Zinc, cadmium, and mercury complexes with fluorinated selenolate ligands

Article abstract of DOI:10.1021/ic1002989

Reductive cleavage of C₆F₅SeSeC₆F ₅ with elemental M (M = Zn, Cd, and Hg) in pyridine results in the formation of (py)₂Zn(SeC₆F₅)₂, (py)₂Cd(SeC₆F

Full text of DOI:10.1021/ic1002989

7304 Inorg. Chem. 2010, 49, 7304–7312
DOI: 10.1021/ic1002989
Zinc, Cadmium, and Mercury Complexes with Fluorinated Selenolate Ligands
Thomas J. Emge,* Michael D. Romanelli, Brian F. Moore, 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 February 12, 2010
Reductive cleavage of C6F5SeSeC6F5 with elemental M (M = Zn, Cd, and Hg) in pyridine results in the formation of
(py)2Zn(SeC6F5)2, (py)2Cd(SeC6F5)2, and Hg(SeC6F5)2. Structural characterization of the Zn and Cd compounds
reveals tetrahedral coordination environments, while the Hg compound shows a complicated series of linear structures
with two short, nearly linear Hg-Se bonds, up to two longer and perpendicular Hg Se interactions, and no
3 3 3
coordinated pyridine ligands. All three compounds exhibit well-defined intermolecular π-π-stacking interactions in the
solid state. They are volatile and decompose at elevated temperatures to give MSe and either (SeC6F5)2 or Se(C6F5)2.
Introduction
Of the monodentate anions of the group 16 elements, the
fluorinated phenoxide OC6F5 has been used throughout the
periodic chart, in main-group,2 transition-metal,3 lanthanide,4
and actinide5 chemistry. This phenoxide imparts chemical
stability, particularly with metal ions in high oxidation states,
and improves solubility properties. The more electropositive
metal ions tend to form dative M-F interactions6 that are
interesting as models for understanding the first step in C-F
bond activation processes. There is also a tendency of
M(OC6F5)x compounds to crystallize in lattices with signifi-
cant π-π-stacking interactions.
Fluorinated ligands impart unique chemical and physical
properties to inorganic compounds, including superior solu-
bility/volatility characteristics, unusual crystal packing mo-
tifs, and stabilization of the elements in high oxidation
states.1 There exists an extensive group of fluorinated ligands,
including alkyls, aryls, amides, alkoxides, acetonylacetates,
carboxylates, phosphine oxides, phosphines, and thiolates.
Each ligand class confers unique advantages for the synthesis
of compounds with particular chemical or physical properties.
The fluorinated thiolate SC6F5 has been used similarly in
s-,7 p-,8 d-,9 and f-block10-13 research, again giving products
*To whom correspondence should be addressed. E-mail: bren@rci.
rutgers.edu (J.G.B.), emge@rci.rutgers.edu (T.J.E.).
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r
pubs.acs.org/IC
Published on Web 07/23/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 16, 2010 7305
with superior solubility properties and leading to the forma-
tion of products with distinctive structural characteristics.
Most recently, these SC5F6 ligands were used to make a series
of (DME)2Ln(SC6F5)3 (Ln = Nd,11 Er,12 and Tm13) co-
ordination complexes that had, at that time, the highest near-
infrared (NIR) emission quantum efficiencies ever reported
for molecular lanthanide sources. These thiolates are con-
siderably more emissive than the analogous phenoxides4b
because the low Ln-S stretching frequencies are not as well-
matched to the NIR transition energies, whereas the Ln-O
vibrations are considerably higher in energy and are more
likely to vibrationally quench the excited-state Ln ion.
The analogous fluorinated selenolate chemistry is essen-
tially undeveloped. The SeC6F5 ligand is not commercially
available as either the selenol or the diselenide, but a reliable
synthesis of C6F5Se-SeC6F5 has been reported.14 There exists
a description of Tl(SeC6F5) and heterometallic M/Tl com-
pounds with SeC6F5 ligands that contained dative Tl-F
interactions,15 and a mer-octahedral lanthanide compound
with a significant structural trans influence.16 Hg(SeC6F5)2
has also been prepared by the direct combination of Hg with
the diselenide, although no structural characterization details
were included.17
The fact that there has been no systematic investigation
into the chemistry of the group 12 metals (M = Zn, Cd, and
Hg) with fluorinated selenolates is surprising, because the
same desirable characteristics noted for the phenoxides and
thiolates can be expected for the selenolates, and these
properties can be exploited in a wide range of disciplines.
For example, II-VI materials with fluorinated selenolates
will likely show increased solubility in organic matrices,
which is potentially important for the doping of selenolate
passivated quantum dots18 into polymers.19 The often displayed
π-π-stacking interactions can potentially lead to new forms
of old materials, whether it be new cluster structures20 or
dimensionally restricted solid-state materials.21 In more ionic
chemistry, the Hg derivative would be particularly useful as a
transmetalation reagent for connecting SeC6F5 ligands with
electropositive metals, and Ln/M cluster compounds with
fluorinated selenolates should be particularly bright NIR or
visible emission sources, because the low-energy M-Se vibra-
tion and the reduced number of emission quenching C-H
bonds should favor radiative over vibrational relaxation
processes. Finally, in chemical vapor deposition, simple
M(SeC6F5)n coordination compounds should be more vola-
tile than their hydrocarbon counterparts. For these reasons,
we have begun to examine the systematic inorganic chemistry
of the fluorinated selenolate ligand and describe here the
synthesis, characterization, and thermal decomposition of
M(SeC6F5)2 (M = Zn, Cd, and Hg).
