Heterometallic lanthanide Group 12 metal iodides

Article abstract of DOI:10.1021/ic049560f

Neodymium tri-iodide reacts with Group 12 metal (M; M = Zn, Cd, Hg) iodides to form heterometallic compounds. These Lewis acidic M cleave Nd-I bonds to give either ionic {[(THF)₅NdI₂][MI₃THF]; M = Zn, Cd} or charge-neutral {(THF)₅NdI(μ2I)HgI₃} compounds. Differences in structure are interpreted primarily in terms of M-L bond strengths, rather than Nd-L bond strengths. Experiments with Yb indicate that if there is any excess iodide present in these syntheses then the most readily isolated product is a triiodide salt, i.e., [(THF)₅YbI ₂][I₃]. In conventional solvents the presence of Lewis acid is not required for iodide displacement-from pyridine, YbI ₃ crystallizes as [(Py)₅YbI₂][I]. These compounds are potentially useful as heterometallic sources of lanthanide-doped iodide matrixes, they illustrate the ease with which iodides are displaced from lanthanide coordination spheres, and they underscore the complexity associated with using lanthanide iodides as Lewis acid catalysts.

Full text of DOI:10.1021/ic049560f

Inorg. Chem. 2004, 43, 5659−5664
Heterometallic Lanthanide Group 12 Metal Iodides
Louise Huebner, Anna Kornienko, Thomas J. Emge, and John G. Brennan*
Department of Chemistry and Chemical Biology, Rutgers, the State UniVersity of New Jersey,
610 Taylor Road, Piscataway, New Jersey 08854-8087
Received April 4, 2004
Neodymium tri-iodide reacts with Group 12 metal (M; M ) Zn, Cd, Hg) iodides to form heterometallic compounds.
These Lewis acidic M cleave Nd−I bonds to give either ionic {[(THF)5NdI ][MI THF]; M ) Zn, Cd} or charge-
2
3
neutral {(THF)5NdI(µ2I)HgI } compounds. Differences in structure are interpreted primarily in terms of M−L bond
3
strengths, rather than Nd−L bond strengths. Experiments with Yb indicate that if there is any excess iodide present
in these syntheses then the most readily isolated product is a triiodide salt, i.e., [(THF)5YbI ][I ]. In conventional
2
3
solvents the presence of Lewis acid is not required for iodide displacementsfrom pyridine, “YbI ” crystallizes as
3
[(py)5YbI ][I]. These compounds are potentially useful as heterometallic sources of lanthanide-doped iodide matrixes,
2
they illustrate the ease with which iodides are displaced from lanthanide coordination spheres, and they underscore
the complexity associated with using lanthanide iodides as Lewis acid catalysts.
Introduction
cated by the disparate natures of the ionic Ln and covalent
M, i.e., finding ligand systems that coordinate to both metals,
or solvent systems that can be used to recrystallize ionic/
covalent combinations rather than deliver mixtures of mono-
metallic products, is often frustrating.
Multifunctional ligand systems have been developed1
extensively to deliver a large family of heterometallic com-
pounds with specific physical properties. Much of this work
focuses on the preparation of materials with controlled elec-
tronic structure, but other efforts have been devoted to en-
hancing or optimizing Lewis acid reactivity.1c
Heterometallic compounds containing lanthanides (Ln) and
transition metals (M) continue to be investigated as poten-
tially useful electronic materials with readily tailored elec-
tronic or magnetic properties.1-7 This chemistry is compli-
* Author to whom correspondence should be addressed. E-mail: bren@
rutchem.rutgers.edu.
(1) (a) Imbert, D.; Cantuel, M.; Bu¨nzli, J..; Bernardinelli, G.; Piguet, C.
J. Am. Chem. Soc. 2003, 125, 15698-15699. (b) Rodriguez-Cortinas,
R.; Avecilla, F.; Platas-Iglesias, C.; Imbert, D.; Bu¨nzli, J.; de Blas,
A.; Rodriguez-Blas, T. Inorg. Chem. 2002, 41, 5336-5349. (c) Bu¨nzli,
J. G.; Piguet, C. Chem. ReV. 2002, 102, 1897-1928. (d) Glover, P.
B.; Ashton, P. R.; Childs, L. J.; Rodger, A.; Kercher, M.; Williams,
R. M.; De Cola, L.; Pikramenou, Z. J. Am. Chem. Soc. 2003, 125,
9918-9919. (e) Lin, X.; Doble, D. M. J.; Blake, A. J.; Harrison, A.;
Wilson, C.; Schroeder, M. J. Am. Chem. Soc. 2003, 125, 9476-9483.
