Hydrothermal synthesis of two copper helical coordination polymers with acentric three-dimensional framework constructing from mixed pyridine carboxylates

Two copper helical coordination polymers, [Cu(2-pc)(3-pc)]_n1 and [Cu(2-pc)(4-pc)]_n2 (2-pc=2-pyridine carboxylate, 3-pc=3-pyridine carboxylate, 4-pc=4-pyridine carboxylate) have been hydrothermally synthesized directly from pyridine carboxylic acids and copper nitrate. The crystal structure were determined by single-crystal X-ray diffraction with the following data: compound 1, orthorhombic, P2₁2₁2₁, a=6.591(3) Å, b=8.692(5) Å, c=20.548(9) Å, V=1177.2(9) Å³, Z=4; compound 2, orthorhombic, Pna2₁, a=21.160(10) Å, b=9.095(5) Å, c=6.401(3) Å, V=1231.9(11) Å³, Z=4. The acentric three-dimensional (3D) framework of 1 is constructed from right-handed helical Cu(2-pc) chains and left-handed Cu(3-pc) helices. As for 2, Cu(2-pc) helical chains, in which left- and right-handed helices are coexisting, and Cu(4-pc) zigzag chains combined together to form acentric 3D architecture of 2 as well. Additionally, besides general spectral characterization, we first introduce generalized 2D correlation spectroscopy to explore the coordination polymers and ascertain the stretching vibration location of carboxylate groups of compounds 1 and 2.