Experimental Section
General Methods. All syntheses were carried out under ultra-
pure nitrogen (Welco Praxair), using conventional drybox or
Schlenk techniques. Pyridine (Aldrich) was purified with a dual-
column Solv-Tek solvent purification system and collected
immediately prior to use. Se2(C6F5)2 was prepared according
to literature procedures.14 Zinc (J.T. Baker), cadmium
(Aldrich), and mercury (Aldrich) metals were purchased and
used as received. Melting points were recorded in sealed capil-
laries and are uncorrected. IR spectra were recorded on a
Thermo Nicolet Avatar 360 FTIR spectrometer from 4000 to
450 cm-1 as Nujol mulls on CsI plates. UV-vis absorption
spectra were recorded on a Varian DMS 100S spectrometer with
the samples dissolved in pyridine, placed in either a 1.0 mm ꢀ
1.0 cm Spectrosil quartz cell or a 1.0 cm2 special optical glass
1
cuvette, and scanned from 190 to 800 nm. H, 19F, and 77Se
NMR spectra were obtained on Varian spectrometers. Electro-
spray ionization mass spectrometry (ESI-MS) data were re-
corded on a Thermo Finnigan LCQ DUO system with the
sample dissolved in a 10:1 MeOH/CH3COOH mixture. Mass
spectra were acquired in the negative-ion detection mode,
scanning a mass range from m/z 150 to 1000. In the case of
isotopic patterns, the value given is for the most intense peak.
Powder X-ray diffraction (PXRD) data were obtained on a
Bruker HiStar area detector using Cu KR radiation from a
Nonius 571 rotating-anode generator. Elemental analyses were
performed by Quantitative Technologies, Inc. (Whitehouse,
NJ).
€
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(c) Kedarnath, G.; Kumbhare, L. B.; Jain, V. K.; Wadawale, A.; Dey, G. K.;
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Synthesis of (py)2Zn(SeC6F5)2 (1). Zn (0.065 g, 0.99 mmol),
Hg (0.020 g, 0.099 mmol), and Se2(C6F5)2 (0.492 g, 1.00 mmol)
were combined in pyridine (ca. 25 mL), and the mixture was
stirred at room temperature for 10 days. The solution was
filtered to remove Hg, concentrated to ∼5 mL, and held at -5 °C
to give near-colorless laths (0.604 g, 85%) that begin to melt at
154 °C and melt completely at 163 °C. IR: 2921 (s), 2717 (w),
2357 (w), 1605 (m), 1507 (m), 1462 (s), 1372 (s), 1217 (w), 1070
(m), 964 (m), 813 (m), 718 (m), 637 (w), 420 (w) cm-1. UV-vis:
This compound gives an optical absorption maximum at 477
nm. Anal. Calcd for C22H10N2F10ZnSe2: C, 36.9; H, 1.40; N,
3.91. Found: C, 36.7; H, 1.42; N, 3.90. 1H NMR (399.89 MHz,
acetone-d6; δ, ppm): 7.75 (dt, 2H), 8.22 (tt, 1H), 8.77 (dd, 2H).
19F NMR (376.22 MHz, acetone-d6; δ, ppm): -121.13 (dd, 2F),
-158.55 (t, 1F), -161.02 (tt, 2F). 77Se NMR (76.28 MHz,
pyridine-d5; δ, ppm): 476.6 (s) (vs PhSeSePh at 468.0 ppm as
an external standard). ESI-MS: m/z 738 (MNaþ), 494 (F5C6Se-
SeC6F5þ), 247 (SeC6F5þ).
Synthesis of (py)2Cd(SeC6F5)2 (2). Cd (0.056 g, 0.498 mmol)
and Se2(C6F5)2 (0.245 g, 0.498 mmol) were combined in pyridine
(ca. 25 mL), and the mixture was stirred at room temperature for

7306 Inorganic Chemistry, Vol. 49, No. 16, 2010
Emge et al.
Table 1. Summary of Crystallographic Details for 1-4a
1
2
3
4
empirical formula
fw
space group
C22H10F10N2Se2Zn
715.61
P21/n
C22H10F10N2Se2Cd
762.64
P21/n
9.086(3)
23.255(7)
12.034(4)
C12F10HgSe2
692.63
P1
14.6756(6)
17.8623(9)
21.629(2)
C12H10HgSe2
512.71
P21/c
14.7309(8)
5.5967(3)
7.3167(4)
˚
a (A)
9.3073(5)
17.0503(9)
14.8291(8)
78.392(3)
100.020(1)
77.348(3)
2317.4(2)
4
2.051
100(2)
0.710 73
4.297
0.0190
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
109.276(6)
83.452(2)
103.399(1)
3
˚
V (A )
Z
2400(1)
4
5404.5(6)
15
3.192
100(2)
0.710 73
15.841
0.0515
0.1205
586.80(6)
2
2.902
100(2)
0.710 73
19.279
0.0172
0.0425
D(calcd) (g/cm3)
temperature (K)
2.110
100(2)
0.710 73
2.145
0.0438
0.0842
˚
λ (A)
abs coeff (mm-1
)
R(F)b [I > 2 σ(I)]
Rw(F2)c [I > 2 σ(I)]
0.0461
P
P
P
a Additional crystallographic details are given in the Supporting Information. b Definitions: R(F) = ||Fo| - |Fc||/ |Fo|. c Rw(F2) = { [w(Fo
-
2
P
Fc2)2]/ [w(Fo2)2]}1/2
.
1 week. The solution was filtered, concentrated to ∼5 mL, and
held at -5 °C to give colorless plates (0.239 g, 63%) that begin to
melt at 150 °C and melt completely at 175 °C. IR: 2900 (s), 1602
(m), 1510 (m), 1504 (m), 1462 (s), 1459 (s), 1376 (s), 1264 (w),
1037 (w), 1010 (w), 814 (m), 693 (m), 629 (w), 463 (w) cm-1. This
compound does not have an absorption maximum between 320
and 800 nm. Anal. Calcd for C22H10N2F10CdSe2: C, 34.6; H,
1.32; N, 3.67. Found: C, 34.5; H, 1.51; N, 3.54. 1H NMR (499.77
MHz, DMSO-d6; δ, ppm): 8.63 (dt, 2H), 7.45 (dt, 1H), 7.25 (m,
2H). 19F NMR (470.25 MHz, DMSO-d6; δ, ppm): -124.64 (d,
2F), -163.42 (t, 1F), -165.21 (t, 2F).
the wurtzite (hexagonal) form of CdSe23 (2003 JCPDS card
no. 77-2307). The volatile product, a yellow crystalline material,
was identified as (SeC6F5)2 by single-crystal XRD24 and its
melting point.25
As was done previously for 1, 3 (10 mg) deposited a dark
powder at the region of the tube furnace where the quartz sample
tube exited the alumina furnace tube. The powder was identified
as cubic HgSe26 by PXRD (2003 JCPDS card no. 065-4590), and
GC-MS analysis identified the volatile product as Se(C6F5)2.
