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)(NO₃)₂]_n1, [Pb(dimb)(SCN)₂]_n2 [dimb = 1,3-bis(imidazol-1-ylmethyl)-benzene], {[Pb(bimb)_1.5(NO₃)₂](DMF)}_n3 [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 × 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 × 10⁻¹⁹ m² W⁻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 d¹⁰ 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.