Comparative structure activity relationship for heterogeneous phosphatase-like catalytic activities of one-dimensional Cu(ii) coordination polymers

Abstract

A group of one-dimensional Cu(II) coordination polymers {[Cu₃(L¹)(NO₃)₂(DMF)(H₂O)]·3(DMF)}_n (1), [Cu₃(L¹)(Cl)₂(DMF)₂]_n (2), [Cu₃(L²)(NO₃)₄(H₂O)₄]_n (3) with different coordination environments, was chosen to investigate their potential in heterogeneous catalytic studies for the cleavage of phosphate ester bond. In complexes 1, 2 and 3 the trinuclear copper units are connected by μ₂-O⁻, μ₂-Cl and μ-[O–N–O] bridging modes that leads to the formation of sheet like or stacking layer arrangement of coordination polymers with different metal–metal distance. Moreover these complexes have different donor sites of ligands and exogenous ligands in their coordination environment. Therefore the role of different coordination environments of these complexes was explored for transesterification of DNA model substrate, 2-hydroxypropyl-p-nitrophenylphosphate (HPNP). The reaction between the copper(II) complexes and HPNP was investigated spectrophotometrically to understand mechanistic aspects of phosphate ester bond cleavage in HPNP. Kinetic experiments were performed to determine initial rate of reactions and the activity order follows: 1 > 3 >2. Various structural factors of complexes such as coordinating solvents, mode of bridging and metal–metal distance play a significant role in the catalytic activities. The maximum phosphatase like activity of complex 1 (k_cat = 9.6 × 10⁻³ s⁻¹) can be attributed to coordinated water molecules, shorter metal–metal distance and exposed metal centers.