Structural trends in alkaline earth and rare earth metal 3,5-diisopropylpyrazolates

Article abstract of DOI:10.1002/ejic.200600767

A series of 3,5-diisopropylpyrazolates of magnesium, calcium, and strontium in addition to a divalent europium analog continues our investigation on the differences and similarities between the alkaline earth and divalent rare earth metal elements. The alkane elimination reaction between dibutylmagnesium and excess 3,5-diisopropylpyrazole (iPr₂pzH) in toluene afforded the dinuclear magnesium pyrazolate [{Mg(iPr₂pz)₂(iPr ₂pzH)}₂] (1). [{Ca(iPr₂pz)₂(iPr ₂pzH)₂}₂] (2) and [{Eu(iPr₂pz) ₂(iPr₂pzH)₂}₂] (3) were obtained as the product of redox-transmetallation/ligand-exchange reactions between an excess of the corresponding metal, 2 equiv. of iPr₂pzH, and Hg(C ₆F₅)₂ in toluene. This reaction with Sr metal led to the isolation of a unique byproduct, [Hg₃(iPr ₂pz)₄-(C₆F₅)2] (4). High-temperature direct metallation of barium with iPr₂pzH afforded [{Ba(iPr ₂pz)₂(py)₃)₂] (5) upon treatment of the hydrocarbon-insoluble homoleptic [{Ba(iPr₂pz)₂}n] with pyridine (py). X-ray crystal structure analyses revealed dinuclear structures for compounds 1-3 and 5 with μ-ηⁿ:η^m bridging pyrazolato ligands, including the new μ-η¹:η⁵ linkage, and further stabilization of 1-3 by intramolecular hydrogen bonding between the terminal pyrazole donor and terminal 1 or bridging pyrazolato ligands in 2 and 3. The trinuclear 4 displays the first example of a complex with an open, triangular Hg₃ unit. It has μ-η¹: η¹ bridging pyrazolato ligands and terminal pentafluorophenyl groups. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200600767

FULL PAPER
DOI: 10.1002/ejic.200600767
Structural Trends in Alkaline Earth and Rare Earth Metal
3,5-Diisopropylpyrazolates
Julia Hitzbleck,[a,b] Glen B. Deacon,[b] and Karin Ruhlandt-Senge*[a,b]
Keywords: Alkaline earth metals / Lanthanoids / N ligands / Coordination modes
A series of 3,5-diisopropylpyrazolates of magnesium, cal-
with iPr2pzH afforded [{Ba(iPr2pz)2(py)3}2] (5) upon treatment
cium, and strontium in addition to a divalent europium ana- of the hydrocarbon-insoluble homoleptic [{Ba(iPr2pz)2}n] with
log continues our investigation on the differences and simi-
larities between the alkaline earth and divalent rare earth
metal elements. The alkane elimination reaction between di-
pyridine (py). X-ray crystal structure analyses revealed dinu-
clear structures for compounds 1–3 and 5 with µ-ηn:ηm bridg-
ing pyrazolato ligands, including the new µ-η1:η5 linkage,
and further stabilization of 1–3 by intramolecular hydrogen
bonding between the terminal pyrazole donor and terminal
1 or bridging pyrazolato ligands in 2 and 3. The trinuclear 4
displays the first example of a complex with an open, tri-
angular Hg3 unit. It has µ-η1:η1 bridging pyrazolato ligands
and terminal pentafluorophenyl groups.
butylmagnesium
and
excess
3,5-diisopropylpyrazole
(iPr2pzH) in toluene afforded the dinuclear magnesium pyra-
zolate [{Mg(iPr2pz)2(iPr2pzH)}2] (1). [{Ca(iPr2pz)2(iPr2pzH)2}2]
(2) and [{Eu(iPr2pz)2(iPr2pzH)2}2] (3) were obtained as the
product of redox-transmetallation/ligand-exchange reactions
between an excess of the corresponding metal, 2 equiv. of
iPr2pzH, and Hg(C6F5)2 in toluene. This reaction with Sr
metal led to the isolation of a unique byproduct, [Hg3(iPr2pz)4-
(C6F5)2] (4). High-temperature direct metallation of barium
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Considerable effort in our laboratories has shed light on
the chemistry of alkaline earth and rare earth metal pyrazol-
ates, and we recently reported on several metal-based syn-
theses of alkaline earth 3,5-diphenyl- and 3,5-dimethylpyr-
azolates Ph2pz and Me2pz.[5c] Structural analysis revealed the
expected similar coordination modes to the previously re-
ported rare earth metal pyrazolates[3e,3k,3m,6f] and identical
Introduction
The coordination chemistry of the pyrazolate ligand sys-
tem has been a point of interest for quite some time, and
the recognized array of binding modes keeps increasing as
this work continues.[1] Many of the pyrazolato complexes
reported in the literature to date involve transition met-
als,[1b,1d,2] followed by a much smaller number of lan-
thanoid pyrazolates.[3] Nevertheless, triggered by the poten-
tial use of this ligand system for chemical vapor deposition
(CVD) precursor materials,[3i,4] the pyrazolate series was ex-
tended to the more electropositive alkaline earth metals in
recent years.[4c,5] Despite the numerous coordination modes
reported (e.g. C- or N-η1, η2, η5, µ-ηn:ηm)[3,5,6] and the close
structural similarities with the analogous lanthanoid pyr-
azolates, suitable group 2 CVD precursor materials have not
been obtained as of yet, because of the thermal instability
of the compounds.[5] Hence the custom design of such ma-
terials still requires a more in-depth understanding of the
coordination chemistry of alkaline earth metals and the re-
sulting structure–reactivity relationship of their com-
pounds.
