Cryst. Res. Technol.

34 1999 7 925–928

L. JIANMIN , *, Z. HUAQIANGA, Z. YUGEN *, C. JINHUA ,

AC B A

K. YANXIONG , , W. QUANMING , W. XINTAO

AC C C

a
Department of Chemical Physics, bDepartment of Chemistry, University of Science and Technology
of China, Hefei, Anhui 230026, P.R.China.
c
State Key Laboratory of Structural Chemistry, Fujian Institute of Research of Structure of Matter,
Chinese Academy of Science, Fuzhou, Fujian 350002, P.R.China

The Crystal Structure of [La(NO3)6{Cu(2,2’-

bipy)2}2][La(NO3)6Cu(2,2’-bipy)2]•CH3CN with the Most
Profuse Modes of Nitrate Coordination

The title compound [La(NO3)6{Cu(2,2’-bipy)2}2][La(NO3)6Cu(2,2’-bipy)2]•CH3CN was synthesized,

the crystal and molecular structures were determined at room temperature. The complex formed
monoclinic crystals, space group P21/n(No.14), , a = 10.354 (3) Å, b = 23.440 (9) Å, c = 32.817 (9) Å,
β = 90.39 (2)o, Z = 4. The crystal structure consisted of a discrete [La(NO3)6{Cu(2,2’-bipy)2}2]+ cation
-
and [La(NO3)6Cu(2,2’-bipy)2] anion and a non-coordinated CH3CN molecule. Each La(III) ion was 12-
coordinate with twelve oxygen atoms from six chelating nitrate ligands. There were four modes of
nitrate coordination and the coordination geometry of all three copper ions was different in the crystal
structure.
Keywords: crystal structure, nitrate coordination

Introduction

There was much current interest in the syntheses and structures of mixed copper-lanthanide
complexes. This work was chiefly motivated by (I) their use as the precursor complexes of
the superconducting materials in MOCVD; (II) the unusual magnetic interactions between d-
and f-block elements. Many advances in this general area were focused on studies of the
properties of bridging ligands such as dbm (dibenzoyl methane) (MIELE, P. et al.), alkoxides
and β-diketonates (BIDELL, W. et al.), amino alcohols (CHEN, L. et al.), 2-hydroxypyridine or
its derivatives (BLAKE, A. J. et al.) etc. In contrast, d- and f-block metals bridged by only
nitrate groups has been unprecedented, although nitrate group was a very common bridging
ligand. And note in passing that there was also a growing interest in materials in which metal
ions were linked through oxoanions such as phosphate groups (BUJOLI, B. et al. and
MARCOS, M. D. et al.). On the other hand, it was usually difficult to isolate these Cu-Ln
(lanthanide) complexes from solution due to their high solubility and tendency to form oily
material in common organic solvents (WANG, S. et al.), thus making the investigation of their
syntheses, structures, physical and chemical properties difficult. We therefore explored the
syntheses of Cu-La complexes with La(NO3)3 and Cu(NO3)2 and other simple, non-bridging
ligands in the various solutions and reported herein a novel complex of [La(NO3)6{Cu(2,2’-
bipy)2}2][La(NO3)6Cu(2,2’-bipy)2]•CH3CN (I) with the most profuse modes of nitrate
coordination and three different copper coordination structures.

Experimental
Preparation of the crystal

To a mixture of Cu(NO3)2•3H2O (241.63 mg, 0.75 mmol) and La(NO3)3•6H2O (357.35 mg,
0.30 mmol) in 30 ml CH3CN was added 1.5 mmol of 2,2’-bipyridine of 15 ml CH3CN. Dark
926 L. JIANMIN et al.: The Crystal Structure

blue solution was obtained and allowed to crystallize by slow evaporation, producing X-ray
quality deep blue crystals after several days. Elemental analysis was found: Cu, 8.51; C,
35.25; H, 2.35; N, 16.38; Calc. For (I): Cu, 8.82; C, 33.99; H, 2.35; N, 15.98.