(f) He, Z.; He, C.; Gao, E.; Wang, Z.; Yang, X.; Liao, C.; Yan, C.
Inorg. Chem. 2003, 42, 2206-2208. (g) Cui, Y.; Qian, Y.-T.; Huang,
J.-S. Polyhedron 2001, 20, 1795-1802.
(2) (a) James, C.; Willand, P. S. J. Am. Chem. Soc. 1916, 38, 1497. (b)
Bailey, W. E.; Williams, R. J.; Milligan, W. O. Acta Crystallogr. 1973,
B29, 1365. (c) Knoeppel, D. W.; Liu, J.; Meyers, E. A.; Shore, S. G.
Inorg. Chem. 1998, 37, 4828-4837. (d) Liu, J.; Knoeppel, D. W.;
Liu, S.; Meyers, E. A.; Shore, S. G. Inorg. Chem. 2001, 40, 2842-
2850. (e) Du, B.; Meyers, E. A.; Shore, S. G. Inorg. Chem. 2001, 40,
4353-4360. (f) James, C.; Willand, P. S. J. Am. Chem. Soc. 1916,
38, 1497. (g) Harada, K.; Yuzunihara, J.; Ishii, Y.; Sato, N.;
Kambayashi, H.; Fukada, Y. Chem. Lett. 1995, 887.
There is extensive literature describing the use of pseudoha-
lide ligands (CN,2 SCN,3 SPh,4 SePh5) to connect Ln with
M. These heterometallic materials, representing the earliest
heterometallic chemistry containing Ln ions,2a often exhibit
thought-provoking magnetic and electronic properties. Within
this molecular class, both charge-neutral and ionic species
have been generated by careful balance of relative M-L and
Ln-L bond strengths. A recent extension of this work to
chalcogenido clusters6 led to the preparation of cluster salts,
with separate cationic LnE and anionic ME cluster cores.
Of the molecular heterometallic compounds in the litera-
ture, all but two contain M and Ln bridged either by organic
or oxo ligands. The exceptions are poly-Mn compounds with
Cl, oxo, and catecholate bridges linking Mn with La.7 Oddly
(3) Amirkhanov, V. M.; Kapshuk, A. A.; Kramarenko, F. G.; Skopenko,
V. V. Russ. J. Inorg. Chem. 1994, 39, 1155.
(4) Brewer, M.; Emge, T.; Brennan, J. Inorg. Chem. 1995, 34, 5919-
5924.
(5) (a) Freedman, D.; Emge, T. J.; Brennan, J. G. J. Am. Chem. Soc. 1997,
119, 11112-11113. (b) Lee, J.; Emge, T.; Brennan, J. Inorg. Chem.
1997, 36, 5064-5068. (c) Berardini, M. (d) Emge, T.; Brennan, J.
Inorg. Chem. 1995, 34, 5327. (e) Berardini, M.; Emge, T.; Brennan,
J. J. Am. Chem. Soc. 1994, 116, 6941.
(6) Kornienko, A.; Huebner, L.; Freedman, D.; Emge, T.; Brennan, J.
Inorg. Chem. 2003, 42, 8476-8480.
(7) Reynolds, R. A.; Coucouvanis, D. J. Am. Chem. Soc. 1998, 120, 209.
10.1021/ic049560f CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/05/2004
Inorganic Chemistry, Vol. 43, No. 18, 2004 5659

Huebner et al.
Synthesis of [(THF)5NdI2][(THF)CdI3] (3). As for 2, Nd (0.29
g, 2.0 mmol), I2 (0.76 g, 3.0 mmol), THF (25 mL), Cd (0.23 g,
2.0 mmol), and more I2 (0.51 g, 2.0 mmol) gave colorless lathes
(0.40 g, 19%) that turn black at 150 °C and melt at 255 °C.
Anal. Calcd for C24H48O6NdCdI5: C, 21.8; H, 3.65. Found: C,
20.8; H, 3.86. The compound is colorless, but exposure to air
produces an optical absorption maximum at 368 nm in THF. IR:
2958 (w), 2921 (w), 2852 (w), 2357 (s), 2337 (s), 1941 (s), 1605
(s), 1454 (m), 1409 (m), 1377 (m), 1262 (w), 1099 (w), 1021 (w),
866 (m), 805 (s), 6946 (m), 670 (m) cm-1. Cell data from single-
crystal X-ray diffraction (87 reflections with 2° < θ < 21°): a )
8.582(4) Å, b ) 9.065(4) Å, c ) 24.691(13) Å, â ) 82.76(2)°, V
) 1905.7(16) Å3.
enough, simple homoleptic halides have never been used as
starting materials in heterometallic syntheses. Such an un-
complicated approach to heterometallic chemistry could
present an entry to new optoelectronic materials, as metal
halide lattices have relatively low phonon energies,8 and so
Ln-doped halide matrixes have potentially useful transmis-
sion windows.9
In this work we outline our first attempts to prepare het-
erometallic iodide compounds containing both Ln and the
group 12 metals Zn, Cd, and Hg. Difficulties associated with
producing heterometallic iodides are identified, and the
various structures of isolated heterometallic compounds are
discussed in terms of relative M-I bond strengths.
