A polynuclear complex, {[Cu(bpe)2](NO3)}, with interpenetrated diamondoid networks: synthesis, properties and catalytic behavior

Abstract

A polynuclear complex {[Cu(bpe)₂](NO₃)} (1), with five-fold interpenetrated diamondoid nets, was synthesized following a hydrothermal procedure, starting from a copper(II) salt, Cu(NO₃)₂·2.5H₂O, and using a molar ratio Cu(NO₃)₂ : monoethanolamine : bpe : H₂O of 1 : 3 : 1 : 500. The well stirred mixture was introduced into a Teflon-lined stainless steel autoclave, heated at 423 K, and kept at this temperature for 3 days. Red single crystals containing complex 1 were fully characterized by chemical analysis, FTIR, single-crystal X-ray diffraction, powder XRD, DR-UV-Vis, TG–heat flow analysis, sorption isotherms of N₂ at 77 K, and X-ray photoelectron spectroscopy (XPS). The characterization results indicated that these crystals corresponded to a copper–organic network with a microporous-like structure in which part of the channels are blocked by water molecules and nitrate ions. The synthesis led to a structure in which all the Cu ions were well stabilized as a Cu(I) species, although the precursor was a Cu(II) compound. This structure exhibits remarkable properties: high thermal stability and capacity to totally exchange NO₃⁻ anions, without causing any damage to the microporous texture. The catalytic behavior was investigated in NO decomposition and NO reduction with hexane in the presence of O₂, revealing very interesting and high catalytic activity. Cu was well preserved in a Cu(I) state after the catalytic tests, which provided new information about the mechanism of NO reaction on copper.