Enhancing Thermal Stability and Volatility of Barium Complexes through Cyclic Nitrogen-Containing Auxiliary Ligands.

By introducing three ligands, cyclen (CYC), tetraazatetramethyl-12-crown-4 (TMCYC), and 1,4,10,13-tetaaoxa-7,16-diazacyclooctadecane (DCRO), into Ba(TMHD)2·H2O (1) system, we successfully synthesized [Ba(TMHD)2(CYC)(H2O)]2 (2), Ba(TMHD)2(TMCYC) (3), and Ba(TMHD)2(DCRO) (4) via very simple one-pot alcohol-water reaction, achieving mononuclear/dinuclear structures with enhanced coordination stability. Structural elucidation through single-crystal X-ray diffraction revealed nitrogen/oxygen-coordinated bonds that suppress polymerization tendencies, while thermogravimetric analysis demonstrated a remarkable 111 °C reduction in initial volatilization temperature (212 °C for 4) compared to commercial precursor 1, accompanied by single-stage weight loss, indicative of intact molecular frameworks at elevated temperatures, in contrast to the multistage weight loss of linear ligand-coordinated barium complexes. Furthermore, the residual mass at 600 °C improved markedly for the macrocyclic systems, with 3 achieving a 9.4% residue, indicating enhanced thermal stability and reduced volatile byproduct formation. DFT-D3 calculations indicated that ligand N atoms had strong electron-donating capabilities, and van der Waals interactions stabilized molecular packing. This cyclic ligand strategy optimizes barium precursor performance for YBCO thin film MOCVD and provides a paradigm for designing metal-organic compounds with tailored thermal stability and volatility.