Organometallic compound, organic light-emitting device including the organometallic compound, and diagnostic composition including the organometallic compound

1. An organometallic compound represented by Formula 1:

wherein, in Formula 1,

M is beryllium, magnesium, aluminum, calcium, titanium, manganese, cobalt, copper, zinc, gallium, germanium, zirconium, ruthenium, rhodium, palladium, silver, rhenium, platinum, or gold,

X 1 to X 4 are each independently N or C,

Y 1 is C, Si, Ge, B, N, or P,

X 5 is O, S, B(R′), N(R′), P(R′), C(R′)(R″), Si(R′)(R″), Ge(R′)(R″), C(═O), B(R′)(R″), N(R′)(R″), or P(R′)(R″),

two bonds of a bond between X 5 and M, a bond between X 2 and M, a bond between X 3 and M, and a bond between X 4 and M are each a covalent bond, and the others thereof are each a coordinate bond,

ring CY 1 to ring CY 5 are each independently a C 5 -C 30 carbocyclic group or a C 1 -C 30 heterocyclic group,

T 1 and T 2 are each independently a single bond, a double bond, *—N(R 6 )—*′, *—B(R 6 )—*′, *—P(R 6 )—*′, *—C(R 6 )(R 7 )—*′, *—Si(R 6 )(R 7 )—*′, *—Ge(R 6 )(R 7 )—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O) 2 —*′, *—C(R 6 )═*′, *═C(R 6 )—*′, *—C(R 6 )═C(R 7 )—*′, *—C(═S)—*′, or *—C≡C—*′, and * and *′ each indicate a binding site to a neighboring atom, wherein T 2 is not a single bond,

R 7 and R 8 are optionally linked via a single bond, a double bond, or a first linking group to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with at least one R 10a , or a combination thereof,

T 3 is a single bond, a double bond, *—N(R 8 )—*′, *—B(R 8 )—*′, *—P(R 8 )—*′, *—C(R 8 )(R 9 )—*′, *—Si(R 8 )(R 9 )—*′, *—Ge(R 8 )(R 9 )—*′, *—S—*′, *—Se—*′, *—O—*′, *—C(═O)—*′, *—S(═O)—*′, *—S(═O) 2 —*′, *—C(R 8 )═*′, *═C(R 8 )—*′, *—C(R 8 )═C(R 9 )—*′, *—C(═S)—*′, or *—C≡C—*′, and * and *′ each indicate a binding site to a neighboring atom,

R 8 and R 9 are optionally linked via a single bond, a double bond, or a second linking group to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with a at least one R 10a , or a combination thereof,

R 1 to R 9 , R′, and R″ are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, —SF 5 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60 alkyl group, a substituted or unsubstituted C 2 -C 60 alkenyl group, a substituted or unsubstituted C 2 -C 60 alkynyl group, a substituted or unsubstituted C 1 -C 60 alkoxy group, a substituted or unsubstituted C 3 -C 10 cycloalkyl group, a substituted or unsubstituted C 2 -C 10 heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10 cycloalkenyl group, a substituted or unsubstituted C 2 -C 10 heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60 aryl group, a substituted or unsubstituted C 6 -C 60 aryloxy group, a substituted or unsubstituted C 6 -C 60 arylthio group, a substituted or unsubstituted C 1 -C 60 heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), or —P(═O)(Q 8 )(Q 9 ),

a1 to a5 are each independently an integer from 0 to 20,

two or more of a plurality of neighboring R 1 are optionally linked to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with at least one R 10a , or a combination thereof,

two or more of a plurality of neighboring R 2 are optionally linked to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with at least one R 10a , or a combination thereof,

two or more of a plurality of neighboring R 3 are optionally linked to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with at least one R 10a , or a combination thereof,

two or more of a plurality of neighboring R 4 are optionally linked to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with at least one R 10a , or a combination thereof,

two or more of a plurality of neighboring R 5 are optionally linked to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with at least one R 10a , or a combination thereof,

two or more R 1 to R 9 are optionally linked to form a C 5 -C 30 carbocyclic group that is unsubstituted or substituted with at least one R 10a , a C 2 -C 30 heterocyclic group that is unsubstituted or substituted with at least one R 10a , or a combination thereof,

