Preparation and crystal structure of a 1:4 diaqua(benzo-15-crown-5)(perchlorato-O)calcium perchlorate and diaqua(4′-nitrobenzo-15-crown-5)(perchlorato-O)calcium perchlorate solid solution

Abstract

A 1 : 4 diaqua(benzo-15-crown-5)(perchlorato-O)calcium perchlorate and diaqua(4`-nitrobenzo-15-crown-5)(perchlorato-O)calcium solid solution [Ca(ClO 4 )L . H 2 O) 2 ] + ClO 4 ! [L = (B15C5) 0.2 (4`-NO 2 -B15C5) 0.8 ] was prepared and studied by X-ray diffraction. The complex cation [Ca(ClO 4 )L(H 2 O) 2 ] + is of the guest3host type. The coordination polyhedron of its Ca 2+ cation is irregular, viz. a distorted prism with two different bases: pentagonal (of five ether oxygen atoms of mixed crown ligand L) and trigonal (of one oxygen atom of the anionic ligand ClO 4 ! and two oxygen atoms of the two water molecules). The packing of the complex cations and disordered ClO 4 ! anions in the crystal structure of this solid solution was determined to find that these ions are connected by hydrogen bonds into infinite three-dimensional layers.In the present work we originally planned to obtain a complex of diaqua(benzo-15-crown-5)(perchlorato-O)calcium perchlorate (II) by replacing the anionic ligands in the complex (benzo-15-crown-5)bis(nitrato-O,O`)calcium (I) by its treatment with concentrated aqueous perchloric acid. The guest3host complexes I and II have both been earlier prepared by conventional procedures, and their crystal structures have been studied by X-ray diffraction [1, 2], but full crystallographic data for complex II [2] have so far been unvailable.The reaction of complex I with perchloric acid gave not only complex II, but also, in a much higher yield, a complex with a nitro-substituted crown ligand diaqua(4`-nitrobenzo-15-crown-5)(perchlorato-O)-calcium perchlorate (III). Thus, the overall scheme of this reaction appeared to be as follows. 7776 III (~80%)This reaction was exothermic, and, as seen from the scheme, most benzo-15-crown-5 (B15C5) ligands proved to be nitrated by the liberated free nitric acid. Heating of the reaction mixture proved to be insufficient to nitrate all the B15C5 ligands in the reaction mixture.Crystals of compound IV of unknown composition were precipitated from the reaction mixture upon solvent evaporation. The X-ray diffraction analysis of the crystals showed that they are a solid solution of complexes II and III of the following composition: IV = II 0.2 III 0.8 (the definition of solid solution has been considered, for example, in the monograph [3]). These are the results of this X-ray analysis that allowed us to propose the abovementioned reaction scheme. A fragment of the molecular ionic crystal packing of solid solution IV is shown in the figure; the bond lengths and the principal bond and torsion angles are given in Tables 133. The independent part of the crystal unit cell of complex IV contains one disordered ClO 4 ! anion (its atoms are labeled B and B`) and one complex cation [Ca(ClO 4 )L(H 2 O) 2 ] (IVa) with a mixed crown ligand L = (B15C5) 0.2 (4`-NO 2 -B15C5) 0.8 with the benzene ring containing in the 4p osition (at C 17 ) a nitro group comprising N 20 , O 21 , and O 22 (probability 80%) or H 17 (probability 20%).Cation IVa is a guest3host complex [4]: Its Ca 2+ ...