The influence of functional group orientation on the structure of zinc 1,1,4-trimethylthiosemicarbazide dicarboxylates: Probing the limits of crystal engineering strategies

Article abstract of DOI:10.1002/ejic.200390106

The reaction of [Zn(tmtsc)₂](NO₃)₂ [tmtsc = 1,1,4-trimethyl-thiosemicarbazide, MeNHC(S)NHNMe₂] with a range of sodium dicarboxylates has been shown to lie on the borderline between commonly used crystal engineering strategies. The products exhibit a wide range of structural diversity with the main driving force being the relative orientation of the carboxylate groups. Thus, fumarate leads to the hydrogen-bonded aggregate [Zn(tmtsc)₂(OH₂)][fumarate] (2) in which cations and anions are linked by hydrogen bond donor-donor acceptor-acceptor (DD:AA) interactions, whereas isophthalate and (+)-camphorate lead to coordination polymers [Zn(tmtsc)(μ-isophthalate)] (3a) and [Zn (tmtsc)(μ-camphorate)] (4) with the metal centres linked by bridging dicarboxylate ligands. In the case of isophthalate, a hydrated product [Zn(tmtsc)(μ-isophthalate)]·H₂O (3b) was also characterised, although microanalysis and powder X-ray diffraction revealed this to be a minor product. Incorporation of water was shown to lead to a change in carboxylate coordination mode from η¹ in 3a to η² in 3b. Use of terephthalate leads to the compound [(Zn(tmtsc)(OH₂)}₂(μ-terephthalate)]- [terephthalate]·2H₂O (5), in which half of the terephthalates bridge metal centres, to form dimers, and the remainder link the dimeric cations through DD:AA hydrogen bond interactions. Homophthalate leads to discrete dimers [Zn(tmtsc)(μ-homophthalate)]₂ (6), whereas acetylenedicarboxylate yields the unexpected compound [Zn(tmtsc)₂(OH₂)][O₂CCH= CC(O)N(Me)C(=NNMe₂)S]₂·H₂O (7) in which the dicarboxylate has reacted with tmtsc to give a 2-hydrazono-4-oxo-1,3-thiazolidineacetate, which is subsequently trapped in the solid state by DD:AA hydrogen bonding interactions with [Zn(tmtsc)₂(OH₂)]²⁺. All products were characterised by single crystal X-ray crystallography, and the representational nature of these crystal structures to the bulk materials was confirmed by microanalysis and powder diffraction. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200390106

FULL PAPER
The Influence of Functional Group Orientation on the Structure of Zinc
1,1,4-Trimethylthiosemicarbazide Dicarboxylates: Probing the Limits of
Crystal Engineering Strategies
Andrew D. Burrows,*[a] Ross W. Harrington,[a] Mary F. Mahon,[a] and Simon J. Teat[b]
Keywords: Zinc / Carboxylate ligands / Hydrogen bonds / Coordination polymers / Supramolecular chemistry
The reaction of [Zn(tmtsc)2](NO3)2 [tmtsc = 1,1,4-trimethyl-
thiosemicarbazide, MeNHC(S)NHNMe2] with a range of so-
dium dicarboxylates has been shown to lie on the borderline
between commonly used crystal engineering strategies. The
products exhibit a wide range of structural diversity with the
main driving force being the relative orientation of the carb-
mode from η1 in 3a to η2 in 3b. Use of terephthalate leads
to the compound [{Zn(tmtsc)(OH2)}2(µ-terephthalate)]-
[terephthalate]·2H2O (5), in which half of the terephthalates
bridge metal centres, to form dimers, and the remainder link
the dimeric cations through DD:AA hydrogen bond interac-
tions. Homophthalate leads to discrete dimers [Zn(tmtsc)(µ-
oxylate groups. Thus, fumarate leads to the hydrogen-bon- homophthalate)]2 (6), whereas acetylenedicarboxylate yields
ded aggregate [Zn(tmtsc)2(OH2)][fumarate] (2) in which cat-
ions and anions are linked by hydrogen bond donor-donor
acceptor-acceptor (DD:AA) interactions, whereas isophthal-
the unexpected compound [Zn(tmtsc)2(OH2)][O2CCH=
CC(O)N(Me)C(=NNMe2)S]2·H2O (7) in which the dicarb-
oxylate has reacted with tmtsc to give a 2-hydrazono-4-oxo-
ate and (+)-camphorate lead to coordination polymers 1,3-thiazolidineacetate, which is subsequently trapped in the
[Zn(tmtsc)(µ-isophthalate)] (3a) and [Zn(tmtsc)(µ-camphor- solid state by DD:AA hydrogen bonding interactions with
ate)] (4) with the metal centres linked by bridging dicarb-
[Zn(tmtsc)2(OH2)]2+
.
