Structures from powders: Polynuclear Hg(11) complexes containing the flexible bisimidazolylmethane ligand

Article abstract of DOI:10.1021/ic900320h

Several polynuclear Hg(11) complexes containing the flexible ditopic bisimidazolylmethane ligand (C₇H₈N₄, bim) have been prepared by reaction of equimolar quantities of mercury salts (acetate, cyanide, thiocyanate, chlorid

Full text of DOI:10.1021/ic900320h

5
328 Inorg. Chem. 2009, 48, 5328–5337
DOI: 10.1021/ic900320h
Structures from Powders: Polynuclear Hg(II) Complexes Containing the Flexible
Bisimidazolylmethane Ligand
,
†
‡
‡
,§
§
Norberto Masciocchi,* Alessandro Figini Albisetti, Angelo Sironi, Claudio Pettinari,* Corrado Di Nicola, and
Riccardo Pettinari
§
†
Dipartimento di Scienze Chimiche e Ambientali, Universit aꢀ dell’Insubria e CNISM,
‡
via Valleggio, 11, 22100 Como, Italy, Dipartimento di Chimica Strutturale e Stereochimica Inorganica,
Universit aꢀ di Milano, via Venezian, 21, 20133 Milano, Italy, and Dipartimento di Scienze Chimiche,
§
Universit aꢀ di Camerino, via S. Agostino 1, 62032 Camerino (MC), Italy
Received February 17, 2009
Several polynuclear Hg(II) complexes containing the flexible ditopic bisimidazolylmethane ligand (C H N , bim) have
7
8 4
been prepared by reaction of equimolar quantities of mercury salts (acetate, cyanide, thiocyanate, chloride, and iodide)
in EtOH or acetonitrile solution. Their crystal and molecular structures were retrieved from laboratory powder diffraction
data, and their thermal properties were fully characterized, including the determination of the thermal expansion
coefficients and the related strain tensor using thermodiffractometric methods. [Hg(bim)(CH COO) ] consists of cyclic
3
2 2
dimers with chelating acetates, while the [Hg(bim)X ] species (X = Cl, CN, SCN, and I) are one-dimensional polymers,
2
n
with dangling X groups. A further complex of nominal Hg (bim)Cl formulation was also prepared, but the complexity
2
2
and nonideality of its powder diffraction traces prevented the determination of its main structural features.
9
Introduction
and recognition. Recently, when the isolated material was not
available as single crystals of suitable quality, the structural
characterization was performed employing state-of-the-art
Over the past few years, we have been interested in the
coordination chemistry of polydentate ligands possessing
multiple donor sites. Starting from simple heteroaromatic
13
powder diffraction methods coupled with C cross polariza-
1
0
1
2
tion-magic angle spinning (CP-MAS) NMR spectroscopy.
anions, such as pyrazolate, imidazolate, and pyrimidino-
11
3
Over the past few years, bisimidazolylmethane (bim),
a
late, we further increased the complexity of the polytopic N-
ligand employed for the investigation of the biological
ligands employed in the formation of monomeric, oligomeric,
and polymeric species. For example, our recent results of
12
allosteric effect in zinc-gable porphyrin complexes and as
13
4
,5
6
an artificial receptor capable of binding anionic guests, has
been successfully used as a flexible divergent donor to
substituted triazines, scorpionates, and substituted hetero-
7
cycles have allowed us to prepare and characterize a number
1
4
construct coordination polymeric materials. Several Ag,
of functional species, ranging from catalytically active (solu-
15
16
17
18
19
8
Mn, Cd, Zn, Co, and Li monodimensional zigzag
ble) oligomers to extended solids capable of molecular sensing
(
9) Galli, S.; Masciocchi, N.; Tagliabue, G.; Sironi, A.; Navarro, J. A. R.;
*
To whom correspondence should be addressed. E-mail: norberto.
masciocchi@uninsubria.it (N.M.).
1) See, for example: Cingolani, A.; Galli, S.; Masciocchi, N.; Pandolfo,
L.; Pettinari, C.; Sironi, A. J. Am. Chem. Soc. 2005, 127, 6144–6145.
2) See, for example: Masciocchi, N.; Bruni, S.; Cariati, E.; Cariati, F.;
Galli, S.; Sironi, A. Inorg. Chem. 2001, 40, 5897.
3) See, for example: Navarro, J. A. R.; Barea, E.; Rodriguez Dieguez, A.;
Salas, J. M.; Mendez-Li n~ an, L.; Domingo, M.; Perez-Mendoza, M.; Barea,
E. Chem.;Eur. J. 2008, 14, 9890–9901.
(
(
10) Masciocchi, N.; Galli, S.; Alberti, E.; Sironi, A.; Di Nicola, C.;
Pettinari, C.; Pandolfo, L. Inorg. Chem. 2006, 45, 9064–9074.
11) (a) Claramunt, R. M.; Elguero, J.; Meco, T. J. Heterocycl. Chem.
983, 20, 1245–1249. (b) Li, J. Acta Crystallogr. 2006, E62, o1798–o1799.
12) Tabushi, I.; Sasaki, T. J. Am. Chem. Soc. 1983, 105, 2901–2902.
(13) In, S.; Kang, J. J. Inclusion Phenom. Macrocyclic Chem. 2006, 54,
129–132.
(14) Jin, C.-M.; Lu, H.; Wu, L.-Y.; Huang, J. Chem. Commun. 2006,
(
(
1
(
(
Salas, J. M.; Ania, C. O.; Parra, J. B.; Masciocchi, N.; Galli, S.; Sironi, A. J.
Am. Chem. Soc. 2008, 130, 3978–3984 and references therein.
(
4) Casellas, H.; Gamez, P.; Reedijk, J.; Mutikainen, I.; Turpeinen, U.;
Masciocchi, N.; Galli, S.; Sironi, A. Inorg. Chem. 2004, 44, 7918–7924.
5) Casellas, H.; Roubeau, O.; Teat, S. J.; Masciocchi, N.; Galli, S.;
Sironi, A.; Gamez, P.; Reedijk, J. Inorg. Chem. 2007, 46, 4583–4591.
