223:. Increasing the bond order to two by involving another lone pair changes the hybridization at the oxygen to an sp center with an expected expansion in the M-O-R bond angle and contraction in the M-O bond length. If all three lone pairs are included for a bond order of three than the M-O bond distance contracts further and since the oxygen is a sp center the M-O-R bond angle is 180˚ or linear. Similarly with the imidos are commonly referred to as either bent (sp) or linear (sp). Even the oxo can be sp or sp hybridized. The triply bonded oxo, similar to
249:
including the most common linear imidos with a six electron bonding interaction to the metal center. Similarly amido complexes are usually drawn with a single line even though most amido bonds involve four electrons. Alkoxides are generally drawn with a single bond although both two and four electron bonds are common. Oxo can be drawn with two lines regardless of whether four electrons or six are involved in the bond, although it is not uncommon to see six electron oxo bonds represented with three lines.
934:
57:
258:
oxidation state becomes more of a formalism with much of the positive charge distributed between the ligands. This distinction can be expressed by using a Roman numeral for the lower oxidation states in the upper right of the metal atomic symbol and an Arabic number with a plus sign for the higher oxidation states (see the example below). This formalism is not rigorously followed and the use of Roman numerals to represent higher oxidation states is common.
928:
940:
248:
Imido ligands, also known as imides or nitrenes, most commonly form "linear six electron bonds" with metal centers. Bent imidos are a rarity limited by complexes electron count, orbital bonding availability, or some similar phenomenon. It is common to draw only two lines of bonding for all imidos,
257:
There are two motifs to indicate a metal oxidation state based around the actual charge separation of the metal center. Oxidation states up to +3 are believed to be an accurate representation of the charge separation experienced by the metal center. For oxidation states of +4 and larger, the
214:
A ligand described in ionic terms can bond to a metal through however many lone pairs it has available. For example, many alkoxides use one of their three lone pairs to make a single bond to a metal center. In this situation the oxygen is sp
70:
is a formalism. Furthermore, the usage of multiple bonding is not uniform. Symmetry arguments suggest that most ligands engage metals via multiple bonds. The term 'metal–ligand multiple bond" is often reserved for ligands of the type
154:
N), and fluoride. For late transition metals, strong pi-donors form anti-bonding interactions with the filled d-levels, with consequences for spin state, redox potentials, and ligand exchange rates. Pi-donor ligands are low in the
282:"Metal–Ligand Multiple Bonds: The Chemistry of Transition Metal Complexes Containing Oxo, Nitrido, Imido, Alkylidene, or Alkylidyne Ligands" W. A. Nugent and J. M. Mayer; Wiley-Interscience, New York, 1988.
390:
Aliaga-Alcalde, N.; George, S.D.; Mienert, B.; Bill, E.; Wieghardt, K.; Neese, F. "The
Geometric and Electronic Structure of : A Genuine Iron(V) Species with a Ground-State Spin S=1/2"
330:
Rohde,J; In,J.; Lim, M.H.; Brennessel, W.W.; Bukowski, M.R.; Stubna, A.; Muonck, E.; Nam, W.; Que L. "Crystallographic and
Spectroscopic Characterization of a Nonheme Fe(IV)O Complex"
142:, a pi-donor ligand is a kind of ligand endowed with filled non-bonding orbitals that overlap with metal-based orbitals. Their interaction is complementary to the behavior of
645:
150:
for the early transition metals is one consequence of this kind of bonding. Classic pi-donor ligands are oxide (O), nitride (N), imide (RN), alkoxide (RO), amide (R
307:; Johnson, A.M. "Experimental and Crystal Field Study of the Absorption Spectrum at 2000 to 8000 A of to Manganous Perchlorate in Aqueous Perchloric Acid"
1027:
66:
As a cautionary note, the classification of a metal–ligand bond as being "multiple" bond order is ambiguous and even arbitrary because
435:
1145:
1072:
753:
478:
202:
allow for many bonds between ligands and the metal center. A d metal center can accommodate up to 9 bonds without violating the
1067:
493:
367:"Spectroscopic and Quantum Chemical Characterization of the Electronic Structure and Bonding in a Non-Heme FeO Complex"
585:
992:
620:
615:
580:
44:
1176:
816:
630:
625:
610:
1007:
804:
794:
635:
287:
799:
428:
746:
686:
691:
1171:
1062:
1052:
1042:
1017:
987:
503:
833:
575:
539:
444:
421:
20:
1094:
997:
969:
739:
235:
at which point the oxygen no longer bears a partial positive charge and is reactive toward acid.