R 10a is the same as defined in connection with R 1 ,

a substituent of the substituted C 1 -C 60 alkyl group, the substituted C 2 -C 60 alkenyl group, the substituted C 2 -C 60 alkynyl group, the substituted C 1 -C 60 alkoxy group, the substituted C 3 -C 10 cycloalkyl group, the substituted C 2 -C 10 heterocycloalkyl group, the substituted C 3 -C 10 cycloalkenyl group, the substituted C 2 -C 10 heterocycloalkenyl group, the substituted C 6 -C 60 aryl group, the substituted C 6 -C 60 aryloxy group, the substituted C 6 -C 60 arylthio group, the substituted C 1 -C 60 heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group is:

deuterium, —F, —Cl, —Br, —I, —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60 alkyl group, a C 2 -C 60 alkenyl group, a C 2 -C 60 alkynyl group, or a C 1 -C 60 alkoxy group;

a C 1 -C 60 alkyl group, a C 2 -C 60 alkenyl group, a C 2 -C 60 alkynyl group, or a C 1 -C 60 alkoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 3 -C 10 cycloalkyl group, a C 2 -C 10 heterocycloalkyl group, a C 3 -C 10 cycloalkenyl group, a C 2 -C 10 heterocycloalkenyl group, a C 6 -C 60 aryl group, a C 6 -C 60 aryloxy group, a C 6 -C 60 arylthio group, a C 1 -C 60 heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q 11 )(Q 12 ), —Si(Q 13 )(Q 14 )(Q 15 ), —B(Q 16 )(Q 17 ), —P(═O)(Q 18 )(Q 19 ), or any combination thereof;

a C 3 -C 10 cycloalkyl group, a C 2 -C 10 heterocycloalkyl group, a C 3 -C 10 cycloalkenyl group, a C 2 -C 10 heterocycloalkenyl group, a C 6 -C 60 aryl group, a C 6 -C 60 aryloxy group, a C 6 -C 60 arylthio group, a C 1 -C 60 heteroaryl group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group;

a C 3 -C 10 cycloalkyl group, a C 2 -C 10 heterocycloalkyl group, a C 3 -C 10 cycloalkenyl group, a C 2 -C 10 heterocycloalkenyl group, a C 6 -C 60 aryl group, a C 6 -C 60 aryloxy group, a C 6 -C 60 arylthio group, a C 1 -C 60 heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, each substituted with deuterium, —F, —Cl, —Br, —I, —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60 alkyl group, a C 2 -C 60 alkenyl group, a C 2 -C 60 alkynyl group, a C 1 -C 60 alkoxy group, a C 3 -C 10 cycloalkyl group, a C 2 -C 10 heterocycloalkyl group, a C 3 -C 10 cycloalkenyl group, a C 2 -C 10 heterocycloalkenyl group, a C 6 -C 60 aryl group, a C 6 -C 60 aryloxy group, a C 6 -C 60 arylthio group, a C 1 -C 60 heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q 21 )(Q 22 ), —Si(Q 23 )(Q 24 )(Q 25 ), —B(Q 26 )(Q 27 ), —P(═O)(Q 28 )(Q 29 ), or any combination thereof; or

—N(Q 31 )(Q 32 ), —Si(Q 33 )(Q 34 )(Q 35 ), —B(Q 36 )(Q 37 ), or —P(═O)(Q 38 )(Q 39 ), and

Q 1 to Q 9 , Q 11 to Q 19 , Q 21 to Q 29 , and Q 31 to Q 39 are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60 alkyl group, a C 1 -C 60 alkyl group substituted with deuterium, a C 1 -C 60 alkyl group, a C 6 -C 60 aryl group, or any combination thereof, a C 2 -C 60 alkenyl group, a C 2 -C 60 alkynyl group, a C 1 -C 60 alkoxy group, a C 3 -C 10 cycloalkyl group, a C 2 -C 10 heterocycloalkyl group, a C 3 -C 10 cycloalkenyl group, a C 2 -C 10 heterocycloalkenyl group, a C 6 -C 60 aryl group, a C 6 -C 60 aryl group substituted with deuterium, a C 1 -C 60 alkyl group, a C 6 -C 60 aryl group, or any combination thereof, a C 6 -C 60 aryloxy group, a C 6 -C 60 arylthio group, a C 1 -C 60 heteroaryl group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropoly cyclic group.

2. The organometallic compound of claim 1 , wherein

M is Pd, Pt, or Au.

3. The organometallic compound of claim 1 , wherein

X 1 and X 3 are each independently C,

X 2 and X 4 are each independently N, and

Y 1 is B, N, or P.

4. The organometallic compound of claim 1 , wherein

X 5 is O or S.

5. The organometallic compound of claim 1 , wherein

a bond between X 5 and M and a bond between X 3 and M are each a covalent bond, and

a bond between X 2 and M and a bond between X 4 and M are each a coordinate bond.

