Thermally Induced Order-Disorder Transition in Crystals of Lithium Complexes of 1,5-Bis[2-(diphenylphosphorylmethyl)phenoxy]-3-oxapenthane[LiL](ClO4) and [LiL](NCS): Effect of the Anion on the Temperature of Transition

Compounds of 1,5-bis[2-(diphenylphosphorylmethyl)phenoxy]-3-oxapenthane (L) with lithium salts LiXL, where X- = ClO4, NCS, or I, and LiBrL center dot 2H(2)O, are synthesized. The IR spectra and the thermal behavior of complexes are studied. X- ray diffraction studies of isostructural [LiL](ClO4) (I) and [LiL](NCS) (II) crystals are performed. In the [LiL](+) complex, the ligand coordinates the Li atom by five O atoms, forming an environment in the shape of a trigonal bipyramid [in II at 174 K, the Li-O bonds are 1.829(3)-2.341(3) angstrom]. It is found that crystals I and II undergo a reversible phase transition of the order-disorder type with the change of symmetry (P2(1)/n <-> P (1) over bar). The temperatures of transition of crystals I and II differ by similar to 70 degrees. This distinction is explained by different types of disordering of the phenyl rings of the L ligand in the monoclinic phase, namely, dynamic in I and static in II. The analysis of intermolecular contacts allows one to relate the state of disordering of ligand L in the crystal to the strength of its interactions with the anion: in II the NCS- anion is firmly fixed by the C-H center dot center dot center dot S and C-H center dot center dot center dot N hydrogen bonds (at 174 K, H center dot center dot center dot S is 2.77 and H center dot center dot center dot O >= 2.36 angstrom); in I the C-H center dot center dot center dot O interactions of the ClO4- anion with the ligand are weaker (at 215 K, H center dot center dot center dot S >= 2.37 angstrom) and the anion is disordered.