structures for metals with similar ionic radii (e.g. Ca2+
/
Yb2+; Sr2+/Sm2+/Eu2+).[7] Alternatively, where the Yb2+
complexes have not been crystallized,[3j] a prediction can
be made from the structure of the Ca complex and vice
versa.[5c,5d,5f] Furthermore, we could show that, in the ab-
sence of suitable donor solvents, or if ideal steric saturation
cannot be achieved by co-solvent coordination, formation
of oligonuclear species is observed.[5d,5f] While the sterically
demanding alkaline earth metal diphenylpyrazolates
[M(Ph2pz)2(thf)4] (M = Ca, Sr, Ba) form exclusively mono-
nuclear complexes in the presence of thf,[5c] the correspond-
ing di-tert-butylpyrazolates [{M(tBu2pz)2(thf)n}2] crystallize
as dinuclear species with an array of µ-η2:ηn-bridging pyr-
azolato modes.[5f] An even greater variety of coordination
modes is observed in the products of high-temperature me-
tallation, affording linear, homoleptic alkaline earth metal
3,5-di-tert-butylpyrazolates [{M(tBu2pz)2}n] (M = Ca, Sr,
Ba; n = 3, 4, 6 respectively).[5d] Where the corresponding
pyrazoles are coligands,[3l,3m] hydrogen bonding also plays
a major role in determining the structures of alkaline earth
metal derivatives.[5b,5c,8] The coordination of a neutral li-
[a] Syracuse University, Department of Chemistry,
CST 1-014, Syracuse, NY, 13244-4100, USA
Fax: +1-315-443-4070
E-mail: kruhland@syr.edu
[b] School of Chemistry, Monash University,
Victoria 3800, Australia
Fax: +61-3-9905 4597
E-mail: glen.deacon@sci.monash.edu.au
592
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Alkaline Earth and Rare Earth Metal 3,5-Diisopropylpyrazolates
gand is also an important design element of potential CVD
FULL PAPER
For the heavier congeners, metal dialkyls or “heavy Grig-
precursor molecules.[3i,8] Deposition experiments have nard” reagents are less accessible because of their inherent
shown that the addition of the free ligand to the vapor fre- higher reactivity. Even though dibenzyl complexes of the
quently results in increased complex stability,[8] and we re- heavier group 2 metals have been reported,[10] their synthe-
cently reported on enhanced vapor transport of complexes sis is quite involved, making these reagents less competitive
containing free pyrazole as a donor.[5f] Nevertheless, the ef- starting materials for our target compounds. To expand the
fect of ligand bulk on the synthesis of alkaline earth metal synthetic schemes on hand for the alkaline earth metals, we
pyrazolates as well as on their structures is incompletely recently reported on metal-based routes to heavy group 2
understood. We now report a study of the synthesis and pyrazolates, circumventing problems encountered in salt
structures of alkaline earth and a rare earth metal 3,5-di- metathesis.[5a] One of these, redox-transmetallation/ligand-
isopropylpyrazolates. iPr2pz has steric bulk intermediate be- exchange, has now been employed to prepare [{Ca(iPr2pz)2-
tween the Ph2pz and Me2pz ligands, further assisting an (iPr2pzH)2}2] (2) and [{Eu(iPr2pz)2(iPr2pzH)2}2] (3) (Fig-
understanding of this important class of complexes. Par- ure 2 and Figure 3). However, the redox-transmetallation/
ticular features are the influence of the thermal stability of ligand-exchange reaction of excess metal, iPr2pzH and
the ligand in high-temperature syntheses, and the effect of Hg(C6F5)2 (mol ratio 2:1) in toluene (M = Ca, Eu) did not
hydrogen bonding as well as π-Ar–M pyrazolate coordina- go to completion to yield [{M(iPr2pz)2}n]. Instead, only
tion on the geometry of the resulting structures.
50% conversion of the organomercurial and the pyrazole
was observed under these conditions, leading to the isola-
tion of complexes 2 and 3 in good yields with respect to the
pyrazole used (Scheme 2). Redox-transmetallation/ligand-
exchange syntheses are normally carried out in polar sol-
vents (S), giving [Ln(L)nSm] complexes,[3e,3g,3j,3l,5c,11] but use
of a nonpolar solvent such as toluene enabled the prepara-
tion of homoleptic compounds, as demonstrated with [La-
(Odpp)3] (Odpp = 2,6-diphenylphenolate).[12]
The phenomenon of an incomplete reaction due to the
preferred formation of a “free-ligand” stabilized species is
a recurring feature of group 2 pyrazolates syntheses.[5b,5c]
In a similar fashion, the transamination reaction between
alkaline earth metal bis[bis(trimethylsilylamido)] complexes
[M{N(SiMe3)2}2(thf)2] (M = Ca, Sr, Ba) and Me2pzH in thf
yielded monomeric Me2pz analogs [M(Me2pz)2(Me2pzH)4],
instead of the expected Lewis base donor adducts
[M(Me2pz)2(thf)n].[5c] The formation of pyrazole adducts is
a likely consequence of the stabilizing effect of hydrogen
bonding (vide infra) between the anionic ligand and the free
pyrazole, in addition to the strong donor properties of the
latter, as also observed for compounds 1–3. The energy gain
through such a hydrogen bonding stabilization prevents the
complete ligand-exchange reaction since all pyrazole is con-
sumed when 50% of the mercurial is converted.
Results and Discussion
The commercial availability of a variety of magnesium
alkyls offers a straightforward and clean synthetic route to
magnesium amides.[5b,9] Hence the magnesium pyrazolate
[{Mg(iPr2pz)2(iPr2pzH)}2] (1) (Figure 1) was prepared by
alkane elimination from dibutylmagnesium in toluene in the
presence of four equivalents of 3,5-diisopropylpyrazole
(Scheme 1). Despite excess pyrazole (sixfold also examined),
dimerization and coordination of only one pyrazole group
per metal center is observed. This contrasts with the report
on monomeric [Mg(tBu2pz)2(tBu2pzH)2], in which two
equivalents of free pyrazole coordinate to the metal cen-
ter.[5b]
Surprisingly, the same reaction with either strontium or
ytterbium metal repeatedly did not afford analogs of 2 and
3 (Scheme 3), even though this route has been successful
with Ca and Sr in combination with thf or dme and 3,5-
diphenylpyrazole,[5c] or with Yb, 3,5-diphenylpyrazole and
HgPh2.[3j,13] The redox-transmetallation/ligand-exchange
reaction at room temperature led repeatedly to the recovery
Scheme 1.
Scheme 2.
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593

J. Hitzbleck, G. B. Deacon, K. Ruhlandt-Senge
FULL PAPER
of unreacted metal, iPr2pzH, and Hg(C6F5)2. The use of ture comparable to [{Ba(tBu2pz)2}6].[5d] Extraction of the
more forcing conditions in refluxing toluene initiated crude material with pyridine afforded the toluene-soluble
the ligand rearrangement between the already formed dinuclear [{Ba(iPr2pz)2(py)3}2] (5).
strontium pyrazolate and remaining mercurial to form a
unique heteroleptic trinuclear organomercurial [Hg3-
(iPr2pz)4(C6F5)2] (4) (Figure 5).
All compounds were analyzed by spectroscopic methods
(IR; NMR except for 3); 1, 2, and 5 show the expected
signals corresponding to the pyrazole/pyrazolato ligands (1,
2), or the pyridine donor and pyrazolato ligand in 5 in the
1H and 13C NMR spectra of the respective compounds.
Variable temperature NMR studies indicated the fluxional
behavior of complexes 1 and 2 in solution, forfeiting the
differentiation between bridging and terminal pyrazolato or
pyrazole [CH(pzH) and CH(pz)] ligands even at low tem-
perature (–60 °C). This is in contrast to the homoleptic 3,5-
di-tert-butylpyrazolate [{M(tBu2pz)2}n] (M = Ca, Sr, Ba)
analogs where a clear separation of the pyrazolate CH sig-
nals has been observed upon cooling, and they correspond
to the different types of terminal and bridging pyrazolato
ligands in the multinuclear species.[5d] Compound 4 reveals
the characteristic signals of the pentafluorophenyl group,
Scheme 3.
