Metal pyrazolato complexes. Synthesis, characterization, and X-ray powder diffraction studies of group 12 coordination polymers

Article abstract of DOI:10.1021/ic990258u

A number of polymeric pyrazolato complexes have been prepared and characterized by spectroscopy, thermal analyses (DSC and TGA), and X-ray powder diffraction (XRPD) methods. Ab initio XRPD studies showed that the (isomorphous) [Zn(pz)₂]_n and [Cd(pz)₂]_n species (Hpz = pyrazole) are 1-D polymers containing tetrahedrally coordinated metals and M(μ-pz)₂M (M = Zn, Cd) bridges, much alike [Cu(pz)₂]_n [orthorhombic, Ibam, a = 7.4829(4), b = 14.3844(6), c =_7.3831(3) A? (Zn) and a = 7.8591(6), b = 13.652(1), c = 7.9165(4) A? (Cd)]; differently, Hg(pz)₂ [triclinic, P1?, a = 7.4097(3), b = 9.4474(3), c = 5.8345(3) A, a = 96.310(2), β= 96.752(3), and γ = 73.694(2)°] is best described as a mononuclear complex, containing two monodentate pyrazolato ligands loosely interacting, through long(er) Hg?N contacts with neighboring molecules. During the synthesis of the latter, an intermediate phase was obtained, and characterized as Hg(pz)NO₃, which contains a polymeric polycation, [Hg(pz)]_nⁿ⁺, based on Hg(μ-pz)Hg bridges, and uncoordinated NO₃^- groups (orthorhombic, Pcmn, a = 17.2985(9), b = 5.2538(3), c = 7.3912(4) A). All structures were ultimately refined by the Rietveld method.

Full text of DOI:10.1021/ic990258u

Inorg. Chem. 1999, 38, 3657-3664
3657
Metal Pyrazolato Complexes. Synthesis, Characterization, and X-ray Powder Diffraction
Studies of Group 12 Coordination Polymers
Norberto Masciocchi,* G. Attilio Ardizzoia,* Angelo Maspero,‡
,
†,§
,‡,§
Girolamo LaMonica,‡ and Angelo Sironi†
,§
Dipartimento di Chimica Strutturale e Stereochimica Inorganica e Centro CNR, Universit a` di Milano,
Via Venezian 21, 20133 Milano, Italy, Dipartimento di Chimica Inorganica, Metallorganica, ed Analitica
e Centro CNR, Universit a` di Milano, Via Venezian 21, 20133 Milano, Italy, and Dipartimento di
Scienze Chimiche, Fisiche e Matematiche, Universit a` dell’Insubria, via Lucini 3, 22100 Como, Italy
ReceiVed March 3, 1999
A number of polymeric pyrazolato complexes have been prepared and characterized by spectroscopy, thermal
analyses (DSC and TGA), and X-ray powder diffraction (XRPD) methods. Ab initio XRPD studies showed that
the (isomorphous) [Zn(pz)2]n and [Cd(pz)2]n species (Hpz ) pyrazole) are 1-D polymers containing tetrahedrally
coordinated metals and M(µ-pz)2M (M ) Zn, Cd) bridges, much alike [Cu(pz)2]n [orthorhombic, Ibam, a )
7
.4829(4), b ) 14.3844(6), c ) 7.3831(3) Å (Zn) and a ) 7.8591(6), b ) 13.652(1), c ) 7.9165(4) Å (Cd)];
differently, Hg(pz)2 [triclinic, P 1h , a ) 7.4097(3), b ) 9.4474(3), c ) 5.8345(3) Å, R ) 96.310(2), â ) 96.752-
(
3), and γ ) 73.694(2)°] is best described as a mononuclear complex, containing two monodentate pyrazolato
ligands loosely interacting, through long(er) Hg‚‚‚N contacts with neighboring molecules. During the synthesis
of the latter, an intermediate phase was obtained, and characterized as Hg(pz)NO3, which contains a polymeric
n+
-
polycation, [Hg(pz)]n , based on Hg(µ-pz)Hg bridges, and uncoordinated NO3 groups (orthorhombic, Pcmn, a
)
17.2985(9), b ) 5.2538(3), c ) 7.3912(4) Å). All structures were ultimately refined by the Rietveld method.
Introduction
and a number of transition metals such as Cu, Ag, Pd, and Re,5
the main objective of such studies residing in the discovery and
In recent years, there has been a growing interest in preparing
and characterizing coordination polymers for their possible
application in a number of different fields; indeed, some metal-
containing polymeric species have been shown to be photo-
chemically active or to possess interesting electrical, electro-
characterization of the catalytical aspects of their reactivity. On
top of such studies, we also characterized the crystallochemical
properties of several binary (homoleptic) Group 11 diazolato
species (precursors of the catalytic ones), and surprisingly
discovered a wide variety of polynuclear arrangements, ranging
from trimers, tetramers, and hexamers up to polymeric species,
1
chemical, magnetic, or SHG properties, and even antimicrobial
activity.2 Such polymers typically contain a backbone of
transition metal ions in close proximity, joined by polydentate
6
that could be selectively prepared and isolated. Since most of
such species are insoluble and cannot be obtained as single
crystals of suitable quality, the main body of the structural
studies performed so far have been based on the newly emerging
technique of ab initio X-ray powder diffraction crystal structure
3
ligands. In this respect, the pyrazolato anion (and its ring-
substituted derivatives) has proved to be an excellent synthon
since, in the vast majority of its metal complexes, it acts, in the
common exo-bidentate coordination mode, as a four-electron
7
determination, which allowed a complete characterization of
4
donor ligand on two metals at distances in the 3.3-3.8 Å range.
new and unexpected features, such as the presence of polymor-
We have recently been interested in the coordination chem-
istry of polynuclear complexes containing pyrazolato ligands
(5) (a) Ardizzoia, G. A.; Angaroni, M. A.; LaMonica, G.; Cariati, F.;
Moret, M.; Masciocchi, N. J. Chem. Soc., Chem. Commun. 1990,
1
021-1023. (b) Ardizzoia, G. A.; Angaroni, M. A.; LaMonica, G.;
*
Corresponding author. Tel: +39 02 70635120. Fax: +39 02 70635288.
Cariati, F.; Cenini, S.; Moret, M.; Masciocchi, N. Inorg. Chem. 1991,
30, 4347-4353. (c) Ardizzoia, G. A.; Cenini, S.; LaMonica, G.;
Masciocchi, N.; Moret, M. Inorg. Chem. 1994, 33, 1458-1463. (d)
Masciocchi, N.; Moret, M.; Sironi, A.; Ardizzoia, G. A.; LaMonica,
J. Chem. Soc., Chem. Commun. 1995, 1955-1956. (e) Ardizzoia, G.
A.; LaMonica, G.; Maspero, A.; Moret, M.; Masciocchi, N. Inorg.
