Table 1. Calculated (M06-D3/def2-TZVPP) and Experimental M–C and C–O Distances [Å] and Vibrational Shifts of the IR Active C–O Stretching Frequencies Δυ wrt Free CO [cm^–1]^a.

	calcd			exptl
M(CO)n	r(M–C)	r(C–O)	Δυ	r(M–C)	r(C–O)	Δυ
Ni(CO)4 (Td)	1.848	1.132	–84	1.838n	1.141n	–86o
Pd(CO)4 (Td)	2.064	1.129	–72			–73p
Pt(CO)4 (Td)	2.014	1.132	–95			–95q
Fe(CO)5 (D3h)b	1.819/1.820	1.134/1.137	–101/–122	1.811/1.803d	1.117/1.133d	–108/–130o
Ru(CO)5 (D3h)b	1.958/1.971	1.133/1.137	–108/–133	1.941/1.961e	1.126/1.127e	–107/–144o
Os(CO)5 (D3h)b	1.979/1.970	1.134/1.139	–105/–145	1.982/1.987f	1.130/1.131f	–108/–152o
Fe(CO)62+ (Oh)	1.936	1.112	107	1.903–1.917j	1.097–1.114j	62j
Ru(CO)62+ (Oh)	2.041	1.113	67	2.019–2.033j	1.091–1.108j	55j
Os(CO)62+ (Oh)	2.054	1.114	58	2.013–2.034j	1.090–1.125j	46j
Mn(CO)6+ (Oh)	1.911	1.122	–11	1.899–1.914k	1.112–1.124k	–45k
Tc(CO)6+ (Oh)	2.042	1.123	–30	2.025–2.029l	1.113–1.114l
Re(CO)6+ (Oh)	2.054	1.124	–35	1.98–2.07g	1.12–1.19g	–58g
Cr(CO)6 (Oh)	1.917	1.136	–134	1.918c	1.14c	–143o
Mo(CO)6 (Oh)	2.073	1.136	–141	2.063c	1.145c	–139o
W(CO)6 (Oh)	2.080	1.137	–148	2.058c	1.148c	–145o
V(CO)6– (Oh)	1.966	1.152	–257			–(266–296)h
Nb(CO)6– (Oh)	2.139	1.151	–256	2.089h	1.160h	–(267–289)h
Ta(CO)6– (Oh)	2.139	1.152	–262	2.083h	1.149h	–(268–296)h
Ir(CO)63+ (Oh)	2.071	1.108	127
Os(CO)62+ (Oh)	2.054	1.114	58			46j
Re(CO)6+ (Oh)	2.054	1.124	–35	1.98–2.07g	1.12–1.19g	–58g
W(CO)6 (Oh)	2.080	1.137	–148	2.058c	1.148c	–145o
Ta(CO)6– (Oh)	2.139	1.152	–262	2.083h	1.149h	–293h
Hf(CO)62– (Oh)	2.239	1.168	–375	2.174–2.180i	1.162–1.165i	–386i
Ti(CO)8 (Oh)	2.211	1.135	–151
Zr(CO)8 (Oh)	2.349	1.134	–138			–164m
Hf(CO)8 (Oh)	2.335	1.135	–143			–171m
Sc(CO)8– (Oh)	2.325	1.146	–234			–251t
Y(CO)8– (Oh)	2.486	1.144	–214			–239t
La(CO)8– (Oh)	2.687	1.142	–204			–229t
Ca(CO)8 (Oh)	2.602	1.127	–119			–156s
Sr(CO)8 (Oh)	2.748	1.130	–115			–148s
Ba(CO)8 (Oh)	2.944	1.129	–107			–129s
Ca(CO)2 (D∞h)	2.338	1.158	–232
Sr(CO)2 (D∞h)	2.511	1.156	–238
Ba(CO)2 (D∞h)	2.729	1.151	–217
Ba(CO)•+ (C∞v)	2.649	1.139	–173			–232r

^aNegative Δυ values indicate a red-shift, whereas positive values signal a blue-shift.

^bThe first value is for the axial CO, and the second is for the equatorial CO ligands.

^cReferences (132), (133).

^dReference (134).

^eReference (135).

^fReference (136).

^gReference (137).

^hReference (138).

ⁱReference (139).

^jReference (140).

^kReference (141).

^lReference (142).

^mReference (36).

ⁿReference (143).

^oReference (1).

^pReference (144).

^qReference (145).

^rReference (110).

^sReference (39).

^tReference (66).