Among the earliest organometallic complexes was a compound known as cacodyl, or tetramethyldiarsine. This compound, with the chemical formula C₄H₁₂As₂ (shown below at left), was first discovered in 1760 and was known for its toxicity and terrible odor. The first platinum olefin complex, C₂H₄Cl₃KPt (also known as Zeise’s salt; see below, right), was discovered in 1829. This early organometallic complex was influential in establishing some of the essential underlying concepts that have since become crucial to organometallic chemistry. These examples represent just a couple of the first organometallic species, and to date, thousands of organometallic complexes are known.