Synthesis of [(py)5YbI2][I]‚1/2(py) (4). Yb (0.35 g, 2.0 mmol)
and I2 (0.72 g, 2.9 mmol) were combined in THF (40 mL). The
mixture was stirred until all the metal was consumed (3 days) to
give a transparent pale yellow solution and a salmon pink
precipitate. The precipitate was isolated by filtration, dried under
vacuum, and dissolved in pyridine (25 mL) to give a transparent
rust solution. After a day the solution was filtered to remove trace
black precipitate, and layered with hexanes (20 mL) to give yellow
needles (1.10 g, 50%) that turn black and melt at 375 °C. Anal.
Calcd for C27.5H27.5N5.5YbI3: C, 33.4; H, 2.80; N, 7.79. Found: C,
33.2; H, 3.05; N, 7.65. The compound does not show an optical
absorption maximum from 300 to 800 nm in pyridine and was
insoluble in THF. IR: 2922 (w), 2854 (w), 2366 (s), 1634 (s), 1596
(m), 1580 (m), 1521 (s), 1457 (w), 1437 (m), 1377 (m), 1260 (s),
1215 (s), 1144 (s), 1069 (s), 1029 (s), 990 (s), 884 (m), 805 (m),
Experimental Section
General Methods. All syntheses were carried out under high-
purity nitrogen (Airgas), using conventional drybox or Schlenk
techniques. Solvents (Aldrich) were either refluxed continuously
over molten alkali metals or K/benzophenone and collected
immediately prior to use, or purified with a dual column Solv-Tek
Solvent Purification System. Lanthanides were purchased from
Strem. Melting points were taken in sealed capillaries and are
uncorrected. IR spectra were taken on a Thermo Nicolet Avatar
360 FTIR spectrometer, and recorded from 4000 to 600 cm-1 as a
Nujol mull on NaCl plates. Electronic spectra were recorded on a
Varian DMS 100S spectrometer with the samples in a 0.10-mm
quartz cell attached to a Teflon stopcock. Elemental analyses were
performed by Quantitative Technologies, Inc. (Whitehouse, NJ).
Synthesis of (THF)5NdI(µ2-I)HgI3 (1). Nd (0.29 g, 2.0 mmol)
and I2 (0.76 g, 3.0 mmol) were combined in THF (35 mL). The
mixture was stirred until most of the metal was consumed (2 days)
to give a translucent brick red solution. Hg (0.40 g, 2.0 mmol) and
more I2 (0.51 g, 2.0 mmol) were added to the mixture and stirred
for 2 days. The solution was allowed to settle and a tan solid
precipitated. The rust solution was filtered (30 mL) and layered
with hexanes (8 mL) to give colorless rods (0.39 g, 15%) that
turn black at 95 °C and decompose at 310 °C. Anal. Calcd for
C20H40O5NdHgI5: C, 17.9; H, 3.01. Found: C, 17.5; H, 3.15. The
compound does not show an optical absorption maximum from
300 to 800 nm in pyridine or THF. IR: 2964 (w), 2843 (w), 2729
(s), 1459 (m), 1377 (m), 1260 (s), 1096 (s), 1020 (s), 804 (s), 722
743 (m), 700 (w), 668 (s) cm-1
.
Synthesis of [(THF)5YbI2][I3] (5). Yb (0.35 g, 2.0 mmol) and
I2 (0.76 g, 3.0 mmol) were combined in THF (50 mL). The mixture
was stirred for 3 days to give pink powder and a light yellow
solution. The solution was filtered, concentrated to 38 mL, and
layered with hexanes (25 mL) to give long yellow needles (0.59
mg, 25%) that turned brown at 201 °C but did not melt below 296
°C. Anal. Calc. for C20H40O5I5Yb: C, 20.6; H, 3.45. Found: C,
20.0; H, 3.31. IR: 3658 (s), 3583 (s), 2923 (w), 2727 (s), 2670 (s),
2362 (s), 1654 (s), 1461 (w), 1377 (m), 1305 (s), 1261 (s), 1154
(s), 1091 (s), 1018 (s), 800 (s), 722 (s) cm-1
.