In the presence of unreacted bis(pentafluorophenyl)mer-
cury, a rearrangement reaction can occur, leading to prefer-
ential crystallization of the novel complex 4. Bis(penta-
fluorophenyl)mercury is normally resistant to protolysis[14]
and in particular does not react with 3,5-diphenylpyr-
azole.[15] The Sr(C6F5)2 from the rearrangement may un-
dergo protolysis to Sr(iPr2pz)2 or decompose to SrF2 by C–
F activation.
3
with J(Hg,F) appropriate for a mono(pentafluorophenyl)-
mercury compound.[16]
The solid-state structures of the 3,5-diisopropylpyrazol-
ate compounds 1–5 were determined by single-crystal X-
ray crystallography; perspective views of 1–5 are shown in
Figures 1–5. Compounds 1–3 are all dinuclear; 1 contains
one pyrazole per metal center, while the larger metals satisfy
their coordination sphere with two pyrazole donors in 2
and 3, or three pyridine donors in 5. Crystal data are given
in Table 5, and selected bond lengths and angles are sum-
marized in Tables 1–4.
A third synthetic route involving direct metallation at ele-
vated temperatures (Scheme 4) was attempted for the syn-
thesis of homoleptic 3,5-diisopropylpyrazolato complexes
[{M(iPr2pz)2}n] (M = Ca, Sr, Ba). Contrasting the straight-
forward syntheses of the corresponding 3,5-di-tert-butylpy-
razolates [{M(tBu2pz)2}n] (M = Ca, Sr, Ba),[5d] 3,5-diisopro-
pylpyrazole failed to react with calcium and strontium un-
der elevated-temperature conditions, suggesting a slightly
less acidic character for iPr2pzH than for tBu2pzH. The ad-
dition of a drop of elemental mercury to the reaction mix-
The metal centers in the dinuclear compounds
ture for surface amalgamation of the metal has been proven [{M(iPr2pz)2(iPr2pzH)n}2] (n = 1, M = Mg 1; n = 2, M = Ca
to be useful in combination with the slightly less reactive 2, Eu 3, Figure 1) are further stabilized by intramolecular
rare earth metals (e.g.[3h,3k–m]). In contrast, for the group 2 hydrogen bonding involving the acidic proton of the pyr-
metals, direct metallation reactions under such conditions azole donor and the lone pair on the pyridine-like nitrogen
proceeded without the addition of mercury in other pyr- of the η1-bonded pyrazolates. In contrast to the heavier an-
azole systems (Ph2pzH, tBu2pzH).[5c,d,f] Nevertheless, with alogs 2 and 3, but in accordance with the dinuclear magne-
iPr2pzH even mercury addition did not result in the desired sium
tert-butylpyrazolates
[{Mg(tBu2pz)2}2]
and
reaction, and only ligand decomposition was observed in [{Mg(tBu2pz)2(thf)}2],[4c] the bridging ligands in 1 bind
the reaction of Ca and Sr upon increasing temperature. fairly symmetrically in a µ-η1:η1-fashion and are slightly
Only for the most reactive alkaline earth metal barium me- twisted out of plane (Mg1, Mg2, pz3, pz4) to reduce steric
tallation occurred, as indicated by the slowly solidifying re- interactions of the pendant isopropyl groups with the ter-
action mixture. In contrast to the 3,5-di-tert-butylpyrazol- minal ligands. This results in a distorted tetrahedral coordi-
ates, the homoleptic species could not be sublimed in the nation environment for magnesium [maximum deviation
Carius tube. Several extractions with hot toluene were also from the ideal tetrahedral angle 9.7(1)°]. Surprisingly, the
unsuccessful, thus indicating an oligo- or polynuclear struc- terminal Mg–N bonds for the σ-η1-pyrazolates [Mg–N
Scheme 4.
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Alkaline Earth and Rare Earth Metal 3,5-Diisopropylpyrazolates
FULL PAPER
2.077(2)–2.088(2) Å] are slightly elongated as compared of the ligand, leading to an increased torsion angle between
with the bridging ligands [Mg–N 2.053(2)–2.061(2) Å]. In the N–N ligand moiety and the metal–metal axis (N1–N2–
addition, there is no marked difference in Mg–N bond M1–M2 18° 1, 55° 2, 80° 3). The same trend has been re-
length (within experimental error) between the terminal an- ported previously for the structures of [{M(tBu2pz)2(thf)}2]
ionic ligand pz2 and the neutral donor pzH1 [∆(Mg–N) (M = Ca/Yb; Sr/Eu)[3e,5f] and [{M(tBu2pz)}n] (M = Ca, n
0.003(4) Å]. Pz2 and pzH1 display short hydrogen-bonding = 3; M = Sr/Eu, n = 4), where a more extended π-coordina-
contacts between H12 and N22 [1.56(5) Å; N12–H12–N22 tion of the bridging pyrazolato ligand is observed upon in-
155.66°]. Even though the corresponding pz5 and donor creasing metal size (Ca/Yb to Sr/Eu (µ-η2:η2 Ca/Yb, µ-
pzH6 on Mg2 show slightly larger differences [∆(Mg–N) η5:η2 Sr/Eu) in the former complexes, or an overall increase
0.011(4) Å], the hydrogen-bonding contacts are very similar in metal–ligand contact sites in the latter compounds [Σηn
[H62···N52 1.58(4) Å, N62–H62–N52 154.76°].
= 8 (Ca2), 9 (Ca1,3); Σηn = 12 (Sr1), 9 (Sr2)].[3e,3k,5d,5f]
Figure 1. X-ray crystal structure of [{Mg(iPr2pz)2(iPr2pzH)}2] (1);
the isopropyl groups and hydrogen atoms have been removed for
clarity, except for those involved in hydrogen bonding.
A dinuclear structural motif identical to 1 has been re-
ported for the zinc dimethylpyrazolate complex
[{Zn(Me2pz)2(Me2pzH)2}2], with a pseudotetrahedral ge-
ometry around the zinc atoms [N–Zn–N 99.6(2)°
–113.8(2)°].[2a] Analogous to the magnesium complex 1, the
Figure 2. X-ray crystal structure of [{Ca(iPr2pz)2(iPr2pzH)2}2] (2);
the isopropyl groups and hydrogen atoms have been removed for
clarity, except for those involved in hydrogen bonding.