All products were characterised by
oxylate ligands. In the case of isophthalate, a hydrated prod-
single crystal X-ray crystallography, and the representational
uct [Zn(tmtsc)(µ-isophthalate)]·H2O (3b) was also charac- nature of these crystal structures to the bulk materials was
terised, although microanalysis and powder X-ray diffraction
revealed this to be a minor product. Incorporation of water
confirmed by microanalysis and powder diffraction.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
was shown to lead to a change in carboxylate coordination Germany, 2003)
Introduction
placing thiourea ligands to give polymers or dimers in
which the zinc centres are linked by bridging dicarb-
oxylates.[5,6] In contrast, under similar conditions
[M(tsc)2]2ϩ (M ϭ Zn, Ni; tsc ϭ thiosemicarbazide) cations
give ionic structures of the type [M(tsc)2][dicarboxylate] in
which the cations and anions are linked together into tapes
by hydrogen bonds.[5,7] Hence, changing the ligands on the
metal centre from uni- to bidentate has been shown to alter
the mode of supramolecular assembly and consequently the
type of structure formed.
Progress in the field of crystal engineering has largely
arisen as a result of the identification and use of supramole-
cular synthons[1] Ϫ small units within molecules that are
anticipated to interact with each other in a predictable
manner. There are currently two main strategies adopted in
crystal engineering, in which these supramolecular synthons
are based either on metal-ligand interactions[2] or, alternat-
ively, on intermolecular interactions such as hydrogen
bonds,[3] and recently there have been reports using both of
these approaches together.[4] We are particularly interested
in the competitive interplay between the two strategies, and
as a consequence have focussed our attention on systems in
which both types of aggregation are possible.
In this paper we report on the reactions of [Zn(tmtsc)2]2ϩ
[tmtsc ϭ 1,1,4-trimethylthiosemicarbazide, MeNHC(S)-
NHNMe2] with a range of dicarboxylates. The presence of
the tertiary amine group in the tmtsc ligand was expected
to increase its lability relative to tsc,[8] and therefore en-
hance the possibility of ligand displacement from the metal
coordination sphere. This has been borne out and, in con-
As part of this study, we have shown that
[Zn(thiourea)4]2ϩ cations react with dicarboxylates by dis-
trast to the reactions with [Zn(thiourea)4]2ϩ or [M(tsc)2]2ϩ
,
reactions with [Zn(tmtsc)2]2ϩ give a wide variety of struc-
tural types, with that observed from a particular reaction
depending on the relative orientation of the carboxylate
groups within the anion.
[a]
Department of Chemistry, University of Bath,
Claverton Down, Bath BA2 7AY, UK
E-mail: a.d.burrows@bath.ac.uk
[b]
CLRC Daresbury Laboratory,
Daresbury, Warrington WA4 4AD, UK
766
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/03/0204Ϫ0766 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2003, 766Ϫ776

Probing the Limits of Crystal Engineering Strategies
FULL PAPER
Supramolecular Structures of 2؊7
Results and Discussion
The crystal structure of compound
2
consists of
[Zn(tmtsc)2(OH2)]2ϩ cations and fumarate anions. The co-
ordination geometry around the zinc centre is distorted
square pyramidal (τ ϭ 0.39),[9] with mutually trans tmtsc
ligands. Selected bond lengths and angles are given in
Table 2, and hydrogen bonding parameters are given in
Table 3. Two hydrogen bonds between the parallel NH
Synthesis
The complex [Zn(tmtsc)2](NO3)2 was prepared from the
reaction of zinc() nitrate with tmtsc in ethanol. Recrys-
tallisation of the product from water gave single crystals
of [Zn(tmtsc)2(OH2)2](NO3)2 (1), the identity of which was
confirmed crystallographically. Selected bond lengths and
angles for 1 are given in Table 1.
