Comparison of the carbonyl ligands of [7a]²⁺/[7b]²⁺ with M(CO)₅ and [M(CO)₆]²⁺ (M = Ru, Os) using the hitherto applied methods. The CO-bond lengths d_C–O are the averages of the respective carbonyl ligands in the solid state structures [7a]²⁺[Al(OR^F)₄]₂·2C₆F₄H₂ and [7b]²⁺[F{Al(OR^F)₃}₂]⁻₂·C₆F₄H₂.

	Ru(CO)5/Os(CO)5	[7a]2+/[7b]2+				[Ru(CO)6]2+/[Os(CO)6]2+
		COcen,eq	COaverage	COout,eq	COout,ax
d C–O/Å	1.126(2)/1.130(4)	1.126(2)/1.126(6)	1.122(2)/1.121(6)	1.121(2)/1.123(6)	1.115(2)/1.105(5)	1.100(8)/1.109(11)
d M–C/Å	1.941(13)ax& 1.961(9)eq/1.982(20)ax & 1.937(19)eq	1.964(1)/1.963(4)	1.979(2)/1.981(5)	1.981(2)/1.988(5)	1.999(1)/1.987(4)	2.023(3)/2.020(8)
δ 13CCO/ppm	200.4/182.6	195.1/176.8	186.0/	185.0/163.8	171.5/	168.8/150.6
(CO)av/cm−11	-/-	2103/2095	2120/2115	2135/2132	2153/2150	2220/2216
Δ (COfree)/cm−		−40/−48	−23/−27	−8/−11	+10/+7	+77/+73
k CO/N m−1	1728ax & 1653eq/-	1767/1754	1843/1845	1846/1842	1981/2039	2048/2059
q CO (QTAIM)	−0.157/−0.180	−0.090/−0.125	−0.022/−0.046	−0.008/−0.026	+0.055/+0.030	+0.150/+0.128
q M (QTAIM)	0.787/0.900	M cen = 0.610/0.668	M av = 0.771/0.883	M out = 0.851/0.990		1.099/1.231