Design, Structural Characterization and Catalytic Activity of Incomplete Dicubane Clusters of N-Substituted Diethanolamines

Abstract

A series of four new clusters with cationic unit [Co4(µ3-OH)(Rdea)2(L–L)4]4+ [R = –CH3 (1 and 2) or –CH2CH2CH2CH3 (3 and 4), L–L = 1,10-phenanthroline or 2,2′-bipyridine] is designed and characterized by elemental, spectroscopic (FTIR, ESI MS, UV–visible), thermal, electrochemical, magnetic, SEM, EDX, PXRD and single crystal X-ray crystallographic techniques. Spectral and single crystal X-ray studies reveal the complexes 1–4 are tetranuclear clusters where the primary aminoalcohol derivative ligand is present in dianionic form i.e., Medea2− or n Budea2−. It is confirmed from the magnetic and bond valence summation data that the four cobalt ions are present in mixed valent states (Co 2 2+ –Co 2 3+ ), which is further corroborated from the Co–O and Co–N bond lengths in X-ray structure. The bridging two hydroxide ions consolidate the tetranuclear clusters by bonding with three neighboring metal ions and a rare incomplete dicubane core is formed in all the complexes. A supramolecular framework is generated by H-bonding, π–π, CH···π, and H···H interactions. Presence of N-alkyl group and N-heterocyclic chelator facilitates the generation of these non covalent interactions thus stabilizing the framework. Of all the complexes reported here, 1 is found most efficient catalyst for the cobalt-catalyzed aerobic oxidation of neat ethylbenzene and p-xylene.