6) Pettinari, C. Scorpionates II: The Chelating Borate Ligands; Imperial
College Press: London, 2008.
7) Galli, S.; Masciocchi, N.; Cariati, E.; Sironi, A.; Barea, E.; Haj, M. A.;
Navarro, J. A. R.; Salas, J. M. Chem. Mater. 2005, 17, 4815–4824.
8) Ardizzoia, G. A.; Cenini, S.; La Monica, G.; Masciocchi, N.; Moret,
5039–5041.
(
(15) Jin, S.; Chen, W. Inorg. Chim. Acta 2007, 360, 3756–3764.
(16) Jin, S.; Chen, W.; Qiu, H. Cryst. Growth Des. 2007, 7, 2071–2079.
(17) Jin, S.; Wang, D.; Chen, W. Inorg. Chem. Commun. 2007, 10, 685–
689.
(18) Jin, S.-W.; Chen, W.-Z. Polyhedron 2007, 26, 3074–3084.
(19) Hwang, I.-C.; Chandran, R. P.; Singh, N. J.; Khandelwal, M.;
Thangadurai, T. D.; Lee, J.-W.; Chang, J. A.; Kim, K. S. Inorg. Chem.
2006, 45, 8062–8069.
(
(
(
M. Inorg. Chem. 1994, 33, 1458–1463.
pubs.acs.org/IC
Published on Web 05/06/2009
r 2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5329
-
1
Scheme 1. Schematic Drawing of the bim Ligand, Highlighting the
Flexible Torsional Angles Discussed in the Text
atmosphere from 20 to 800 °C at a heating rate of 5 °C min
The ligand bim has been prepared by standard literature
.
2
2-24
methods.
[
Hg(bim)(CH COO) ] , 1. An ethanol (20 mL) solution of
3
2 2
bisimidazolylmethane (0.296 g, 2.0 mmol) was added to an
ethanol (40 mL) solution of mercury(II) acetate, Hg(OAc)
0.636 g, 2 mmol). A colorless precipitate formed. The suspen-
2
(
sion was stirred for 6 h and then was filtered off, and the
colorless residue was washed with a mixture of ethanol/diethyl
ether and identified as 1 (0.887 g, 95% yield). Elem anal. calcd
chains or two-dimensional grid network structures have been
recently reported, and some of them have been described as
promising candidates for application in electronic devices
and catalysis. To date, no mercury derivatives of this ligand
are known, notwithstanding a very recent report on the use of
imidazolyl-based ligands for the preparation of luminescent
polymeric mercury complexes, in which weak interactions
play a significant role in the formation of supramolecular
4 4
for C14H14HgN O : C, 28.30; H, 3.02; N, 12.00. Found: C,
-
1
27.99; H, 2.93; N, 11.80. IR (KBr, cm ): 3114(m), 3024(w),
2935(m), 1559(s), 1523(m), 1504(m), 1391vs(vs), 1332m(vs),
1285(m), 1229(s), 1092(m), 1034(w), 1017(w), 944(w), 931(w),
8
59(w), 786(w), 764(m), 709(m) 666(s), 653(s), 618(m), 390(w).
[
bisimidazolylmethane (0.178 g, 1.2 mmol) was added to an
Hg(bim)(SCN) ] , 2. An ethanol (20 mL) solution of
2 n
20
architectures.
ethanol (40 mL) suspension of mercury(II) thiocyanate, Hg
(
In particular, several oligomeric or polymeric species
containing the neutral bisimidazolylmethane ligand (bim,
see Scheme 1) have been recently prepared and studied by a
2
SCN) (0.316 g, 1.0 mmol). A colorless precipitate immediately
formed. The suspension was stirred for 6 h and then was filtered
off, and the colorless residue was washed with 1:1 ethanol/
diethyl ether (5 mL) and identified as 2 (0.348 g, 75% yield).
Elem anal. calcd for C H HgN S : C, 23.25; H, 1.73; N, 18.08; S,
21
combination of less-conventional structural methods; these
studies included a detailed analysis of the stereochemical
9
8
6 2
-
1
preference about the two rotationally flexible CH -N bonds
13.79. Found: C, 23.58; H, 1.69; N, 17.73; S, 13.93%. IR (cm ):
3121(m), 3025(w), 2113(s), 1521(m), 1499(m), 1441(w), 1419(w),
2
and the thermal characterization of the anisotropic thermal
expansion coefficients and the thermal strain tensor derived
therefrom.
1
8
386(m), 1229(s), 1188(w), 1117(m), 1085(s), 1025(w), 928(m),
47(m), 833(m), 750(s), 702(s). H NMR (DMSO-d , 293 K):
6
1
δ 6.35 (s, 2H, CH2Bim), 7.03 (pd, 2H, CHBim), 7.57 (pt, 2H,
CHBim), 8.18 (pd, 2H, CHBim).
We have now prepared several third-row transition metal
derivatives (Hg(II) complexes), which were studied by X-ray
powder diffraction (XRPD) methods and thermodiffracto-
metry, adding a partial structural interpretation of the
observed thermally induced deformations. Mercury com-
pounds are extremely toxic, and it might appear somewhat
unusual for researchers to systematically pursue their pre-
paration, isolation, and full characterization. However, we
found it very useful to determine the stereochemical prefer-
ences of Hg(II)-based bim-containing polymers, after we
successfully addressed the nature, reactivity, and structure
of several zinc and cadmium analogues in a very recent
[
Hg(bim)(CN) ] , 3. An acetonitrile (20 mL) solution of
2 n
bisimidazolylmethane (0.075 g, 0.5 mmol) was added to an
acetonitrile (40 mL) solution of mercury(II) cyanide, Hg(CN)
0.126 g, 0.5 mmol). A colorless precipitate immediately formed.
