Table 1. Key Metrical Parameters for Aluminum Complexes Containing [C₄O₄]ⁿ⁻ Ions (n = 2, 4, and 6).

		[C4O4]4–		[C4O4]6–	[C4O4]2–
d/Å	[2-K(C7H8)]2	[2-K(THF)]2	[2-Li(OEt2)]2	[4-K2(BEt3)]2	5
C–C	1.507(1)	1.525(4)	1.482(5)	1.481(3)	1.438(2)
	1.373(1)	1.489(3)	1.357(4)	1.377(4)	1.461(2)
		1.376(3)
C–O	1.233(1)	1.213(4)	1.246(5)	1.382(3)	1.257(2)
	1.383(1)	1.247(3)	1.391(4)	1.440(3)	1.265(2)
		1.373(3)
		1.381(3)
Al–C	2.038(1)	2.053(2)	2.063(4)	2.008(2)	n/a
		2.041(3)
Al–O	1.871(1)	1.872(2)	1.877(2)	1.874(2)	1.933(1)
		1.860(2)			1.994(1)