Chem. 1997, 36, 2321-2328. (f) Ardizzoia, G. A.; LaMonica, G.;
Maspero, A.; Moret, M.; Masciocchi, N. Eur. J. Inorg. Chem. 1998,
1503-1512.
E-mail: norbert@csmtbo.mi.cnr.it.
†
Universit a` di Milano, Chimica Strutturale.
Universit a` di Milano, Chimica Inorganica.
Universit a` dell’Insubria, on leave.
‡
§
(
1) (a) Mark, J, E.; Allcock, H. R.; West, R.; Inorganic Polymers; Prentice
Hall: Englewood Cliffs, NJ, 1992. (b) Inorganic and Organometallic
Polymers II; Wisian-Neilson, P., Allcock, H. R., Wynne, K. J., Eds.;
ACS Symposium Series 572, American Chemical Society: Washing-
ton, DC, 1994.
2) The Agrochemicals Handbook, 3rd ed.; Kidd, H., James, D. R., Eds.;
Royal Society of Chemistry Information Services: Cambridge, UK,
(6) (a) Masciocchi, N.; Moret, M.; Cairati, P.; Sironi, A.; Ardizzoia, G.
A.; LaMonica, G.; Cenini, S. J. Am. Chem. Soc. 1994, 116, 7668-
7676. (b) Masciocchi, N.; Cairati, P.; Sironi, A. 1998, 13, 35-40. (e)
Ardizzoia, G. A.; Cenini, S.; LaMonica, G.; Masciocchi, N.; Maspero,
A.; Moret, M. Inorg. Chem. 1998, 37, 4284-4292.
(7) (a) Harris, K. D. M.; Tremayne, M. Chem. Mater. 1996, 8, 2554-
2570. (b) Langford, J. I.; Lou e¨ r, D. Rep. Prog. Phys. 1996, 59, 131-
234. (c) Masciocchi, N.; Sironi, A. J. Chem. Soc., Dalton Trans. 1997,
4643-4650. (d) Poojary, D. M.; Clearfield, A. Acc. Chem. Res. 1997,
30, 414-422.
(
1
991. (b) For recent examples of silver diazolates see: Nomiya, K.;
Tsuda, K.; Sudoj, T.; Oda, M. J. Inorg. Biochem. 1997, 68, 39-44.;
Nomiya, K.; Tsuda, K.; Kasuga, N. C. J. Chem. Soc., Dalton Trans.
1998, 1653-1659.
(
(
3) McCleverty, J. A.; Ward, M. D. Acc. Chem. Res. 1998, 31, 842-851.
4) LaMonica, G.; Ardizzoia, G. A. Prog. Inorg. Chem. 1997, 46, 151-
238.
1
0.1021/ic990258u CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/13/1999

3658 Inorganic Chemistry, Vol. 38, No. 16, 1999
Masciocchi et al.
Figure 1. Plot of the IR spectra (Nujol mulls) for group 12 metal pyrazolates, in the 1600-600 cm-1 range.
8
phic behavior, the reversibility of ring-opening polimerization
Experimental Section
9
reactions, and ordered cocrystallization of hexanuclear and
General. Pyrazole (Hpz) and metal salts were used as supplied
(Aldrich Chemical Co.). Solvents were dried and distilled by standard
methods. Infrared spectra (see Figure 1) were recorded on a Bio-Rad
FTIR 7 instrument. Thermogravimetric analyses were performed on a
Perkin-Elmer TGA-7 system. DSC traces were obtained with the aid
of a Perkin-Elmer DSC 7 calorimeter. Elemental analyses (C, H, N)
were carried out at the Microanalytical Laboratory of the University
of Milan.
polymeric moieties within the same crystal lattice.10
With the aim of extending our studies and methodology to
new, but related, species, we have undertaken the synthesis and
structural, spectroscopical, and thermal characterization of
pyrazolato complexes of Group 12 metals. Indeed, robust one-
dimensional polymers containing zinc atoms bridged by aro-
matic heterocycles have been very recently proven to possess
interesting photoluminescent properties, while “The insoluble
and intractable nature of these species ... enables their usage
in a Variety of semiconducting applications”.11 The results
presented hearefter complement and correct a number of
conflicting reports of poorly characterized metal pyrazolates,
somewhat scattered in the scientific literature.12
2 n 2
Synthesis of [Zn(pz) ] , 1. To a solution of ZnCl (1.00 g, 7.33
mmol) in water (25 mL), pyrazole (1.50 g, 22.1 mmol) was added under
stirring. The clear solution was stirred at room temperature for about
5 min and then NH (0.5 mL, 25% w/w water solution) was added.
3
The white suspension formed was stirred for 30 min. at room
temperature. The solid was then filtered, washed with water and
methanol, and dried under vacuum (1.41 g, 96%). Zn(ClO ) or Zn-
4
2
3
(NO )
2
can be also employed in place of zinc chloride. Anal. Calcd
for C
6
H N Zn: C, 36.11; H, 3.01; N, 28.09. Found: C, 35.94; H, 2.86;
6 4
(
8) Masciocchi, N.; Ardizzoia, G. A.; LaMonica, G.; Moret, M.; Sironi,
A. Inorg. Chem. 1997, 36, 449-454.
-
1
N, 27.87. Main IR bands (Nujol mulls, cm ): 3122 w, 3109 w, 1498
m, 1415 m, 1379 s, 1275 w, 1250 w, 1180 m, 1165 m, 1064 s, 969 w,
919 w, 884 m, 778 m, 759 m, 627 m.
Synthesis of [Cd(pz)(OH)]
mmol) in water (25 mL), pyrazole (1.11 g, 16.3 mmol) was added under
stirring. A white precipitate, identified as [Cd(Hpz) Cl ], suddenly
formed. The suspension was stirred for about 10 min and then NH
(0.5 mL, 25% w/w water solution) was added. After 30 min the white
(
9) Masciocchi, N.; Corradi, E.; Moret, M.; Ardizzoia, G. A.; Maspero,
A.; LaMonica, G.; Sironi, A. Inorg. Chem. 1997, 36, 5648-5650.
(
(
(
10) Masciocchi, N.; Ardizzoia, G. A.; LaMonica, G.; Maspero, A.; Sironi,
n 2
. To a solution of CdCl (1.00 g, 5.45
A. Angew. Chem., Int. Ed. 1998, 37, 3366-3369.
11) Thomsen, L. T.; Papadimitrakopoulos, F. Macromol. Symp. 1997, 125,
2
2
1
43-150.
12) (a) Vos, J. G.; Groeneveld, L. W. Inorg. Chim. Acta 1977, 24, 123-
26. (b) Das, M. K.; Ghosh, S. Indian J. Chem. 1997, 36A, 324-327.