X-ray Structure Determination of 1, 2, 4, and 5. Data for 1,
2, 4, and 5 were collected on a Bruker Smart APEX CCD
diffractometer with graphite monochromatized Mo KR radiation
(λ ) 0.71073Å) at 100 K. The data were corrected for Lorenz
effects and polarization, and absorption, the latter by a multiscan
(SADABS)10 method. The structures were solved by Patterson or
direct methods (SHELXS86).11 All non-hydrogen atoms were
refined (SHELXL97)12 based upon Fobs2. All hydrogen atom
coordinates were calculated with idealized geometries (SHELXL97).
Scattering factors (fo, f ′, f′′) are as described in SHELXL97.
Crystallographic data and final R indices for 1, 2, 4, and 5 are
given in Table 1. ORTEP diagrams13 for 1, 2, 4, and 5 are shown
in Figures 1, 2, 3, and 4, respectively. Significant bond geometries
for 1, 2, 4, and 5 are given in the figure captions. Complete
crystallographic details for 1, 2, 4, and 5 are given in the Supporting
Information.
(s) cm-1
.
Synthesis of [(THF)5NdI2][(THF)ZnI3] (2). Nd (0.29 g, 2.0
mmol) and I2 (0.76 g, 3.0 mmol) were combined in THF (25 mL).
The mixture was stirred until the metal was consumed (5 days) to
give a translucent pale brown solution. Zn (0.13 g, 2.0 mmol) and
more I2 (0.51 g, 2.0 mmol) were added to the mixture and stirred
for 4 days. The mixture was allowed to settle and the tan precipitate
was separated from the golden yellow solution by filtration. The
solution (22 mL) was layered with hexanes (13 mL) to give
colorless rods (0.56 g, 22%) that turn black at 140 °C and melt at
195 °C. Anal. Calcd for C24H48O6NdZnI5: C, 22.6; H, 3.79.
Found: C, 22.6; H, 4.10. The compound is colorless, but exposure
to air produces an optical absorption maximum at 368 nm in THF.
IR: 3769 (s), 3704 (s), 2958 (w), 2920 (w), 2856 (w), 1937 (s),
1598 (s), 1459 (m), 1410 (m), 1378 (m), 1265 (w), 1104 (w), 1018
(10) Bruker-ASX. SADABS, Bruker Nonius Area Detector Scaling and
Absorption Correction, v2.05; Bruker-AXS Inc.: Madison, WI, 2003.
(11) Sheldrick, G. M. SHELXS86, Program for the Solution of Crystal
Structures; University of Go¨ttingen: Germany, 1986.
(w), 862 (m), 808 (s), 706 (m), 658 (m) cm-1
.
(12) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Germany, 1997.
(13) (a) Johnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976. (b) Zsolnai, L. XPMA and
ZORTEP, Programs for InteractiVe ORTEP Drawings; University of
Heidelberg: Germany, 1997.
(8) Singh, R. K. Phys. Rep. 1982, 85, 259-401.
(9) (a) Lucas, J. Solid State Ionics 1990, 39, 105-112. (b) Schedin, F.;
Thornton, G.; Uhrberg, R. I. G. ReV. Sci. Instrum. 1997, 68, 41-46.
(c) Shalem, S.; German, A.; Barkay, N.; Moser, F.; Katzir, A. Fiber
Integr. Opt. 1997, 16, 27-54.
5660 Inorganic Chemistry, Vol. 43, No. 18, 2004

Heterometallic Lanthanide Group 12 Metal Iodides
Table 1. Crystallographic Data and Final R Indices for 1, 2, 4, and 5
compound
1
2
4
5
empirical formula
fw
space group
cryst syst
a (Å)
C20H40HgI5NdO5
1339.85
P212121
orthorhombic
12.5824(9)
13.0371(9)
20.411(1)
90
90
90
3348.1(4)
4
2.658
C24H48I5NdO6Zn
1276.73
Pn
monoclinic
8.5245(7)
9.0424(7)
24.515(2)
90
96.641(1)
90
1877.0(3)
2
C27.5H27.5I3N5.5Yb
988.79
P21/c
monoclinic
25.950(1)
15.8012(7)
16.0894(8)
90
106.302(1)
90
6332.0(5)
8
2.074
100(2)
C20H40I5O5Yb
1168.06
Pbcn
orthorhombic
12.3056(1)
21.741(2)
11.896(1)
90
90
90
3182.7(6)
4
2.438
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D (calcd) (g/cm-3
temperature (K)
λ (Å)
)
2.259
100(2)
100(2)
0.71073
6.149
0.050
0.097
100(2)
0.71073
7.813
0.037
0.075
0.71073
10.748
0.032
0.71073
5.904
0.033
abs coeff (mm-1
)
R(F)a [I > 2 σ(I)]
Rw(F2)a [I > 2 σ(I)]
0.064
0.057
a R(F) ) ∑||Fo| - |Fc||/∑|Fo|; Rw(F2) ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2. Additional crystallographic details are given in the Supporting Information.