2
(
The suspension was stirred for 4 h and then was filtered off, and
the colorless residue was washed by acetonitrile (5 mL) and
identified as 4 (0.150 g, 75% yield). mp: 257 °C dec. Elem anal.
calcd for C H HgN : C, 26.97; H, 2.01; N, 20.97. Found: C,
9
8
6
-
1
2
3
1
7
7.25; H, 1.95; N, 20.60%. IR (cm ): 3142(w), 3117(w),
024(w), 1521(m), 1492(m), 1392(m), 1367(w), 1355(w),
287(m), 1227(s), 1112(m), 1081(s), 1029(w), 921(m), 845(m),
71(m), 747(s), 708(s), 655(s). H NMR (DMSO-d , 293 K):
1
21
6
contribution. In addition, in this particular case, the pre-
sence of a dominant scatterer makes it possible to accurately
follow the trend of Hg Hg interatomic distance changes
δ 6.33 (s, 2H, CH2Bim), 7.00 (pd, 2H, CHBim), 7.52 (pt, 2H,
CHBim), 8.16 (pd, 2H, CHBim).
3
3 3
[Hg(bim)I ] , 4. An acetonitrile (20 mL) solution of bisimida-
2 n
zolylmethane (0.075 g, 0.5 mmol) was added to an acetonitrile
upon thermal treatment, well beyond the typical accuracy
normally granted by intrinsically poor (if compared with
single-crystal) powder diffraction data.
(40 mL) solution of mercury(II) iodide, HgI (0.224 g, 0.5 mmol).
2
The red solution turned colorless in a few minutes, and then a
colorless precipitate formed. The suspension was stirred for
6 h and was then filtered off, and the colorless residue was washed
with acetonitrile (5 mL) and identified as 3 (0.280 g, 93% yield).
Experimental Section
Materials and Methods. All reagents were obtained from
commercial sources and were used without further purification.
Solvents were distilled using the standard methods. The sample
for microanalysis was dried in a vacuum to constant weight
mp: 206-208 °C dec. Elem anal. calcd for C
7 8 2 4
H I HgN : C,
1
3.95; H, 1.34; N, 9.30. Found: C, 14.23; H, 1.28; N, 9.02%.
-1
IR (cm ): 3140(w), 3115(w), 3103(w), 3005(w), 1596(w br),
521(m), 1504(m), 1486(m), 1386(m), 1280(m), 1232(m), 1111(m),
093(s), 1084(s), 1022(m), 928(m), 8448m), 837(m), 771(m), 753(s),
1
(
performed with a Fisons Instruments 1108 CHNS-O Elemental
293 K, ca. 0.1 Torr). Elemental analyses (C, H, N, S) were
1
1
-
1
738(s), 710(s), 652(s). H NMR (DMSO-d , 293 K): δ 6.26 (s, 2H,
6
analyzer. IR spectra were recorded from 4000 to 600 cm using
a Perkin-Elmer Spectrum 100. Melting points (mp’s) were
undertaken with a SMP3 Stuart scientific instrument and in a
capillary apparatus and were uncorrected. A Perkin-Elmer
STA-6000 model thermogravimetric analyzer was used for
determination of the thermal stabilities of mercury complexes.
Samples weighing 5-10 mg were heated in a dynamic nitrogen
CH2Bim), 6.92 (pd, 2H, CHBim), 7.47 (pt, 2H, CHBim), 8.05 (pd, 2H,
CHBim).
[Hg(bim)Cl ] , 5. An acetonitrile (20 mL) solution of bisi-
2 n
midazolylmethane (0.178 g, 1.2 mmol) was added to an acet-
onitrile (40 mL) suspension of mercury(II) chloride,
2
HgCl (0.340 g, 1.1 mmol). A colorless precipitate formed.
(
20) Wang, X.-F.; Yang, L.; Okamura, T.-A.; Kawaguchi, H.; Wu, G.;
Sun, W.-Y.; Ueyama, N. Cryst. Growth Des. 2007, 7, 1125–1133.
21) (a) Masciocchi, N.; Pettinari, C.; Alberti, E.; Pettinari, R.; Di Nicola,
C.; Figini Albisetti, A.; Sironi, A. Inorg. Chem. 2007, 46, 10491–10500.
b) Masciocchi, N.; Pettinari, C.; Alberti, E.; Pettinari, R.; Di Nicola, C.;
Figini Albisetti, A.; Sironi, A. Inorg. Chem. 2007, 46, 10501–10509.
(22) Lorenzotti, A.; Cecchi, P.; Pettinari, C.; Leonesi, D.; Bonati, F. Gazz.
Chim. Ital. 1991, 121, 89–91.
(23) Pettinari, C.; Marchetti, F.; Lorenzotti, A.; Gioia Lobbia, G.;
Leonesi, D.; Cingolani, A. Gazz. Chim. Ital. 1994, 124, 51–55.
(24) Pettinari, C.; Santini, C.; Leonesi, D.; Cecchi, P. Polyhedron 1994, 13,
1553–1562.
(
(

5
330 Inorganic Chemistry, Vol. 48, No. 12, 2009
Masciocchi et al.
The suspension was stirred for 6 h and then was then filtered off,
and the colorless residue was washed with acetonitrile (10 mL)
and identified as 5 (0.369 g, 80% yield). Elem anal. calcd for
C H HgN Cl : C, 20.03; H, 1.92; N, 13.35. Found: C, 19.93; H,
ing technique, as implemented in TOPAS, using for bim a
2
7
partially flexible, rigid, idealized model, independent metal,
and, where pertinent, halide ions, as well as rigid acetate, Hg
(cyanide) , or thiocyanide groups). The final refinements were
7
8
4
2
2
-
1
1
1
1
.87; N, 12.95. IR (cm ): 3117(m), 3011(w), 1499(br),
388(m), 1354(w), 1276(m), 1227(s), 1196(w), 1188(w),
109(m), 1084(s), 1032(w), 1022(w), 943(w), 936(w), 928(w),
52(m), 844(m), 832(m), 782(m), 761(s), 750(s), 707(s), 654(s).
carried out with the Rietveld method, maintaining the rigid
bodies described above and allowing the refinement of the
torsion angles of the methylene-heterocyclic rings linkage.
Peak shapes were defined by the fundamental parameters
approach implemented in TOPAS, while the crystal size effect
was modeled by a Lorentzian broadening. The background
contribution to the total scattering was modeled by Chebyshev’s
polynomials with two to eight coefficients, depending of
the nature of the trace below Bragg peaks. One refinable
isotropic thermal parameter was assigned to the metal
8
1
H NMR (DMSO-d
H, CHBim), 7.48 (pt, 2H, CHBim), 8.07 (pd, 2H, CHBim).