X-ray investigation

Crystal data: [La(NO3)6{Cu(2,2’-bipy)2}2][La(NO3)6Cu(2,2’-bipy)2]•CH3CN, Mw = 2190.68,

monoclinic, Space group: P21/n(No.14), , a = 10.354 (3) Å, b = 23.440 (9) Å, c = 32.817 (9)
Å, β = 90.39 (2)o, Z = 4, V = 7964.7 Å3, F(000) = 4348, Dc = 1.83 g/cm3, T = 296 K, µ (Mo-
Kα) = 19.5 cm-1, λ(Mo-Kα) = 0.71069 Å. A crystal of approximate dimensions
0.25x0.20x0.10 mm3 was mounted on a Rigaku AFC5R diffractometer, using graphite
monochromatized Mo-Kα radiation. Cell constants and orientation matrix for data collection
were obtained from least-squares refinement, using the setting angles of 20 reflections in the
range 8o < θ < 27.5o, measured by the computer controlled diagonal slit method of centering.
Three reflections were monitored periodically as a check for crystal decomposition and
movements. Scan mode of ω-2θ and maximum 2θ value being 50o were used to collect
intensity data. A total of 15263 reflections were collected, of which 15263 were unique, and
3190 had I > 3σ(I) for 538 parameters. The data were corrected for Lorentz and polarization
effects, and absorption was corrected empirically for three reflections. The structure was
solved by direct methods and refined by full matrix least-square calculation. La atoms were
located in the E map, the remaining atoms were located in succeeding difference Fourier
syntheses and H atoms further included as fixed contribution to the structure factor. All
calculations were performed on a COMPAQ computer using MoLEN/PC program (MOLEN).
A weighting scheme with w = 1/[σ2(Fσ)2 + (0.020Fo)2 + 1.000]] was used. Neutral atomic
scattering factors were taken from the International Tables for X-ray Crystallography
(CROMER, D. T. et al.). At final convergence, R = 0.072, Rw = 0.080, GOF = 1.36, maximum
shift/e.s.d = 0.03. The minimum and maximum peaks in final difference Fourier map were
0.22(19) e/ Å3 and 0.99(19) e/ Å3, respectively.
Selected atomic coordinates and equivalent isotropic parameters were given in Table 1.
Selected bond lengths and angles were given in Table 2 and 3, respectively.

Results and discussion

The molecule structure of the title complex consisted of discrete [La(NO3)6{Cu(2,2’-

bipy)2}2]+ cation and [La(NO3)6Cu(2,2’-bipy)2]- anion and a non-coordinated CH3CN
molecule , see Fig. 1 and 2.
It was worth noting that each Cu had different coordination geometry. Cu(3) had a
trigonal bipyramidal [the geometric τ value was 0.55 (ADDISON, A. W. et al.)] coordination
with CuN4O coordination sphere. The coordination geometry around Cu(2) was at least five-
coordinate, and that of a distorted square pyramid (the τ value was 0.41 ). In addition, the
O(133) atom of the coordinated nitrate was involved at a potentially bonding distance of
2.84(2) Å, on the same side of the Cu, N(21)-N(24) plane as O(131), to give an
unsymmetrical bidentate coordinating nitrate group which could also be found in the
structure of [Cu(bipy)2(ONO2)][NO3]H2O (Cu-O(NO3-) bond lengths were 2.301 Å and 2.832
Å (FEREDAY, R. J. et al.)). In the complex {Cu2(dien)2(OH)(ClO4)3}(CASTRO et al.), it was
also found that the weak coordinated Cu-O(ClO4-) distance had reached up to 2.97(2) Å.
Furthermore, the [Cu(2)-O(133)]-[Cu(2)-O(131)] difference of 0.38 Å was much less than
that previously suggested (ADDISON, C. E. et al.) as the limit for an unsymmetrically
coordinated bidentate nitrate group (0.7 Å). These reasonably allowed us to conclude that
Cryst. Res. Technol. 34 (1999) 7 927

geometry around Cu(2) can be considered as a six-coordinate, asymmetrical cis-distorted

bicapped square pyramidal coordination (FEREDAY, R. J. et al.) with a CuN4OO* structure.
Also, one distant oxygen atom (O(153)) completed a 4+1* Cu(1) coordination and Cu(1) was
in square pyramidal environment (τ = 0.14).