2
2
2
Figure 2. Molecular structure of [(THF)5NdI2][(THF)ZnI3]. Thermal
ellipsoids are drawn at the 50% probability level. Significant bond dis-
tances (Å) and angles (°): Nd(1)-O(1), 2.441(6); Nd(1)-O(4) 2.453(6);
Nd(1)-O(3), 2.458(6); Nd(1)-O(2), 2.463(6); Nd(1)-O(5), 2.484(6);
Nd(1)-I(1), 3.0496(7); Nd(1)-I(2), 3.0522(7); Zn(1)-O(6), 2.068(6);
Zn(1)-I(3), 2.5633(11); Zn(1)-I(4), 2.5764(12); Zn(1)-I(5), 2.5783(11);
O(1)-Nd(1)-O(4), 145.4(2); O(1)-Nd(1)-O(3), 143.1(2); O(4)-
Nd(1)-O(3), 71.0(2); O(1)-Nd(1)-O(2), 71.6(2); O(4)-Nd(1)-O(2),
142.6(2); O(3)-Nd(1)-O(2), 71.6(2); O(1)-Nd(1)-O(5), 71.5(2); O(4)-
Nd(1)-O(5), 74.6(2); O(3)-Nd(1)-O(5), 145.4(2); O(2)-Nd(1)-O(5),
142.9(2); O(1)-Nd(1)-I(1), 87.94(14); O(4)-Nd(1)-I(1), 85.27(17);
O(3)-Nd(1)-I(1), 91.06(16); O(2)-Nd(1)-I(1), 93.03(14); O(5)-Nd(1)-
I(1), 89.18(15); O(1)-Nd(1)-I(2), 93.81(14); O(4)-Nd(1)-I(2),
91.07(17); O(3)-Nd(1)-I(2), 89.91(16); O(2)-Nd(1)-I(2), 91.27(14);
O(5)-Nd(1)-I(2), 87.64(15); I(1)-Nd(1)-I(2), 175.68(2); O(6)-Zn(1)-
I(3), 101.9(2); O(6)-Zn(1)-I(4), 102.6(2); I(3)-Zn(1)-I(4), 114.83(4);
O(6)-Zn(1)-I(5), 104.6(2); I(3)-Zn(1)-I(5), 114.28(4); I(4)-Zn(1)-I(5),
116.00(4).
Figure 1. Molecular structure of (THF)5NdI(µ2-I)HgI3. Thermal ellipsoids
are drawn at the 50% probability level. Significant bond distances (Å) and
angles (°): Nd(1)-O(1), 2.445(5); Nd(1)-O(5), 2.451(5); Nd(1)-O(3),
2.453(5); Nd(1)-O(2), 2.454(4); Nd(1)-O(4), 2.463(5); Nd(1)-I(1),
3.0543(6); Nd(1)-I(2), 3.1086(6); I(2)-Hg(1), 3.2452(5); Hg(1)-I(4),
2.7146(6); Hg(1)-I(5), 2.7206(6); Hg(1)-I(3), 2.7250(5); Nd(1)-I(2)-
Hg(1), 126.71(2); I(4)-Hg(1)-I(5), 122.05(2); I(4)-Hg(1)-I(3), 119.78-
(2); I(5)-Hg(1)-I(3), 114.43(2); I(4)-Hg(1)-I(2), 93.14(2); I(5)-Hg(1)-
I(2), 98.66(2); I(3)-Hg(1)-I(2), 97.74(2); I(1)-Nd(1)-I(2), 176.72(2).
Results
The group 12 metal iodides MI2 (M ) Zn, Cd, Hg) react
with LnI3 to form heterometallic compounds with a transfer
of iodide from Ln to M. Saturation of a THF solution of
HgI2/NdI3 results in the isolation of (THF)5NdI(µ-I)HgI3 (1).
A low-temperature single-crystal X-ray diffraction analysis
of this product revealed a structure with pentagonal bipy-
ramidal geometry about the Nd, having two axial I- and five
equatorial THF ligands. Figure 1 gives an ORTEP diagram
of 1, with significant bond lengths and angles in the figure
caption. In the structure of 1, an I- has been extracted from
the Nd(III) coordination sphere, and this I- coordinates the
Hg(II) ion. One of the Nd bound I- also coordinates to the
Hg(II) ion, and while there are four I- about the Hg, the
geometry is better described as trigonal planar HgI3- with a
relatively weak, e.g. dative, interaction between Hg and I(2).