3
1

Metal Pyrazolato Complexes
Inorganic Chemistry, Vol. 38, No. 16, 1999 3659
solid was filtered off, washed with methanol and dried under vacuum
Si(111) peak at 28.44° (2θ). Long overnight scans were performed with
5 < 2θ < 105°, with t ) 10 s and ∆2θ ) 0.02°.
Indexing, using TREOR, of the low angle peaks suggested, for 1
(1.01 g, 94%). Anal. Calcd for C
3 4 2
H CdN O: C, 18.36; H, 2.03; N,
1
4.25. Found: C, 18.41; H, 2.12; N, 14.73. Main IR bands (Nujol mulls,
14
-
1
cm ): 3406 s, 3106 w, 3095 w, 3087 w, 1486 w, 1410 m, 1363 s,
265 w, 1247 m, 1161 m, 1141 w, 1043 m, 946 w, 772 s, 760 s, 681
w, 632 m.
2 2
Synthesis of [Cd(Hpz)(pz) ] . CdO (500 mg, 3.84 mmol) and
and 2, I-centered orthorhombic cells of approximate dimensions a )
1
15
16
7
(
[
.48 Å, b ) 14.38 Å, c ) 7.39 Å for 1 [M(15) ) 18; F(15) ) 24
0.014, 45)] and a ) 7.92 Å, b ) 13.64 Å, c ) 7.92 Å for 2
pseudotetragonal, M(11) ) 13; F(11) ) 9 (0.018, 72)]; differently,
the unit cell determination lead to a primitive orthorhombic cell for 3
pyrazole (5.30 g, 77.9 mmol) were heated at 180 °C in a sealed flask
under nitrogen, without stirring, until the yellowish color of cadmium
oxide disappeared (about 5 h). The mixture was then allowed to cool
and solidify, giving a white solid. The residue was then washed with
acetone in order to eliminate excess pyrazole and finally filtered giving
[
(
a ) 17.27 Å, b ) 5.24 Å, c ) 7.38 Å, M(17) ) 36; F(17) ) 51
0.009, 39)] and to a triclinic lattice for 4 [a ) 7.38 Å, b ) 9.43 Å, c
)
)
5.83 Å, R ) 96.5°, â ) 96.8°, and γ ) 73.5°; M(17) ) 24; F(17)
46 (0.016, 23)]. Systematic absences for 1 and 2 indicated Ibam as
1
.14 g (93% yield) of [Cd(Hpz)(pz)
2 2 9 6
] . Anal. Calcd for C H10CdN :
the probable space group, later confirmed by successful refinement; 3
was solved, and refined, in Pcmn, while centric P 1h was chosen for
complex 4.
C, 34.35; H, 3.18; N, 26.72. Found: C, 33.89; H, 3.34; N, 26.34. Main
-
1
IR bands (Nujol mulls, cm ): 3382 s, 3135 w, 3121 w, 3108 w, 3099
w, 3086 w, 1522 w, 1487 m, 1410 m, 1371 m, 1248 m, 1168 m, 1157
m, 1117 m, 1047 s, 1031 s, 909 w, 880 w, 770 s, 756 s, 674 m, 630
m.
Despite the lattice parameters of 1 and 2, together with their space
group symmetry, could have been indicative of the isomorphous
character of such species with the already known [Cu(pz)
2
]
n
phase
Synthesis of [Cd(pz)
.59 mmol) was placed in a sublimation apparatus and heated to 300
C by means of an heat gun, controlling the temperature ((5 °C) by
2 n 2 2
] , 2. (a) Complex [Cd(Hpz)(pz) ] (500 mg,
(allowing to build the initial, approximate structural models for 1 and
1
°
2
from the published coordinates of the copper analogue, vide infra),
we “solved” their structures by simple geometrical and packing
considerations: indeed, in Ibam, the only crystallographic sites
consistent with four M(pz) molecules per unit cell and meaningful
2
metal coordination geometry and connectivity are those of 222
symmetry. Geometrical modeling was then used to compute ap-
proximate coordinates for the C and N atoms of the pyrazolato ligands.
employing a standard thermocouple. Condensation of solid pyrazole
was observed on the coldfinger of the apparatus. After 30 min heating
was stopped. The solid was allowed to cool and was then removed,
washed with acetone, and dried under vacuum (385 mg, 98%); b) to a
solution of CdCl
g, 33.1 mmol) was added under stirring. The clear solution was stirred
at room temperature for about 5 min, and then NH (0.5 mL, 25%
2
(1.00 g, 5.45 mmol) in water (30 mL), pyrazole (2.25
Structure solution of 3 and 4 was initiated by extracting, using
3
17
EXTRA, 76 and 173 (2θ < 55°) independent F
o
’s, respectively, which
w/w water solution) was added. The white suspension formed was
stirred for 30 min at room temperature. The solid was then filtered,
washed with water and methanol, and dried under vacuum (1.24 g,
afforded easily interpretable Patterson maps and the approximate
location of the mercury atoms. Difference Fourier syntheses and
geometric modeling later afforded approximate coordinates for the
remaining non-hydrogen atoms.
9
2%). Cd(ClO
chloride. Anal. Calcd for C
Found: C, 28.87; H, 2.21; N, 22.86. Main IR bands (Nujol mulls, cm ):
122 w, 3102 w, 1492 m, 1410 m, 1370 s, 1269 w, 1250 w, 1175 m,
156 m, 1055 s, 960 w, 915 w, 877 m, 769 m, 756 m, 624 m.
Synthesis of [Hg(pz)(NO )] , 3. To 25 mL of a filtered saturated
solution of Hg(NO in acetonitrile [about 200 mg of Hg(NO , 0.62
4
)
2
can equally be employed in place of cadmium
6
H
6
CdN : C, 29.21; H, 2.44; N, 22.72.
4
The final refinements were performed with the aid of the GSAS
suite of programs,18 by imposing steric constraints to chemically stiff
and known fragments, such as the pz and NO groups; pyrazolato ring
3
-1
3
1
and N-O bonds were given average literature values of 1.38 and 1.20
Å, respectively (internal ring angles being fixed at 108°, and planar
trigonal geometry assumed for the nitrate). Soft restraints were also
applied to Hg-N distances (2.15 Å in 3 and 4). The peak shapes were
3
n
3
)
2
3 2
)
mmol] was added pyrazole (126 mg, 1.85 mmol) under stirring. The
formed suspension was stirred for 30 min, the solid was then filtered,
washed with water and methanol, and dried under vacuum (197 mg,
1
9
best described by the Thompson/Cox/Hastings formulation of the
pseudo Voigt function, with GV and LY set to zero. The background
functions were described by a cosine Fourier series, while systematic
errors were corrected with the aid of a sample-displacement angular
shift, and, for 1, 2, and 4, a preferred orientation parameter, in the
formulation of March and Dollase20 (with 120, 120, and 010 pole
vectors, and coefficients equal to 0.78, 0.94, and 0.80, respectively).