The additional donor in 2 and 3, in comparison to 1,
metal centers are bridged by two µ-η1:η1-Me2pz ligands, also leads to binding modes of µ-η2:η1-pyrazolato ligands
but with significantly shorter bridging bond lengths [Zn–N in 2 and new µ-η5:η1-pyrazolato ligands in 3 further stabi-
1.991(3) Å] than the terminal ligand [Zn–N 2.025(3) Å]. lized by hydrogen bonding between the pyrazole donor and
The zinc atoms are capped by a Me2pz/Me2pzH pair, which the bridging ligand [N32–H···N42# 2.138(3) Å, 147.88° 2,
is linked together by hydrogen bonding [N1–H1···N2 141°; 2.012(5) Å, 151.20° 3] but not between the terminal iPr2pz
H1···N2 1.77 Å], where the position of the hydrogen atom and iPr2pzH ligands. To better indicate this novel type of
is disordered over two possible sites (Table 1).
bridging coordination of the pyrazolato ligand, the coordi-
The effect of metal size on the pyrazolato binding mode nation mode could also be expressed as µ3-
is nicely demonstrated in the heavier analogs 2 and 3. Here, η1(H):η2(Ca):η1(Ca) in 2 and µ3-η1(H):η5(Eu):η1(Eu) in 3.
the larger size of calcium and europium (Ca2+ = 1.14 Å, This arrangement prevents the second pyrazolate nitrogen
Eu2+ = 1.31 Å, Mg2+ = 0.860 Å; CN = 6)[7] requires the from bridging the metal centers [M1–N42# closest contact
coordination of two equivalents of pyrazole to afford the 3.292(1) Å 2, 3.471(4) Å 3, cf. M–Nbr 2.405(2)–3.003(2) Å
dinuclear structures [{Ca(iPr2pz)2(iPr2pzH)2}2] (2, Figure 2) 2, 2.684(4)–2.794(4) Å 3] and results in rather unsymmetri-
and [{Eu(iPr2pz)2(iPr2pzH)2}2] (3, Figure 3). The larger cal M–N bond lengths induced by the twisting of the bridg-
metals also display a more pronounced side-on coordina- ing pyrazolato ligand. The hydrogen bonding of pzH3 to
tion of the pyrazolate ring, as well as a π-bonding interac- the bridging pyrazolato ligand pz4 leads to closer M–
tion of the europium metal centers with the aromatic core N(pzH3) contacts relative to those of the second pyrazole
Table 1. Selected bond lengths [Å] and angles [°] for compound 1.
Mg1–N11
Mg1–N21
Mg1–N31
Mg1–N41
Mg2–N32
Mg2–N42
Mg2–N51
Mg2–N61
2.080(2)
2.083(2)
2.053(2)
2.056(2)
2.056(2)
2.061(2)
2.077(2)
2.088(2)
N11–Mg1–N21
N11–Mg1–N31
N11–Mg1–N41
N21–Mg1–N31
N21–Mg1–N41
N31–Mg1–N41
99.79(9)
N32–Mg2–N42
N32–Mg2–N51
N32–Mg2–N61
N42–Mg2–N51
N42–Mg2–N61
N51–Mg2–N61
107.87(9)
119.07(9)
106.04(8)
108.98(9)
114.41(9)
100.59(9)
105.97(9)
118.21(9)
117.11(9)
107.91(9)
108.19(9)
Eur. J. Inorg. Chem. 2007, 592–601
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595

J. Hitzbleck, G. B. Deacon, K. Ruhlandt-Senge
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bond for the σ-bonded pyrazolato ligand pz1 to be justified
by the small bite angle [pz1 33.89(6)° 2, 31.5(1)° 3] and
through the centroid (cen) of the N–N bond (2) or pyrazol-
ate core (3) of the bridging ligand pz4. The pz4 (η2 2, η5 3)
and N21 occupy the axial positions (169.4° 2, 174.1° 3),
whereas the angle between N31–M–N41A (92.9° 2, 87.6° 3)
in the equatorial plane is smaller than the others
[cen(N11,12)–M–N31,
cen(N11,12)–M–N41A
128.7°,
135.6° 2, 113.7°, 151.1° 3] because of hydrogen bonding.
The heteroleptic complex [{Ba(iPr2pz)2(py)3}2] (5, Fig-
ure 4) is a centrosymmetric dinuclear compound having
nine-coordinate barium centers bridged by two chelating µ-
η2:η2-pyrazolato ligands. Due to steric interactions with the
third donor, the terminal η2-pyrazolato ligands coordinate
rather unsymmetrically to the metal [Ba–N 2.739(4) Å,
2.838(4) Å]. In contrast, the chelating, bridging ligand
binds more symmetrically [Ba–N 2.806(4) Å, 2.884(4) Å;
Ba–N# 2.991(4) Å, 3.060(4) Å], and the pyrazolate core is
slightly inclined by 9.7(5)° towards Ba1 from an ideal per-
pendicular µ-η2:η2-bridging mode. This ligand inclination
only provides very weak π-interactions between Ba1 and
Figure 3. X-ray crystal structure of [{Eu(iPr2pz)2(iPr2pzH)2}2] (3);
the isopropyl groups and hydrogen atoms have been removed for
clarity, except for those involved in hydrogen bonding.
donor pzH2, which also binds to the metal by means of its
pyridine-like nitrogen [2.567(2) Å 2, 2.693(4) Å 3; cf. pzH3
2.455(2) Å 2, 2.659(4) Å 3] in an almost perpendicular ori-
entation to the σ-bonded pyrazolate pz1 [dihedral angle
88.9(1)° 2, 82.9(1)° 3], thereby preventing further hydrogen-
bonding contacts. Hence the novel type of bridging coordi-
nation of the pyrazolato ligand, µ-η2:η1 in 2 and µ-η5:η1 in
3, is enforced by hydrogen bonding as one pz(N) is unable
to further bridge the metal centers. A related structural fea-
ture of hydrogen-bonded, enforced η1-pyrazolato coordina-
tion has been observed previously in [Nd(η2-Me2pz)2(η1-
Me2pz)(Me2pzH)2(py)].[3l] The Eu–C43,45 distances in 3 are
comparable with π-Eu–C bonds in [{Eu(tBu2pz)2}4],[3k]
which is consistent with the proposal of η5-bonding,
whereas the longer Ca–C distances for the smaller divalent
metal are nonbonding (Table 2).
The coordination environment of the metal (formal coor-
dination numbers 7 for 2, and 8 for 3) can be described in
a simplified manner as a distorted trigonal bipyramid by
considering the bonding through the center of the N–N ity.
Figure 4. X-ray crystal structure of [{Ba(iPr2pz)2(py)3}2] (5); the
isopropyl groups and hydrogen atoms have been removed for clar-
Table 2. Selected bond lengths [Å] and angles [°] for compounds 2, 3.
