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

Three novel Pb(II) coordination complexes, [Pb(dimb)(DMF)(NO3)(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 Angstrom, 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, n(2), are -5.96 x 10(-19) m(2) W-1 for 1, -8.34 x 10(-19) m(2) W-1 for 2, and -7.15 x 10(-19) m(2) 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 chi((3)) values of complexes 1, 2 and 3 were calculated to be 4.46 x 10(-13), 6.25 x 10(-13) and 5.42 x 10(-13) esu, respectively.