X-ray Structure Determination. Data for 1-3 and for Hg-
(SePh)2 4 were collected on a Bruker Smart APEX CCD
diffractometer with graphite-monochromatized Mo KR radia-
Synthesis of Hg(SeC6F5)2 (3). Hg (0.100 g, 0.498 mmol) and
Se2(C6F5)2 (0.245 g, 0.497 mmol) were combined in pyridine (ca.
25 mL), and the mixture was stirred at room temperature for 1
week. The solution was filtered to remove unreacted Hg and
brought to dryness. The solid was washed with hexanes, redis-
solved in ∼8 mL of toluene, and heated to 60 °C for 30 min
before cooling back to room temperature. The solution was then
held at -5 °C for 1 week to give colorless needles (0.215 g, 62%)
that melt at 115 °C. This melting point is significantly lower than
the temperature at which sublimed Hg(SeC6H5)2 (4) melts,
which implies that the two purification techniques lead to
different molecular phases.17 IR: 2850 (s), 1602 (m), 1510 (m),
1504 (m), 1462 (s), 1459 (s), 1376 (s), 1264 (w), 1037 (w), 1010
(w), 814 (m), 693 (m), 629 (w), 463 (w) cm-1. This compound
does not have an optical absorption maximum between 320 and
800 nm. Anal. Calcd for C12F10HgSe2: C, 20.8. Found: C, 20.3.
19F NMR (470.25 MHz, DMSO-d6; δ, ppm): -125.22 (dd, 2F),
-158.10 (t, 1F), -162.95 (m, 2F).
˚
tion (λ = 0.710 73 A) at 100 K. Crystals were immersed in
paratone oil and examined at low temperatures. The data were
corrected for Lorenz effects and polarization and absorption,
the latter by a multiscan (SADABS)27 method. The structures
were solved by direct methods (SHELXS86).28 All non-H
atoms were refined (SHELXL97)29 based upon Fobs2. All
H-atom coordinates were calculated with idealized geometries
(SHELXL97). Scattering factors (fo, f 0, f 00) are as described in
SHELXL97. Crystallographic data and final R indices for 1-4
are given in Table 1. ORTEP diagrams30 for 1-4 are shown in
Figures 1, 3, 5, and 7, respectively. Packing diagrams for 1-4 are
given in Figures 2, 4, 6, and 8, respectively. Complete crystal-
lographic details are given in the Supporting Information.
Results and Discussion
The group 12 metals all react with C6F5SeSeC6F5 in
pyridine over a period of days to weeks. Reactions proceed
slowly, and not to completion, in relatively apolar solvents
Thermolysis of 1-3. A sample of 1 (20 mg) was placed in a
quartz thermolysis tube that was sealed under vacuum, and the
sample end was placed into a model 847 Lindberg tube furnace.
The “cold” end of the glass tube was held at -196 °C by
immersion in liquid nitrogen. The sample was heated to 650 °C
at a ramp rate of 10 °C/min and then held at 650 °C for 5 h, at
which time itwas cooled to 25 °C at a rate of 3.5°C/min. The black
powder that was formed at the sample end of the quartz tube was
identified as cubic ZnSe22 (2003 JCPDS card no. 88-2345).
A volatile, polycrystalline thermolysis product found at the cold
region of the quartz tube was identified as Se(C6F5)2 by gas
chromatography (GC)-MS.
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€
Structures; University of Gottingen: Gottingen, Germany, 1986.
(29) (a) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (b) Sheldrick,
As was done previously, 2 (10 mg) was heated at 650 °C for
2.2 h. PXRD revealed that the only crystalline phase present was
G. M. SHELXL97, Program for Crystal Structure Refinement; University of
Gottingen: Gottingen, Germany, 1997.
€
€
(30) Graphics programs. ORTEP-3 for Windows: Farrugia, L. J. J. Appl.
Crystallogr. 1997, 30, 565. Burnett, M. N.; Johnson, C. K. ORTEP-III: Oak
Ridge Thermal Ellipsoid Plot Program for Crystal Structure Illustrations. Oak
Ridge National Laboratory Report ORNL-6895; 1996; Persistence of Vision Pty.
Ltd.: Persistence of Vision Raytracer (Version 3.6) 2004.
(22) Lao, P. D.; Gou, Y.; Siu, G. G.; Shen, S. C. Phys. Rev. B: Condens.
Matter Mater. Phys. 1993, 48, 11701.
(23) Freeman, D. K.; Mair, S. L.; Barnea, Z. Acta Crystallogr., Sect. A
1977, 33, 355.

Article
Inorganic Chemistry, Vol. 49, No. 16, 2010 7307
Figure 1. ORTEP diagram of 1 with the H atoms removed for clarity
˚
and ellipsoids at the 50% probability level. Significant bond lengths [A]
and angles [deg]: Zn1-N1, 2.055(1); Zn1-N2, 2.060(1); Zn1-Se1,
2.4130(2); Zn1-Se2, 2.4175(3); Se1-C1, 1.905(2); Se2-C7, 1.904(2);
N1-Zn1-N2, 105.75(5); N1-Zn1-Se1, 111.01(4); N2-Zn1-Se1,
108.39(4); N1-Zn1-Se2, 103.74(4); N2-Zn1-Se2, 110.45(4); Se1-
Zn1-Se2, 116.914(9).