Ca1–N11
Eu1–N11
Ca1–N12
Eu1–N12
Ca1–N21
Eu1–N21
Ca1–N31
Eu1–N31
2.391(1)
2.550(4)
2.388(1)
2.590(4)
2.567(1)
2.693(4)
2.455(1)
2.659(4)
Ca1–N41
Eu1–N41
Ca1–N42
Eu1–N42
Ca1–C43*
Eu1–C43
Ca1–C44*
Eu1–C44
Ca1–C45*
Eu1–C45
Ca1–N41#
Eu1–N41#
3.003(1)
2.794(4)
2.467(1)
2.760(4)
3.367(2)
3.019(4)
4.209(2)
3.178(5)
3.992(2)
3.051(4)
2.405(1)
2.684(4)
N11–Ca1–N12
N11–Eu1–N12
N11–Ca1–N21
N11–Eu1–N21
N12–Ca1–N21
N12–Eu1–N21
N21–Ca1–N31
N21–Eu1–N31
N31–Ca1–N41
N31–Eu1–N41
N31–Ca1–N41A
N31–Eu1–N41A
N41–Ca1–N42
N41–Eu1–N42
33.89(6)
31.46(12)
82.43(6)
75.95(12)
80.87(6)
77.84(12)
87.36(6)
82.72(11)
75.88(6)
94.92(11)
92.93(6)
87.65(11)
27.39(5)
29.13(10)
#1 indicates symmetry generated atoms: 2–x, 1–y, 1–z: 2; 1–x, 1–y, 1–z: 3. * nonbonding distance.
596
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 592–601

Alkaline Earth and Rare Earth Metal 3,5-Diisopropylpyrazolates
FULL PAPER
C23, 25 [3.464(4) Å, 3.499(4) Å], contrasting the strong π-
In the structure of [Hg3(iPr2pz)4(C6F5)2] (4, Figure 5), an
coordination observed in the absence of additional donors open triangle of mercury atoms (Hg···Hg···Hg 55.66–
in the related complex [{Ba(tBu2pz)2}6] [Ba–C 3.10(1)– 67.22°) displays Hg1,2 as well as Hg2,3 [Hg···Hg
3.39(1) Å].[5d] The overall coordination sphere around the 3.6395(6) Å, 3.7026(6) Å] each linked by two µ-η1:η1-3,5-
metal in 5 can be described as distorted octahedral with diisopropylpyrazolato ligands, one nearly in the Hg3 plane
three pyridine donors and the N–N centroid (Ncen) of the [Hg1,3, pz5 7.2(5)°; Hg2,3, pz3 26.9(5)°] and the other
bridging pyrazolato ligand in the equatorial plane [angles above or below the plane [Hg1,2, pz4 65.9(2)°; Hg2,3, pz2
between neighboring ligands N31, N41, N51, Ncen(21,22), 77.0(3)°]. Both Hg1 and Hg3 have terminal C6F5 groups,
N31 94.1°, 82.0°, 90.9°, 97.1° respectively], whereas the ax- and they form the open edge of the Hg3 triangle [Hg···Hg
ial positions are occupied by the terminal and the sym- 4.0644(7) Å]. It could be considered that the structure arises
metry-generated
bridging
pyrazolato
ligands from the coordination of a [Hg(iPr2pz)4]2– moiety to two [Hg-
[Ncen(21A,22A)–Ba–Ncen(11,12) 164.2°]. The Ba–N dis- (C6F5)]+ ions.
tances of the neutral pyridine donors range from 2.856(4) Å
to 2.959(4) Å and thus lie between the bond lengths for the
bridging pyrazolato ligand [2.806(4) Å–3.060(4) Å], though
they are significantly longer than those for the terminal pyr-
azolato ligand [2.739(4) Å, 2.838(4) Å], as anticipated for a
neutral donor (Table 3).
Table 3. Selected bond lengths [Å] and angles [°] for compound 5.
Ba1–N11
Ba1–N12
Ba1–N21
Ba1–N22
Ba1–C23
Ba1–C24
Ba1–C25
Ba1–N21#
Ba1–N22#
Ba1–N31
Ba1–N41
Ba1–N51
2.739(4)
2.838(4)
2.806(4)
2.884(4)
3.464(4)
3.937(4)
3.499(4)
3.060(4)
2.991(4)
2.914(4)
2.959(4)
2.856(4)
N11–Ba1–N12
N21–Ba1–N22
N21#–Ba1–N22#
N31–Ba1–N41
N41–Ba1–N51
N31–Ba1–N51
Ba1–N21–Ba1#
Ba1–N22–Ba1#
28.8(1)
79.9(1)
74.3(1)
94.1(1)
82.0(1)
168.7(1)
96.6(1)
96.5(1)
Figure 5. The crystal structure of [Hg3(iPr2pz)4(C6F5)2] (4); the iso-
propyl groups and hydrogen atoms have been omitted for clarity.
#1 indicates symmetry generated atoms: 2–x, 2–y, 1–z.
The difference in steric demand of iPr2pz compared with
Each terminal mercury atom, Hg1,3, is strongly bonded
that of the tBu2pz ligand is apparent in the monomeric to a carbon and a nitrogen donor atom [Hg–C(N) ≈ 2.10 Å]
structure of the magnesium complex [Mg(tBu2pz)2- and a further, more distant, nitrogen atom [Hg–N ≈
(tBu2pzH)2] [H···N 2.745(2) Å, N–H···N 153(3)°],[5b] which, 2.43 Å]. Even the larger Hg–N bonds are well within the
despite the common metal, shows more similarity to the sum of the van der Waals radii of mercury (1.73 Å,[17] which
heavier monomeric dimethylpyrazolato analogs [M(Me2pz)2- is a conservative value, see also 1.9–2.0 Å,[17,18] or 2.1–
(Me2pzH)4] (M = Ca, Sr) with hydrogen bonding between 2.2 Å[19]) and nitrogen (1.60 Å[20]). The geometry deviates
the terminal η1-pyrazolato ligands and pyrazole donors considerably from the expected T-shape[21] (where the
[H···N 2.01(2) Å, N–H···N 156(2)° for Ca].[5c] The preferen- strongly bound ligands are linear) towards trigonal (angles
tial formation of the present dinuclear, hydrogen-bonded ≈ 154°, 116°, 90°). Although coordination of the more dis-
complexes can be explained by the additional stabilization tant nitrogen causes considerable bending of C1,11–Hg1,3–
provided by the bridging of the metal centers, as the average N41,21, any effect on the Hg–C distances [2.09(1) Å,
bond length in 1 is shorter than in the monomeric 2.08(1) Å] is marginal, as they are near the Hg–C bond
[Mg(tBu2pz)2(tBu2pzH)2] whereas the overall metal coordi- lengths observed in the homoleptic organomercurial
nation number is the same.[5b] The dinuclear formulation Hg(C6F5)2 [Hg–C 2.047(6)–2.052(6) Å][22] in the trinuclear
enables the formation of stronger/shorter hydrogen bonds. [{Hg(C6F4)}3]·(C6H6) [Hg–C 2.058(8) Å][23] or in the T-
As the formation of 1 was also observed with an excess of shaped three-coordinate [Hg(C6F4OH-p)2(OH2)] [Hg–C
iPr2pzH, targeting the formation of
a
monomeric 2.047(7), 2.058(7) Å].[21b] Both the short and longer Hg–N
[Mg(iPr2pz)2(iPr2pzH)2], the role of secondary interactions distances are close to the values (ca. 2.15 Å, ca. 2.5 Å from
in coordination compounds must play a crucial role, a fact X-ray powder diffraction data) for pseudo-polymeric mer-
also observed in lanthanoid pyrazolate Nd(η2-Me2pz)2- curic pyrazolate.[24] By contrast with Hg1,3, Hg2 is four-
(η1-Me2pz)(Me2pzH)2(py)].[3l] For the larger analogs the di- coordinate with two short Hg–N bonds in a transoid ar-
merization leads to an increase in coordination number (2 rangement [N32–Hg2–N52 163.5(4)°] and with two more
CN = 7, 3 CN = 8; cf. CN = 6 in [M(Me2pz)2(Me2pzH)4] M distant nitrogen donors each nearly perpendicular to the
= Ca, Sr),[5c] while the average bond lengths are comparable N32–Hg2–N52 vector, resulting in overall sawhorse geome-
despite the difference in coordination number.