6. The organometallic compound of claim 1 , wherein

ring CY 1 to ring CY 5 are each independently a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a cyclopentadiene group, a 1,2,3,4-tetrahydronaphthalene group, a furan group, a thiophene group, a silole group, an indene group, a fluorene group, an indole group, a carbazole group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, a benzosilole group, a dibenzosilole group, an azafluorene group, an azacarbazole group, an azadibenzofuran group, an azadibenzothiophene group, an azadibenzosilole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a phenanthroline group, a pyrrole group, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isoxazole group, a thiazole group, an isothiazole group, an oxadiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzothiazole group, a benzoxadiazole group, a benzothiadiazole group, a 5,6,7,8-tetrahydroisoquinoline group, a 5,6,7,8-tetrahydroquinoline group, an indazole group, a benzofluorene group, a benzocarbazole group, a naphthobenzofuran group, a naphthobenzothiophene group, or a naphthobenzosilole group.

7. The organometallic compound of claim 1 , wherein

T 1 is a single bond, and

T 2 is *—N(R 7 )—*′, *—B(R 7 )—*′, *—P(R 7 )—*′, *—C(R 7 )(R 8 )—*′, *—Si(R 7 )(R 8 )—*′, *—Ge(R 7 )(R 8 )—*′, *—S—*′, or *—O—*′.

8. The organometallic compound of claim 1 , wherein

T 3 is a single bond.

9. The organometallic compound of claim 1 , wherein

R 1 to R 9 , R′, and R″ are each independently:

hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, —SF 5 , a C 1 -C 20 alkyl group, or a C 1 -C 20 alkoxy group;

a C 1 -C 20 alkyl group or a C 1 -C 20 alkoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10 alkyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cycloctyl group, an adamantyl group, a norbornyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, or any combination thereof;

a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cycloctyl group, an adamantyl group, a norbornyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, a phenoxy group, or a naphthoxy group;

a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cycloctyl group, an adamantyl group, a norbornyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, a phenoxy group, or a naphthoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20 alkyl group, a C 1 -C 20 alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cycloctyl group, an adamantyl group, a norbornyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —Si(Q 33 )(Q 34 )(Q 35 ), or any combination thereof; or

—N(Q 1 )(Q 2 ), —Si(Q 3 )(Q 4 )(Q 5 ), —B(Q 6 )(Q 7 ), or —P(═O)(Q 8 )(Q 9 ), and

Q 1 to Q 9 and Q 33 to Q 35 are each independently:

—CH 3 , —CD 3 , —CD 2 H, —CDH 2 , —CH 2 CH 3 , —CH 2 CD 3 , —CH 2 CD 2 H, —CH 2 CDH 2 , —CHDCH 3 , —CHDCD 2 H, —CHDCDH 2 , —CHDCD 3 , —CD 2 CD 3 , —CD 2 CD 2 H, or —CD 2 CDH 2 ;

an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a phenyl group, or a naphthyl group; or

an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a phenyl group, or a naphthyl group, each substituted with deuterium, a C 1 -C 10 alkyl group, a phenyl group, or any combination thereof.

10. The organometallic compound of claim 1 , wherein

a group represented by

in Formula 1 is a group represented by one of Formulae CY1-1 to CY1-34:

wherein, in Formulae CY1-1 to CY1-34,

X 1 and R 1 are each independently the same as described in claim 1 ,

X 11 is O, S, N(R 11 ), C(R 11 )(R 12 ), or Si(R 11 )(R 12 ),

R 11 to R 18 are each independently the same as defined in connection with R 1 in claim 1 ,

a16 is an integer from 0 to 6,

a15 is an integer from 0 to 5,

a14 is an integer from 0 to 4,

a13 is an integer from 0 to 3,

a12 is an integer from 0 to 2,

* indicates a binding site to X 5 in Formula 1, and

*′ indicates a binding site to Y 1 in Formula 1.

11. The organometallic compound of claim 1 , wherein

a group represented by

in Formula 1 is a group represented by one of Formulae CY2-1 to CY2-7:

wherein, in Formulae CY2-1 to CY2-7,

X 2 , Y 1 , T 3 , R 2 , and R 5 are each independently the same as described in claim 1 ,

a22 is an integer from 0 to 2,

a54 is an integer from 0 to 4,

a53 is an integer from 0 to 3,

*indicates a binding site to M in Formula 1,

*′ indicates a binding site to ring CY 1 in Formula 1, and

*″ indicates a binding site to T 1 in Formula 1.