720:
605:
194:) ligands are generally assigned to high oxidation states with low d electron counts. The high
156:
139:
1138:
1099:
640:
216:
183:
1133:
1057:
948:
811:
770:
595:
458:
40:
231:
at the oxygen atom. When such a complex is reduced, the triple bond can be converted to a
8:
959:
823:
789:
715:
534:
508:
463:
220:
1123:
878:
529:
483:
354:
143:
1109:
898:
858:
848:
710:
681:
671:
600:
392:
369:
364:
340:
332:
309:
283:
56:
48:
1150:
890:
863:
676:
570:
473:
468:
404:
381:
347:
321:
304:
203:
199:
351:
228:
1128:
1002:
873:
549:
544:
224:
195:
43:
featuring multiply bonded ligands are of both scholarly and practical interest.
1037:
838:
666:
565:
488:
1165:
1086:
1046:
979:
933:
908:
781:
762:
661:
1032:
413:
408:
344:
191:
108:
1118:
868:
590:
232:
168:
325:
51:
reaction. Metal oxo intermediates are pervasive in oxidation catalysis.
358:
147:
67:
36:
16:
Chemical interaction of certain ligands with metals of bond order >1
385:
853:
828:
702:
498:
209:
60:
Most common classes of complexes showing metal–ligand multiple bonds
927:
731:
227:, is partially positive at the oxygen atom and unreactive toward
179:
171:
127:
28:
187:
175:
32:
297:
939:
646:
Arene complexes of univalent gallium, indium, and thallium
107:(n = 0, 1) where R is H or an organic substituent, or
206:, whereas a d species can only accommodate 6 bonds.
210:Reactivity explained through ligand hybridization
126:are not included in this classification, nor are
1163:
252:
198:stabilizes the highly reduced ligands. The low
162:
747:
429:
443:
754:
740:
530:Oxidative addition / reductive elimination
436:
422:
243:
1146:Polyhedral skeletal electron pair theory
479:Polyhedral skeletal electron pair theory
298:Further reading (specialized literature)
55:
278:
276:
1164:
735:
417:
27:describes the interaction of certain
586:Transition metal fullerene complexes
273:
133:
13:
761:
621:Transition metal carbyne complexes
616:Transition metal carbene complexes
581:Transition metal indenyl complexes
45:transition metal carbene complexes
14:
1188:
631:Transition metal alkyne complexes
626:Transition metal alkene complexes
938:
932:
926:
636:Transition-metal allyl complexes
611:Transition metal acyl complexes
363:Decker, A.; Rohde,J.; Que, L.;
238:
1:
352:10.1126/science.299.5609.1037
266:
253:Representing oxidation states
146:. The existence of terminal
7:
687:Shell higher olefin process
494:Dewar–Chatt–Duncanson model
163:Multiple bond stabilization
10:
1193:
844:Metal–ligand multiple bond
576:Cyclopentadienyl complexes
540:β-hydride elimination
514:Metal–ligand multiple bond
167:Metals bound to so-called
25:metal–ligand multiple bond
1108:
1085:
1016:
978:
958:
947:
924:
907:
889:
780:
769:
700:
654:
641:Transition metal carbides
558:
522:
451:
445:Organometallic chemistry
21:organometallic chemistry
606:Half sandwich compounds
244:Bonding representations
1177:Coordination chemistry
721:Bioinorganic chemistry
409:10.1002/anie.200462368
157:spectrochemical series
140:coordination chemistry
61:
41:Coordination complexes
692:Ziegler–Natta process
596:Metal tetranorbornyls
393:Angew. Chem. Int. Ed.
59:
834:Coordinate (dipolar)
701:Related branches of
459:Crystal field theory
1008:C–H···O interaction
790:Electron deficiency
716:Inorganic chemistry
535:Migratory insertion
509:Agostic interaction
464:Ligand field theory
326:10.1021/ja01557a001
221:valence bond theory
144:pi-acceptor ligands
993:Resonance-assisted
601:Sandwich compounds
559:Types of compounds
484:Isolobal principle
95:(n = 0, 1, 2) and
62:
39:greater than one.
