Inclusion of unique four-clawed crown-like nitrate–water cluster [(NO3)6(H2O)6]6− anions into the inter-spaces of a 3D H–bonded cationic net formed by a cationic calix[4]arene

Abstract

Reaction of 5,11,17,23-tetramino-25,26,27,28-tetrahydroxy-calix[4]arene (1) with MeI and NaOAc·3H₂O in DMF produced a tetracationic calix[4]arene [H₄L]I₄ (2) {H₄L = [5,11,17,23-tetrakis(trimethylammonium)-25,26,27,28-tetrahydroxycalix[4]arene]} in 90% yield. Anion exchange of 2 with [Ag(MeCN)₄](PF₆) in MeCN afforded [H₄L](PF₆)₄ (3). Treatment of 3 with Na₂CO₃ or NaNO₃ in MeCN afforded two mono-deprotonated complexes [H₃L](PF₆)₃·MeCN (4·MeCN) and [(H₃L)₂{(NO₃)₆(H₂O)₆}]·4MeCN (5·4MeCN). Compounds 4·MeCN and 5·4MeCN have been characterized by elemental analysis, IR spectra, ¹H NMR, and single-crystal X-ray crystallography. 4·MeCN contains a 3D cationic H–bonded [H₃L]_n³ⁿ⁺ net in which PF₆⁻ anions are embedded into its 1D channels. 5·4MeCN consists of another 3D cationic H–bonded [H₃L]_n³ⁿ⁺ net in which the unique four-clawed crown-like nitrate–water cluster [(NO₃)₆(H₂O)₆]⁶⁻ anions are included into the inter-spaces between the layers of [H₃L]³⁺ trications. The formation of this nitrate–water cluster anion may demonstrate interesting information about the hydration of nitrate in water-related systems.