Catena-Poly[disodium [[diformato-tricopper(II)]-di-μ3- formato-tetra-μ2-formato]]: A new mode of bridging between binuclear and mononuclear formate-copper(II) units

Article abstract of DOI:10.1107/S0108270106001636

The novel title polymeric copper(II) complex, {Na₂[Cu ₃-(CHO₂)₈]}_n, consists of sodium cations and infinite anionic chains, in which neutral dinuclear [Cu ₂(O₂CH)₄] moieties alternate with dianionic [Cu(O₂CH)₄]^2- units. Both metal-containing moieties are located on crystallographic inversion centers. The syn-syn bridging configuration between the mononuclear and dinuclear components yields a structure that is significantly more dense than the structures previously reported for mononuclear-dinuclear copper(II) carboxylates with syn-anti or anti-anti bridging modes.

Full text of DOI:10.1107/S0108270106001636

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
apical distance, Cu1ÐO42, is signi®cantly longer
Ê
[2.104 (5) A]. The distortion of the square-pyramidal
Communications
arrangement of the O atoms around atom Cu1 is very small; ꢀ
is 0.005 (Addison et al., 1984). The CuÁ Á ÁCu separation within
ISSN 0108-2701
Ê
the dimer is 2.620 (1) A. This and the bond distances in the
catena-Poly[disodium [[diformato-
tricopper(II)]-di-l3-formato-tetra-l2-
formato]]: a new mode of bridging
between binuclear and mononuclear
formate±copper(II) units
Æ
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Amalija Golobic,* Martina Malekovic and Primoz Segedin
Faculty of Chemistry and Chemical Technology, University of Ljubljana,
Ï
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Askerceva 5, 1000 Ljubljana, Slovenia
Correspondence e-mail: amalija.golobic@fkkt.uni-lj.si
Received 23 November 2005
Accepted 16 January 2006
Online 11 February 2006
dimer are comparable to those in other dinuclear copper
formates (Bernard et al., 1979; Bukowska-Strzyzewska, 1966;
Uekusa et al., 1989; Yamanaka et al., 1991; Goodgame et al.,
1969; Cejudo et al., 2002; Sapina et al., 1994). The apical
formate ligand is coordinated through atom O41 to the second
copper ion, Cu2, thus bridging dimeric and monomeric units to
form the polymeric chain. The coordination polyhedron of
atom Cu2, which is also located on an inversion centre, is an
axially elongated octahedron of O atoms from the three pairs
of symmetry-related formate anions. This coordination may be
viewed as 4+2, which is quite typical and expected for six-
coordinate CuII in view of Jahn±Teller effects (Hathaway,
1987). The equatorial O atoms (O41 from the bridging
formate and O31 from the only formate ligand that is not
The novel title polymeric copper(II) complex, {Na2[Cu3-
(CHO2)8]}n, consists of sodium cations and in®nite anionic
chains, in which neutral dinuclear [Cu2(O2CH)4] moieties
alternate with dianionic [Cu(O2CH)4]2 units. Both metal-
containing moieties are located on crystallographic inversion
centers. The syn±syn bridging con®guration between the
mononuclear and dinuclear components yields a structure that
is signi®cantly more dense than the structures previously
reported for mononuclear±dinuclear copper(II) carboxylates
with syn±anti or anti±anti bridging modes.
Comment
Ê
coordinated to Cu1) are closer than 2 A to Cu2. Two O atoms,
viz. O11 and its symmetry equivalent, which lie at a signi®-
Although a large number of dimeric copper(II)±carboxylate
complexes of the paddle-wheel-cage type have been structu-
rally characterized, only nine structures of formate derivatives
are known (Bernard et al., 1979; Bukowska-Strzyzewska, 1966;
Uekusa et al., 1989; Yamanaka et al., 1991; Goodgame et al.,
1969; Cejudo et al., 2002; Sapina et al., 1994). In only one of
these (Bukowska-Strzyzewska, 1966) are dimeric formate±
copper(II) units found to be linked into a polymeric structure.
Not only is the title compound, (I), a new example of such an
extended structure, it is also the ®rst formate±copper(II)
structure that contains both mono- and dinuclear carboxylate±
copper(II) units. A view along the a axis of the cell is given in
Fig. 1. In®nite chains, formed by [Cu2(O2CH)4] dimers bridged
by [Cu(O2CH)4]2 anions, propagate along the [011] direction.
The charge is balanced by sodium cations, located between the
polymeric chains. Fig. 2 shows the coordination of formate
ligands around the metal ions. The dimeric unit is centro-
symmetric, with four bidentate formate syn±syn bridges
between Cu1 atoms, which are in a 4+1 environment. The
basal coordination of atom Cu1 is formed by four coplanar O
atoms from two pairs of symmetry-related formate anions,
Ê
cantly longer distance [2.492 (5) A], are part of the bridging
Figure 1
The packing of the title compound, viewed along the a axis.
Ê
with an average CuÐObasal distance of 1.968 A (Table 1). The
m102 # 2006 International Union of Crystallography
DOI: 10.1107/S0108270106001636
Acta Cryst. (2006). C62, m102±m104