Hg (bim)Cl ] , 6. An acetonitrile (20 mL) solution of
6
, 293 K): δ 6.28 (s, 2H, CH2Bim), 6.94 (pd,
2
[
2
2 x
bisimidazolylmethane (0.178 g, 1.2 mmol) was added to an
acetonitrile (40 mL) suspension of mercury(I) chloride, Hg Cl
0.236 g, 0.5 mmol). A colorless precipitate formed. The suspen-
2
2
(
2
˚
sion was stirred for 1 h and was then filtered off, and the
colorless residue was washed with acetonitrile (10 mL)
and identified as 6 (0.280 g, 90% yield). Elem anal. calcd for
atom, augmented by 2.0 A for lighter atoms. A preferred
orientation correction was introduced (in the March-Dollase
formulation) along the [111] direction for compound 3. The final
Rietveld refinement plots are shown in Figure 1. Table 1 con-
tains a summary of crystal data and data collection parameters
and structural analysis.
C
7
H
8
Hg
H, 1.30; N, 8.87. IR (cm ): 3143(w), 3117(m), 3017(w), 1526
m), 1508(m), 1492(m), 1427(w), 1394(m), 1353(w), 1285(m),
2 4 2
N Cl : C, 13.56; H, 1.30; N, 9.03. Found: C, 13.86;
-
1
(
1
9
229(s), 1196(m), 1115(m), 1097(m), 1086(s), 1035(w), 1025(w),
35(m), 850(m), 845(m), 760(s), 744(s), 708(s).
Thermodiffractometric experiments were performed in the
air from 25 °C up to the decomposition temperatures using a
custom-made sample heater, assembled by Officina Elettrotec-
nica di Tenno, Ponte Arche, Italy. Diffractograms at different
temperatures (in 20 °C steps) were recorded typically in
[
equiv of DMSO in CH
identified as 5 DMSO. Elem anal. calcd for C H Cl HgN OS:
4
C, 21.72; H, 2.83; N, 11.26; Found: C, 21.77; H, 3.02; N, 11.55.
IR (cm ): 3118(w), 2995(w) 2912(w)), 1530(w), 1507(w)
1
9
Hg(bim)Cl ] xDMSO, 7. Reaction between 5 and 2
2 x
3
2 2
Cl yields a powder that has been
3
9
14
2
28
the range 8-35° 2θ. Linear parametric Le Bail refinements
-
1
eventually afforded the “best” set of cell parameters at
the different temperatures. Linear thermal expansion coeffi-
cients were then derived from (1/x)(∂x/∂T ) versus T plots (x
being either a lattice parameter or the cell volume). Later,
for each compound, we selected the cell data at two well-
separated temperatures (typically, 25 °C and the last useful
point before decomposition, falling in the 125-245 °C range)
and computed the thermal strain tensor and its eigenvalues and
eigenvectors, using a locally developed program based on
309(w) 1290(w), 1234(m), 1092(br), 1043(s), 1017(s), 951(m),
31(m), 896(w), 852(w), 765(m), 746(m), 697(m) 667(m).
X-Ray Powder Diffraction Analysis. Powdered, micro-
crystalline samples of 1-5 were gently ground in an agate
mortar, then deposited in the hollow of an aluminum sample
holder (equipped with a zero-background plate). Diffraction
data were collected with overnight scans (16 h long) in the
5
-105° 2θ range on a Bruker AXS D8 Advance diffractometer,
2
9
Ohashi’s algorithm. Thermal strain tensors were visualized
equipped with a linear position-sensitive Lynxeye detector,
primary beam Soller slits, and Ni-filtered Cu KR radiation
3
0
with WinTensor, which produces a VRML three-dimensional
surface to be displayed, together with the (properly oriented)
whole crystal structure, with the CORTONA VRML client.
Crystal structures VRML pictures produced with Accelrys DS
Visualizer 2.0.
˚
(
λ = 1.5418 A), sampling interval (in continuous mode)
Δ2θ = 0.02°; divergence slit, 1.0°; goniometer raidus,
3
00 mm; generator setting, 40 kV, 40 mA. A standard peak
2
5
search, followed by indexing with TOPAS, allowed the detec-
tion of the approximate unit cell parameters, later improved by
LeBail refinements. Indexing figures of merit (M/GoF, falling in
the 23-77 value range) can be found in Table 1. Space group
determinations, performed using systematic extinction condi-
tions, in conventional mode as well using a structureless full
pattern profile match, indicated as probable space groups (later
confirmed by successful structure solutions and refinements)
Results and Discussion
Synthesis and Spectroscopy. Complexes 1 and 2 were
synthesized by mixing an equimolar quantity of the
mercury salts and bim in ethanol at room temperature,
whereas 3-5 were isolated as colorless precipitates from
MeCN solutions. All complexes are stable at room tem-
perature and highly insoluble in water and in alcoholic
and chlorinated solvents. Compound 6 has been obtained
by reacting Hg Cl with excess bim. Derivatives 2-5 were
2
6
P2
1 1 1
/n for 1, P2 /c for 2, C2/c for 3, and P2 /m for 4 and 5.
Structure solutions were performed (with the simulated anneal-
2
2
(
(
25) TOPAS, version 3.0; Bruker AXS: Karlsruhe, Germany, 2005.
26) Acentric Cc, a proper subgroup of C2/c, was also considered as a
found to be moderately soluble in DMSO, their oligo-
meric or polymeric nature being likely modified by
DMSO solvation or coordination: for example, from a
possible candidate. The complexity of the structure of species 3 within such a
description (requiring the introduction of stiff restraints in order to reach
convergence to a chemically significant model) and the absence of a
cristallochemical clue (suggesting that a centrosymmetric structure is not
tolerable), together with the presence of a dominating scatterer (the Hg ion),
makes it impossible to assess from powder data only, the significance of the
agreement factor lowering observed upon doubling the number of free
structural parameters; therefore, the centric model was eventually adopted,
which we believe to be consistent with all chemical and crystallographic data
in our hands.