The three terminal iodides on Hg have similar bonding
geometries, both in terms of bond lengths [Hg(1)-I(4),
2.7146(6) Å; Hg(1)-I(5), 2.7206(6) Å; Hg(1)-I(3),
2.7250(5) Å] and angles [I(4)-Hg(1)-I(5), 122.05(2)°;
I(4)-Hg(1)-I(3), 119.78(2)°; I(5)-Hg(1)-I(3), 114.43(2)°].
In contrast, the distance between Nd and I(2) is 3.2542(3)
Å, and the average I(2)Hg-I angle is 96.5°. The mutual
effects of each metal on the others M-iodide bond length
is apparent not only in the Hg-I bond but also, in a less
dramatic way, in the bonds to Nd, where the Nd-I(1) bond
length is 3.0543(6) Å and Nd-I(2) bond length is longer at
3.1086(6) Å.
The more acidic MI2 compounds also extract I- from LnI3,
but the bridging Ln-I--M interaction present in 1 has been
disrupted by THF coordinated to both Ln and M to give the
ionic compounds [(THF)5NdI2][(THF)MI3] [M ) Zn(2),
Cd(3)]. Figure 2 gives an ORTEP diagram of 2, with signifi-
cant bond lengths and angles in the figure caption. The unit
cell data for the Cd compound 3 indicated that it is iso-
structural with 2. The cationic Nd fragment has considerable
precedence in the literature,14 while the overall geometries
of the main group anions are similar to those of other M(II)
anions.
Inorganic Chemistry, Vol. 43, No. 18, 2004 5661

Huebner et al.
Similarly, when an excess of iodine is added toYbI3 in
THF the resultant deep red solution can be saturated to give
[(THF)5YbI2][I3] (5), a salt that can be prepared in 25% yield.
These yellow-orange crystals routinely grow to >1 cm long.
Structural characterization of 5 revealed a cationic structure
similar to that found in 4, with a pentagonal bipyramidal
Yb(III) ion containing two axial I- and five equatorial THF
ligands. The counterion in this case was the well-known tri-
-
iodide, I3 . Figure 4 gives an ORTEP diagram of 5, with
significant bond lengths and angles included in the figure
caption. Tri-iodides were always noted as minor cocrystal-
lized products in the synthesis of 1-4 if an excess of I2 was
present, or if solutions of these compounds were exposed to
air.
Figure 3. Molecular structure of [(py)5YbI2][I]. Thermal ellipsoids are
drawn at the 50% probability level. Significant bond distances (Å) and angles
(°): Yb(1)-N(3), 2.454(4); Yb(1)-N(1), 2.474(4); Yb(1)-N(4), 2.474-
(3); Yb(1)-N(2), 2.474(4); Yb(1)-N(5), 2.482(3); Yb(1)-I(2), 2.9645-
(3); Yb(1)-I(1), 2.9729(3); N(3)-Yb(1)-N(1), 144.64(11); N(3)-Yb(1)-
N(4), 70.67(11); N(3)-Yb(1)-N(2), 70.88(11); N(1)-Yb(1)-N(2), 73.79(11);
N(1)-Yb(1)-N(5), 74.97(11); N(4)-Yb(1)-N(5), 69.75(11). The second
independent (py)5YbI2 cation has nearly the same bond distances and angles,
but several torsion angles are quite different (e.g., as a rotational isomer).
Discussion
Of the three heterometallic products described herein, only
the mercury compound 1 crystallizes as a molecular product,
with the Zn and Cd analogues 2 and 3, as well as the pyridine
complex 4 and triiodide compound 5, crystallizing as salts.
All compounds serve to illustrate the particular ease with
which iodides are removed from lanthanide coordination
spheres. Variations in the Group 12 compounds reflect the
relatively covalent nature of Hg, compared with Cd or Zn.
Precedence for MI3- and MI42- anions is noted16 for all three
of the group 12 metals.
Iodide chemistry of the Group 12 metals has been
thoroughly examined. Mercuric iodide is certainly the most
complicated of the group. A light-sensitive material,17 solid-
state HgI2 is complex, with a remarkable range of Hg-I
interactions: there is a red form containing Hg in a distorted
tetrahedral geometry [four 2.783 Å Hg-I bonds, I-Hg-I
) 103.1° and 112.7°], and a yellow form that contains
essentially linear HgI2 molecules (I-Hg-I ) 178.3°) with
two short (2.615 and 2.620 Å) and four long (2 × 3.507 Å
and 2 × 3.510 Å) Hg-I bonds.18 HgI2 has often incorporated
additional I- within the primary Hg(II) coordination sphere,
resulting in a multitude of Hg coordination geometries.