Figure 3. ORTEP diagram of 2 with the H atoms removed for clarity
˚
and ellipsoids at the 30% probability level. Selected Bond lengths [A] and
angles [deg]: Cd1-N1, 2.286(5); Cd1-N2, 2.289(4); Cd1-Se1, 2.5645(9);
Cd1-Se2, 2.596(1); Se1-C1, 1.902(6); Se2-C7, 1.901(6); N1-Cd1-N2,
105.8(2); N1-Cd1-Se1, 110.5(1); N2-Cd1-Se1, 109.9(1); N1-
Cd1-Se2, 111.3(1); N2-Cd1-Se2, 95.07(1); Se1-Cd1-Se2, 122.15(3).
pyridine, giving a complicated structure with two short
Hg-Se bonds and an array of significantly longer Hg-Se
interactions. The Hg-containing compound is similar in
molecular structure to, but quite different in crystal packing
motif from, 4. The structure of 4 had been reported31 to have
molecules on 2-fold sites of the C-centered C2 cell, but our
analysis of weak- and intermediate-intensity X-ray reflec-
tions revealed that the true lattice was primitive and centro-
symmetric and that the true site symmetry of the molecule 4
was inversion. The molecular structures of 1-4 are shown in
Figures 1, 3, 5, and 7, respectively, with significant bond
geometries for 1 and 2 given in the figure captions and
selected bonding and nonbonding geometries for 3 listed in
Table 2.
The Zn compound 1 (Figure 1) has a slightly distorted
tetrahedral coordination with a wide range of ligand-Zn-
ligand angles (105.8-116.9°, average 109.3°). There are two
˚
statistically equivalent Zn-N bond lengths of 2.058(1) A that
are typical for Zn-pyridine interactions, and there are two
Figure 2. (Top) ORTEP diagram illustrating the 1-D stacking of mole-
cules with π-π interactions for 1, viewed approximately along the a-b
˚
nearly equal Zn-Se bond lengths [2.4130(2) and 2.4175(3) A]
vector. (Bottom) ORTEP diagrams of close-ups of two distinct ring
ring interactions for adjacent and coparallel rings in (py)2Zn(SeC6F5)2
viewed normal to the phenyl rings.
that are also within the normal range found for Zn-Se bonds
found in the Cambridge Structural Database (CSD).41 A pair
of similar (py)2Zn(SeR)2 compounds in the literature affords
an opportunity to evaluate the effect of fluorination on the
3 3 3
such as toluene or tetrahydrofuran (THF), but in pyridine the
metals dissolve completely [reaction (1)], and extraction of
the product with toluene, followed by saturation, gives high
yields of M(SeC6F5)2.
32
Zn-Se bond length: in (3,5-Me2-C5H3N)2Zn(SeSiMe3)2
˚
˚
[Zn-Se = 2.396(2) A; Zn-N = 2.10(1) A] and (py)2Zn(SeC6-
33
˚
˚
H2Me3-2,4,6)2 [Zn-Se = 2.377(1) A; Zn-N = 2.118(4) A],
the Zn-Se bonds are all slightly but significantly shorter than
the Zn-Se bond lengths found in 1, which would be consistent
with a higher degree of polarization of the electron density
away from the Zn-Se bond in 1.
M þ C6F5SeSeC6F5 f ðpyÞxMðSeC6F5Þ2
ðM ¼ Zn or Cd, x ¼ 2; M ¼ Hg, x ¼ 0Þ
ð1Þ
There is no evidence for any significant Zn-F interaction
(closest intramolecular Zn F is for F6 at 2.98 A; closest
Low-temperature single-crystal XRD of the Zn and Cd
compounds shows that they crystallize as the pyridine ad-
ducts 1 and 2, while the Hg compound 3 crystallizes without
˚
3 3 3
˚
intermolecular Zn F is for F8;1 þ x, y, z at 3.55 A), but
3 3 3
there are clearly defined π-π-stacking interactions present in
(31) Lang, E. S.; Dias, M. M.; Abram, U.; Vazquez-Lopez, E. M. Z.
Anorg. Allg. Chem. 2000, 626, 784. The synthesis of 4 is described in this
reference. Unfortunately, the authors appear to have missed the weak primitive
lattice reflections in their crystallographic analysis, giving rise to erroneous
molecular and crystal structures.
(32) Azad, M.; Malik, M.; Motevalli, M.; O’Brien, P. Polyhedron 1999,
18, 1259.
(33) DeGroot, M. W.; Corrigan, J. F. Organometallics 2005, 24, 3378.

7308 Inorganic Chemistry, Vol. 49, No. 16, 2010
Emge et al.
Figure 4. (Top) ORTEP diagram illustrating the isolated stacking of four pentafluorophenyl rings and two pyridine rings indicating π-π interactions for
2. (Bottom) ORTEP diagram of the intramolecular π-π interactions for two adjacent pairs of C6F5 rings (e.g., three consecutive interplanar separations of
about 3.5 A) in the crystal structure of 2. The view is perpendicular tothe phenylringbondedtoSe1. (Left) Related molecules are x, y, z (solid bonds) for that
˚
containing Se1 and 1 - x, -y, 1 - z (open bonds and above) for Se10. (Right) Related molecules are x, y, z (solid bonds) for Se2 and 1 - x, -y, 2 - z (open
bonds and below) for Se20.
Figure 5. ORTEP diagram of adjacent 1-D arrays of 3 viewed approximately along the crystallographic b* axis. The horizontal direction is along the
crystallographic b-3c direction. The π-π interactions between C6F5 rings are possible along the 1-D array shown as well as between adjacent arrays. The
treatment of site disorder by use of a four-part model is demonstrated here by the separate colors of each part (see the text). The shortest Hg Se contacts
˚
(<3.35 A) to adjacent molecules are indicated by dashed lines (see Table 2).
3 3 3
the solid state (Figure 2). While there are no intramolecular
π-π interactions and no π-π interactions involving the
pyridine ligands, there are two distinct types of intermolecu-
lar packing interactions between the fluorinated phenyl rings
of two adjacent molecules, namely, those related by the
inversion center at (1/2, 0, 1/2) or (1/2, 0, 1) for rings bonded
to Se1 or Se2, respectively (Figure 2). In one case, there is the
more direct π-π interaction with the Se atoms distant to the
rings, and in the other case, there is the familiar Se over the
ring motif observed in other aromatic selenido compounds
including the selenofulvalenes. Because the SeC6F5 ligands
are located on approximately opposite sides of the molecule
(e.g., no close intramolecular association of SeC6F5 ligands),
the π-π (or Se ring) interactions in 1 allow for a 1-D
3 3 3
arrangement of closely interacting molecules along the crys-
tallographic c axis. The SHELXL mean-plane calculations
for the phenyl ring of SeC6F5 in 1 yielded plane-plane
˚
separations of 3.458(4) and 3.373(5) A between planes con-
taining Se1 and its inversion symmetry neighbor, Se10, and
Se2 and its inversion symmetry neighbor, Se20, respectively.
