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2] Rotananes were first prepared by solid-phase synthesis (I. T. Harrison. S. Harrison. J. Am. C h m . Soc. 1967, 89. 5723-5724) and by directed synthesis (G. Schill. H Zollenkopf, Liehigs Ann. Clium 1969. 721. 53-74). For an early use o f the hydrophobic effect to direct rotaxane synthesis see H. Ogino. J Am. Chmi. Soc. 1981Soc. , 103, 1303Soc. -1304. For some recent rotaxanes see: a) D. B.

Combined crystallographic and IR spectroscopic study of the hydrogen bond network in the synthetic sex steroid mestranol indicates that a C•C-H ... O hydrogen bond can be considerably enhanced if the C•C-H donor simultaneously accepts an O-H ...

In the crystal structuores of three terminal alkynes, long GC-H * G42 contacts with H C separations in the range 2.7-3.1 A are observed. Despite the long distances, these contacts possess the characteristic infrared spectroscopic features of weak hydrogen bonds. This provides direct evidence that the range of C-H A interactions donated by sufficiently acidic C-H groups extends beyond van der Waals separation. In two of the crystal structures, the C-H --4 R interactions form interconnected systems C S -H CZEZE-H * CEEEE-H.

A series of O,N-chelated vanadium(IV) oxo bis(phenolate) complexes (1a-i) have been prepared from [VOCl 2 -(THF) 2 ] and several ortho-amino-functionalized phenols in the presence of a base. The intermediates in the synthesis of these compounds are mono(phenolato)vanadate complexes, as was shown by the reaction of [VOCl 2 (THF) 2 ] with 1 equiv of HOC 6 H 2 (CH 2 NMe 2 ) 2 -2,6-Me-4 in the absence of base. This yielded [VOCl 2 (OC 6 H 2 (CH 2 NMe 2 )-2-Me-4-(CH 2 NHMe 2 )-6)] (2), in which the second amine function acts as an internal base, assisting in binding the formed equivalent of HCl. Complex 2 exists in the solid state as the dichlorovanadate(IV) species with the protonated amine function forming a three-centered intramolecular hydrogen bridge in which both a chloride atom and the oxygen atom of the phenolate ligand participate. EPR, UV-vis, and cyclic voltammetry analysis of the complexes with meta or para substituents (1a-g) on the aryloxy ring showed the hyperfine coupling constant, the HOMO-LUMO transition, and the oxidation potential, respectively, to be linearly related to the Hammett σ constants of the substituents on the monoanionic aryloxy ring. The oxidation potential shows a large dependence (dE ox /dσ ) 170 mV (per phenoxy ligand)) on the Hammett constant. Crystal data: 1a, orthorombic, Pbca, a ) 9.4321 (7)

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