Chapter 8 Some Cu(II) Binuclear
Transition-Metal Complexes
With little modification, we may use the N 2 O 4 valence-bond and molecular orbital
theory of Sections 7-1 and 7-2 to examine the magnetic behaviour for some
binuclear Cu(II) complexes with (3d)
9 configurations for the Cu
2+ ions. As
examples, we shall consider the Cu(II)-carboxylate, Cu(II)-chloro and Cu(II)hydroxo dimers
2
2 4
(Cu (RCO ) , L n with n = 0 or 2, and
2
2
2
Cu X
 with X = Cl or
OH. Their geometries are displayed in Figure 8-1. Initially we shall not include
the copper 4s and 4p orbitals in the bonding schemes.
8-1 Cu(II) Carboxylate Dimers, Cu 2 (RCO) 4 L n
8-1(a) Valence-Bond Structures For those Cu(II) carboxylate dimers that have
the geometries displayed in Figure 8-1, singly-occupied
2
2
x y
3d  orbitals of the
Cu
2+ ions can overlap with a lone-pair atomic orbital on each of the oxygen atoms
of the carboxylate ligands, as shown in Figure 8-2 for two ligands. The
2
2
x y
3d 
orbitals also overlap with each other to form a very weak δ-bond
4 . In Fig. 8-2,
each O-Cu(II)-O moiety involves five electrons and three overlapping atomic
orbitals, as is also the case for
2
NO and both O-N-O linkages of 2 4
N O (see Figs.
6-1 and 7-2). The Cu
2+ ions of Cu(II) carboxylate dimers are equivalent
5 to the
nitrogen atoms of NO 2 and N 2 O 4 . Therefore, for each O-Cu(II)-O moiety, with one
unpaired or magnetic electron, we can write down Lewis structures of the types
(1), (2) and (3); resonance between them may be summarized by using the Pauling
“3-electron bond” structures (4) and (5).
Ó Springer International Publishing Switzerland 2016
R.D. Harcourt, Bonding in Electron-Rich Molecules,
Lecture Notes in Chemistry 90, DOI 10.1007/978-3-319-16676-6_8
105