Effect of pH on the charge‐assisted hydrogen‐bonded assembly of the anionic [Cu(oxalate) 2 2 ] 2? 2? building unit and N N , N N ′‐ditopic cations

摘要

By the solvothermal reaction under acidic conditions of Cu(NO 3 ) 2 ·3H 2 O, Na 2 C 2 O 4 and the N , N ′‐ditopic organic coligands 1‐(pyridin‐4‐yl)piperazine (ppz) and 1,2‐bis(pyridin‐4‐yl)ethane (bpa), two novel anionic copper(II) coordination compounds were obtained, namely the one‐dimensional coordination polymer catena ‐poly[4‐(pyridin‐1‐ium‐4‐yl)piperazin‐1‐ium [[(oxalato‐κ 2 O 1 , O 2 )copper(II)]‐μ‐oxalato‐κ 3 O 1 , O 2 : O 1′ ]], {(C 9 H 15 N 3 )[Cu(C 2 O 4 ) 2 )]} n or {(H 2 ppz)[Cu(C 2 O 4 ) 2 ]} n , (I), and the discrete ionic complex 4,4′‐(ethane‐1,2‐diyl)dipyridinium bis(oxalato‐κ 2 O 1 , O 2 )copper(II), (C 12 H 14 N 2 )[Cu(C 2 O 4 ) 2 ] or (H 2 bpa)[Cu(C 2 O 4 ) 2 ], (II). The products were characterized by single‐crystal X‐ray diffraction, elemental analysis, powder X‐ray diffraction, thermogravimetric analyses and UV and IR spectroscopic techniques. The [Cu(C 2 O 4 ) 2 ] 2? units for (I) and (II) are stabilized by H 2 ppz 2+ and H 2 bpa 2+ cations, respectively, via charge‐assisted hydrogen bonds. Also, a study of the pH‐controlled synthesis of this system shows that (I) was obtained at pH values of 2–4. When using bpa, a two‐dimensional square‐grid network of [Cu(C 2 O 4 )(bpa)] n was obtained at a pH of 4. This indicates that the pH of the reaction also plays a key role in the structural assembly and coordination abilities of oxalate and N , N ′‐ditopic coligands.