Crystal structures and third-order NLO properties in DMF solution of Co(II)-bpfp coordination polymers (bpfp=N,N′-bis(pyridylformyl)piperazine)

Two novel Co(II) coordination polymers {[Co(H2O)2(CH3OH)2(4-bpfp)](NO3)2}n1 (4-bpfp=N,N′-bis(4-pyridylformyl)piperazine) and [Co(NCS)2(CH3OH)2(3-bpfp)]n2 (3-bpfp=N,N′-bis(3-pyridylformyl)piperazine) have been synthesized and characterized by single crystal X-ray diffraction. Both the polymers consist of one-dimensional chains constructed by bridging bpfp ligands and Co(II) ions. The existence of O⋯H–O hydrogen bond in 1 and S⋯H–O hydrogen bond in 2 play important roles in creating interesting supramolecular structures. Their third-order nonlinear optical (NLO) properties in DMF solution have been studied by Z-scan technique. The results reveal that polymers 1 and 2 exhibit strong NLO absorption effects (α2=9.00×10−11 m W−1 for 1; 1.41 × 10−10 m W−1 for 2) and self-focusing performance (n2=3.24×10−16 esu for 1; 3.05 × 10−16 esu for 2) in DMF solutions. The corresponding effective NLO susceptibilities χ(3) values are 3.08 × 10−12 esu (1) and 4.70 × 10−12 esu (2). All of the values are comparable to those of the reported good NLO materials. Additionally, the TG-DTA results of the two polymers are in agreement with the crystal structures.