1159:
1158:
1110:Electron counting
1081:
1080:
970:London dispersion
922:
921:
899:Metal aromaticity
729:
728:
711:Organic chemistry
682:Olefin metathesis
672:Grignard reaction
571:Grignard reagents
386:10.1021/ja0498033
370:J. Am. Chem. Soc.
310:J. Am. Chem. Soc.
49:olefin metathesis
1184:
1172:Chemical bonding
1151:Jemmis mno rules
1003:Dihydrogen bonds
956:
955:
942:
936:
930:
864:Hyperconjugation
778:
777:
756:
749:
742:
733:
732:
677:Monsanto process
474:d electron count
469:18-electron rule
438:
431:
424:
415:
414:
291:
280:
204:18 electron rule
200:d electron count
134:Pi-donor ligands
125:
124:
123:
114:
111:. Historically,
106:
105:
104:
94:
93:
92:
82:
81:
80:
1192:
1191:
1187:
1186:
1185:
1183:
1182:
1181:
1162:
1161:
1160:
1155:
1104:
1077:
1020:
1012:
974:
961:
951:
943:
937:
931:
918:
903:
885:
773:
765:
760:
730:
725:
696:
650:
566:Gilman reagents
554:
550:Carbometalation
545:Transmetalation
518:
447:
442:
300:
295:
294:
281:
274:
269:
255:
246:
241:
225:carbon monoxide
212:
196:oxidation state
165:
153:
136:
122:
120:
119:
118:
116:
112:
103:
100:
99:
98:
96:
91:
88:
87:
86:
84:
79:
76:
75:
74:
72:
17:
12:
11:
5:
1190:
1180:
1179:
1174:
1157:
1156:
1154:
1153:
1148:
1143:
1142:
1141:
1136:
1131:
1126:
1115:
1113:
1106:
1105:
1103:
1102:
1097:
1091:
1089:
1083:
1082:
1079:
1078:
1076:
1075:
1070:
1065:
1060:
1055:
1050:
1040:
1035:
1030:
1024:
1022:
1014:
1013:
1011:
1010:
1005:
1000:
995:
990:
984:
982:
976:
975:
973:
972:
966:
964:
953:
949:Intermolecular
945:
944:
925:
923:
920:
919:
917:
916:
913:
911:
905:
904:
902:
901:
895:
893:
887:
886:
884:
883:
882:
881:
876:
866:
861:
856:
851:
846:
841:
836:
831:
826:
821:
820:
819:
809:
808:
807:
802:
797:
786:
784:
775:
771:Intramolecular
767:
766:
763:Chemical bonds
759:
758:
751:
744:
736:
727:
726:
724:
723:
718:
713:
707:
705:
698:
697:
695:
694:
689:
684:
679:
674:
669:
667:Cativa process
664:
658:
656:
652:
651:
649:
648:
643:
638:
633:
628:
623:
618:
613:
608:
603:
598:
593:
588:
583:
578:
573:
568:
562:
560:
556:
555:
553:
552:
547:
542:
537:
532:
526:
524:
520:
519:
517:
516:
511:
506:
501:
496:
491:
486:
481:
476:
471:
466:
461:
455:
453:
449:
448:
441:
440:
433:
426:
418:
412:
411:
388:
361:
328:
299:
296:
293:
292:
271:
270:
268:
265:
264:
263:
254:
251:
245:
242:
240:
237:
229:Brønsted acids
211:
208:
164:
161:
151:
135:
132:
121:
101:
89:
77:
64:
63:
15:
9:
6:
4:
3:
2:
1189:
1178:
1175:
1173:
1170:
1169:
1167:
1152:
1149:
1147:
1144:
1140:
1137:
1135:
1132:
1130:
1127:
1125:
1124:Hückel's rule
1122:
1121:
1120:
1117:
1116:
1114:
1111:
1107:
1101:
1098:
1096:
1093:
1092:
1090:
1088:
1087:Bond cleavage
1084:
1074:
1071:
1069:
1066:
1064:
1061:
1059:
1056:
1054:
1053:Intercalation
1051:
1048:
1044:
1043:Metallophilic
1041:
1039:
1036:
1034:
1031:
1029:
1026:
1025:
1023:
1019:
1015:
1009:
1006:
1004:
1001:
999:
996:
994:
991:
989:
986:
985:
983:
981:
977:
971:
968:
967:
965:
963:
960:Van der Waals
957:
954:
950:
946:
941:
935:
929:
915:
914:
912:
910:
906:
900:
897:
896:
894:
