The compound
[{Cu(tzq)
2
(HCO
2
)}
2
(µ-HCO
2
)
2
]·4H
2
O
(tzq = [1,2,3]triazolo[1,5-a]quinoline) was
obtained under mild conditions by reaction between the hydrazone of
quinoline-2-carbaldehyde and copper(
II) formate in ethanolic
aqueous solution and its crystal and molecular structure have been
determined by X-ray diffraction methods: triclinic, space group
P
![[1 with combining macron]](https://www.rsc.org/images/entities/char_0031_0304.gif)
, Z = 1,
a = 8.209(4),
b = 12.156(4),
c = 12.649(4) Å,
α = 63.21(3), β = 81.42(3),
γ = 89.12(3)°. The compound is built of
centrosymmetric neutral dimeric
[{Cu(tzq)
2
(HCO
2
)}
2
(µ-HCO
2
)
2
] entities linked through hydrogen bonds
involving water molecules and carboxylate groups. The copper atom is
involved in a CuN
2
O
2
O′ chromophore and lies
in a tetrahedrally distorted square-pyramidal environment. The four
equatorial donors are two trans nitrogen atoms from two tzq
molecules and two oxygen atoms from two formate groups. One of the
oxygens acts as a bridging ligand occupying the apical position of the
symmetry-related copper atom in the dimer structure, which is viewed as
two edge-sharing distorted square pyramids. This co-ordination behaviour
(monoatomic bridging) is very unusual for the
HCO
2
-
anion. The EPR spectrum is
characteristic of a triplet state with non-negligible zero-field
splitting. Magnetic susceptibility measurements in the range
1.8–200 K showed weak antiferromagnetic exchange between the
copper(
II) ions (2J = -1.05
cm
-1
). The observed behaviour is discussed on the basis
of the crystal structure and compared with those reported for related
µ-oxo carboxylate-bridged [CuO
2
Cu] dimers with
parallel-planar geometry.