31
DMSO solution of 5, [HgCl (DMSO) ] was always
2
2
recovered in quantitative yield; at variance, when an
equimolar quantity of DMSO was added to a CH OH
3
suspension of 5, the coordination polymer 5 was recov-
ered unaltered. Finally, when 1 equiv of 5 was reacted
with 2 equiv of DMSO, a new species was obtained,
(
27) For compounds 1, 2, and 3, the Cartesian coordinates of bim derived
from literature data were used (CCDC code: EZESEH), optimized by
molecular mechanics, using Tinker (http://dasher.wustl.edu/tinker/). In
species 4 and 5, where the bim ligand is bisected by mirror planes, we
(
(
28) Stinton, G. W.; Evans, J. S. O. J. Appl. Crystallogr. 2007, 40, 87–95.
29) Ohashi, Y. In Comparative Crystal Chemistry; Hazen, R. M., Finger,
L. W., Eds.; Wiley: New York, 1982; pp 92-102.
˚
adopted the z-matrix formalism, defining regular pentagons (C-X, 1.343 A;
(30) Kaminsky, W. Wintensor: Tensor-drawing and calculation tool for
Windows 95/98/NT/2000/XP; University of Washington: Seattle, WA.
(31) Jain, S. C.; Rivest, R. Inorg. Chim. Acta 1969, 3, 552–558. James, B.
R.; Morris, R. H. Spectrochim. Acta A 1978, 34A, 577–582.
˚
C-H, 0.950 A) for the heterocyclic ring (with their correct atomic species),
˚
hinged about a methylene bridge (CH
geometry.
2
-N, 1.457 A) of idealized tetradedral

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5331
Table 1. Crystal Data and Refinement Details for the Compounds 1-5
-
-
-
-
-
compound [Hg(Bim)X
2
]
n
1, CH
3
COO
2, SCN
3, CN
4, I
5, Cl
emp. form.
C
11
H
8
Hg
460.80
monoclinic
P2 /n, 4
2
N
4
O
4
C
9
H
8
HgN
464.94
monoclinic
P2 /c, 4
6
S
2
C
400.79
9
H
8
HgN
6
C
7
H
8
HgN
602.56
monoclinic
P2 /m, 2
4
I
2
C
7
H
8
HgN
419.66
monoclinic
P2 /m, 2
4 2
Cl
-
1
fw, g mol
cryst syst
space group, Z
monoclinic
C2/c, 8
14.2670(2)
11.9344(1)
14.8441(2)
65.787(1)
2305.13(5)
2.310
1472
251.3
Bruker D8
298(2)
5-105
SVD
28.2
5001
1332
0.073, 0.095
8.426
15.106
1
1
1
1
˚
a, A
9.4490(2)
15.0057(3)
10.2300(2)
96.409(2)
1441.43(5)
2.123
856
193.4
Bruker D8
298(2)
5-105
SVD
68.7
5001
1666
0.072, 0.096
7.547
16.522
360.4
14.2249(3)
11.0098(3)
9.1580(2)
110.300(2)
1345.19(6)
2.296
864
233.70
Bruker D8
298(2)
5-105
SVD
23.3
5001
1554
0.050, 0.067
2.823
5.816
9.1194(2)
9.4293(1)
8.4101(1)
118.519(1)
635.43(2)
3.149
528
596.5
Bruker D8
298(2)
5-105
SVD
71.3
5001
792
0.045, 0.058
3.814
7.296
8.3477(2)
9.4314(2)
6.8644(2)
90.765(2)
540.39(2)
2.579
384
298.3
Bruker D8
298(2)
5-105
SVD
76.7
5001
617
0.041, 0.053
2.765
7.032
˚
b, A
˚
c, A
β, deg
3
˚
V, A
-
3
Fcalcd, g cm
F(000)
-1
μ(Cu-KR), cm
diffractometer
T, K
2θ range, deg
indexing method
M/GoF
N
N
data
obsd
a
R
R
χ
p
, Rwp
a
Bragg
a
2
3
˚
V/Z, A
336.3
288.1
317.7
270.2
P
P
P
P
P
P
P
a
2
2 1/2
2
2
R
p
=
i
|yi,o - yi,c|/
i
|yi,o|. Rwp = [
i
w
i
(yi,o - yi,c) /
i
w
i
(yi,o) ] . R
B
=
and yi,c are the observed and calculated profile intensities, respectively, while In,o and In,c are the observed and calculated intensities. The summations run
n
|In,o - In,c|/
n
I
n,o. χ =
i i
w (yi,o - yi,c) /(Nobsd - Npar), where yi,o
over i data points or n independent reflections. Statistical weights w
i
are normally taken as 1/yi,o
.
identified by elemental analysis and IR as 5 DMSO, a
compound analogous to the already known [HgI (dpb)-
It is worth noting that, differently from that observed in
the case of the already reported zinc and cadmium
derivatives, when Hg(II) ions are used in the starting
3
2
32
21b
(DMSO)] polymer (dpb = 2,3-di-(4-pyridyl)-2,3-butanediol).
n
Differently, compound 1 is poorly soluble also in DMSO,
in contrast with its molecular (dimeric) structure (vide infra).
However, when a DMSO suspension of 1 was heated at
materials, only species showing the 1:1 HgX /bim stoi-
2
chiometry were isolated, independently of the metal-to-
ligand ratio employed. As expected, 6 shows a different
stoichiometry, being the only species containing Hg in a
lower oxidation state.
90 °C for 30 min, displacement of the bim ligand from the
mercury coordination sphere was observed.
Our observations suggest that, at room temperature,
only excess DMSO is able to disrupt the polymeric
structure of 2-5, interacting with the tetrahedral mercury
centers and breaking the Hg-N coordination bonds,
whereas it was unable to interact with the dinuclear
species 1, in which the mercury ions are in an approxi-
mately coordinatively saturated pseudo-octahedral en-
The IR spectra of these solid species typically show
several bands usually associated with the organic ligand:
signals of weak and medium intensity at ca. 3000 cm
-
1
(C-H stretching modes) and other more intense bands
between 1600 and 1500 cm (typical of ring breathing)
-
1
are present, shifted to lower frequency by about 15-
20 cm from the reference free ligand values.