In addition, these π-π interaction distances apparently
include the steric effects of the Se atoms but to different

Article
Inorganic Chemistry, Vol. 49, No. 16, 2010 7309
Figure 7. ORTEP diagram of 4 with the ellipsoids at the 50% prob-
˚
ability level for non-H atoms. Significant bond lengths [A] and angles
[deg]: Hg1-Se1, 2.4802(2); Hg1-Se10, 2.4802(2); Se1-C1, 1.922(2);
Se1-Hg1-Se10, 180.0.
Figure 6. ORTEP diagram of the projection of all 12 component
molecules modeled in the SHELXL refinement of 3 viewed along the
crystallographic b-3c vector, indicatingseveral sites for Hg and Se (larger
spheres), despite the generally consistent placement of the C6F5 group for
nearest-neighbor molecules.
˚
degrees for Se1 and Se2, which are 0.04 and 0.01 A further
away from their respective mean planes. The shift (or linear
0
˚
offset) of rings containing Se1 and Se1 is ∼1.9 A greater than
that for the rings containing Se2 and Se20 and places atom
Se10 directly above the ring of Se1 (see Figure 2). The
combination of wider separation between the rings, greater
out-of-plane distance, and positioning of Se10 above the ring
of Se1 indicates that this Se ring interaction is not likely
3 3 3
attractive and more likely a result of steric considerations of
the nearby Se10 atom.
The Cd compound 2 (Figure 3) also contains a similarly
distorted tetrahedralmetal ion ligand-Cd-ligand angle with
a broad range of 95-122° (average 109.1°). There are two
pyridine donors with statistically equivalent Cd-N bond
˚
lengths [2.288(5) A] that are within the range found for
Cd-pyridine interactions.34,41 The location of the Cd atom
is significantly displaced from either of the mean pyridine
planes in the Cd complex, with separations of 0.165(8) and
˚
0.414(8) A, respectively, to the py1 and py2 planes. This
situation contrasts with the very small separations in the Zn
complex, at 0.089(2) and 0.038(2) A, respectively. Such
displacements are not unusual for monomeric pyridine com-
plexes of large metals but are in contrast to the values for the
smaller Zn metal complex here. Also, as was found for the Zn
structure, the two Cd-Se bond lengths are slightly different:
˚
Figure 8. ORTEP diagram of adjacent 1-D arrays of 4 viewed approxi-
mately along the crystallographic b þ c diagonal axis. The horizontal
direction is along the crystallographicb - c direction. The top and bottom
arrays are related by inversion through the point (0, /2, /2). The π-π
interactions between C6F5 rings in 3 are not possible here, owing to the
near-perpendicular relationship between adjacent aromatic (Ar) rings.
1
1
Only H Ar interactions are possible.
3 3 3
˚
˚
Cd1-Se1 = 2.564(1) A and Cd1-Se2 = 2.596(1) A. The
only related CdN2Se2 complex that has been structurally
characterized in the literature is (bpy)Cd(SeC6H2 Pr3-2,4,6)2
two distinct intermolecular π-π interactions of 2 are found on
either side of the intramolecular π-π interaction and involve
i
[Cd-Se = 2.553(4) A; Cd-N = 2.33(1) A],35 and the M-Se
bonds in 2 are significantly longer than the Cd-Se bonds in
the bpy compound. This could be a result of the steric
requirements of the bpy ligand in that complex, or, more
likely, the longer Cd-Se bonds in 2 are a result of the
polarizing influence of the fluorine substituent.
˚
˚
˚
inversion-related Se1 selenolate rings [with a 3.774(1) A cen-
troid-to-centroid distance] or the Se2 selenolate ring and the N1
pyridine ring of a third molecule [30.2(2)° dihedral and 3.583(1)
0
A centroid-to-C16 and 3.460(1) A C7 C170 distances, as in
˚
˚
3 3 3
Figure 4]. Beyond the N1 pyridine ring, the N2 pyridine of a
fourth molecule appears to terminate the stacking of several of
these rings along the crystallographic a-c direction, with the
There is no evidence for any Cd-F interaction in 2, with
˚
shortest intra- and intermolecular Cd F distances of 3.03 (to
perpendicular H21 N1 interaction distance of 2.93 A be-
3 13 3
3 3 3
1
˚
F10; x, y, z) and 4.30 A (toF6;x, -yþ /2, zþ /2), respectively,
tween pyridine rings that have a 82.4(1)° dihedral. Because
there is inversion symmetry, there are a total of eight rings that
are involved in the “pocket” of π-π interactions, as shown in
Figure 4. In summary, the interaction distances between
neighboring or approximately parallel rings for 2 are in the
but there are both intra- and intermolecular π-π interactions
present in the solid-state structure of 2 (Figure 4). The
intramolecular π-π interaction is between the two selenolate
˚
rings and has a centroid-to-centroid distance of 3.64(1) A.
˚
These two rings are not required by symmetry to be parallel,
and they have a small 8.9(4)° dihedral. Other noteworthy
distances within this intramolecular π-π interaction are
range 3.4-3.8 A, which is consistent with many aromatic
ligand metal complexes in the literature.36,41 Unlike the pure
˚
˚
C6 C12 at 3.412(8) A and C3 C8 at 3.798(9) A. The
3 3 3 3 3 3
(36) (a) Reger, D. L.; Horger, J.; Smith, M. D.; Long, G. J. Chem.
Commun. 2009, 41, 6219. (b) Corona-Rodriguez, M.; Hernandez-Ortega, S.;
Valdes-Martinez, J.; Morales-Morales, D. Supramol. Chem. 2007, 19, 579.
(c) Sonoda, Y.; Goto, M.; Tsuzuki, S.; Tamaoki, N. J. Phys. Chem. A 2007,
111, 13441.
(34) Hu, C.; Li, Q.; Englert, U. Cryst. Eng. Commun. 2003, 5, 519.