metal-organic compounds
formate groups from the dimeric [Cu2(O2CH)4] unit and form
a second bridge between the monomeric and dimeric units.
This additional bridge is possible because the ®rst mode of
bridging between dimer and monomer (through bonds Cu1Ð
O42 and Cu2ÐO41) is syn±syn. A syn±anti or anti±anti mode
of bridging could not have brought the units close enough for
such additional stabilization. The consequence of this new
mode of bridging is that the density (2.275 Mg m 3) is signif-
icantly greater than the densities of analogous copper(II)
structures (Wang et al., 2000; Valigura et al., 1986; Escuer et al.,
O42Á Á ÁO42( x + 1, y + 1, z) and O32Á Á ÁO32( x + 1,
y + 1, z) edges into in®nite chains, which run along the
b axis.
Experimental
Sodium formate was prepared by evaporating an equimolar aqueous
solution of methanoic acid and sodium hydroxide to dryness. Sodium
formate (1.09 g, 16 mmol) was dissolved with stirring in a mixture of
methanol (50 ml) and distilled water (2 ml) acidi®ed with a few drops
of methanoic acid. The solution obtained was ®ltered into a solution
of CuCl2Á2H2O (0.68 g, 4.0 mmol) in acidi®ed methanol (10 ml). The
solution was left to stand at 278 K for 24 h. The green crystalline
product was ®ltered off and dried over KOH in a desiccator over-
night. The average yield from the synthesis was 87%. The same
product was obtained in lower yields using a similar procedure if
Cu(NO3)2Á3H2O or anhydrous copper formate (ꢁ form) were used as
starting materials. All samples were checked by powder X-ray
diffraction, which gave d spacings and relative intensities in agree-
ment with the values calculated from the single-crystal structure
analysis. Single crystals, stable in air and suitable for structural
analysis, were obtained by the above procedure using more dilute
solutions.
È
1999; Hokelek et al., 1998; Zubkowski et al., 1997; Chiari et al.,
1993; Valo & Nasakkala, 1994; Petrenko & Kiosse, 2000; Kani
Ï
et al., 2000; Neels et al., 1995; Dunaj-Jurco et al., 1995) with
syn±anti or anti±anti bridging modes between mono- and
dinuclear units. In the latter, the densities are less than
1.79 Mg m 3. For instance, in {K2[{Cu2(O2CCH3)4}{Cu(O2C-
CH3)4}]}n (Valo & Nasakkala, 1994), whose formula is very
similar to that of the title compound, but in which the bridging
mode between monomeric and dimeric units is syn±anti, the
density is only 1.558 Mg m 3. Also, the intra-chain distance
between atoms Cu1 and Cu2 in {K2[{Cu2(O2CCH3)4}-
Ê
{Cu(O2CCH3)4}]}n is 5.088 (1) A. The corresponding distance
Crystal data
Ê
in the title compound is 3.7103 (7) A. On the other
hand, the shortest inter-chain distances between copper
Ê
ions are similar in the two structures, viz. 6.503 (1) A in
Ê
{K2[{Cu2(O2CCH3)4}{Cu(O2CCH3)4}]}n and 6.526 (1) A in the
