The use of tetrahydroxy-
p-benzoquinone as a slow source of dihydroxy
malonato and oxalato ligands led to theisolation under open-air
mild reaction conditions of five different co
mpounds, two of the
m prepared for the firstti
me: [Cu(bpy)(dh
mal)]
2 (
1) and [{SiW
12O
40}{Cu
2(bpy)
2(H
2O)(ox)}
2]·16H
2O (
5) (bpy, 2,2'-bipyridine; dh
mal,dihydroxy
malonate; ox, oxalate). A possible
mechanis
m for the oxidation of the benzoquinone to give the croconatedianion, which undergoes further ring-opening oxidation to deco
mpose into dihydroxy
malonate and oxalate, isproposed. All co
mpounds have been characterized by ele
mental analysis, ther
mogravi
metry, infrared spectroscopy,and powder X-ray diffraction. Single-crystal X-ray diffraction, electron para
magnetic resonance, and
magneticsusceptibility
measure
ments have been perfor
med for co
mpounds
1 and
5. A co
mplete band assign
ment of theexperi
mental FT-IR spectra is given through co
mparison with the ones calculated using density functional theory(DFT). The neutral di
mer
1 constitutes the first structurally characterized exa
mple of a transition
metal-dh
malco
mplex, and it contains two copper ato
ms bridged by two dihydroxy
malonato ligands acting in a
mages/entities/
mgr.gif">
2-
mages/gifchars/kappa.gif" BORDER=0 >
3O,O',O' ':
mages/gifchars/kappa.gif" BORDER=0 >
1O coordination fashion, so that an
equatorial-axial Cu
2(
mages/entities/
mgr.gif">
2-O)
2 rho
mboid core is for
med. On the other hand, theinorganic-
metalorganic hybrid co
mpound
5 shows a two-di
mensional arrange
ment of Keggin polyanions linked byone of the Cu ato
ms of the oxalate cationic di
mers to give layers parallel to the (10
mages/entities/one
macr.gif">) plane, the re
maining ox-Cu-bpy frag
ments acting as interla
mellar separators. In both cases,
magnetic and EPR results are discussed withrespect to the crystal structure of the co
mpounds and, for co
mpound
1, also with respect to DFT calculations ofthe exchange coupling constant.