(35) Subramanian, R.; Givindaswamy, N.; Santos, R. A. Inorg. Chem.
1998, 37, 4929.

7310 Inorganic Chemistry, Vol. 49, No. 16, 2010
Emge et al.
a
˚
Table 2. Selected Hg-Se Bond and Hg Se Contact Lengths [A] and Angles [deg] for 3
3 3 3
Intramolecular
Hg1-Se11
2.4623(5)
2.4623(5)
2.4674(5)
2.4685(5)
2.4661(7)
2.4848(6)
2.466(1)
2.473(1)
2.4797(5)
2.5006(5)
2.479(1)
2.507(1)
Hg4B-Se44
Hg4B-Se43
Hg5A-Se51
Hg5A-Se52
Hg6B-Se64
Hg6B-Se63
Hg6A-Se61
Hg6A-Se62
Hg7-Se72
2.490(3)
2.494(3)
2.4859(6)
2.5162(6)
2.4793(7)
2.4796(8)
2.459(1)
2.490(1)
2.4702(6)
2.4737(5)
2.4656(5)
2.4703(5)
Hg1-Se110
Hg2-Se21
Hg2-Se22
Hg3A-Se31
Hg3A-Se32
Hg3B-Se33
Hg3B-Se34
Hg4A-Se42
Hg4A-Se41
Hg5B-Se53
Hg5B-Se54
Hg7-Se71
Hg8-Se81
Hg8-Se82
Se11-Hg1-Se110
Se21-Hg2-Se22
Se31-Hg3A-Se32
Se33-Hg3B-Se34
Se42-Hg4A-Se41
Se53-Hg5B-Se54
180.0
Se44-Hg4B-Se43
Se51-Hg5A-Se52
Se64-Hg6B-Se63
Se61-Hg6A-Se62
Se72-Hg7-Se71
Se81-Hg8-Se82
161.46(12)
168.65(2)
171.37(2)
170.42(4)
173.04(2)
177.67(1)
175.44(1)
173.16(2)
177.91(4)
169.77(2)
169.16(3)
˚
Intermolecular and Orthogonal to the Hg-Se Bond (Estimated Standard Deviation Range 0.001-0.003 A)
Hg1-Se22
Hg1-Se220
Hg2-Se11
Hg2-Se32
Hg3A-Se21
Hg3B-Se42
Hg4A-Se33
Hg4A-Se53
Hg5B-Se41
3.704(1)
3.704(1)
3.739(1)
3.643(1)
3.809(1)
3.287(1)
3.204(2)
3.251(2)
3.340(1)
Hg4B-Se52
Hg5A-Se44
Hg5A-Se63
Hg6B-Se51
Hg6A-Se72
Hg7-Se62
Hg7-Se82
Hg8-Se71
Hg8-Se8100
3.267(2)
3.660(3)
3.299(2)
3.281(1)
3.678(1)
3.312(1)
3.800(1)
3.662(1)
3.730(1)
Intermolecular Angles with Hg and Se (Estimated Standard Deviation Range 0.02-0.1°)
Se11-Hg1-Se22
Se110-Hg1-Se22
Se11-Hg1-Se220
Se110-Hg1-Se220
Se22-Hg1-Se220
Hg1-Se11-Hg2
Se21-Hg2-Se32
Se22-Hg2-Se32
Se21-Hg2-Se11
Se22-Hg2-Se11
Se32-Hg2-Se11
Hg2-Se21-Hg3A
Hg2-Se22-Hg1
Se31-Hg3A-Se21
Se32-Hg3A-Se21
Hg3A-Se32-Hg2
Se33-Hg3B-Se42
Se34-Hg3B-Se42
Hg3B-Se33-Hg4A
Se42-Hg4A-Se33
Se41-Hg4A-Se33
Se42-Hg4A-Se53
Se41-Hg4A-Se53
Se33-Hg4A-Se53
Hg4A-Se41-Hg5B
Hg4A-Se42-Hg3B
Se53-Hg5B-Se41
Se54-Hg5B-Se41
Hg5B-Se53-Hg4A
Se44-Hg4B-Se52
88.4
91.6
91.6
88.4
180.0
91.6
91.3
91.8
89.3
87.5
179.4
88.8
92.4
89.2
87.3
92.4
78.9
102.6
101.5
80.4
99.0
99.3
81.0
178.0
97.8
99.0
79.5
96.8
100.6
90.3
Se43-Hg4B-Se52
Hg4B-Se44-Hg5A
Se51-Hg5A-Se63
Se52-Hg5A-Se63
Se51-Hg5A-Se44
Se52-Hg5A-Se44
Se63-Hg5A-Se44
Hg5A-Se51-Hg6B
Hg5A-Se52-Hg4B
Se64-Hg6B-Se51
Se63-Hg6B-Se51
Hg6B-Se63-Hg5A
Se61-Hg6A-Se72
Se62-Hg6A-Se72
Hg6A-Se62-Hg7
Se72-Hg7-Se62
Se71-Hg7-Se62
Se72-Hg7-Se82
Se71-Hg7-Se82
Se62-Hg7-Se82
Hg7-Se71-Hg8
Hg7-Se72-Hg6A
Se81-Hg8-Se71
Se82-Hg8-Se7100
Se81-Hg8-Se81
Se82-Hg8-Se8100
Se71-Hg8-Se8100
Hg8-Se81-Hg800
Hg8-Se82-Hg7
92.5
87.8
80.3
97.7
98.8
81.4
171.2
99.3
96.6
96.5
80.8
98.9
90.5
81.9
97.9
90.3
93.8
88.7
86.8
175.9
93.1
89.4
91.6
90.0
87.9
90.5
179.0
92.1
89.9
a Symmetry transformations used to generate equivalent atoms: 0, -x, -y, -z; 00, -x, -y - 1, -z þ 3.
