 This paper examines the presence of formate defects in MOF-74, an important class of MOFs with open metal sites. Using multidimensional solid-state nuclear magnetic resonance, NMR, it was found that these defects were caused by decomposition of N-N-dimethylformamide, DMF, solvent during synthesis. DFT calculations and in situ NMR analysis revealed the location and coordination structure of the formate defects, which partially eliminated open metal sites and decreased the amount of nitrogen and carbon dioxide adsorbed. This study provides a comprehensive strategy for searching, elucidating, and manipulating defects in MOFs. This article was authored by Yo Fu, Ifeng Yo, Alexander C. Force, and others.