A compound comprising a hexadentate ligand of Formula I coordinated to a metal selected from the group consisting of iridium, rhodium, and osmium; wherein rings A, B, C, D, E, and F are independently a 5-membered or 6-membered heteroaryl ring, or a 6-membered aryl ring; T1, T2, T3, T4, T5, and T6 are independently selected from C or N, wherein two to four of T1 to T6 are C, and two to four of T1 to T6 are N; Z1, Z2, Z3, and Z4 are independently selected from C or N, wherein if Z1 and Z2 are each N then T1 is a carbene carbon and two of T2 to T6 are N; Y1 and Y2 are independently selected from the group consisting of CR, SiR, B, or N; W1-W7 are independently selected from the group consisting of a direct bond, BR, BRR′, NR, PR, O, S, Se, C═X, S═O, SO2, CR, CRR′, SiRR′, GeRR′, alkyl, cycloalkyl, aryl, heteroaryl, and combinations thereof; wherein X is selected from the group consisting of O, S, Se, NR′, and CR″R′″; RA to RF independently represent mono to the maximum allowable substitution, or no substitution; each R, R′, R″, R′″, and RA to RF is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, boryl, arylalkyl, alkoxy, aryloxy, amino, silyl, germyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, selenyl, and combinations thereof, and any two adjacent substituents R, R′, R″, R′″, and RA to RF are optionally joined to form a fused ring.