Heteroleptic strontium complexes stabilized by donor-functionalized alkoxide and β-diketonate ligands

Heteroleptic complexes of strontium (1-7) were prepared by employing β-diketonates and donor-functionalized alkoxides as coordinating ligands. The results illustrate the effect of alkoxide substituent groups on the overall structures of the complexes. The presence of a terminal methoxy group in the alkoxide ligands leads to the formation of trimeric complexes 1-4, whereas the substituents on the amine nitrogen prove to have less influence in determining the structure. The attempts to increase steric bulkiness of the aminoalkoxide ligands by introducing ethyl groups on the amine nitrogen and to the alkoxy carbon did not lead to a structural change from the dimeric form in 5-7 but resulted in structurally interesting strontium complexes. In trimeric complexes 2-4, the three strontium atoms were held together by two μ₃-O bonds using alkoxide oxygen atoms and two μ₂-O bonds using a combination of alkoxide and β-diketonate ligand oxygens. The strontium metal centers in these complexes exhibit seven-coordination states in 2 and 4, whereas 3 exhibits one six-coordinated and two seven-coordinated strontium metals in its structure. All of the complexes were characterized using FT-NMR, FT-IR, elemental analyses, and thermogravimetric (TG) analyses.