-
1
22-24
vironment. Apparently, bim possesses
a
greater
Somewhat more informative are the IR spectra of
the thiocyanate and cyanide complexes 2 and 4: the
2
+
coordinating ability toward Hg with respect to DMSO.
Accordingly, when an equimolar quantity of bim is added
to a MeOH solution of [HgCl (DMSO) ], immediate
-
1
well-defined absorption found at ca. 2110 cm
the weaker one at ca. 2176 cm
and
are typical of
monodentate S-CN and CN coordination modes,
respectively.
-
1
2
2
3
3
34
precipitation of 5 is observed.
The NMR data in DMSO of compounds 2-5 are not
significantly different from those of the free ligand bim,
suggesting that the polynuclear chains are completely
destroyed in DMSO solution. Interestingly, the H NMR
spectrum of a mixture containing an equimolar quantity of
As for derivative 1, it is generally accepted that it is
possible to distinguish between ionic, monodentate, che-
lating bidentate, or bridging bidentate groups on the basis
of the Δ = ν (COO)-ν (COO) value. On the basis of
1
a
s
-
1
DMSO and species 5 (CDCl solution) exhibits signals
3
the observed Δ value of 170 cm , a chelating bidentate
35
acetate is here predicted. We have in fact compared the
different from those found for the free bim in the same
solvent, suggesting that under these conditionsnot all Hg-
N bonds are lost. As anticipated, when a large excess of
DMSO-d is added to the CDCl solution of 5, then
3
6
spectrum of 1 with those of a number of mononuclear
and polynuclear mercury(II) acetate complexes and
3
7
6
3
formation of the Hg(DMSO) Cl species is observed. In
2
(33) Mahmoudi, G.; Morsali, A.; Zhu, L. G. Polyhedron 2007, 26, 2885–
2893.
2
1
addition, the H NMR spectrum of a suspension of 1 in
(
34) Goel, R. G.; Henry, W. P.; Ogini, W. O. Can. J. Chem. 1979, 57, 762–
66.
35) Mahmoudi, G.; Morsali, A.; Hunter, A. D.; Zeller, M. Inorg. Chim.
Acta 2007, 360, 3196–3202.
36) Roberts, P. J.; Ferguson, G.; Goel, R. G.; Ogini, W. O.; Restivo, R. J.
DMSO-d , recorded at 90 °C, shows only signals of free
6
7
bim, further supporting our hypothesis.
(
(
(
32) Niu, Y.; Guo, X.; Liu, X.; Wang, Q.; Zhang, N.; Zhu, Y.; Hou, H.;
J. Chem. Soc., Dalton Trans. 1978, 253–256.
Fan, Y. J. Chem. Crystallogr. 2006, 36, 643–646.
(37) Morsali, A.; Zhu, L.-G. Helv. Chim. Acta 2006, 89, 81–93.

5
332 Inorganic Chemistry, Vol. 48, No. 12, 2009
Masciocchi et al.
Figure 1. Rietveld refinement plots for compounds 1-5 with peak markers and difference plots at the bottom.
found that the spectrum of 1 shows strict similarity with
spectra of Hg(O CCH ) (PR ) species, containing
unsymmetrical chelating carboxylates. Chelating biden-
tate acetates normally have values of Δ less than
3
8
-1 39
100 cm
,
but this seems not to be applicable in the
2
3 2
3 2
(39) Alcock, N. W.; Tracy, V. M.; Waddington, T. C. J. Chem. Soc.,
(
38) Alyea, E. C.; Dias, S. A. Can. J. Chem. 1979, 57, 83–90.
Dalton Trans. 1976, 2243–2246.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5333
case of Hg(O CCH3)2 complexes. In fact, the Hg-
2
(
O CCH ) itself, for which two-coordination has been
2 3 2
-
1
assigned, has a Δ value of 270 cm , very different from
the Δ found for 1.
4
0
Thermogravimetric Analysis. In order to examine the
thermal stabilities of complexes 1-6, thermal gravimetric
analyses were carried out between 30 and 500 °C. The
thermogravimetric analysis (TGA) curves for compounds
1
-6 are supplied as Supporting Information, Figures
S1-S6. Compound 1 is stable up to 144 °C, where it
begins to decompose with a first exothermic effect. The
observed weight loss (ca. 10.9%) has been assigned to the
evolution of acetic anhydride and to the concomitant
formation of a new species, which, on the basis of
elemental analyses and IR spectroscopy, was formulated
as [Hg (bim) (CH COO) (O)]. Indeed, the IR spectrum
Figure 2. Schematic drawing of the structure of the [Hg(bim)-
(
analysis.
3 2 2
CH COO) ] (1) molecule, as derived by our powder diffraction
(likely as Cl ), and then elimination of elemental Hg are
2
42
2
2
3
2
observed.
of the residue recovered after controlled heating at 200 °C
exhibits a different absorption pattern in the 1700-
Structural Analysis. Our XRPD structure determination
of 1revealed the existence of cyclic, centrosymmetric dimers,
crystallizing in the monoclinic P2 /n space group. In each
-
1
300 cm region, suggesting a significant change in the
1
1
coordination of the two residual acetates, which, in
the heated material, likely act in the chelating or bridging
chelating form. The second (complex) step of weight
loss begins at ca. 255 °C and is complete at about
dimeric molecule (shown in Figure 2), Hg(II) ions are hexa-
coordinated, thanks to the presence of two chelating acet-
˚
ates (Hg-O distances in the 2.22-2.32 A
nitrogen atoms from two different bim ligands (Hg-N
distances 2.32-2.35 A, restrained). The bim ligand bridges
fairly distant Hg(II) ions, separated by 8.87 A, thanks to the
nearly C conformation induced by the two CH -im tor-
range) and two
3
60 °C: a loss of acetic anhydride, sublimation of the
˚
organic ligand and Hg, and partial formation of a black
residue (carbon), were observed. The thermal behavior
of this compound is completely different from that re-
˚
s
2
sional angles. This conformation is not rare, as it has been
already observed in oligomeric as well as polymeric metal
complexes, both of the transition (Cu, Zn, Cd, Rh) or post-
transition (Sn) type. Worthy of note, another common
0
ported for [Hg( μ-4,4 -bipy)( μ-AcO)(AcO)] n/ H O,
n
3
2
2
which shows two exothermic and one endothermic event
up to 310 °C, finally forming HgO.
