Klv. Mann et al., Tetranuclear grid-like copper(II) complexes with pyrazolate bridges: syntheses, structures, magnetic and EPR spectroscopic properties, J CHEM S DA, (3), 1999, pp. 339-348
Citations number
45
Categorie Soggetti
Inorganic & Nuclear Chemistry
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
Reaction of 3-(2-pyridyl)pyrazole (HL1) and 6-(3-pyrazolyl)-2,2'-bipyridine
(HL2) with nickel(rr) and zinc(II) salts afforded the simple mononuclear p
seudo-octahedral complexes [M(HL1)(3)][PF6](2) and [M(HL2)(2)][PF6](2) resp
ectively (M = Ni or Zn) in which the ligands co-ordinate as neutral mononuc
leating chelates in the same manner as e.g. 2,2'-bipyridine or 2,2' :6',2 "
-terpyridine respectively. However with Cu-II the complexes [Cu-4(L-1)(6)(s
olv)(2)][PF6](2) (solv = dmf or MeOH) and [Cu-4(L-2)(4)(dmf)(4)][PF6](4) we
re isolated and crystallographically characterised: in all cases containing
four tetragonally elongated square-pyramidal copper(rr) ions which are lin
ked by pyrazolate bridges from the now deprotonated ligands L-1 and L-2. Th
e approximate orthogonality of the different ligands within each complex an
d the approximately square array or metal ions result in a grid-like struct
ure. In [Cu-4(L-1)(6)(solv)(2)][PF6](2) there are successively two, one, tw
o and one pyrazolate bridges between adjacent copper(rr) ions around the Cu
, square resulting in two clearly different magnetic coupling pathways; in
[Cu-4(L-2)(4)(dmf)(4)][PF6](4) however, which has approximate S-4 symmetry,
each Cu ... Cu edge has a single pyrazolate bridge and the coupling pathwa
ys are all virtually equivalent. Prolonged drying of these compounds result
ed in loss of the axial dmf ligands to give [Cu-4(L-1)(6)][PF6](2) and [Cu-
4(L-2)(4)][PF6](4). Magnetic susceptibility studies on these showed the pre
sence of two antiferromagnetic exchange pathways for [Cu-4(L-1)(6)][PF6](2)
with J > 172 cm(-1) and J' < 155 cm(-1) (strong correlation between the pa
rameters precludes a more precise determination), but only one antiferromag
netic exchange pathway for [Cu-4(L-2)(4)][PF6](4) with J = 63.5 cm(-1), con
sistent with the crystal structures of the dmf adducts. The EPR spectra of
[Cu-4(L-1)(6)][PF6](2) and [Cu-4(L-2)(4)][PF6](4) at a variety of frequenci
es and temperatures can be well simulated as arising from triplet species;
however the spectrum of [Cu-4(L-1)(6)][PF6](2) also contains a feature whic
h may be ascribed to the expected thermally populated quintet state.