try. This is as expected for two strong and two weak donors
Eur. J. Inorg. Chem. 2007, 592–601
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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597

J. Hitzbleck, G. B. Deacon, K. Ruhlandt-Senge
FULL PAPER
bound to mercury,[21a,22,23] though distorted square planar cantly influence the overall complex geometry. It is interest-
geometry has also been observed.[21b,25] Both short and ing to note that compounds 1–3 form preferentially over
long Hg–N bond lengths compare favorably to those ob- analogs of the oligonuclear [M(tBu2pz)2]n (M = Ca, Sr, Ba;
served at Hg1,3 (Table 4).
n = 3–6),[5d] as rationalized by the decreased steric demand
of the iPr2pz ligand and hence insufficient shielding of the
metal centers. A polynuclear formulation for [Ba(iPr2pz)2]x
provides an explanation for its hydrocarbon insolubility and
the need for additional donors as in 5 to induce solubility
and enable crystallization.
Table 4. Selected bond lengths [Å] and angles [°] for compound 4.
Hg1–C1
2.086(10)
2.079(10)
2.101(8)
2.422(9)
2.489(8)
2.066(9)
2.472(8)
2.051(9)
2.113(8)
2.442(9)
N41–Hg1–N51
N41–Hg1–C1
N51–Hg1–C1
N22–Hg2–N32
N22–Hg2–N42
N22–Hg2–N52
N32–Hg2–N42
N32–Hg2–N52
N42–Hg2–N52
N21–Hg3–N31
N21–Hg3–C11
N31–Hg3–C11
91.1(3)
152.6(4)
115.7(4)
92.2(3)
85.0(3)
96.3(3)
96.1(3)
163.5(4)
98.8(3)
87.7(3)
155.0(4)
116.7(4)
Hg3–C11
Hg1–N41
Hg1–N51
Hg2–N22
Hg2–N32
Hg2–N42
Hg2–N52
Hg3–N21
Hg3–N31
Experimental Section
General Remarks: All preparations were carried out under an atmo-
sphere of purified nitrogen. Pentane and toluene were predried with
sodium, distilled under nitrogen from sodium/benzophenone, and
stored in Schlenk flasks fitted with Teflon taps, or freshly distilled
from sodium/potassium alloy and degassed in three freeze-pump-
thaw cycles; pyridine was distilled from CaH2 under nitrogen and
stored in Schlenk flasks fitted with Teflon taps. 3,5-Diisopropylpyr-
azole, dibutylmagnesium (1.0  solution in heptane), calcium,
strontium, ytterbium, and europium metals were obtained commer-
cially (+99.9% distilled ingots; europium ingots stored under oil);
Hg(C6F5)2 was prepared by a literature method.[28] IR data (4000–
650 cm–1) were obtained for Nujol or mineral oil mulls sandwiched
between NaCl plates with a Perkin–Elmer 1600 or Perkin–Elmer
Paragon FTIR spectrometer. 1H and 13C NMR spectra were re-
corded with Bruker Avance spectrometers (300 MHz; 25 °C) in
[D6]benzene and the chemical shifts referenced to the residual sol-
vent signals. Melting points of air-sensitive compounds were ob-
tained in capillaries sealed under nitrogen and are uncorrected.
The structural motif of trinuclear mercury complexes has
been reported for a number of compounds,[26] although
many structures contain mixed-valent or fractional valence
species,[27] as seen in a series of [{Hg[P(Ph2)CH2P-
(Ph2)]}3][A]n with a range of different counterions (A =
CH3SO3, CF3SO3, PF6, SiF6, CF3CO2),[27a] leaving the
(ortho-phenylene)mercury derivatives [{Hg(C6F4)}3] and
[{Hg(C6H4)}3] as the most closely related species.[23,26]
However, these display closed Hg3 unit, whereas 4 is open.
Another difference of such compounds from 4 is the planar
metal/ligand arrangement, favoring π-stacking with a vari-
ety of arenes (benzene, toluene, naphthalene, etc.).[23,26k] In
the heteroleptic complex 4, the trinuclear metal center is
shielded by two pyrazolato ligands above and below the
plane. In addition, the steric bulk provided by the isopropyl
substituents prevents any potential stabilizing arene–Hg in-
teractions.
Synthesis of Compounds 1–5
[{Mg(iPr2pz)2(iPr2pzH)}2] (1): 3,5-Diisopropylpyrazole (0.63 g,
4.0 mmol) was dissolved in toluene (30 mL), dibutylmagnesium
(1.0  in heptane; 1.0 mL, 1.0 mmol) was added with a syringe, and
the reaction mixture was heated at reflux for 2 h. Filtration, re-
moval of the solvent, and recrystallization from hot pentane yielded
very thin, colorless plates of 1 at room temperature (0.40 g, 84%).
