A redox-active two-dimensional coordination polymer: Preparation of silver and gold nanoparticles and crystal dynamics on guest removal

A two-dimensional (2D) square-grid coordination polymer, {[Ni(cyclam)] ₂[BPTC]}_n·2nH₂O (1), has been assembled from [Ni(cyclam)](ClO₄)₂ (cyclam = 1,4,8,11- tetraazacyclotetradecane) and H₄BPTC (H₄BPTC = 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acid) in H ₂O/MeOH (2.5:1, v/v) in the presence of triethylamine. When solid 1 was immersed in the EtOH solutions of AgNO₃ (1-3 × 10 ^-1 M) and NaAuCl₄2H₂O (3.4 × 10 ^-2 M), respectively, for 5 min at room temperature, solids including Ag (3.7 ± 0.4 nm, diameter) and Au (2 nm, diameter) nanoparticles were formed by the redox reactions between Ni(II) ions incorporated in 1 and metal ions, as evidenced by HRTEM images, EPR, and XPS spectra. When single-crystal 1 was heated at 180 °C under 10^-5 Torr for 24 h, it was transformed to dehydrated compound {[Ni(cyclam)]₂[BPTC]}_n (2) in the single-crystal-to-single-crystal manner. The X-ray crystal structure of 2 reveals extensive dynamic motions of the molecular components in response to guest removal, involving rotation of the carboxylate and macrocycle, swing of the biphenyl, and bending of the macrocyclic coordination plane toward the carboxylate plane, which reduces the interlayer distance.