1-D Polymeric divalent metal m-ferrocenylbenzoates: Structures, NLO and electrochemical properties

Three 1-D metal-organic polymers containing m-ferrocenylbenzoate components: {Pb(μ₂-η²-OOCH₄C₆Fc)₂] · (CH₃OH)₂}_n (1), Zn(OOCH₄C₆Fc)₂(bpe)]_n (2) and Mn(η²-OOCH₄C₆Fc)₂(4,4′-bpy)]_n (3) were synthesized and structurally characterized. In polymer 1, each m-FcC₆H₄COO⁻ anion adopts a tridentate fashion, bridging the central Pb(II) ions to form a 1-D chain. Polymers 2 and 3 give similar zigzag chain structures. Their third-order NLO properties were investigated with 532 nm laser pulses of 8 ns duration by Z-scan experiment in DMF solution. All of the polymers exhibit good NLO refractive properties with self-focusing behaviors. The third-order NLO refractive indexes n₂ are 2.44 × 10⁻¹¹ esu for 1, 2.33 × 10⁻¹¹ esu for 2, and 2.10 × 10⁻¹¹ esu for 3, respectively. Through quantum chemistry calculations, we conclude that the nonlinear refractive behaviors of the three polymers mainly come of the ferrocenyl units and organic adjuvant ligands; Mn(II) ions and Pb(II) ions have also some influence on NLO properties. The solution-state differential pulse voltammetrys indicate that the half-wave potential of the ferrocenyl moiety in 3 has slightly higher value than those of 1 and 2. This may be because the HOMO orbitals in 1 and 2 are located in the m-FcC₆H₄COO⁻ groups, while in 3 the HOMO orbital is located in the m-FcC₆H₄COO⁻ and Mn(II)groups, the charge transitions of the metal cores may play an important role in the change of the Fe(II)/Fe(III) oxidation potential of 3, so the Fe(II) centers of 1 and 2 are more easily oxidized to Fe(III) centers than that of 3.