title: Molecular Co(II) and Co(III) heteroarylalkenolates as efficient precursors for chemical vapor deposition of Co3O4 nanowires.
abstract: Two new cobalt precursors, Co(II)(PyCHCOCF3)2(DMAP)2 (1) and Co(III)(PyCHCOCF3)3 (2), based on Co(II) and Co(III) centers were synthesized using a redox active ligand system. The different chemical configurations of 1 and 2 and differential valence states of cobalt were confirmed by crystal structure determination and comprehensive analytical studies. Whereas 1 could not be studied by NMR due to the paramagnetic nature of the central atom, 2 was unambiguously characterized by multinuclear 1D and 2D NMR experiments in solution. Both compounds are efficient precursors for catalyst-free growth of Co3O4 nanowires on Si and Al2O3 substrates by a chemical vapor deposition process. The different valence states of cobalt species influenced their chemical decomposition pathways in the gas phase; for instance, 1 was partially oxidized (Co(2+) → Co(3+)), and 2 underwent reduction (Co(3+) → Co(2+)) to form pure cobaltite in both cases that verified the metal-ligand redox interplay. Co3O4 nanowires with nanometric diameters (50-100 nm) were obtained irrespective of the chosen cobalt precursor. Investigations on the humidity sensing behavior of CVD deposits demonstrated their potential as promising sensor materials.
authors.affiliation: Institute of Inorganic Chemistry, University of Cologne , Greinstrasse 6, Cologne 50939, Germany.
authors.forename: Mehtap
authors.initials: M
authors.lastname: Büyükyazi
authors.forename: Corinna
authors.initials: C
authors.lastname: Hegemann
authors.forename: Thomas
authors.initials: T
authors.lastname: Lehnen
authors.forename: Wieland
authors.initials: W
authors.lastname: Tyrra
authors.forename: Sanjay
authors.initials: S
authors.lastname: Mathur