A compound including a Ligand L of Formula I: as well as, a first device and a formulation containing the same, are disclosed. In the compound including the Ligand L of Formula I: X is selected from the group consisting of S, Se, SiRR′ and GeRR′; R1, R2, R, and R′ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; any adjacent substitutions or substituents of R1, R2, R, and R′ are optionally linked together to form a ring; the Ligand L is coordinated to a metal M having an atomic number of 40 or greater; and the Ligand L is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.