1
M.p. 76–79 °C. H NMR (300 MHz, C6D6, 25 °C): δ = 1.22 [s, 72
Conclusions
H, CH(CH3)2], 3.02–2.87 [m, 12 H, CH(CH3)2], 5.86 [s, 2 H, C4-
H(pzH)], 5.88 [s, 2 H, C4-H(pzter)], 5.99 [s, 2 H, C4-H(pzbr)], 11.02
[br. s, 2 H, (pz)NH] ppm. 13C NMR (300 MHz, C6D6, 25 °C): δ =
23.3 [pzH, CH(CH3)2], 24.7 [pz, CH(CH3)2], 27.6 [pzH, CH-
(CH3)2], 28.7 [pz, CH(CH3)2], 97.3 [CH(pzH)], 97.6 [CH(pzter)],
98.6 [CH(pzbr)], 159.0 [ipso-C(pzH)], 165.0 [ipso-C(pz)] ppm. IR
The increasing metal size in the 3,5-diisopropylpyrazol-
ates 1–3 and 5 leads to a stepwise increase in coordination
number [Mg 4, Ca 7, Eu 8, Ba 9], in addition to changes in
the bridging ligand orientation from the exobidentate pyr-
azolato ligands in the magnesium complex 1, via the already
tilted, hydrogen-bonded µ-η1:η2-bridging pyrazolato li-
gands in the heavier metal analog 2 and µ-η1:η5 in 3, to
the almost perpendicular µ-η2:η2-bridging ligand and three
pyridine donors in the barium complex 5. These com-
pounds display further examples of the amazing variety of
binding modes of the pyrazolato ligand system and illus-
trate the unique role of secondary interactions in the stabili-
zation of labile or highly reactive compounds. Intramolecu-
lar hydrogen bonding in pyrazolato complexes has pre-
viously only been reported between terminal ligands,[2a,4c,5b]
enforcing an η1-coordination over the otherwise preferred
terminal η2-chelation. The interaction with the µ-η1:ηn
bridging ligands is a new structural feature and implies that
minor steric effects or the potential of additional stabiliza-
(Nujol): ν = 3307 (w), 3166 (m), 3087 (m), 1867 (m), 1728 (w), 1674
˜
(w), 1575 (m), 1522 (s), 1504 (s), 1467 (s), 1422 (m), 1360 (m), 1302
(s), 1263 (s), 1176 (m), 1102 (s), 959 (w), 922 (m), 866 (s), 786 (s),
725 (m), 700 (m), 665 (m) cm–1.
Attempted preparation of [Mg(iPr2pz)2(iPr2pzH)4] by reaction of
3,5-diisopropylpyrazole (0.95 g, 6.0 mmol) and dibutylmagnesium
(1.0  in heptane; 1.0 mL, 1.0 mmol) in toluene (30 mL) led to the
cocrystallization of thin plates of 1 and thin needles of iPr2pzH.
[{Ca(iPr2pz)2(iPr2pzH)2}2] (2): Calcium metal in pieces (0.20 g,
5.0 mmol), bis(pentafluorophenyl)mercury (0.54 g, 1.0 mmol), and
3,5-diisopropylpyrazole (0.31 g, 2.0 mmol) were stirred in toluene
(40 mL) for two days. Filtration, reduction of the solvent volume
(20 mL), and cooling to –20 °C yielded colorless rods of 2 (0.29 g,
89% on pyrazole). M.p. 116–120 °C. 1H NMR (300 MHz, C6D6,
25 °C): δ = 1.21 [bd, 96 H, CH(CH3)2], 3.03 [br. s, 16 H, CH-
tion via hydrogen bonding of the ligand/donor can signifi- (CH3)2], 5.92 [s, 8 H, C4-H(pz)], 11.86 (b, 4 H, N-H) ppm. 13C
598 Eur. J. Inorg. Chem. 2007, 592–601
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Alkaline Earth and Rare Earth Metal 3,5-Diisopropylpyrazolates
FULL PAPER
NMR (300 MHz, C6D6, 25 °C): δ = 24.0 [CH(CH3)2], 28.2 cooling to –20 °C. Yield 0.26 g (56%). M.p. 63–65 °C, 115 °C (so-
[CH(CH3)2], 97.8 [CH(pz)], 157.8 [ipso-C(pz)] ppm. IR (Nujol): lidifies again), Ͼ235 °C (decomposition). IR (Nujol): ν = 3178 (m),
˜
ν = 3338 (m), 3167 (m), 3100 (w), 1638 (m), 1612 (w), 1561 (m), 3101 (m), 1858 (w), 1574 (s), 1502 (s), 1405 (s), 1360 (s), 1304 (s),
˜
1510 (s), 1460 (s), 1416 (m), 1303 (m), 1293 (m), 1276 (m), 1251 1261 (s), 1218 (w), 1177 (s), 1129 (sh), 1105 (s), 1047 (w), 994 (s),
(m), 1176 (m), 1134 (s), 1070 (s), 1050 (m), 1011 (m), 991 (m), 966
(s), 892 (w), 878 (w), 805 (m), 782 (m), 726 (m), 692 (w), 669 (w)
cm–1.
882 (m), 846 (m), 725 (s), 747 (w), 699 (s), 682 (sh), 673 (w) cm–1.
3
1H NMR (300 MHz, [D6]benzene, 25 °C): δ = 8.48 [td, J(H,H)
=
3.0 Hz, 6 H, o-H(py)], 6.98 [tt, 3J(H,H) = 8.0 Hz, 3 H, p-H(py)], 6.66
[tt, 3J(H,H) = 4.0 Hz, 6 H, m-H(py)], 5.97 (s, 4 H, H4-pz), 3.02 [sept,
8 H, CH(CH3)2], 1.26 [d, 48 H, CH(CH3)2] (partially desolvated)
ppm. 13C NMR: δ = 157.2 [ipso-C(pz)-iPr], 150.6 [o-C(py)], 135.7
[p-C(py)], 123.9 [m-C(py)], 98.1 [CH(pz)], 28.3 [CH(CH3)2], 24.0
[CH(CH3)2] ppm.
[{Eu(iPr2pz)2(iPr2pzH)2}2] (3): Europium metal in pieces (0.76 g,
5.0 mmol), bis(pentafluorophenyl)mercury (0.54 g, 1.0 mmol), and
3,5-diisopropylpyrazole (0.31 g, 2.0 mmol) were stirred in toluene
(40 mL) for two days. Filtration, reduction of the solvent volume
(20 mL), and cooling to –20 °C yielded dark yellow rods of 3
(0.37 g, 96% on pyrazole). M.p. 88 °C. IR (Nujol): ν = 3329 (m),
Attempted Preparation of [{Yb(iPr2pz)2(iPr2pzH)2}2]: Ytterbium
˜
3088 (m), 1930 (w), 1860 (w), 1819 (w), 1763 (w), 1713 (w), 1638 metal in pieces (0.88 g, 5.0 mmol), bis(pentafluorophenyl)mercury
(m), 1556 (m), 1506 (s), 1464 (s), 1373 (s), 1275 (m), 1178 (m), 1135 (0.54 g, 1.0 mmol), and 3,5-diisopropylpyrazole (0.31 g, 2.0 mmol)
(m), 1069 (s), 1019 (m), 967 (s), 805 (m), 721 (m) cm–1.
were stirred in toluene (40 mL) for two days. Filtration, reduction
of the solvent volume (20 mL), and cooling to –20 °C led to the
subsequent recovery of 3,5-diisopropylpyrazole and bis(pentafluor-
ophenyl)mercury toluene solvate.
