( Dibenzo-18-crown-6 ) ( 2-phenylamidopyridine )-rubidium ( I )

# 2004 International Union of Crystallography Printed in Great Britain ± all rights reserved The title complex, [Rb(C11H9N2)(C20H24O6)], has rubidium in an irregular eightfold coordination, with a hexadentate crown ether ligand and a chelating bidentate amidopyridine ligand, each occupying one hemisphere of the coordination. The chelate RbNCN ring is essentially planar, but the two rings of the amidopyridine ligand are not coplanar, because of steric interaction of H atoms on the rings. The RbÐN(amido) bond is shorter than the RbÐN(pyridine) bond.

The title complex, [Rb(C 11 H 9 N 2 )(C 20 H 24 O 6 )], has rubidium in an irregular eightfold coordination, with a hexadentate crown ether ligand and a chelating bidentate amidopyridine ligand, each occupying one hemisphere of the coordination. The chelate RbNCN ring is essentially planar, but the two rings of the amidopyridine ligand are not coplanar, because of steric interaction of H atoms on the rings. The RbÐN(amido) bond is shorter than the RbÐN(pyridine) bond.
Like the analogous complex (18-crown-6)Rb(L), the title complex (dibenzo-18-crown-6)Rb(L), (I), consists of discrete neutral molecules with no special intermolecular interactions. The crown ligand is hexadentate and occupies one coordination hemisphere, with the bidentate amide ligand occupying the other, giving irregular eightfold coordination for the rubidium ion. The complex may be described as a contact ionpair, in contrast to several of the crown-ligated complexes of alkali metals with the amide L À , which exist in the solid state as separated ion pairs (Liddle et al., 2004).
The molecular structure of (I) ( Fig. 1 and Table 1) is very similar to that of the (18-crown-6) complex, which has already been described and compared with related complexes (Liddle et al., 2004). The main differences are probably due predominantly to the greater rigidity of dibenzo-18-crown-6 compared with 18-crown-6. The range of RbÐO bond lengths is somewhat smaller, and the two RbÐN bonds are both shorter in (I), by about 0.05±0.08 A Ê , with the shorter bond to the amide N atom in both complexes. The Rb + ion lies 1.0945 (6) A Ê out of the mean plane of the six O atoms of the crown (r.m.s. deviation 0.111 A Ê ), displaced towards the amide ligand, and the two benzene rings of the crown are folded out of the oxygen mean plane towards the amide ligand by 22.93 (7) and 25.94 (7) , presumably as a result of intermolecular packing interactions in the absence of an obvious electronic factor. As expected, the crown ether ring displays a sequence of anti (or trans) conformations about CÐCÐOÐC and gauche conformations about OÐCÐCÐO linkages, except for the near-zero torsion angles for OÐCÐCÐO at the constrained benzo fusions (Table 1).
Chelation by the amide ligand forces a syn arrangement for the two N atoms. The two rings are not coplanar, however, because of steric interaction of the H atoms bonded to C4 and C11; the dihedral angle between the rings is 58.10 (5) . The four-membered chelate ring (RbNCN) is essentially planar, the dihedral angle between the RbN 2 and CN 2 planes being only 0.3 (3) . Experimental n-Butyllithium (0.4 ml of a 2.5 M solution in hexanes, 1.0 mmol) was added dropwise to a solution of 2-phenylaminopyridine (0.17 g, 1.0 mmol) and dibenzo-18-crown-6 (0.36 g, 1.0 mmol) in tetrahydrofuran (THF, 40 ml), followed by rubidium 2-ethylhexoxide (0.22 g, 1.0 mmol) in THF (10 ml), to give a pale yellow precipitate. Volatile components were removed in vacuo and the remaining solid was washed with petroleum ether (3 Â 5 ml). Recrystallization from hot toluene containing a little hexamethylphosphoramide (HMPA) gave yellow crystals of (I) (yield 0.31 g, 51%). Chemical analysis results were satisfactory, and the 1 H and 13 C{ 1 H} NMR signals could be assigned on the basis of the crystal structure (Liddle, 2000).
We thank the EPSRC for ®nancial support. The molecular structure of (I), showing the atom labels and 50% probability displacement ellipsoids for non-H atoms. Crystal data [Rb(C 11