1-D π-π stacking of molecules in the crystal structure of 1 via
selenolate ligands on opposing sides of the molecule (see
Figure 2), the stacking of molecules in the crystal structure of
2 is via the pair of selenolates on one side of the molecule 2 and
the N1 pyridine on the opposite side. Also, because the
selenolate interactions are in two directions, i.e., toward the
inversion-related selenolate and the N1 pyridine of a third
molecule, the overall π-π interaction motif is 3-D, with sheets

Article
Inorganic Chemistry, Vol. 49, No. 16, 2010 7311
of closely interacting rings in the crystallographic ac plane
linked via the selenolate and N1 pyridine “arms” of one
molecule extending along the þ and - c axis.
refining the structure. The (3Dþ1) formalism of the above-
described modulation was used in the program JANA2006 to
model the unique Hg0.5SeC6F5 unit38 but failed to produce
realistic values for the highly correlated modulation, the
heavy-atom ADP parameters, and the several disordered
sites of the Hg and Se atoms. However, refinement of the 15
molecules in the supercell unit cell described here proceeded
with apparently only minor detrimental correlation effects,
which were overcome by the use of appropriate restraints of
ADP parameters in the refinement program SHELXL.29
Because of spatial overlap of the component molecules of
partially occupied sites, the geometries of all molecules in 3
were restrained in the least-squares refinement by the require-
ment of similar bonds and angles for the rigid SeC6F5 groups
(SHELXL instruction SAME) and the atomic displacement
parameters were restrained to be nearly isotropic (SHELXL
instructions ISOR, DELU, and SIMU). In the present
model, there are not only the two crystallographic inversion
centers of the triclinic cell (see Table 1) at (0, 0, 0) and (0, 0.5,
0.5) but also a noncrystallographic inversion center at ap-
proximately (1.00, 0.77, 0.70) or in between atoms Hg4A and
Hg5A. As a result of the noncrystallographic symmetry, large
correlations between nearly equivalent molecules of the four
completely occupied and eight partially occupied sites exist.
The intermolecular geometries of all molecules are best
described by four parts, each with three molecules (of various
occupancies that sum to 15 per unit cell). These parts are (1)
molecules in the vicinity of the inversion center at (0, 0, 0),
represented by the red molecules of Figure 5, (2) molecules in
the vicinity of the inversion center at (0, 0.5, 0.5), represented
by the orange molecules of Figure 5, (3) molecules on one side
of the pseudoinversion center, represented by the blue mole-
cules of Figure 5, and (4) molecules on the other side of the
pseudoinversion center, represented by the green molecules
of Figure 5. As a result, intermolecular geometries are only
defined for adjacent molecules within each of the four parts,
namely, (1) Hg3A, Hg2, Hg1, Hg20, Hg3A0, (2) Hg6A, Hg7,
Hg8, Hg80, Hg70, Hg6A0, (3) Hg3B, Hg4A, Hg5B, and (4)
Hg4B, Hg5A, Hg6B, where primed atoms in parts 1 and 2 are
related by crystallographic inversion symmetry and the
molecules in part 3 versus part 4 are related to each other
by the pseudoinversion symmetry. Noteworthy intra- and
intermolecular geometries are described by the distances and
angles in Table 2. On the basis of a search of the CSD,41
typical “short” intermolecular Hg Se and Hg F inter-
The Hg-containing compound3 is chemically distinctfrom
1 and 2 in that it crystallizes without coordinated pyridine
(Figure 5). A similar situation is found for the nonfluorinated
relative of 3, namely, 4 (Figure 7). The aromatic selenolates
are on either side of the Hg atom in both cases with
Se-Hg-Se angles at or near 180°. The only other compound
in the CSD to have aromatic selenolates bonded to a metal
(divalent or other) with a ∼180° Se-M-Se angle is
(py)4Yb(SeC6H5)2.37,41 One of the molecules in 3 has the
same inversion site symmetry as that of the single molecule in
4, and this conformation can be considered a trans motif,
with inversion-related rings extending away from the Se
atoms at near right angles and the extended C-Se Se-C
3 3 3
torsion angle at 180°. The other seven unique molecules in 3
deviate from this trans motif by different degrees (see below).
The crystal structure of 3 is comprised of 1-D arrays of
molecules that stack approximately along the crystallo-
graphic b-3c direction, which is the approximate view
direction in Figure 6, with nearly constant spacing of
˚
∼3.6 A between centers of mass of the nearly parallel
pentafluorophenyl rings of adjacent molecules (Figure 5).
In this motif, π-π interactions are found for all C6F5 rings
within the array, but not between arrays, and their geometries
fluctuate in a way that is consistent with variation in the
intramolecular C-Se Se-C torsional (or in-plane
3 3 3
rotational) angles from one molecule to the next for the eight
unique molecules within the 1-D array while maintaining
nearly coparallel SeC6F5 planes. This situation is in contrast
to 1, 2, and 4, which have only one unique molecule per unit
cell, and additionally contrasting to 1 where the two SeC6F5
planes are not coparallel. As a result, there are significant
local variations in the Hg and Se atom positions about the
average linear arrangement of the central Se-Hg-Se atoms,
asshown by theprojection of all eight uniquemolecules along
the 1-D array direction in Figure 6.
The local variations of the Hg and Se atoms in adjacent
molecules of 3 allow for some close Hg Se interactions
3 3 3
between pairs of molecules in two orthogonal directions
approximately perpendicular to the Hg-Se bond, so that
the coordination environment of the Hg atom in these cases
appears to be square-planar, as detailed in Table 2. Specifi-
cally, for the 12 complete or disordered molecules modeled
3 3 3
3 3 3
˚
actions would have distances of less than 3.8 and 3.0 A,
within the extended 1-D array, there are 18 intermolecular
˚
respectively, compared to formal Hg-Se and Hg-F bonds
Hg Se distances in the range 3.20-3.81 A, eight of which
3 3 3
˚
˚
of less than 3.0 and 2.7 A, respectively. For the Hg Se
are considered close (e.g., <3.35 A). Between adjacent
3 3 3
contact distances within the structure of 3, there are eight less
than 3.35 A, and these are indicated by dashed lines in
molecular arraysin the crystallographicbcplane and between
those separated by the crystallographic a axis, there are no
˚
˚
Figure 5. There are no Hg F contacts shorter than
Hg Se bonds less than 3.8 A, in agreement with the 1-D
characteristic of the arrays.
