Novel Pb(II) coordination frameworks: Synthesis, crystal structures and unusual third-order nonlinear optical properties

Abstract

Three novel Pb(II) coordination complexes, [Pb(dimb)(DMF)(NO 3)2]n 1, [Pb(dimb)(SCN)2] n 2 [dimb = 1,3-bis(imidazol-1-ylmethyl)-benzene], {[Pb(bimb) 1,5(NO3)2](DMF)}n 3 [bimb = 4,4′-bis(imidazol-1-methyl)-biphenyl], were synthesized and characterized by X-ray crystallography. Complex 1 exhibits a one-dimensional (1D) zigzag chain structure, which has two crystallographically independent Pb(II) atom centers. Complex 2 possesses a two-dimensional (2D) corrugated network, which contains 24-membered M2L2 metallocyclic rings. Complex 3 has a 1D infinite non-interpenetrated molecular ladder, which has very large cavities with dimensions of 17.89 x 20.34 Å, and DMF molecules fill the channel formed by adjacent two ladders. The third-order nonlinear optical (NLO) properties of the three complexes were measured by a Z-scan technique in DMF solution. All three complexes possess weak absorption and strong refraction. Their third-order NLO refractive coefficients, n2, are -5.96 × 1019 m2W-1 for 1, -8.34 × 10 -19 m2 W-1 for 2, and -7.15 × 10 -19 m2 W-1 for 3. It is notable that two Pb(II) complexes 1 and 3 with 1D structure show strong self-defocusing behavior, which are different from the reported 1D coordination complexes containing d 10 metal ions; also, complex 2 is the first 2D coordination compound that possesses strong self-defocusing behavior. The χ(3) values of complexes 1, 2 and 3 were calculated to be 4.46 × 10-13, 6.25 × 10-13 and 5.42 × 10-13 esu, respectively.