˚
Table 2. Selected bond lengths (A) and angles (°) for compounds 2
˚
and 7
Table 1. Selected bond lengths (A) and angles (°) for compounds
1, 3a, 3b and 6
2
7
[a]
1
3a
3b
6
Zn(1)ϪS(1)
Zn(1)ϪS(2)
Zn(1)ϪN(1)
2.3127(8)
2.3073(8)
2.306(2)
2.280(2)
1.986(2)
2.3425(8)
2.3319(8)
2.240(2)
2.239(2)
1.993(2)
Zn(1)ϪS
2.4186(5)
2.2513(15)
2.1224(14)
2.327(2)
2.098(5)
1.933(4)
2.3267(9)
2.195(2)
2.078(2)
2.334(2)
2.343(2)
2.056(2)
84.09(6)
2.3814(7)
2.162(2)
2.0165(16)
2.540(2)
2.2823(19)
2.054(2)
84.15(6)
Zn(1)ϪN(1)
Zn(1)ϪO(1)
Zn(1)ϪO(2)
Zn(1)ϪO(3)Ј
Zn(1)ϪO(4)Ј
N(1)ϪZn(1)ϪS
O(1)ϪZn(1)ϪOЈ
Zn(1)ϪN(4)
Zn(1)ϪO(w)[a]
S(1)ϪZn(1)ϪS(2)
N(1)ϪZn(1)ϪN(4)
N(1)ϪZn(1)ϪS(1)
N(4)ϪZn(1)ϪS(2)
O(w)ϪZn(1)ϪN(1)
O(w)ϪZn(1)ϪN(4)
O(w)ϪZn(1)ϪS(1)
O(w)ϪZn(1)ϪS(2)
141.34(3)
143.74(3)
1.930(4)
164.60(7)
82.25(5)
82.68(5)
97.15(7)
98.23(7)
108.10(6)
110.56(6)
168.84(7)
82.38(5)
81.99(5)
95.40(7)
95.75(7)
102.55(5)
113.69(6)
81.76(4)
86.66(14)
116.13(17) 103.61(8)
[b]
137.90(8)
[a]
Primed atoms generated by symmetry transformations Ϫx ϩ
3/2, yϪ1/2, z ϩ /2 (3a), Ϫx ϩ 1, yϪ1/2, Ϫz ϩ /2 (3b) and Ϫx ϩ 1,
Ϫy ϩ 1, Ϫz (6). OЈ ϭ O(3)Ј for 3a; OЈ ϭ O(4)Ј for 3b and 6.
1
1
[b]
[a]
Reaction of [Zn(tmtsc)2](NO3)2, in aqueous solution,
with sodium salts of fumaric, (ϩ)-camphoric, terephthalic,
homophthalic and acetylenedicarboxylic acids gave com-
pounds [Zn(tmtsc)2(OH2)][fumarate] (2), [Zn(tmtsc)-
O(w) ϭ O(5) for 2, O(w) ϭ O(7) for 7.
˚
Table 3. Hydrogen bond lengths (A) and angles (°) for com-
pounds 2؊7
(µ-(ϩ)camphorate)]
(4),
[{Zn(tmtsc)(OH2)}2(µ-tere-
˚
˚
d(D···A)/A d(H···A)/A Մ(DH···A)/°
phthalate)][terephthalate]·2H2O (5), [Zn(tmtsc)(µ-homo-
phthalate)]2 (6) and [Zn(tmtsc)2(OH2)][O2CCHϭCC(O)N-
(Me)C(ϭNNMe2)S]2·H2O (7), as the only isolated com-
pounds in good yield. The analogous reaction with iso-
phthalate gave two compounds, [Zn(tmtsc)(µ-isophthalate)]
(3a) and [Zn(tmtsc)(µ-isophthalate)]·H2O (3b), with the an-
hydrous complex 3a the major product. The empirical for-
mulae of compounds 2, 3a, 4, 5, 6 and 7 were confirmed by
microanalyses, and the structures of all the compounds
were determined by single crystal X-ray analyses. A com-
parison of the experimental powder diffraction data with
that simulated from the single-crystal data confirmed
that the crystal structures are representative of the bulk
materials, with the experimental data for isophthalate con-
sistent with 3a. The dicarboxylates used are illustrated in
Scheme 1.
