Structural and spectroscopic studies of the 1:1 complex of lasalocid acid with 1,5,7-triazabicyclo[4.4.0]dec-5-ene

The crystal structure of the 1:1 complex of lasalocid acid with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) has been studied by X-ray diffraction, FT-IR spectroscopy and 1H NMR. The crystal space group is P212121 with a = 11.401(2) Å, b = 13.393(3) Å, c = 30.063(6) Å and Z = 4. In the crystal of the complex a cooperative system involving inter and intramolecular hydrogen bonds is formed. The protonated TBD and two ends of the lasalocid acid anion are hydrogen bonded. These NH⋯O hydrogen bonds are, with a length of 2.907(9) and 2.930(8) Å, relatively long. In the crystal structure the oxygen atoms of the carboxylate group are involved in three intramolecular hydrogen bonds of different length: O(4)H⋯O(1) of 2.848(7) Å, O(8)H⋯O(1) of 2.938(6) Å and O(3) H⋯O(2) of 2.460(8) Å. In chloroform and acetonitrile solutions the crystal structure of the 1:1 complex is only partially preserved, and additionally a new structure, in which the ketone carbonyl group is hydrogen bonded, is formed. The structures have been modeled using the semiempirical PM5 method.