13. gg Delta bonds: (d xy ± d xy ) or (d x2-y2 ± d x2-y2 ) (d xy + d xy ) or (d x2-y2 + d x2-y2 )

14. *u*u gg Delta bonds: (d xy ± d xy ) or (d x2-y2 ± d x2-y2 ) (d xy - d xy ) or (d x2-y2 - d x2-y2 ) (d xy + d xy ) or (d x2-y2 + d x2-y2 )

15. Bonding scheme for dimers of transition metal dications, M 2+ d  g (z 2 )  u (xz, yz)  g * (xz, yz)  u * (xy, x 2 -y 2 )  g (xy, x 2 -y 2 ) d M 2+ M 2 4+  u * (z 2 )

16. Example: dimerization of Cr 2+ to form Cr 2 4+ d4d4  g (z 2 )  u (xz, yz)  g * (xz, yz)  u * (xy, x 2 -y 2 )  g (xy, x 2 -y 2 ) d4d4 Cr 2+ Cr 2 4+  u * (z 2 )

17. Example: dimerization of Cr 2+ to form Cr 2 4+ d4d4  g (z 2 )  u (xz, yz)  g * (xz, yz)  u * (xy, x 2 -y 2 )  g (xy, x 2 -y 2 ) d4d4 Cr 2+ Cr 2 4+  u * (z 2 ) Bond order = ½ (8-0)= 4 (quadruple bond!!!)

18. F. Albert Cotton…. King of multiple metal-metal bonds!!

19. Example: dimerization of Mn 2+ to form Mn 2 4+ d5d5  g (z 2 )  u (xz, yz)  g * (xz, yz)  u * (xy, x 2 -y 2 )  g (xy, x 2 -y 2 ) d5d5 Mn 2+ Mn 2 4+  u * (z 2 ) Bond order = ½ (10-0)= 5 (quintuple bond!!!)

20. Example: dimerization of Fe 2+ to form Fe 2 4+ d6d6  g (z 2 )  u (xz, yz)  g * (xz, yz)  u * (xy, x 2 -y 2 )  g (xy, x 2 -y 2 ) d6d6 Fe 2+ Fe 2 4+  u * (z 2 ) Bond order = ½ (10-2)= 4

21. Example: dimerization of Hg 2+ to form Hg 2 4+ d 10  g (z 2 )  u (xz, yz)  g * (xz, yz)  u * (xy, x 2 -y 2 )  g (xy, x 2 -y 2 ) d 10 Hg 2+ Hg 2 4+  u * (z 2 ) Bond order = ½ (10-10)= 0 (No bond!!)