2
1
The thiocyanate derivative 2 behaves in a different
manner: after melting at ca. 164 °C, it starts to lose weight
above 220 °C. At 300 °C, sublimation of the organic
ligand is complete. The IR spectrum of the residue
recovered after heating at 225 °C exhibits a signal corre-
sponding to the SCN group, suggesting that at this
temperature mercury thiocyanate is not decomposed
to HgS. The solid residue formed at around 300 °C
conformation, of ideal C symmetry, has been observed
2
and the relative geometric stereochemical preferences esti-
mated on energetic grounds.
Similar cyclic oligomers have been found for zinc
4
3
(another group 12 metal) and rhodium, but not for
2
1b
cadmium complexes. Moreover, zinc dimers contain-
ing halides (Cl, Br) as ancillary ligands resulted to be very
2
1b
different from the corresponding acetate,
which
is the ligand-free Hg(SCN) , which is stable up to
showed a one-dimensional chain topology (thus not
crystallizing as discrete entities).
2
3
90 °C and decomposes exothermically at higher tem-
peratures. Species 3, the cyanide analogue of 2, is stable
up to 239 °C, where it starts to release bim and Hg (up
to 340 °C).
Our structural studies of 2-5 revealed that all of these
species contain monodimensional chains determined by
the juxtaposition of [-Hg-(bim)-] monomers, with the
anionic ligands coordinated to the Hg(II) ions in a more-
or-less ideal tetrahedral fashion. The most relevant geo-
metrical features of the HgN X chromophores are col-
Interestingly, species 3, [Hg(bim)I ] , melts at ca. 210 °C
2
n
and, at higher temperatures, completely decomposes into
bim, molecular iodine, and Hg with a number of exother-
2
2
41
mic effects. Slightly more interesting is the thermal beha-
vior of the chloro-derivatives 5 and 6. Indeed, 6 [a Hg(I)
complex] is stable only below 100 °C, where is starts losing
Hg and transforming to 5, in agreement with the following
disproportionation equation:
lected in Table 2, together with some ancillary
stereochemical information. Schematic drawings of the
infinite chains present in the [Hg(bim)X ] species are
shown in Figure 3a-d.
Despite sharing a similar shape and conformation [the
2
n
bim ligand is nearly;or exactly in 4 and 5;C ], several
s
1
=x½Hg ðbimÞCl2ꢀ f1=n½HgðbimÞCl2ꢀ þ Hg
differences must be highlighted, both at the local coordi-
nation sphere of Hg(II) and at a supramolecular level.
The dicyanide species 3 manifests the largest deviation
from a tetrahedral coordination, with a (NC)Hg(CN)
bond angle (>160°) approaching linearity. A similar
coordination was found in mercury(II) bispyrazolate,
with nearly linear N-Hg-N coordination and two
significantly longer contacts in the plane normal to the
2
x
n
Above the transition temperature, the TG spectra of 5and 6
are coincident; in particular, melting at ca. 250 °C, followed
by the release of bim, elimination of the two chlorine atoms
(
(
40) Cooney, R. P. J.; Hall, J. R. J. Inorg. Nucl. Chem. 1972, 34, 1519.
41) Mahmoudi, G.; Morsali, A.; Zeller, M. Solid State Sci. 2008, 10, 283–
2
90.
42) Popovi ꢁc , Z.; Soldin, Z; Pavlovi ꢁc , G.; Matkovi ꢁc -Calogovi ꢁc , D.;
Mrvo ꢂs -Sermek, D.; Raji ꢁc , M. Struct. Chem. 2002, 13, 425–436.
ꢂ
ꢂ
(
(43) Masciocchi, N.; Figini Albisetti, A.; Sironi, A.; Pettinari, C.;
Marinelli, A. Powder Diffr. 2007, 22, 236–240.

5
334 Inorganic Chemistry, Vol. 48, No. 12, 2009
Masciocchi et al.
a
˚
Table 2. Synoptic Collection of Most Relevant Geometric Parameters (A and deg) for Compounds 1-5
Compound
Hg
3 3 Hg
Hg-N
N-Hg-N
Hg-X
X-Hg-X
bim symmetry
1-D chain // to
3
1
2
3
4
5
8.87
9.16
9.30
9.43
9.43
2.32-2.35*
2.37*
2.40
91.9
91.7
96.1
92.3
96.5
2.22-2.24, 2.30-2.32
2.42-2.43
2.05*
C
C
C
C
C
s
s
s
s
s
135.3
161.1
128.9
115.9
[001]
[110]
[010]
[010]
2.38
2.36
2.67-2.70
2.39-2.42
a
Starred values (*) have been subjected to soft restraints.
7 8 4 2 n 7 8 4 2 n 7 8 4 2 n 7 8 4 2 n
Figure 3. Schematic drawings of the structures of the [Hg(C H N )(SCN) ] (2), [Hg(C H N )(CN) ] (3), [Hg(C H N )I ] (4), and [Hg(C H N )Cl ]
(5) molecules (top to bottom), as derived by our powder diffraction analysis.
4
4
N-Hg-N vector. With the caveats imposed by the
intrinsic low resolution of the method (particularly for
the determination of light atoms in the presence of a
heavy scatterer), it is however rewarding to see that the
Hg-X trend nicely depends on the size of the ligand or
that of the atom directly bound to the mercuric ion.
Moreover, it should be noted that, no matter what the
coordination of this ion is (pseudotetrahedral or nearly
digonal with ancillary Hg-N contacts), N-Hg-N an-
gles fall in a rather narrow range (92-97°), centered well
below the ideal tetrahedral value of 109.5°.
Significant differences can also be found at the supra-
molecular level. This is particularly evident for the diio-
dide (4) and dichloride (5) couple, which in spite of
sharing the same crystal system and space group (the
not so common P2 /m one) when viewed down b, as
1
shown in Figure 4, clearly manifest the different organi-
zation of adjacent chains.
