Isabel Castro, M. Luisa Calatayud, Jorunn Sletten, Francesc Lloret and Miguel Julve
Two dinuclear nickel(II) complexes
[Ni2(C2O4)(tren)2][ClO
4]21 and
[Ni2(C4O4)(tren)2(H2
O)2][ClO4]22
[tren = tris(2-aminoethyl)amine,
C2O42- = oxalate
dianion and
C4O42- = dianion of
3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid)] have been
synthesized and characterized by single-crystal X-ray diffraction. Their
structures consist of dinuclear nickel(II) cations and
unco-ordinated perchlorate anions. The nickel environment is distorted
octahedral NiN4O2 in both complexes: four nitrogen
atoms of the tren group acting as a tetradentate ligand and two oxygen
atoms of oxalate (1) or a water molecule and a squarate oxygen
(2) comprise the co-ordination. The oxalate acts as a
bis(chelating) ligand whereas the squarate adopts a
µ-1,2-bis(monodentate) co-ordination mode. The intradimer
metal–metal separation is 5.413(1) and 6.224(1) Å in
1 and 2, respectively. The co-ordinated water molecule
in 2 forms an intramolecular hydrogen bond to an unco-ordinated
squarate-oxygen atom. Variable-temperature susceptibility measurements
revealed the occurrence of relatively strong (1) and weak
(2) intramolecular antiferromagnetic coupling, the relevant
parameters being J = -28.8
cm-1 and g = 2.16 for 1
and J = -0.4 cm-1 and
g = 2.15 for 2 (J being the
exchange parameter in the isotropic spin Hamiltonian
=
-J
A·
B). A
comparative study of the ability of
oxalate and squarate groups to mediate electronic interactions in the
structurally characterized oxalato- and squarato-bridged
nickel(II) complexes was carried out.