Molybdocalix[4]arene <italic>N</italic>,<italic>O</italic>-Schiff-base ligands*.

The ‘one-pot’ reaction of 2-hydroxy-3,5-di-<italic>tert</italic>-butylsalicylaldehyde with <italic>in situ</italic> generated ‘amino calixarene’ (from {Mo[(2-NC₆H₄)₂CH₂CH₂]Cl₂(DME)}, KO<italic>t</italic>Bu and p-<italic>tert</italic>-butylcalix[4]areneH₄<bold>L</bold>H₄) afforded, after work-up, the heterobimetallic salt K(NCMe)₂[Mo(NCMe)(OEt)(2-C₆H₄CH₂CH₂C₆H₄NH₂-2)<bold>L</bold>] (<bold>1</bold>∙2MeCN). By constrast, use of the ‘amino calixarene’ [Mo(NCMe)(2-C₆H₄CH₂CH₂C₆H₄NH₂-2)<bold>L</bold>] afforded the potassium/ethoxide-free complex [Mo(NCMe)(2-C₆H₄CH₂CH₂C₆H₄N-2-CHC₆H₂-2′-(OH)-3′,5′-<italic>t</italic>Bu)<bold>L</bold>] (<bold>2</bold>∙2MeCN). Reaction of the ‘amino calixarene’ (two equivalents) with the dialdehyde [1,3-(CHO)₂-5-MeC₆H₃OH-2] led, following work-up, to the isolation of the cation-anion pair [C₄₆H₄₂N₄O₂]²⁺[Mo₆O₁₉]²⁻·C₂H₃N (<bold>3</bold>∙MeCN). The molecular structures of <bold>1·</bold>2MeCN, <bold>2·</bold>2MeCN and <bold>3·</bold>MeCN are reported, for which it was necessary to use synchrotron radiation for data collection. Complex <bold>1</bold> contains an eliptical calixarene conformation as a result of <italic>π</italic>-interactions between the K⁺ and the arene groups and a distorted O₅N octahedral geometry at the molybdenum centre, whereas in ‘K⁺/ethoxide-free’ <bold>2</bold>, the calixarene retains the cone conformation and the metal possesses a distorted octahedral O₄N₂ coordination environment. In <bold>3</bold>, a protonated macrocyclic cation, formed via hydrolysis, has weak intermolecular interactions with the polyoxomolybdate anion. [ABSTRACT FROM AUTHOR]