Compound 1, with three well-defined Hg-I bonds (bond
lengths range from 2.7146(4) to 2.7250(5) Å and average
2.720(1) Å) can be described either as a grossly distorted
tetrahedron or a trigonal planar Hg with an additional weak
Hg-I (3.2452(3) Å) interaction. Precedence for each type
of geometry already exists.16,19 It should be noted that in the
absence of Lewis base solvents, there appears to be no
reaction of HgI2 with LnI3.20
Figure 4. Molecular structure of [(THF)5YbI2][I3]. Thermal ellipsoids are
drawn at the 50% probability level. Significant bond distances (Å) and angles
(°): Yb(1)-O(2A)′, 2.341(4); Yb(1)-O(2A), 2.341(4); Yb(1)-O(1), 2.349-
(6); Yb(1)-O(3)′, 2.351(4); Yb(1)-O(3), 2.351(4); Yb(1)-I(1)′, 2.9505-
(5); Yb(1)-I(1), 2.9505(5); I(2)-I(3), 2.9058(5); I(2)-I(3)′′, 2.9058(5);
O(2A)′-Yb(1)-O(1), 72.1(1); O(2A)-Yb(1)-O(1), 72.1(1); O(2A)′-
Yb(1)-O(3)′, 71.99(14); O(2A)-Yb(1)-O(3), 71.99(14); O(3)′-Yb(1)-
O(3), 71.9(2); I(1)′-Yb(1)-I(1), 179.57(2); I(3)-I(2)-I(3)′′, 180. Atom
C5 is modeled as disordered 55:45 about two sites (site A shown here).
Symmetry operations used: ′ ) -x, y, -z + 1/2, and ′′ ) -x, -y, -z + 1.
Solvent selection is crucial to the isolation of heterome-
tallic iodides. In pyridine, analogous reactions did not yield
a crystalline product with Nd. However, saturation of solution
containingYbI3 in pyridine results in the crystallization of
[(py)5YbI2][I] (4) an ionic compound with a pentagonal
bipyramidal Yb ion having two axial iodides, five equatorial
pyridine ligands, and the monoanion I-. Figure 3 gives an
ORTEP drawing of the molecule, with significant bond
lengths and angles given in the figure caption. Both Yb-I
and Yb-N bond lengths are consistent with previously
reported trivalent Yb compounds.15 The deep yellow color
of this compound presumably originates from an iodide to
ytterbium charge-transfer absorption that tails from the UV
into the visible spectrum.
(15) Kornienko, A.; Emge, T.; Hall, G.; Brennan, J. Inorg. Chem. 2002,
41, 121-126. Kornienko, A.; Emge, T.; Brennan, J. J. Am. Chem.
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D.; Emge, T.; Brennan, J. J. Am. Chem. Soc. 1999, 121, 10247-10248.
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5662 Inorganic Chemistry, Vol. 43, No. 18, 2004

Heterometallic Lanthanide Group 12 Metal Iodides
Introduction of Lewis bases leads to a rich HgI2 coordina-
tion chemistry, with an even more complicated range of Hg
coordination geometries.19 In addition to the plethora of
regular and distorted Td structures, there are compounds such
as R3PHgI2,19b a trigonal bipyramidal molecule with three
strong bonds to Hg (P, I, I) and two weak HgI interactions
between neighboring molecules. In this class of materials,
structures often appear to be influenced by lattice require-
ments, brought to prominence because bonds to Hg are
generally less than robust and form more open complexes
with lower coordination numbers, particularly when the
ligands are relatively electropositive.