Metal atoms were given a refinable isotropic displacement parameter
9
6% yield). Anal. Calcd for C
Found: C, 10.69; H, 1.22; N, 12.77. Main IR bands (Nujol mulls, cm ):
141 w, 3130 w, 3121 w, 1507 w, 1434 w, 1355 m, br, 1191 m,
075 m, 909 w, 822 w, 763 m, 725 w, 620 w.
Synthesis of Hg(pz) , 4. To the aforementioned suspension, Et
0.5 mL) was added dropwise. The consistency of the solid rapidly
3 3 3 3
H HgN O : C, 10.92; H, 0.91; N, 12.74.
-1
3
1
21
2
3
N
(
changed and a decrease of its volume was also observed. After 15 min
stirring, the solid was filtered, washed with water and methanol, and
[Uiso(M)], while lighter atoms’ U’s were arbitrarily given [Uiso(M) +
2
0
.02] Å values. The contribution of the hydrogen atoms to the scattered
dried under vacuum (202 mg, 98%). Anal. Calcd for C
6 6 4
H HgN : C,
intensity was neglected. Scattering factors, corrected for real and
imaginary anomalous dispersion terms, were taken from the internal
library of GSAS. Final R , Rwp, and R agreement factors, together with
p F
2
1.52; H, 1.79; N, 16.74. Found: C, 21.88; H, 1.91; N, 16.26. Main
-1
IR bands (Nujol mulls, cm ): 3133 w, 3120 w, 3107 w, 3094 w, 1485
m, 1418 m, 1371 m, 1270 m, 1261 m, 1181 m, 1169 m, 1072 m, 1065
sh, 1055 m, 1041 m, 956 w, 946 w, 914 w, 868 w, 755 s, 668 w, 626
m.
(
14) Werner, P. E.; Eriksson, L.; Westdahl, M. J. Appl. Crystallogr. 1985,
18, 367-370.
X-ray Powder Diffraction Analysis of 1, 2, 3, and 4. The powders
were gently ground in an agate mortar, than cautiously deposited in
the hollow of an aluminum holder equipped with a zero background
plate (supplied by The Gem Dugout, State College, PA) with the aid
of glass slide. The samples were rotated at about 60 rpm about the
scattering vector, to improve particle statistics and to minimize preferred
(15) De Wolff, P. M. J. Appl. Crystallogr. 1968, 1, 108-113.
(16) Smith, G. S.; Snyder, R. L. J. Appl. Crystallogr. 1979, 12, 60-65.
(17) Altomare, A., Burla, M. C.; Cascarano, G.; Giacovazzo, C.; Guagliardi,
A.; Moliterni, A. G. G.; Polidori, G. J. Appl. Crystallogr. 1995, 28,
842-846.
(
(
(
18) Larson, A. C.; Von Dreele, R. B. LANSCE, MS-H805, Los Alamos
National Laboratory: Los Alamos, NM, 1990.
19) Thompson, P.; Cox, D. E.; Hastings, J. B. J. Appl. Crystallogr. 1987,
1
3
orientation effects. Diffraction data (Cu KR, λ ) 1.5418 Å) were
collected on a horizontal scan D III/Max Rigaku diffractometer,
equipped with parallel (Soller) slits, a secondary beam curved graphite
monochromator, a Na(Tl)I scintillation detector and pulse height
amplifier discrimination. The generator was operated at 40 KV and 40
mA. Slits used: divergence 1.0°, antiscatter 1.0° and receiving 0.3 mm.
Nominal resolution for the present setup is 0.14° 2θ (fwhm) for the
20, 79-83.
20) (a) March, A. Z. Kristallogr. 1932, 81, 285-297. (b) Dollase, W. A.
J. Appl. Crystallogr. 1986, 19, 267-272.
(21) Conventional optical microscropy did not reveal, for any of the
prepared polycrystalline species, clearly defined crystal morphologies,
the typical grain size being lower than 10 µm. The odd, experimentally
determined, 120 preferred orientation pole vector for compounds 1
and 2 is however in good agreement with a cleavage plane of
pseudohexagonally packed chains of the orthorhombic crystals, running
along [001].
(
13) At least in the plane normal to the scattering vector. See for example:
Parrish, W.; Huang, T. C. AdV. X-ray Anal. 1983, 26, 35-44.

3660 Inorganic Chemistry, Vol. 38, No. 16, 1999
Masciocchi et al.
Table 1. Crystal Data and Refinement Parameters for Compounds 1, 2, 3, and 4
1
2
3
4
species
[Zn(pz)
2
]
Zn
n
[Cd(pz)
CdN
246.54
orthorhombic
Ibam
7.8591(6)
13.6520(10)
7.9165(4)
90
90
90
849.38(8)
4
1.928
2
]
n
Hg(pz)NO
3
Hg(pz)
HgN
4
334.73
triclinic
P1h
7.4097(3)
9.4473(3)
5.8345(3)
96.310(2)
96.752(3)
73.694(2)
388.01(4)
2
2
formula
fw, g mol
cryst syst
space group
a, Å
b, Å
c, Å
C
6
H N
6 4
C
H
6 6
4
C
3 3
H
HgN
3
O
3
C
H
6 6
-
1
199.81
orthorhombic
Ibam
7.4829(4)
14.3844(6)
7.3831(3)
90
90
90
794.70(4)
4
1.667
329.66
orthorhombic
Pcmn
17.2985(7)
5.2538(3)
7.3912(4)
90
90
90
671.73(8)
4
3.259
R, deg
â, deg
γ, deg
3
V, Å
Z
F
calc, g cm-
3
2.865
678.7
-
1
µ(Cu KR), cm
diffractometer
T, K
71.8
382.1
Rigaku D-III Max
298
789.6
298
298
298
2
N
N
θ range, deg
obs
17-97
17-97
17-97
17-97
4001
743
4001
4001
4001
refl
212
226
432
wR
p
, R
p
0.132, 0.104
0.125, 3.00
0.098, 0.077
0.066, 1.06
0.110, 0.080
0.066, 3.21
0.105, 0.081
0.058, 2.85
F
R , ø
Figure 2. Rietveld refinement plots for 1, 2, 3, and 4. Difference plot and peak markers at the bottom.
details of the data collections and analyses for the four crystal phases
can be found in Table 1. In the final cycles, data below 17° (2θ), i.e.,
those most affected by instrumental aberrations and incident beam
overflow, were omitted; Figure 2a-d shows the final Rietveld
refinement plots for 1, 2, 3, and 4, respectively. Final fractional
coordinates and full lists of bond distances and angles are supplied as
Supporting Information.
