Synthesis, crystal structure, thermal properties of a homoleptic Schiff base cobalt complex bis(N-tert-pentyl salicylaldimine)cobalt(II) as precursor for coating Co3O4 thin film by a plasma enhanced MOCVD

Abstract

A Schiff base complex of cobalt namely, bis(N-tert-pentyl-salicylaldimine)cobalt(II) (2) was synthesized by treating the parent complex, bis(salicylaldehydato)cobalt(II) (1) with n-tert-pentylamine in a methanolic medium. Complex 2 was analysed by dynamic TG/DTA using high purity Ar as purge gas at ambient pressure and was found to be volatile without undergoing decomposition leaving a negligible amount of (1.8 %) residue at 322 °C after melting sharply at 155 °C. The parent complex (1) wherein four oxygen atoms are coordinated to cobalt yielded a residue of 58 % at 400 °C. The dissimilarity in thermal property of 2 (CoN2O2) from that of 1 (CoO2O2) arises from the bonding of nitrogen atoms to cobalt by introducing n-tert-pentylamine which caused replacement of aldehyde O (–CH = O) with azomethine nitrogen (–CH = N). Single crystal XRD analysis of complex 2 revealed it to crystallise in orthorhombic crystal system with a space group of P212121. Further 2 was characterised by FTIR, elemental analysis and mass spectrometry. Transpiration TG technique was employed to evaluate the temperature dependence of saturated vapour pressure (pe) and enthalpy of vaporization (ΔvapH° = 102.3 ± 2.5 kJ mol−1) for 2 in the temperature range of 443–545 K. Complex 2 was transformed in to Co3O4 thin film at 350 °C in an Ar plasma by using a lab made plasma assisted chemical vapour deposition (CVD) process at 1.2 mbar deposition pressure. XRD revealed a preferential growth of cubic Co3O4 in the (311) plane. The SEM images confirmed a dense but scattered growth of cauliflower shaped structures. The particle size was found to be 19.3 nm. Kubelka-Munk function yielded a band gap of 2.01 eV.