Figure 4. Schematic drawing of the crystal packing of [Hg(C
7 8 4 2 n
H N )I ]
(4) and [Hg(C H N )Cl ] (5) highlighting their nonisomorphic character
8
7
4
2 n
(see text), a axis in red and c axis in blue.
shown here), but this is much less surprising, since sig-
nificant stereochemical differences are already present at
the local level (vide supra). Perhaps, the most interesting
supramolecular feature of compound 3 is the presence of
crossed, but not weaved, polymeric chains running along
Additionally, the cyanide and sulfocyanide couple also
manifest significantly different crystal packings (not
[
110] (and its symmetry equivalent direction, [-110]).
Thermodiffractometric Analysis. Aiming at studying
the dynamic behavior of these systems, we employed
thermodiffractometric techniques to estimate the cell
variations on increasing the temperature in “in situ”
(
44) Masciocchi, N.; Ardizzoia, G. A.; La Monica, G.; Maspero, A.;
Sironi, A. Inorg. Chem. 1999, 38, 3657–3664.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5335
Figure 5. Temperature evolution of the lattice parameters of compounds 1-5, normalized to their room temperature values.
experiments, using the anisotropic shifts of the diffraction
peaks, and to build the corresponding strain tensor.
times more than the others. However, simple axis deforma-
4
5
tions may be misleading when the lattice vectors are not
orthogonal. In such cases, it is better to resort to strain
tensors as represented by the anisotropic thermal expansion
coefficient isosurfaces drawn in green in Figure 6a-e.
The deformation of a crystal by a change in the
temperature is expected to be minimal in the direction
of the highest atomic density, that is, the direction of
strongest interactions; accordingly, all of the polymeric
species (but 3, vide infra) show small(er) thermal distor-
tion along the chain elongation axis. At variance, the
softer direction is that parallel to the vector bisecting the
BIM N-C-N angle, which is substantially “perpendicu-
lar” to the pseudostacking of the imidazolyl rings (and to
the chain elongation axis). This said, it is now clear why
3 has an “oblate” rather then a “prolate” strain tensor.
Indeed, in 3 the ab plane contains both the chain elonga-
tion axes and the BIM N-C-N bisecting vectors of
The numerically extracted results can be schematized as
shown in Figure 5a-e, where the relative variations for
the cell axes are plotted versus T. Figure 6a-e, instead,
visualizes the thermal strain tensors, derived therefrom,
positioned in the unit cell.
As can be observed in the plots of Figure 5, all cell
axes increase with temperature, although at different
rates. While this is a common behavior for intrinsically
anisotropic molecular crystals, where most contacts are
given by van der Waals interaction and are weak and,
therefore, very sensitive to increased molecular motions
(
internal degrees of freedom, such as bond distances and
angles being typically more rigid), in compounds 2 and 5,
there is one axis (b and a, respectively), which changes 5-10
(
45) Zotov, N. Acta Crystallogr. 1990, A46, 627–628.

5
336 Inorganic Chemistry, Vol. 48, No. 12, 2009
Masciocchi et al.
Figure 6. Thermal expansion coefficients’ isosurface (thermal strain tensors) drawn within the crystal structure of compounds 1 (along c,a from left to
right, b from bottom to top), 2 (the same orientation as for 1), 3 (the same orientation as for 1), 4 (along b,a from left to right, c from top to bottom), and 5
(along b,a from left to right and c from bottom to top).
the two crossed polymers. Thus, the hardest elongation
direction of one polymer couples with the softest one of
the other polymer, and this eventually explains why, in 3,
the polymeric chains are apparently aligned with the
softer directions.
Further (less common) structural information was
derived from structural refinements of the polymeric
species on all collected XRPD data sets: thanks to the
large contribution to the total scattering of the unique Hg
ions, we derived the temperature dependence of the (bim-
bridged) Hg Hg distances, collectively shown in Fig-
3
3 3
˚
ure 7. As shown therein, a large change, of nearly 0.10 A,
occurs for the cyanide derivative 3, which is, after all, a
definite outlier in our structural analysis, for it shows a
nearly diagonal coordination and an unusual crystal
packing with crossed polymeric chains. According to
the explanation given above for the anomalous shape of
the strain tensor, we must conclude that Hg Hg elon-
Figure 7. Temperature evolution of the intramolecular Hg
tance in polymers 1-5.
3 3 Hg dis-
3
adjacent metal ions (increasing structural dimensionality), in
our cases, only chain polymers were obtained where the
3
3 3
gation is here triggered by the lateral vibrations of the
orthogonal” crossed chains.
bridging linker is the N -donor ligand.
2
“
Our thermogravimetric studies demonstrated that, in the
case of the halide and pseudohalide polymeric complexes, the
Conclusions
interaction between the N -ligand and the mercury ion is
2
In summary, we have here presented the complete struc-
tural characterization of several novel mercury complexes
weak, breaking of the Hg-N bonds with dissociation into the
starting free ligand and mercury salts being observed in the
temperature range 150-230 °C. On the other hand, these
complexes, although not very stable on heating, were found
to be rather resistant to solvent attack (with the notable,
though expected, exception of DMSO). Work can be antici-
pated in the direction of studying the structure versatility of
this system, for example, by employing different anions or
synthetic conditions.
(one cyclic dimer and several chain polymers) from powder
diffraction data, together with some of the material perfor-
mances derived from thermodiffractometric analysis, linking
a structural interpretation with the (apparently incoherent)
observed lattice deformation.
It is very interesting that, in contrast to other SCN, CN,
and I complexes where the anions acted as bridges over

Article
Acknowledgment. This work was supported by
Inorganic Chemistry, Vol. 48, No. 12, 2009 5337
Supporting Information Available: TGA traces for com-
pounds 1-6, the tables of the lattice parameter evolution as
obtained from Le Bail fits on selected portions of the XRPD
trace, and the crystallographic data for compounds 1-5.
This material is available free of charge via the Internet at
http://pubs.acs.org. CCDC 720632-720635 can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
MUR (PRIN2006: “Materiali Ibridi Metallo-Organici
Multifunzionali con Leganti Poliazotati”) and Fonda-
zione CARIPLO (Project 2007-5117). We gratefully
acknowledge the help of one reviewer, which allowed
us to make this paper, in its final version, more easily
readable.