reaction of Zn2+ or Cd2+ with racemic 3-(3-pyridyl)-3-aminopropionic acid (rac-HPAPA). Compounds I and 2 crystallized in chiral space group P2(1)2(1)2(1). At 105degreesC, racemic 3-pyridyl-3-aminopropionic acid (rac-HPAPA) reacted with Zn(ClO4)(2).6H(2)O and dehydrogenated in situ to form the first chiral coordination polymer [Zn{(E)-3-C5H4N-C(NH2)=CH-COO}]ClO4 (1) with a beta-dehydroamino acid. Beyond 120degreesC, the reaction of rac-HPAPA with Zn(ClO4)(2).6H(2)O deaminates in situ to form chiral coordination polymer [Zn{(E)-3-C5H4N-CH=CH-COO}(OH)] (2). At relatively low temperatures (70degreesC), the solvothermal reaction of Zn(NO3)(2).6H(2)O with rac-HPAPA in methanol does not lead to any change in the ligand and results in the formation of a chiral (P2(1)2(1)2(1)) coordination polymer [Zn(papa)(NO3)] (3). The same reaction of Cd(ClO4)(2).6H(2)O with HPAPA also does not lead to any change in ligand and results in the formation of noncentric (Cc) coordination polymer [Cd(papa)(Hpapa)]ClO4.H2O (4). The network topology of both 1 and 3 is 10,3a, while 2 has a diamondoid-like (KDP-like, KDP=potassium dideuterophosphate) network. Particularly interesting from a topological perspective is that 4 has an unprecedented three-dimensional network. Compounds 1, 2, 3, and 4 are all second harmonic generation (SHG) active with I exhibiting the strongest response, while only 4 also displays good ferroelectric properties.