3-Iodo-5-[2-(2-pyridinyl)ethynyl]-benzonitrile-d4 is the isotope analog of 3-Iodo-5-[2-(2-pyridinyl)ethynyl]-benzonitrile. 3-Iodo-5-[2-(2-pyridinyl)ethynyl]-benzonitrile is used in the synthetic preparation of 3,5-disubstituted thiazolylethynyl- and pyridinylethynylbenzenes as potent mGluR5 antagonists.