Results and Discussion
Synthesis. The aim of the synthetic approaches adopted in
this work was 2-fold: first, to prepare analytically pure species
and, second, to obtain samples in microcrystalline forms,
suitable for an XRPD analysis and, therefrom, for their complete
structural determination. The first task has been only partially

Metal Pyrazolato Complexes
Inorganic Chemistry, Vol. 38, No. 16, 1999 3661
tackled by two groups, which independently reported the
The IR spectrum of [Cd(Hpz)(pz)2]2 shows a strong absorp-
tion at 3382 cm attributable to the ν(N-H) of the neutral
1
2
-1
synthesis of group 12 binary metal-pyrazolate complexes.
Zinc. The synthetic route employed by Vos and Groeneveld
12a
coordinated pyrazole molecules. The sharpness of this band
excludes strong interactions (hydrogen bonds) between the
pyrazolate and the pyrazole ligands, similar to those observed
in a number of species complexes containing both pyrazolate
groups and pyrazole molecules in sterically favorable environ-
has been successfully adapted to the synthesis of [Zn(pz)2]n.
When an aqueous solution of ZnCl2 was treated with a 3-fold
excess of pyrazole in the presence of NH3, complex 1 was
isolated in quantitative yields. [Zn(pz)2]n can also be obtained
by using different zinc salts, such as nitrate or perchlorate (eq
2
4
ments. Two other absorptions of medium intensity are
-
1
1
).
observed at 1522 and 1485 cm and can be assigned to the
so-called ring breathing of the neutral and anionic heterocyclic
2
5
NH3
rings, respectively. The formulation presented above is also
based on the analogy with a strictly related derivative, [Zn-
1
ZnX + 2Hpz -
8 / [Zn(pz) ] (X ) Cl, NO , ClO )
2
n
2 n
3
4
NH4X
(
Hdmpz)(dmpz)2]2 (Hdmpz ) 3,5-dimethylpyrazole), synthe-
(1)
sized from metallic zinc and Hdmpz at 90 °C under an oxygen
atmosphere and structurally characterized.
2
6
According to this formulation the IR spectrum of 1 does not
show any absorption attributable to N-H stretching. Moreover,
On heating [Cd(Hpz)(pz)2]2 at 300 °C under N2, sublimation
of free pyrazole was observed (as also quantitatively confirmed
by thermogravimetric analyses), and the selective formation of
1
2b
and different from what was observed by Das and Ghosh
who, however, employed a different synthetic procedure), no
(
[Cd(pz)2]n was achieved (eq 5):
coordinated water was evidenced.
Cadmium. The reaction of cadmium chloride with pyrazole
follows a different pathway from that of ZnCl2. When CdCl2
was reacted with pyrazole (Cd/Hpz ) 1:3) in water, the initial
formation of [Cd(Hpz)2Cl2]22 was observed. The addition to the
reaction medium of an aqueous solution of NH3 or NaOH causes
the formation of a species exhibiting, in its IR spectrum, a quite
3
00 °C
2
[
Cd(Hpz)(pz)2]2
8 / [Cd(pz) ] + 2Hpz
(5)
n
2 n
When the reaction between CdCl2 and pyrazole is carried
out with a large excess of pyrazole, the intermediate formation
of the insoluble [Cd(Hpz)2Cl2] was not observed, and the
presence of Et3N caused the precipitation of [Cd(pz)2]n in an
analytically pure form. Presumably, the intermediacy of an ionic
tetrapyrazole cadmium complex, [Cd(Hpz)]Cl2 avoids the
formation of the hydroxo/pyrazolate species observed when [Cd-
Hpz)2Cl2] was present. Such complex behavior of the Cd /
pyrazole system is also reflected by the incomplete analytical
data and spectroscopic characterization attempted by Vos et al.
-1
sharp band of medium intensity centered at 3406 cm . On the
basis of this observation, and with the support of analytical data
(
see Experimental Section) we formulate this species as a
hydroxo/pyrazolate complex of cadmium(II), i.e., [Cd(OH)-
pz)]n; the absence of significant peaks in the powder diffraction
(
II
(
pattern of this (probably polymeric) species prevented, however,
its structural characterization.
On heating [Cd(OH)(pz)]n at 240 °C, under N2, the formation
of CdO and [Cd(pz)2]n was observed, as suggested by IR,
XRPD, and TGA monitoring (eq 2):
12a
12b
and Das et al.
Mercury. When an acetonitrile solution of Hg(NO3)2 was
treated with Hpz (Hg/Hpz ) 1:3) the formation of a species
analyzed as Hg(pz)(NO3), 3, was observed (eq 6):
2
40 °C
2
1
/n[Cd(OH)(pz)]n
8 CdO + / [Cd(pz) ] + H O
(2)
n
2 n
2
Hg(NO ) + Hpz f Hg(pz)(NO ) + HNO
3
(6)
3
2
3
The formation of CdO can be explained by a condensation
reaction of the pyrazolate ion with the hydroxyl moiety, as in
Noteworthy, the deprotonation of the pyrazole molecule to
the pyrazolato group takes place without the need of any
deprotonating agent. This behavior was already observed in the
2
3
(eq 3):
1
24a
presence of a soft metal like silver. The full crystallographic
/n[Cd(OH)(pz)] f CdO + Hpz
(3)
n
characterization of 3 was performed by means of XRPD (see
below) revealing the polymeric ionic nature of the species and
the absence of short Hg-O contacts. Therefore, as will be
explained below, a more suitable formulation of 3 is [Hg(pz)]n-
Concerning the formation of [Cd(pz)2]n, a reasonable as-
sumption was that it can be derived from the reaction between
CdO and Hpz. To substantiate this hypothesis, and with the aim
of obtaining [Cd(pz)2]n in an analytically pure form, the reaction
of CdO with molten pyrazole was carried out. Indeed, cadmium
oxide reacts with pyrazole at 180 °C, allowing the selective
formation of a new species, formulated (analytical and spec-
troscopic data) as the dinuclear pyrazole/pyrazolate [Cd(Hpz)-
(NO3)n.