title compound.
The syn±syn bridging mode between dimeric and mono-
meric units is novel among copper carboxylates and is prob-
ably sterically feasible only for formates. This notion is
supported by the fact that such a structural motif (within metal
carboxylates) has only been observed in one structure, viz.
[Cr3(O2CH)6Á2H2O], also a formate compound (Cotton et al.,
1978).
Na2[Cu3(CHO2)8]
Mr = 596.76
Triclinic, P1
a = 7.6594 (2) A
b = 7.7717 (1) A
Z = 1
Dx = 2.275 Mg m
Mo Kꢁ radiation
3
Ê
Ê
Ê
Cell parameters from 1672
re¯ections
c = 8.7972 (2) A
ꢄ = 2.9±27.5ꢀ
ꢅ = 3.76 mm
T = 293 K
1
ꢁ = 113.248 (1)ꢀ
ꢂ = 108.653 (1)ꢀ
ꢃ = 97.495 (1)ꢀ
Prism, green
0.12 Â 0.10 Â 0.07 mm
3
Ê
V = 435.61 (2) A
Data collection
Nonius KappaCCD diffractometer
' and ! scans
Absorption correction: multi-scan
(DENZO±SMN; Otwinowski &
Minor 1997)
1966 independent re¯ections
1775 re¯ections with F2 > 2ꢆ(F2)
Rint = 0.038
ꢄmax = 27.5ꢀ
The sodium cations are surrounded by seven formate O
h = 9 ! 9
Ê
atoms at distances ranging from 2.319 (9) to 2.699 (9) A. The
sodium coordination polyhedra are connected through
Tmin = 0.64, Tmax = 0.77
5090 measured re¯ections
k = 10 ! 10
l = 9 ! 11
Re®nement
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.052
wR(F2) = 0.152
S = 1.04
1775 re¯ections
148 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
(Á/ꢆ)max = 0.001
3
Ê
Áꢇmax = 1.77 e A
3
Ê
1.72 e A
Áꢇmin
=
Table 1
Selected geometric parameters (A, ).
ꢀ
Ê
Cu1ÐO11
Cu1ÐO12i
Cu1ÐO21
Cu1ÐO22i
1.965 (5)
1.987 (6)
1.965 (6)
1.956 (7)
Cu1ÐO42
Cu2ÐO11
Cu2ÐO31
Cu2ÐO41
2.104 (5)
2.492 (5)
1.937 (6)
1.987 (6)
O11ÐCu1ÐO12i
O11ÐCu1ÐO21
O11ÐCu1ÐO22i
O11ÐCu1ÐO42
O12iÐCu1ÐO21
O12iÐCu1ÐO22i
O12ÐCu1ÐO42
168.7 (2)
88.9 (2)
89.7 (3)
101.9 (2)
90.3 (2)
88.9 (3)
89.4 (2)
O21ÐCu1ÐO22i
O21ÐCu1ÐO42
O22iÐCu1ÐO42
O11ÐCu2ÐO31
O11ÐCu2ÐO41
O31ÐCu2ÐO41
169.0 (3)
93.6 (2)
97.4 (3)
90.2 (2)
95.1 (2)
92.1 (2)
Figure 2
An ORTEP-3 drawing (Farrugia, 1997), with displacement ellipsoids
shown at the 50% probability level. Dashed lines depict the additional
connections between binuclear and mononuclear formate copper(II)
units. [Symmetry codes: (i) x + 2, y, z; (ii) x + 1, y, z; (iii) x + 2,
y + 1, z + 1; (iv) x + 1, y + 1, z; (v) x 1, y, z.]
Symmetry code: (i) x + 2, y, z.
ꢁ
Ï
Acta Cryst. (2006). C62, m102±m104
Golobic et al. Na2[Cu3(CHO2)8] m103

metal-organic compounds
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Ï
Ï
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Ê
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Ê
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Ê
Ê
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ꢁ
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m104 Golobic et al. Na2[Cu3(CHO2)8]
Acta Cryst. (2006). C62, m102±m104