892:
888:
880:
877:
875:
872:
871:
870:
867:
865:
862:
860:
857:
855:
852:
850:
847:
845:
842:
840:
837:
835:
832:
830:
827:
825:
822:
818:
815:
814:
813:
810:
806:
803:
801:
798:
796:
793:
792:
791:
788:
787:
785:
783:
779:
776:
772:
768:
764:
757:
752:
750:
745:
743:
738:
737:
734:
722:
719:
717:
714:
712:
709:
708:
706:
704:
699:
693:
690:
688:
685:
683:
680:
678:
675:
673:
670:
668:
665:
663:
662:Carbonylation
660:
659:
657:
653:
647:
644:
642:
639:
637:
634:
632:
629:
627:
624:
622:
619:
617:
614:
612:
609:
607:
604:
602:
599:
597:
594:
592:
589:
587:
584:
582:
579:
577:
574:
572:
569:
567:
564:
563:
561:
557:
551:
548:
546:
543:
541:
538:
536:
533:
531:
528:
527:
525:
521:
515:
512:
510:
507:
505:
502:
500:
497:
495:
492:
490:
489:π backbonding
487:
485:
482:
480:
477:
475:
472:
470:
467:
465:
462:
460:
457:
456:
454:
450:
446:
439:
434:
432:
427:
425:
420:
419:
416:
410:
406:
403:, 2908–2912.
402:
398:
395:
394:
389:
387:
383:
380:, 5378–5379.
379:
375:
372:
371:
366:
365:Solomon, E.I.
362:
360:
356:
353:
349:
346:
342:
338:
335:
334:
329:
327:
323:
320:, 6471–6477.
319:
315:
312:
311:
306:
303:Heidt, L.J.;
302:
301:
289:
285:
279:
277:
272:
261:
260:
259:
250:
236:
234:
230:
226:
222:
219:according to
218:
207:
205:
201:
197:
193:
189:
185:
181:
177:
173:
170:
169:triply bonded
160:
158:
149:
145:
141:
131:
129:
110:
69:
58:
54:
53:
52:
50:
47:catalyze the
46:
42:
38:
34:
30:
26:
22:
1129:Baird's rule
849:Charge-shift
843:
812:Hypervalence
655:Applications
591:Metallocenes
513:
400:
396:
391:
377:
373:
368:
336:
331:
317:
313:
308:
305:Koster, G.F.
256:
247:
213:
166:
137:
109:pseudohalide
65:
24:
18:
1119:Aromaticity
1095:Heterolysis
1073:Salt bridge
1018:Noncovalent
988:Low-barrier
869:Aromaticity
859:Conjugation
839:Pi backbond
504:spin states
339:1037–1039.
239:Conventions
233:double bond
148:oxo ligands
1166:Categories
1047:aurophilic
1028:Mechanical
452:Principles
288:0471854409
267:References
217:hybridized
68:bond order
37:bond order
1139:spherical
1100:Homolysis
1063:Cation–pi
1038:Chalcogen
998:Symmetric
854:Hapticity
703:chemistry
523:Reactions
499:Hapticity
1068:Anion–pi
1058:Stacking
980:Hydrogen
891:Metallic
782:Covalent
774:(strong)
345:12586936
1033:Halogen
879:bicyclo
824:Agostic
359:3833551
337:VOL 299
333:Science
186:), and
184:nitrido
180:nitride
172:carbyne
128:halides
35:with a
31:with a
29:ligands
1134:Möbius
962:forces
952:(weak)
357:
343:
286:
1112:rules
1021:other
909:Ionic
817:3c–4e
805:8c–2e
800:4c–2e
795:3c–2e
355:JSTOR
188:oxide
176:imide
33:metal
874:homo
829:Bent
397:2005
374:2004
341:PMID
314:1959
284:ISBN
262:vs.
115:and
83:and
23:, a
405:doi
382:doi
378:126
348:doi
322:doi
192:oxo
138:In
19:In
1168::
401:44
399:,
376:,
318:80
316:,
275:^
178:,
174:,
159:.
130:.
117:NO
113:CO
97:OR
85:NR
73:CR
1049:)
1045:(
755:e
748:t
741:v
437:e
430:t
423:v
407::
384::
350::
324::
290:.
190:(
182:(
152:2
102:n
90:n
78:n
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
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