When Et3N was added to the reaction medium, a different
species, analyzed as Hg(pz)2, 4, was isolated (eq 7). As revealed
by the crystallographic study (see below), crystals of 4, in
contrast with the zinc and cadmium analogues, can be best
(
pz)2]2 complex [containing, beside the two neutral pyrazole
(
24) See for example: (a) Ardizzoia, G. A.; La Monica, G.; Cenini, S.;
Moret, M.; Masciocchi, N. J. Chem. Soc., Dalton Trans. 1996, 1351-
1357. (b) Masciocchi, N.; Ardizzoia, G. A.; LaMonica, G.; Moret,
M.; Sironi, A. Inorg. Chem. 1997, 36, 449-454. (c) Burger, W.;
Str a¨ hle, J. Z. Z. Anorg. Allg. Chem. 1986, 539, 27-33. (d) Carmona,
D.; Oro, L. A.; Lamala, M. P.; Elguero, J.; Apreda, M. C.; Foces-
Foces, C.; Cano, F. H. Angew. Chem., Int. Ed. Engl. 1986, 25, 1114-
ligands, two double-brigding (exo-bidentate) and two mono-
dentate pyrazolate groups] (eq 4):
1
80 °C
2CdO + 6Hpz
8 [Cd(Hpz)(pz) ] + 2H O (4)
2 2 2
1116.
(
22) Van Ooijen, J. A. C.; Van der Put, P. J.; Reedijk, J. Chem. Phys. Lett.
(25) Reedijk, J. Rec. TraV. Chim. 169, 88, 1451-1460.
(26) (a) Ehlert, M. K.; Rettig, S. J.; Storr, A.; Thompson, R. C.; Trotter, J.
Can. J. Chem. 1990, 68, 1494-1498. (b) For a cobalt analogue see:
Ehlert, M. K.; Rettig, S. J.; Storr, A.; Thompson, R. C.; Trotter, J.
Can. J. Chem. 1993, 71, 1425-1436.
1977, 51, 380-382.
(
23) That the reaction depicted in eq 2 does not occur in a single step is
also confirmed by closely overlapping events traceable in the DSC
and TGA analyses.

3662 Inorganic Chemistry, Vol. 38, No. 16, 1999
Masciocchi et al.
Figure 4. Drawing of a portion of the polymeric [Zn(pz)
Metal atoms are shaded and H atoms are not shown. The isomorphous
Cd(pz) phase looks, at the drawing resolution, similar.
2 n
] chain.
[
2 n
]
the polymeric nature of complexes 1 and 2 (see Figure 4); one-
dimensional chains of tetrahedrally coordinated metal atoms,
bridged by µ-pz ligands, run along [001], the intermetallic
distance being determined by c/2 value (3.69 and 3.96 Å, for 1
and 2, respectively). In both cases, metals sit on a high-symmetry
2 n 2 n 2
Figure 3. TGA traces for [Zn(pz) ] , 1, [Cd(pz) ] , 2, and Hg(pz) , 4.
(
222) position, while all pyrazolato ligands are bisected by a
described as containing weakly interacting (nonpolymeric)
mononuclear species.
mirror plane (normal to c) passing through the midpoint of the
N-N vector and the C(4) position. Therefore, only a single
independent M-N interaction occurs, which was refined at
Et N
3
1
.970(7) and 2.24(1) Å, for 1 and 2, respectively.
On the basis of the final coordinates, it is possible to conclude
Hg(NO ) + 2 Hpz
8 Hg(pz) + 2(Et NH)NO (7)
2 3 3
3
2
that the isomorphous character of the zinc and cadmium
derivatives can also be extended to the previously reported [Cu-
Thermal Behavior of 1, 2, 3, and 4. The thermal stability
of these pyrazolato species has been investigated by TGA (see
Figure 3), DSC, and preparatiVe thermal treatments. Compound
(
4X-pz)2]n series (4X-Hpz ) 4-substituted pyrazole; X ) H,
3
0
CH3, Cl, Br). However, as briefly reported in synoptic Table
, where the most relevant geometric features of species 1, 2,
1
is a rather stable species, which can be heated to 440 °C
2
without decomposition; at this temperature, a severely endot-
II
-1
and [Cu(4X-pz)2]n are collected, the high(er) tendency of Cu ,
hermic reaction occurs (∆H ≈ 220 kJ mol ), forming the stable
II
II
2
7
than Zn or Cd , toward a more flattened (square-planar)
coordination results in large differences in the N-M-N angles,
those of the copper derivatives heavily deviating from ideal
tetrahedral MN4 coordination; additionally, very uniform M‚‚‚M
(
Tdec ≈ 800 °C ) Zn(CN)2 compound in a highly crystalline
28
form and extruding CH3CN molecules (GC-MS evidence).
For the sake of comparison, the [Zn(dmpz)2]n polymer was
found to decompose at ≈ 300 °C, thus implying that it may
adopt a different structure, possibly in order to minimize the
heavy overlap of methyl groups from pyrazolate ligands attached
to the same metal. Species 2 decomposes at lower temperatures
26a
II
values are observed for the four different Cu species (3.85-
3
.89 Å), while a much shorter intermetallic distance is found
for 1 (3.69 Å). Accordingly, the isomorphous character between
and [Cu(4H-pz)2]n, was detected only a posteriori, since the
1
(
≈380 °C) than 1 but, owing to the much lower stability of its
packing environments of the zinc and copper chains result in
rather different unit cell parameters, but identical space group
symmetry and topology. These results confirm, again, the high
versatility of the pyrazolato ligand, which can bridge metal
atoms at a variety of distances, depending on the geometric
dicyanide (Tdec ≈ 200 °C), the formation of acetonitrile is
accompanied by reduction to metallic cadmium and cyanogen
evolution; such a decomposition path is therefore similar to that
suffered, near 320 °C, by Hg(CN)2.27
A more complex thermal behavior is associated with Hg-
3
1
requirements of each metal center.
(pz)2. Pyrazole is released near 140 °C as colorless needles; on
All species reported in Table 2 possess chains pseudohex-
agonally packed, in the [hk0] plane, by van der Waals (mostly
the basis of analytical, TGA, and spectroscopic data, the
remaining white (amorphous) powder is tentatively given a [Hg-
II
H‚‚‚H and, for Cu species, H‚‚‚X) contacts. If an eccentricity
(C3H2N2)]n formulation, particularly because its IR pattern is
2
2
2 1/2
value ꢀ is evaluated (ꢀ ) 1 - [(a + b )/a ] /2; ꢀ ) 0 for
ideal hexagonal packing), values of ca. 12, 8.6, and 0.4% can
be computed for [Cu(pz)2]n, 1, and 2, respectively. It is worthy
of note that the very small ꢀ value observed for the [Cd(pz)2]n
species, together with the odd coincidence of a, c, and, as
very similar to that of 4, with the notable exception of one
-1
missing strong band near 1418 cm . Such hydrogen abstraction
might be accompanied by ring-C-mercuriation, as observed, for
29
example, for the reaction between Hdmpz and HgCl2, prevent-
ing, therefore, the formation of the Hg(CN)2 species; consis-
tently, further heating does not show any decomposition near
2
2
discussed, (a + b )/2 (7.86, 7.92, and 7.88 Å, respectively),
apparently simplifies the powder pattern, but may unpredictably
affect its RF factor, which requires the difficult partitioning of
many reflections underlying the same observed peak (i.e., those
3
20 °C (see above), nor formation of a (known to be unstable)
Hg(CN) complex, a slowly varying loss of material being
observed up to 400 °C. In addition, we also tried to thermally
characterize the mixed-ligand species 3; upon heating at about
2
2
2
sharing a common h +3k +l value).