Fig. 1: The crystal structure of the title Fig. 2: The molecular structure of the title compound.
compound.

Each of the two La(III) ions was 12-coordinate with twelve oxygen atoms from six chelating
nitrate ligands. The averaged La-O bond lengths 2.673 Å was in agreement with the value of
2.655 Å found in the [L.H3+O][La(NO3)6](TANG, Y. et al.). A rough estimate of the cationic
distortions was furnished by the extensive equation ∆ = (1/12)Σ((Ri-R)/R)2 based on the
literature equation (BROWN, I. D. et al.), Ri being the individual bond length and R the
average bond length. The calculated values, ∆(La(1)) = 0.020% and ∆(La(2)) = 0.014%,
were relatively higher than that found in the [L.H3+O][La(NO3)6] (∆(La) = 0.004%), a result
which was in accord with the individual coordination environment.
There were four different coordination modes of nitrate ligands in the title complex. One
was the simple bidentate nitrate. The nitrate group only coordinated to La(III) through two
oxygen atoms. The second mode was the bridging (bidentate, unidentate) nitrate N(150)-two
oxygen atoms (O(151) and O(152)) of the nitrate coordinated to La(1), while the other
oxygen atom (O(153)) coordinated to Cu(1). The interaction between Cu(1) and O(153),
although weak, could take into account the fact that the distance of N(150)-O(153) was 1.29
Å, slightly longer than that of N(150)-O(151) (1.19(3) Å) and N(150)-O(152) (1.24(3) Å).
The third mode was the bridging (bidentate, unidentate) nitrate (N(230))-the nitrate ligand
spanned La(2) and Cu(3) with one oxygen atom (O(232)). The other oxygen atom (O(231))
was only coordinated to La(2). The fourth unusual mode was the bridging (bidentate,
bidentate) nitrate (N(130))-the nitrate ligand bridged La(1) and Cu(2) with one oxygen
(O(131)), the remaining two oxygen atoms (O(132) and O(133)) coordinated to the La(1)
and Cu(2), respectively. These various bridging modes leaded to several metal-metal
contacts with La(1)--Cu(1) 5.67, La(1)--Cu(2) 5.03, and La(2)--Cu(3) 4.89 Å. Here, two
copper atoms were linked by La(NO3)6 group forming a bent-chain arrangement, similar to
those found in other LaCu2 compounds (BENCINI, A. et al.). The nitrate ligand can coordinate
928 L. JIANMIN et al.: The Crystal Structure

to metal ion in many ways. Most nitrate complexes contained only one or two coordination
modes; it was very rare to have more than two nitrate modes within one compound. As far as
we were aware, only two complexes, [{Ph2Te(NO3)}2O]2-Ph2Te(NO3)(OH) (ALCOCK, N. W.
et al.) and [Nd(H3dha3tren)(NO3)3]n (YANG, L. W. et al.) had three nitrate modes. The
structure of the title complex was the first example that contained four distinct nitrate modes
in one crystal structure.
In conclusion, it was seen that the nitrate group could be used as a bridging ligand to
form d-f block bimetallic complexes. We can envisage a wide range of compounds with this
ligand system. Although we cannot predict or control the likely product of any individual
reaction, we can produce a series of compounds with differing Cu:Ln ratios, with different
bridging modes of the ligand and with different partial arrangements of the metals, if La(III)
is replaced by other trivalent or divalent lanthanide. This type of complexes may prove
valuable in the study of 3d-4f metal ion interaction.

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(Received April 16, 1997; Accepted May 19, 1998)

Authors’ addresses:

Li JIANMIN
Department of Chemical Physics,
University of Science & Technology of China,
Hefei, Anhui 230026, P.R.China
e-mail: jmli@dchp.chp.ustc.edu.cn

Zhang YUGEN
Department of Chemistry,
University of Science & Technology of China,
Hefei, Anhui 230026, P.R.China
e-mail: zhangyg@mail.ach.ustc.edu.cn