[Hg3(iPr2pz)4(C6F5)2] (4): Strontium metal in pieces (0.44 g,
5.0 mmol), bis(pentafluorophenyl)mercury (0.27 g, 0.5 mmol), 3,5-
diisopropylpyrazole (0.32 g, 2.0 mmol) were heated at reflux in tol-
uene (30 mL) for 48 h. Filtration and reduction of the solvent vol-
ume (20 mL) led to the isolation of very small, colorless plates after
several days at room temperature. Yield 0.09 g (18% on mercury).
Attempted Preparation of [{Sr(iPr2pz)2(iPr2pzH)2}2]: Strontium
metal in pieces (0.44 g, 5.0 mmol), bis(pentafluorophenyl)mercury
(0.54 g, 1.0 mmol), and 3,5-diisopropylpyrazole (0.31 g, 2.0 mmol)
were stirred in toluene (40 mL) for two days. Filtration, reduction
M.p. 76–82 °C (melted), Ͼ110 °C (clear). IR (Nujol): ν = 3180 (m),
˜
3097 (m), 1634 (m), 1573 (m), 1506 (s), 1362 (s), 1300 (m), 1263 of the solvent volume (20 mL), and cooling to –20 °C led to recov-
(m), 1177 (m), 1128 (m), 1097 (s), 1076 (s), 1044 (s), 1010 (s), 963 ery of 3,5-diisopropylpyrazole and bis(pentafluorophenyl)mercury.
(s), 874 (w), 792 (s), 718 (s) cm–1. 1H NMR (300 MHz,
[D6]benzene, 25 °C): δ = 5.89 [s, 4 H, C4-H(pz)], 2.83 [m, 8 H,
CH(CH3)2], 1.18 [d, 48 H, CH(CH3)2] ppm. 13C NMR: δ = 129.8
[ipso-C(pz)iPr], 98.1 [CH(pz)], 28.6 [CH(CH3)2], 24.0 [C(CH3)2]
Changing the ligand/mercurial stoichiometry to a ratio of 4:1 and
heating the reaction mixture at reflux led to the isolation of 4.
X-ray Crystallography: For compounds 1–5 a hemisphere of low
temperature data was collected (monochromatic Mo-Kα radiation,
λ = 0.71073 Å) by using a Bruker AXS SMART system, complete
with 3-circle goniometer and APEX-CCD detector, for 1 and 4 and
an Enraf–Nonius CCD area-detector instrument for 2, 3, 5
(Table 5). A total of N unique reflections (No [IϾ2σ(I)] “ob-
served”) were used in least-squares refinement [anisotropic U for
3
ppm; C6F5 undetected. 19F NMR: δ = –115.8 (td, J(F-F) = 20 Hz,
3
3J(Hg-F) = 502 Hz, 4 F, F2,6), –155.3 (t, J(F-F) = 20 Hz, 2 F, F4),
3
–161.9 (t, J(F-F) = 20 Hz, 4 F, F3,5) ppm.
[{Ba(iPr2pz)2(py)3}2] (5): Barium metal in pieces (0.65 g, 5 mmol)
and 3,5-diisopropylpyrazole (0.31 g, 2 mmol) were heated to 170 °C
for 5 d in a sealed and evacuated (approx. 1؋10–3 Torr) Carius
tube until the contents of the tube solidified. Extraction of the
crude product [{Ba(iPr2pz)2}n] with a mixture of toluene (30 mL)
and pyridine (15 mL) led to the isolation of colorless plates upon
non-hydrogen atoms, (x, y, z, Uiso H constrained] after structure
)
solution by Direct Methods as included in the XSEED or
SHELXTL-Plus program package.[29] Absorption corrections were
performed with the programs SADABS (1, 4) and maXus (2, 3,
Table 5. Experimental crystallographic data for compounds 1–5.
1
2
3
4
5
Empirical formula
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C54H92Mg2N12
958.02
C72H124Ca2N16
1294.03
monoclinic
P21/a (No. 14)
13.9033(2)
20.8058(4)
14.5525(3)
90
107.131(1)
90
4022.83(13)
2
C72H124Eu2N16
1517.79
C48H60F10Hg3N8
1540.81
C66H90Ba2N14
1354.20
triclinic
triclinic
triclinic
triclinic
¯
¯
¯
¯
P1 (No. 2)
P1 (No. 2)
P1 (No. 2)
P1 (No. 2)
10.860(1)
14.508(2)
20.711(3)
73.904(3)
87.431(3)
70.313(3)
2947.7(7)
2
11.8046(3)
11.8805(4)
15.3057(5)
90.978(2)
101.478(2)
111.050(2)
1954.0(1)
1
10.398(1)
12.550(1)
22.846(2)
79.775(2)
88.313(2)
71.375(2)
2779.1(4)
2
11.9467(1)
13.2047(2)
13.9593(2)
114.553(1)
92.137(1)
116.411(1)
1725.96(5)
1
β [°]
γ [°]
V [Å3]
Z
T [K]
87(2)
1.079
0.084
24216
123(2)
1.068
0.189
38992
123(2)
1.290
1.639
28465
123(2)
1.841
8.338
22783
91(2)
1.303
1.181
26109
Density δcalcd. [gcm–3
]
Absorption coefficient [mm–1
Reflections collected
]
Reflections unique
10365 (Rint = 0.0605) 7075 (Rint = 0.0597) 6823 (Rint = 0.0738)
9780 (Rint = 0.0543)
R = 0.0742
Rw = 0.1241
6055 (Rint = 0.0923)
R = 0.0593
Rw = 0.1499
Final R-indices [I Ͼ 2σ(I)][a]
R = 0.0609
R = 0.0483
R = 0.0420
Rw = 0.1268
Rw = 0.1079
Rw = 0.0955
[a] R = Σ||Fo| – |Fc||/∑|Fo|; Rw = [Σw(Fo – Fc ) /Σw(Fo2)2]1/2
.
2
2 2
Eur. J. Inorg. Chem. 2007, 592–601
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599

J. Hitzbleck, G. B. Deacon, K. Ruhlandt-Senge
FULL PAPER
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N–H hydrogen atoms were located in the respective difference Fou-
rier maps and refined isotropically.
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CCDC-283035 to -283037 (for 1–3), -608636 (for 4), -299836 (for
5) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_requ-
est/cif.
Acknowledgments
We gratefully acknowledge support from the Monash University
Small Grant Scheme, the Australian Research Council, and the
National Science Foundation [Grants CHE-0108098 (including a
supplement) and CHE-0505863], enabling the collaboration be-
tween Monash University and Syracuse University. Purchase of the
X-ray diffraction equipment at Syracuse was made possible with
grants from the National Science Foundation (Grants CHE-
9527858 and CHE-0234912), Syracuse University, and the W. M.
Keck Foundation.
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Eur. J. Inorg. Chem. 2007, 592–601

Alkaline Earth and Rare Earth Metal 3,5-Diisopropylpyrazolates
FULL PAPER
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Received: August 17, 2006
Published Online: December 27, 2006
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