2
N(2)ϪH(2)···O(1)
N(3)ϪH(3)···O(2)
N(5)ϪH(5)···O(3)
N(6)ϪH(6)···O(4)
2.803(2)
2.730(2)
2.831(3)
2.731(3)
1.94(2)
1.86(2)
1.95(2)
1.87(2)
1.82(2)
1.71(2)
2.01(6)
2.19(6)
2.10(3)
2.08(3)
2.15(4)
2.13(4)
1.91(2)
2.16(2)
1.89(3)
2.13(3)
2.00(2)
1.91(2)
1.80(3)
1.79(2)
2.01(2)
2.07(3)
1.94(2)
2.19(2)
1.79(2)
2.03(2)
1.77(2)
1.95(2)
1.78(2)
1.81(2)
1.83(2)
2.20(3)
173(2)
172(2)
177(3)
176(3)
170(2)
172(4)
142(5)
138(5)
146(3)
171(3)
163(4)
163(4)
167(3)
141(3)
164(4)
144(4)
170(2)
179(2)
173(3)
173(4)
166(3)
145(4)
159(3)
151(3)
173(2)
179(2)
177(2)
171(2)
170(3)
165(2)
169(3)
159(5)
O(5)ϪH(5A)···O(4) 2.649(2)
O(5)ϪH(5B)···O(2)
2.588(2)
2.765(6)
2.909(7)
2.793(3)
2.869(3)
3a N(2)ϪH(2)···O(2)
N(3)ϪH(3)···O(2)
3b N(3)ϪH(3)···O(3)
N(2)ϪH(2)···O(5)
O(5)ϪH(5A)···O(2) 2.890(4)
O(5)ϪH(5B)···O(1)
N(2)ϪH(2)···O(2)
N(3)ϪH(3)···O(8)
N(5)ϪH(5)···O(4)
N(6)ϪH(6)···O(5)
N(2)ϪH(2)···O(1)
N(3)ϪH(3)···O(2)
2.877(3)
2.758(4)
2.907(4)
2.747(4)
2.892(4)
2.871(2)
2.779(2)
4
5
O(5)ϪH(5A)···O(6) 2.654(3)
O(5)ϪH(5B)···O(3) 2.665(3)
O(6)ϪH(6A)···O(1) 2.854(3)
O(6)ϪH(6B)···O(4)
N(2)ϪH(2)···O(2)
N(3)ϪH(3)···O(2)
N(2)ϪH(2)···O(2)
N(3)ϪH(3)···O(1)
N(5)ϪH(5)···O(4)
N(6)ϪH(6)···O(5)
O(7)ϪH(7A)···O(1) 2.640(2)
O(7)ϪH(7B)···O(8) 2.640(2)
O(8)ϪH(8A)···O(5) 2.697(3)
O(8)ϪH(8B)···N(12) 3.034(3)
2.812(3)
2.790(3)
2.982(3)
2.676(2)
2.901(2)
2.651(2)
2.831(2)
6
7
Scheme 1. Structures of the dicarboxylates used
Eur. J. Inorg. Chem. 2003, 766Ϫ776
767

A. D. Burrows, R. W. Harrington, M. F. Mahon, S. J. Teat
FULL PAPER
groups on the tmtsc ligands and the two oxygen atoms of in Table 1 and hydrogen bonding parameters are given in
the carboxylate groups serve to link the cations and anions Table 3.
together into tapes (Figure 1). These hydrogen bond donor-
The coordination geometry around the zinc centre in
donor acceptor-acceptor (DD:AA) interactions are similar compound 3a is distorted tetrahedral with the carboxylates
to those observed in [Zn(tsc)2(OH2)2][terephthalate]·2H2O[5] η1-coordinated (Figure 2, top), as observed in [Zn(thio-
and in nickel thiosemicarbazide dicarboxylates[7] [graph urea)2(µ-dicarboxylate)] polymers.[6] Coordination of the
set[10] R22(8)]. The cation···anion tapes in 2 are linked into carboxylates prevents the formation of DD:AA interac-
sheets by OϪH···O hydrogen bonds from the aqua ligands tions, although hydrogen bonding is still present, linking
in a neighbouring plane to carboxylate oxygen atoms. Since the chains through two NϪH···O interactions from the NH
the aqua ligands within each tape are all orientated in the groups to a single carboxylate oxygen atom [graph set
same direction, these OϪH···O hydrogen bonds ensure that R12(6)].
