The use of tetrahydroxy-
p-benzoquinone as a slow source of dihydroxymalonato and oxalato ligands led to theisolation under o
pen-air mild reaction conditions of five different com
pounds, two of them
pre
pared for the firsttime: [Cu(b
py)(dhmal)]
2 (
1) and [{SiW
12O
40}{Cu
2(b
py)
2(H
2O)(ox)}
2]·16H
2O (
5) (b
py, 2,2'-bi
pyridine; dhmal,dihydroxymalonate; ox, oxalate). A
possible mechanism for the oxidation of the benzoquinone to give the croconatedianion, which undergoes further ring-o
pening oxidation to decom
pose into dihydroxymalonate and oxalate, is
pro
posed. All com
pounds have been characterized by elemental analysis, thermogravimetry, infrared s
pectrosco
py,and
powder X-ray diffraction. Single-crystal X-ray diffraction, electron
paramagnetic resonance, and magneticsusce
ptibility measurements have been
performed for com
pounds
1 and
5. A com
plete band assignment of theex
perimental FT-IR s
pectra is given through com
parison with the ones calculated using density functional theory(DFT). The neutral dimer
1 constitutes the first structurally characterized exam
ple of a transition metal-dhmalcom
plex, and it contains two co
pper atoms bridged by two dihydroxymalonato ligands acting in a
2-
![](/images/gifchars/ka<font color=)
ppa.gif" BORDER=0 >
3O,O',O' ':
![](/images/gifchars/ka<font color=)
ppa.gif" BORDER=0 >
1O coordination fashion, so that an
equatorial-axial Cu
2(
2-O)
2 rhomboid core is formed. On the other hand, theinorganic-metalorganic hybrid com
pound
5 shows a two-dimensional arrangement of Keggin
polyanions linked byone of the Cu atoms of the oxalate cationic dimers to give layers
parallel to the (10
![](/images/entities/onemacr.gif)
)
plane, the remaining ox-Cu-b
py fragments acting as interlamellar se
parators. In both cases, magnetic and EPR results are discussed withres
pect to the crystal structure of the com
pounds and, for com
pound
1, also with res
pect to DFT calculations ofthe exchange cou
pling constant.