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)}(n) 1 (4-bpfp = N,N'-bis(4-pyridylformyl)piperazine) and [Co(NCS)(2)(CH3OH)(2)(3-bpfp)](n) 2 (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 (alpha(2) = 9.00 X 10(-11) m W-1 for 1; 1.41 x 10(-10) m W-1 for 2) and self-focusing performance (n(2) = 3.24 x 10(-16) esu for 1; 3.05 X 10(-16) esu for 2) in DMF solutions. The corresponding effective NLO susceptibilities chi((3)) values are 3.08 x 10(-12) esu (1) and 4.70 x 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. (C) 2004 Elsevier B.V. All rights reserved.