the sheets exist as bilayers, with weaker CϪH···O interac-
The presence of the lattice water molecule in compound
tions linking these bilayers into the gross structure. Similar 3b leads to differences in the manner in which the chains are
DD:AA interactions were observed between the tmtsc li- linked together (Figure 2, bottom). One of the NH groups
gands and the nitrate anions in the structure of 1. However, hydrogen bonds to a carboxylate oxygen atom, whereas the
a mismatch in both the charge and shape of the ions guar- other forms an NϪH···O hydrogen bond to the included
antees that the DD:AA interactions do not lead to tape water molecule. Two OϪH···O hydrogen bonds from the
formation in the nitrate
[Zn(tmtsc)2(OH2)2](NO3)2 units are linked only by bonding, with one of these leading to the formation of
OϪH···O hydrogen bonds.
R33(10) rings. Significant πϪπ interactions are also present,
Ϫ
instead, discrete water to carboxylate oxygen atoms complete the hydrogen
The crystal structures of compounds 3a and 3b reveal with the shortest C···C distance between isophthalate rings
˚
that, in contrast to 2, both compounds are coordination being 3.45 A. In order to accommodate the hydrogen bond-
polymers with isophthalates bridging between metal centres ing in 3b there is a change in the metal coordination geo-
(Figure 2). In both structures each zinc() centre is coordin- metry relative to that in 3a, with both carboxylate groups
ated to a tmtsc ligand and two isophthalate ligands; in 3b unsymmetrically η2-coordinated, thus affording distorted
included water molecules are also present in the lattice. Se- octahedral geometry at the metal centre. Consequently the
lected bond lengths and angles for both 3a and 3b are given longer ZnϪO distances have been reduced from 2.838(5)
Figure 1. The solid state structure of [Zn(tmtsc)2(OH2)][fumarate] (2)
768
Eur. J. Inorg. Chem. 2003, 766Ϫ776

Probing the Limits of Crystal Engineering Strategies
FULL PAPER
Figure 2. The solid state structures of (top) [Zn(tmtsc)(µ-isophthalate)] (3a) and (bottom) [Zn(tmtsc)(µ-isophthalate)]·H2O (3b)
Eur. J. Inorg. Chem. 2003, 766Ϫ776
769

A. D. Burrows, R. W. Harrington, M. F. Mahon, S. J. Teat
FULL PAPER
˚
˚
˚
and 3.071(4) A in 3a to 2.334(2) and 2.343(2) A in 3b on
incorporation of the water. The increase in coordination
number has little effect on the ZnϪS distance, but leads to
a significant increase in the ZnϪN bond length and a re-
duction of the tmtsc bite angle (Table 1).
Table 4. Selected bond lengths (A) and angles (°) for compound 4
Zn(1)ϪS(1)
Zn(1)ϪN(1)
Zn(1)ϪO(1)
Zn(1)ϪO(8)Ј
Zn(1)ϪO(7)Ј
2.3564(8)
2.169(2)
1.968(2)
2.081(2)
2.254(2)
2.3494(9)
2.163(3)
2.124(3)
2.251(2)
1.978(2)
83.48(7)
128.68(9)
83.93(7)
130.73(10)
[a]
Compound 4, incorporating the (ϩ)-camphorate dian-
ion, also exists as a coordination polymer, with the (ϩ)- Zn(2)ϪS(2)
Zn(2)ϪN(4)
camphorates linking the zinc centres. The asymmetric unit
Zn(2)ϪO(5)
of this compound contains two independent Zn(tmtsc)
Zn(2)ϪO(6)
groups and two independent (ϩ)-camphorates. Both zinc
Zn(2)ϪO(3)
centres are five-coordinate, with one carboxylate group
bound η1 and the other η2. Selected bond lengths and
angles are given in Table 4 and hydrogen bonding para-
meters are given in Table 3. The two independent (ϩ)-cam-
phorate dianions differ in that one contains two η1-carb-
oxylates whereas the other contains two η2-carboxylates.