12. The organometallic compound of claim 1 , wherein

a group represented by

in Formula 1 is a group represented by one of Formulae CY3-1 to CY3-26:

wherein, in Formulae CY3-1 to CY3-26,

X 3 and R 3 are each independently the same as described in claim 1 ,

X 31 is O, S, N(R 31 ), C(R 31 )(R 32 ), or Si(R 31 )(R 32 ),

R 31 to R 38 are each independently the same as defined in connection with R 3 in claim 1 ,

a35 is an integer from 0 to 5,

a34 is an integer from 0 to 4,

a33 is an integer from 0 to 3,

a32 is an integer from 0 to 2,

*″ indicates a binding site to T 1 in Formula 1,

* indicates a binding site to M in Formula 1, and

*′ indicates a binding site to T 2 in Formula 1.

13. The organometallic compound of claim 1 , wherein

a group represented by

in Formula 1 is a group represented by one of Formulae CY4-1 to CY4-34:

wherein, in Formulae CY4-1 to CY4-34,

X 4 and R 4 are each independently the same as described in claim 1 ,

X 41 is O, S, N(R 41 ), C(R 41 )(R 42 ), or Si(R 41 )(R 42 ),

R 41 to R 48 are each independently the same as defined in connection with R 4 in claim 1 ,

a46 is an integer from 0 to 6,

a45 is an integer from 0 to 5,

a44 is an integer from 0 to 4,

a43 is an integer from 0 to 3,

a42 is an integer from 0 to 2,

* indicates a binding site to M in Formula 1, and

*′ indicates a binding site to T 2 in Formula 1.

14. The organometallic compound of claim 1 , wherein,

in Formula 1,

a group represented by

is a group represented by one of Formulae CY1(1) to CY1(31),

a group represented by

is a group represented by one of Formulae CY2(1) to CY2(8),

a group represented by

is a group represented by one of Formulae CY3(1) to CY3(18), and

a group represented by

is a group represented by one of Formulae CY4(1) to CY4(76):

wherein, in Formulae CY1(1) to CY1(31), CY2(1) to CY2(8), CY3(1) to CY3(18), and CY4(1) to CY4(76),

X 1 to X 4 , Y 1 , T 3 , and R 1 to R 5 are each independently the same as described in claim 1 ,

X 11 is O, S, N(R 11 ), C(R 11 )(R 12 ), or Si(R 11 )(R 12 ),

X 31 is O, S, N(R 31 ), C(R 31 )(R 32 ), or Si(R 31 )(R 32 ),

X 41 is O, S, N(R 41 ), C(R 41 )(R 42 ), or Si(R 41 )(R 42 ),

R 1a to R 1d , R 11 , and R 12 are each independently the same as defined in connection with R 1 in claim 1 ,

R 3a to R 3c , R 31 , and R 32 are each independently the same as defined in connection with R 3 in claim 1 ,

R 4a to R 4d , R 41 , and R 42 are each independently the same as defined in connection with R 4 in claim 1 ,

R 1 to R 5 , R 1a to R 1d , R 11 , R 12 , R 3a to R 3c , R 31 , R 32 , R 4a to R 4d , R 41 , and R 42 are not hydrogen,

in Formulae CY1(1) to CY1(31), * indicates a binding site to X 5 in Formula 1, and *′ indicates a binding site to Y 1 in Formula 1,

in Formulae CY2(1) to CY2(8), * indicates a binding site to M in Formula 1, *′ indicates a binding site to ring CY 1 in Formula 1, and *″ indicates a binding site to T 1 in Formula 1,

in Formulae CY3(1) to CY3(18), *″ indicates a binding site to T 1 in Formula 1, * indicates a binding site to M in Formula 1, and *′ indicates a binding site to T 2 in Formula 1, and

in Formulae CY4(1) to CY4(76), * indicates a binding site to M in Formula 1, and *′ indicates a binding site to T 2 in Formula 1.

15. The organometallic compound of claim 1 , wherein

the organometallic compound is one of Compounds 1 to 200:

16. An organic light-emitting device comprising:

a first electrode;

a second electrode; and

an organic layer between the first electrode and the second electrode and comprising an emission layer,

wherein the organic layer comprises at least one organometallic compound of claim 1 .

17. The organic light-emitting device of claim 16 , wherein

the first electrode is an anode,

the second electrode is a cathode,

the organic layer further comprises a hole transport region between the first electrode and the emission layer and an electron transport region between the emission layer and the second electrode,

the hole transport region comprises a hole injection layer, a hole transport layer, an electron blocking layer, a buffer layer, or any combination thereof, and

the electron transport region comprises a hole blocking layer, an electron transport layer, an electron injection layer, or any combination thereof.

18. The organic light-emitting device of claim 16 , wherein

the emission layer comprises the organometallic compound.

19. The organic light-emitting device of claim 18 , wherein

the emission layer further comprises a host, and an amount of the host is larger than an amount of the organometallic compound.

20. A diagnostic composition comprising at least one organometallic compound of claim 1 .