3 3 3
3 3 3
˚
3.20 A, except for Hg5A
F35B, which may be as short as
3 3 3 3
˚
2.80 A but is not clearly known because the occupancy of the
group containing the F35B atom was refined to only 7%. By
use of these four parts, the unusual modulation of the
occupancies of the eight molecules is also adequately mana-
ged in the superstructure model used here, with freely refined
occupancies of pairs of components, e.g., Hg3A and Hg3B,
The periodicity of the unit cell of 3 reported here is also
0
˚
consistent with a 1c ꢀ 3b ꢀ 5a supercell of the a = 4.223 A,
0
0
0
0
˚
˚
b = 5.911 A, c = 14.495 A, R = 79.122°, β = 85.09°, and
γ0 = 85.823° modulated structure with space group P1(abg)0
and single q vector (-0.129a0* þ 0.339b0* þ 0.330c0*) that is
nearly commensurate (i.e., -2/15a0*, 1/3b0*, 1/3c0*). Satellite
reflections of up to fourth-order were quite intense, allowing
for either the modulated structure or supercell approach for
(38) Petricek, V.; Dusek, M.; Palatinus, L. JANA2006. The crystallo-
graphic computing system; Institute of Physics: Praha, Czech Republic, 2006.
Further calculations on the modulation of 3 are in preparation for Acta
Crystallogr.
(37) Brewer, M.; Khasnis, D.; Buretea, M.; Berardini, M.; Emge, T. J.;
Brennan, J. G. Inorg. Chem. 1994, 33, 2743.

7312 Inorganic Chemistry, Vol. 49, No. 16, 2010
Emge et al.
Hg4A and Hg4B, Hg5A and Hg5B, and Hg6A and Hg6B,
summing to unity, as expected here. Further calculations of
the modulated model using JANA2006 with new descriptions
of the modulation of occupancies and the use of crenels for
the disordered molecular sites are the subject of a future
report.38
are also found in the high-pressure (NaCl-like) phase of HgSe,
˚
in which there are two short [2.541(4) A] Hg-Se bonds and
˚
two pairs of longer [2.891(4) and 3.2409(5) A] Hg Se
3 3 3
interactions.40
The compounds 1-3 are significantly more volatile than
their hydrocarbon counterparts and, in particular, the Hg
derivative sublimes quantitatively at 120 °C and decomposes
at elevated temperatures to give HgSe. The Zn and Cd
compounds are less volatile, but heating under vacuum still
results in substantial sublimation and eventual decomposi-
tion to give MSe. This contrasts directly with earlier work on
fluorinated thiolates, where M(SC6F5)2 (M = Zn and Cd)
were shown to deliver both MF2 and MSe phases upon
thermolysis.8 The difference in reactivity can be understood
by considering the relative bond strengths involved. The
C-Se bond in the selenolate is substantially weaker than
the C-S bond in the thiolate, and so cleavage to give MSe
should occur more readily at the relatively low temperatures
necessary to effect thermal decomposition.
The molecular structure of 4 has three features that are
quite similar to those of 3, namely, (A) a linear Se-Hg-Se
arrangement, with a 180° angle, (B) two short Hg-Se bonds,
˚
both at 2.480 A, and (C) two pairs of close Hg Se
3 3 3
interactions nearly perpendicular to the Hg-Se molecular
vector, at 3.38 and 3.56 A. For comparison, the nearly linear
˚
Se-Hg-Se central atoms in 3 have angles that range from
168 to 180° (average 173°) and Hg-Se bond lengths that
˚
˚
range from 2.46 to 2.52 A (average 2.48 A) and the Hg Se
3 3 3
contacts orthogonal to the Hg-Se bonds in 3 are desribed
above and in Table 2. However, 4 is distinctly dissimilar to 3
in its crystal packing motif. This difference is the direct result
of the nonparallel arrangement of two adjacent Hg(SePh)2
molecules, with respect to the 54.5° dihedral angle between
C6H5 rings (Figure 7), in stark contrast to all C6F5 rings in 3,
which are approximately parallel to each other (Figure 5).
Thus, the nonparallel arrangement of the phenyl rings in 4
prohibits π-π interactions but allows 2-D interactions of the
Conclusion
The fluorinated selenolate ligand SeC6F5 forms stable
divalent compounds with the group 12 metals Zn, Cd, and
Hg. Coordination compounds isolated from pyridine sol-
vents have either tetrahedral (Zn and Cd) or nearly linear
(Hg) geometries, and there are significant π-π-stacking
interactions evident throughout all structures. In contrast
to the analogous fluorinated thiolate compounds, these
selenolates all decompose at elevated temperatures to give
solid-state MSe and as such are promising reagents for
delivering new forms of II-VI materials.
type H Ar, resulting in an ordered subcell of the Hg0.5
-
3 3 3
(SePh) unit, while the parallel and 1-D arrangement of C6F5
rings in 3 permits rather direct π-π interactions, but at the
expense of requiring a 15-fold supercell for the overall
crystallographic periodicity.
The chelating pyridine selenolate Hg(Se-2-NC5H4)2 has
similar structural characteristics,39 with a linear arrangement
˚
of two short Hg-Se bonds [2.458(1) A] and two orthogonal
˚
Hg-Se bonds that are considerably longer, at 3.435(1) A. In
Hg(Se-2-NC5H4)2, the chelating pyridine N donors complete
Acknowledgment. We acknowledge support of the NSF
(Grant CHE-0747165). We also thank Vaclav Petricek
for his own calculations and advice on the refinement
of the Hg0.5SeC6F5 model within the modulated 3Dþ1
formalism of JANA2006.
an octahedral distribution of donor atoms. Again, in 3 the
Hg Se distances (Table 2) are slightly longer than (although
3 3 3
often statistically equal to) the comparable molecular Hg-Se
bonds in the literature. These weak/versus/strong interactions
(39) Cheng, Y.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 1994, 33, 3711.
(40) Nelmes, R. J.; McMahon, M. I.; Belmonte, S. A. Phys. Rev. Lett.
1997, 79, 3668.
Supporting Information Available: X-ray crystallographic files
in CIF format for the crystal structures of 1-4. This material is
available free of charge via the Internet at http://pubs.acs.org.
(41) Allen, F. H. Acta Crystallogr. 2002, B58, 380.