In 2 and 3, the more acidic MI2 (M ) Zn, Cd) moieties
coordinate an additional THF ligand rather than the terminal
I bound to Nd. Similar reactivity has been noted in chloride
systems, for example where LaCl3 reacts with FeCl3 in the
presence of OPPh3 to give [(OPPh3)5LaCl][FeCl4]2,21 in the
preparation of [(THF)5YbCl2][(THF)W(O)Cl4],14a or in Cu
chemistry, i.e., [GdCl2(OPPh3)4][CuCl3].22 In these cases, the
stronger chloride ligands are removed from Ln(III) in the
presence of highly charged (Fe(III), W(V), Cu(II)) Lewis
acids. The Cd product 3 could, conceivably, find use as a
Ln-doping source in the synthesis of cadmium halide
glasses.23
Iodide extraction has often been noted in lanthanide
chemistry, and can be achieved by interaction with either
acids or bases. While it was long known that the strongest
Lewis bases would displace I- to form ionic materials,24 the
diversity of reagents that cleave Ln-I bonds, as revealed in
the present study, is surprising. Early work examining the
coordination chemistry of LnI documented the formation
of conducting solutions with a variety of Lewis bases,
including urea,24a dimethylacetamide,24b ethylenediamine,24c
DMSO, DMF,24d and bipyrimidine.24e The number of dis-
placed iodides paralleled the donor strength, i.e., DMSO
formed a 1:3 electrolyte whereas bipyrimidine displaced only
a single I-.
DME, pyridine) will certainly benefit from analyses of simple
coordination chemistry, particularly if lanthanide iodides are
to be developed as catalysts.25 In the present work, it is clear
that even a monodentate nitrogen-containing donor such
as pyridine is sufficiently basic so as to displace I- from
Ln(III) coordination spheres. This reactivity does not neces-
sarily apply to the larger, early lanthanides, given that in
the chemically similar actinide series, UI3, which has an ionic
radius slightly larger than Nd, crystallizes from pyridine as
molecular (py)4UI3.26
Displacement of I- by pyridine is important when examin-
ing the catalytic behavior of lanthanide iodides, because it
suggests that even in the conventional monodentate solvents
currently used in synthetic chemistry, both neutral and
charged species are possible. For example, in the reported
polymerization of butyl-4-vinylbenzoate with SmI2, the
presence of SmI3 had a dramatic impact on molecular weight
distribution.27 Clearly, the possibility that ((THF)6SmI)+,
Sm(THF)72+, or polynuclear species are the superior catalysts
must be considered. Related examples of I- extraction by a
Lewis acid can be found in reports describing the self-
+
- 14b,c,d
ionization of LnI3 to give LnI2 /LnI4 .
Extraction of I- from YbI3 by I2, as evidenced by the
structure of 5, again serves as a reminder that catalysis with
lanthanide iodides can be complicated by an abundance of
neutral and ionic species in solution. Surprisingly, this com-
pound is isostructural with the analogous La derivative,28
making this formulation one of the rare instances in which
all the lanthanides can form an isostructural series of com-
pounds. In the La and Yb crystal structures, the I-I-I anions
have inversion symmetry requiring equivalent I-I (e.g.,
2.508 Å in 5) bond lengths. It has often been noted that a
slight excess of Ln enhances the yield of 1-3, presumably
because any adventitious oxygen/water does not result in the
generation of excess I2, which would otherwise react with
LnI3 to form particularly insoluble (THF)5LnI2(I3).
The shift away from synthetic methodologies using these
strong donor solvents, toward preparative inorganic/organo-
metallic chemistry involving less polar solvents (i.e., THF,
This iodide chemistry has frequent parallels with pseudoha-
lide ligand systems. With respect to cyanide ligands, there
exist structures with CN linking ionic/covalent combinations2
such as Sm/Ni or Yb/Fe. There is also a thiocyanate bridge
linking La and Hg where, as expected, N coordinates to La
and S coordinates to Hg.3 In recently described chalcogeno-
late reactivity group 12 M(EPh)2 compounds were used to
stabilize Ln(EPh)x compounds. Selenolates were often ex-
tracted from Ln(II) by Hg(II) ions, while more acidic metals
such as Zn(II) or Fe(III) were necessary to effect SePh
extraction from Ln(III).4 Thiolates have been displaced from
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Inorganic Chemistry, Vol. 43, No. 18, 2004 5663

Huebner et al.
Ln coordination spheres, but only in the presence of
multidentate Lewis bases.29
displacement of I- by pyridine. All of these compounds
illustrate the facility with which iodide is removed from Ln
coordination spheres.
Conclusion
Acknowledgment. This work was supported by the
Discrete complexes comprised of LnI3 with the group 12
metal iodides MI2 can be prepared and isolated either as ionic
or molecular products. A common feature to all three
products, the extraction of I- by M from the Ln coordination
sphere, is also noted in the extraction of I- by I2 and the
National Science Foundation under Grant CHE-0303075.
Supporting Information Available: X-ray crystallographic files
in CIF format for the crystal structures of 1, 2, 4, and 5. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(29) Mashima, K.; Nakayama, Y.; Shibahara, T.; Fukumoto, H.; Nakamura,
A. Inorg. Chem. 1996, 35, 93-99.
IC049560F
5664 Inorganic Chemistry, Vol. 43, No. 18, 2004