-
1
Crystal Structures: The Mixed-Metal Species. Since the
copper, zinc, and cadmium pyrazolates are strictly isomorphous,
2
50 °C, NO2 is clearly evolved (∆H ≈ -40 kJ mol ) and an
intractable and amorphous dark-red powder was obtained.
Crystal Structures: The Zn and Cd Derivatives. The
crystal structure determination from XRPD data clearly revealed
(
30) (a) Ehlert, M. K.; Rettig, S. J.; Storr, A.; Thompson, R. C.; Trotter, J.
Can. J. Chem. 1989, 67, 1970-1974. (b) Ehlert, M. K.; Storr, A.;
Thompson, R. C.; Einstein, F. W. B.; Batchelor, R. J. Can. J. Chem.
1993, 71, 331-334. (c) Ehlert, M. K.; Rettig, S. J.; Storr, A.;
Thompson, R. C.; Trotter, J. Can. J. Chem. 1991, 69, 432-439.
(
(
(
27) Trotman-Dickerson, A. F. ComprehensiVe Inorganic Chemistry;
Pergamon Press: Oxford, UK, 1973.
28) Indeed, it is known that Zn(CN)2 can be prepared from zinc powder
and nitrogen-containing organic molecules.
(31) Indeed, pyrazolato-bridged M‚‚‚M distances as low as 2.35 Å (Barron,
A. R.; Wikinson, G.; Motevalli, M.; Hursthouse, M. B. Polyhedron
1985, 4, 1131-1134.) and as high as 4.56 Å (Sakagami, N.;
Nakahanada, M.; Ino, K.; Hioki, A.; Kaizaki, S. Inorg.Chem. 1996,
35, 683-688.) have been observed.
29) (a) De Luca, G.; Panattoni, C.; Renzi, G. Tetrahedron, 1976, 32, 1909-
1910. (b) Cingolani, A.; Lorenzotti, A.; Leonesi, D.; Bonati, F. Inorg.
Chim. Acta 1984, 81, 127-134.

Metal Pyrazolato Complexes
Inorganic Chemistry, Vol. 38, No. 16, 1999 3663
Table 2. Structural Data for Isomorphous (Orthorhombic, Ibam) [M(4X-pz)
2
]
n
Species
[Cu(4Br-pz)
[
Cu(4H-pz)
]
2 n
[Cu(4Me-pz)
2
]
n
[Cu(4Cl-pz)
9.152(6)
2
]
n
]
2 n
[Zn(4H-pz)
2
]
n
2 n
[Cd(4H-pz) ]
a, Å
b, Å
c, Å
V, Å
7.917(1)
11.491(2)
7.778(1)
708
9.777(8)
12.630(8)
7.748(7)
952
9.44(1)
13.32(2)
7.70(1)
968
7.48a
14.38
7.38
7.86a
13.65
7.92
849
13.021(7)
7.734(8)
916
3
795
color
green
3.89
1.957(2)
94-139
270
green
3.87
1.96
94-139
270
green
3.87
1.96
94-140
290
green
3.85
1.96
92-141
290
colorless
3.69
1.970(7)
109-111
441
pale yellow
3.96
2.24(1)
99-120
353
M‚‚‚M, Å (c/2)
M-N, Å
N-M-N, deg
Tdec, °C
a
Actual values and their e.s.d.’s are reported in Table 1.
we decided to investigate the possible formation of mixed-metal
pyrazolates as (random) copolymers, i.e., to determine their
mutual (solid-state) solubility.
Starting from an equimolecular amount of Cu(ClO4)2, Zn-
(
ClO4)2, excess pyrazole, and aqueous NH3, a highly insoluble
2
Figure 5. Drawing of a portion of the pseudo-polymeric Hg(pz) chain.
Metal atoms are shaded and H atoms are not shown. Fragmented bonds
refer to loose Hg‚‚‚N contacts (see text).
green species was obtained, which was not (XRPD evidence) a
mixture of the [Cu(pz)2]n and [Zn(pz)2]n phases nor an ordered
copolymer of larger periodicity. Its quasi-amorphous XRPD
pattern showed, however, a large peak near 2θ ) 8.4° (d )
nuclear molecules packed in space by weak(er) intermolecular
contacts (see Figure 5). That a discrete Hg(pz)2 molecule,
bearing two nearly linearly coordinated monodentate pz ligands,
exists, should not be surprising; similar examples can be found
for mercury(II) halides and analogous species with N-donor
1
0.5 Å), about 0.8° wide, indicating that some correlation is
present. If Et3N is used instead of aqueous ammonia, a similar
XRPD pattern is observed, with the notable exception of the
presence of four additional broad peaks, reminiscent of their
parent (and isomorphous) structures. The refined lattice param-
eters for such [(Cu,Zn)(pz)2]n species (a ) 7.55 Å, b ) 14.05
Å, and c ) 7.45 Å) are closer to those of the [Zn(pz)2]n, than
to the [Cu(pz)2]n values; accordingly, we tentatively suggest that
such violation of Vegard’s law is related to the high(er)
32
2+
ligands, demonstrating the high tendency of Hg ions toward
bicoordination. However, a detailed analysis of the packing
environment of the Hg(pz)2 molecules clearly shows that the
swinging ends of monodentate pz of (symmetry related)
molecules lean toward neighboring metal centers, at distances
for which Hg‚‚‚N interactions cannot be neglected (ca. 2.5 Å,
vs ca. 2.15 Å for Hg-N bonding contacts). This allowed, inter
alia, the correct labeling of the C/N atoms next to the mercury-
bonded N atom. Thus, a 1-D network of strong and weak(er)
bonds extends throughout the crystals, running along c. That
these ancillary ligands really participate in the coordination
sphere of Hg(II) is also supported by the observed bending of
the N-Hg-N angle [162.0(5)°, away from the two Hg‚‚‚N
contacts] and by the observation of the very poor solubility of
species 4. Therefore, the Hg(pz)2 species can also be considered
a coordination polymer built by bis-spiro[M-N-N-M-N-
N-] rings, but, since the N-Hg-N angles heavily deviate from
tetrahedral values (Hg being closer to a sawhorse geometry,
with cis-N-H‚‚‚N angles in the 88-108° range), the Hg atoms
are not collinear anymore (Hg‚‚‚Hg‚‚‚Hg ca. 123°, see Figure
5).
II
flexibility of Cu . Indeed, it is much easier to accommodate
copper ions (capable of sustaining a number of different
stereochemistries) in the Zn(pz)2 crystal lattice, than to force
heavy local distortion of zinc ions coordination. The above
results also point out that the kinetics of the [(Cu,Zn)(pz)2]n
phase formation is responsible for the appearance of Bragg
peaks, which are completely absent in the samples obtained
using ammonia.
In a similar effort, a (very pale) yellow powder was obtained
by reacting an equimolecular mixture of zinc and cadmium
perchlorates with excess pyrazole. XRPD data clearly showed
a crystalline pattern, which could be indexed by an I-centered
orthorhombic cell (a ) 7.69 Å, b ) 14.34 Å, and c ) 7.59 Å);
therefore, such mixed-metal phase is isostructural to its end-
members and the sharp diffraction peaks indicate that the
(random) copolymer obtained does not experience strain or other
crystal defects, as observed in the Cu/Zn case. Accordingly,
the bis-pyrazolato-bridged M‚‚‚M distance (3.80 Å ) c/2)
closely matches the average M‚‚‚M value of the pure phases
On the basis of the above considerations, we expected the
mixed pyrazolato-nitrato species 3 to be a structural analogue
of 4, i.e., a mononuclear species with, possibly, an extended
(2-D or 3-D) network of Hg‚‚‚O contacts throughout the crystal
lattice. Surprisingly, our XRPD structure determination revealed
(3.82 Å).
Finally, a deep blue copper/cadmium mixed-metal phase was
n+
the presence of polymeric [Hg(pz)]n polycations, containing
also prepared, but was found to possess a rather complex, so
far uninterpreted, XRPD pattern. Interestingly, this new crystal
phase demonstrates the lack of mutual solubility of [Cu(pz)2]n
and 2, and, as suggested by its color, may contain copper atoms
in a rather different geometric (square-planar?) environment,
not compatible with the structural features determined for the
pure end-members. Analogously, earlier attempts in doping zinc
-
exo-bidentate pyrazolates and embedding NO3 groups at rather
large distances from the mercury atoms (>2.70 Å, see Figure
6
); such disposition, therefore, closely resembles that found in
3
3
Hg(OH)NO3, where µ-OH bridges (Hg-O ) 2.06 Å) of the
n+
[Hg(OH)]n polycation show much stronger interactions with
-
(bidentate) mercury ions than NO3 groups (Hg‚‚‚ONO2 > 2.66
1
2a
Å). That the nitrato groups are not to be considered as part of
the coordination sphere of mercury is also suggested by the
and cadmium pyrazolates with small amounts of cobalt showed
II
II
that Co ions, very much like Cu in the present study, may
‘
dissolve’ into 1, but not in 2.
Crystal Structures: The Hg Derivatives. Different from
(
32) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon
Press: Oxford, UK, 1984.
its lighter analogues, Hg(pz)2, 4, can be described, as a first
approximation, as a molecular solid, containing discrete mono-
(33) Ribar, B.; Matkovic, B.; Sljukic, M.; Gabela, F. Z. Kristallogr. 1971,
134, 311-318.

3664 Inorganic Chemistry, Vol. 38, No. 16, 1999
Masciocchi et al.
ize a number of elusive polymeric species; the discovery and
characterization of such thermally robust one-dimensional metal-
containing polymers add new pieces of structural and chemical
information, which are of interest in light of the recently reported
3
4
anticorrosion properties of metal azolates. With these aspects
in mind, it is our goal to extend the reported synthetic and
analytical experiments to further examples of coordination
polymers, including different ligands, metals, and/or oxidation
states. Indeed, preliminary work has shown that monophasic
2
+
2+
crystalline powders of Ni
and [Hg2]
pyrazolates, not
isostructural with the species presented above, can be prepared;
these will be discussed in a forthcoming paper.
In addition, we have illustrated how the isomorphous nature
of the Zn and Cu species (which, apart from the similarity of
the cell parameters and the identity of the space group symmetry
operations, in the single-crystal case would be evident at a
glance, once the 3-D hkl intensity distributions are compared),
on using XRPD data can be somewhat obscured, owing to the
1
-D projection of the reciprocal space into the 2θ dimension.
That is, powder diffraction peaks, sorted on ascending d* values,
may occur in rather scrambled positions, even if (roughly)
maintaining similar F’s; as a consequence, what is considered
a ‘structural fingerprint’ cannot be easily recognized as such if
lattice parameters suffer anisotropic inflation (or, as in the
present case, changes of signs). Accordingly, the isomorphous
character of the copper, zinc, and cadmium species was also
missed in previously reported XRPD work, confirming that
a complete structural analysis (solution and refinement) is
mandatory in order to certify simple, but important, structural
features.
Figure 6. Drawing of portions of the polymeric [Hg(pz)] n+
100] projection. Metal atoms are shaded and H atoms are not shown.
The noncoordinating nitrates are also shown.
chains,
n
[
approximately linear [N-Hg-N 173(1)°] coordination geom-
etry; within each chain, zigzagging throughout the crystal in
the c direction (and winding up about a glide plane normal to
a), the Hg atoms lie on an approximate straight line (Hg‚‚‚Hg‚
1
2a
‚‚Hg 178°) with pyrazolato ligands coplanar to each other; both
such features differ in observation from the strictly topologically
equivalent R-[Cu(pz)]n and [Ag(pz)]n chains,6 where bending
at the Cu and Ag hinges occurs in order to avoid short H‚‚‚H
contacts, which, for large(r) intermetallic distances (Hg‚‚‚Hg
ca. 3.69 Å, vs Cu‚‚‚Cu and Ag‚‚‚Ag values of 3.16 and 3.40
Å, respectively) are more easily tolerated. On the basis of the
observed structure, it might be possible that anion exchange in
powders of Hg(pz)NO3, soaked in concentrated saline solutions,
occurs, but this chemical reactivity has not been investigated
so far.
a
Acknowledgment. We thank the Italian Consiglio Nazionale
delle Ricerche and MURST for funding. We also acknowledge
financial support from ICDD, International Centre for Diffrac-
tion Data.
Supporting Information Available: Full list of fractional atomic
coordinates, bond distances and angles for compounds 1, 2, 3, and 4.
This material is available free of charge via the Internet at http://
pubs.acs.org.
Conclusions
IC990258U
The present work has shown that on coupling selective
synthetic procedures with spectroscopic, thermal, and, above
all, powder diffraction analyses, it is possible to fully character-
(
34) (a) Richmond, W. N.; Faguy, P. W.; Weibel, S. C. J. Electroanal.
Chem. 1998, 448, 237-244. (b) Tsarenko, I. V.; Chizhik, S. A.;
Makarevich, A. V. Protect. Met. 1999, 35, 81-84.