The structure of 4 differs from those for 3a and 3b by
N(1)ϪZn(1)ϪS(1)
O(1)ϪZn(1)ϪO(8)Ј
N(4)ϪZn(2)ϪS(2)
O(3)ϪZn(2)ϪO(5)
[a]
Primed atoms generated by symmetry transformation x, y,
z Ϫ 1.
virtue of the manner in which the coordination polymers previously in the structure of cis-[Ni(4-Et-tsc)2][terephthal-
interact with each other. In 4 this is through two NϪH···O ate],[11] although in the nickel complex the cis orientation
hydrogen bonds from each of the tmtsc ligands, with the of the ligands results in the formation of a new DD face
acceptors being oxygen atoms on separate carboxylate which is involved in hydrogen bonding. This does not hap-
groups (Figure 3). One of these oxygen atoms is non-coord- pen for 4 however, and the loss of potential secondary inter-
inated [O(2) or O(4)] whereas the other forms the longer actions is compensated by the formation of four strong
ZnϪO bond of an η2-carboxylate [O(5) or O(8)]. This hy- hydrogen bonds.
drogen bonding pattern is facilitated by a change in con-
The crystal structure of compound 5 consists of
formation of the tmtsc ligand. A rotation of 180° around [{Zn(tmtsc)(OH2)}2(µ-terephthalate)]2ϩ cations, terephthal-
the CϪN(amino) bond means that the two NH groups ate anions and included water molecules. The geometry
within each ligand are no longer orientated in the same dir- around the zinc centres in 5 is distorted square pyramidal
ection. Such a conformational change has been observed (τ ϭ 0.36[9]), with the carboxylate unsymmetrically coordin-
Figure 3. The solid state structure of [Zn(tmtsc)(µ-(ϩ)camphorate)] (4), with all carbon-bound hydrogen atoms omitted for clarity
770
Eur. J. Inorg. Chem. 2003, 766Ϫ776

Probing the Limits of Crystal Engineering Strategies
FULL PAPER
ated. Selected bond lengths and angles are given in Table 5 importance of dicarboxylates in crystal engineering this is,
and hydrogen bonding parameters are given in Table 3. The to the best of our knowledge, the first occasion a structure
cation in 5 can be regarded in hydrogen bonding terms as has been observed in which the anion fulfils both discrete
an ‘‘expanded’’ [Zn(tmtsc)2]2ϩ cation, since both contain coordination and hydrogen bonding roles.
the same number and relative orientation of NH groups.
The crystal structure of compound 6 consists of discrete
The cations and anions in 5 interact through two hydrogen [Zn(tmtsc)(µ-homophthalate)]2 molecules (Figure 5), in
bonds in a similar DD:AA manner to that observed in 2, which the two zinc centres are crystallographically equiva-
which overall serves to link the ions into tapes (Figure 4). lent, related through an inversion centre. Selected bond
These tapes are connected into sheets by hydrogen bonding lengths and angles are given in Table 2, and hydrogen bond-
to water molecules, although, in contrast to 2, these involve ing parameters are given in Table 3. Each carboxylate group
both water included within the lattice and coordinated is unsymmetrically η2-coordinated, though the Zn(1)ϪO(2)
˚
water ligands from tapes above and below the sheets. Since distance is long [2.540(2) A]. This oxygen atom is involved
each cation contains two axial coordinated water molecules, in NϪH···O hydrogen bonding (see below). The distorted
pointing in opposite directions, the sheets are all linked in octahedral coordination geometry around the metal centres
the same manner, which contrasts with the bilayers ob- is similar to that observed in 3b. The dimeric structure of 6
served in 2. The structure of 5 can be regarded as interme-
diate between those of 2 and 3, as half the dicarboxylates
link the metal centres together through coordinative bonds
while the remaining half link the metal centres through hy-
drogen bonds to the coordinated tmtsc ligands. Despite the
˚
Table 5. Selected bond lengths (A) and angles (°) for compound 5
Zn(1)ϪS(1)
Zn(1)ϪN(1)
Zn(1)ϪO(3)
Zn(1)ϪO(4)
2.3036(7)
2.119(2)
2.289(2)
2.005(2)
1.993(2)
86.55(5)
60.62(8)
137.87(9)
159.58(7)
106.94(9)
90.68(8)
103.89(8)
109.56(6)
Zn(1)ϪO(5)
N(1)ϪZn(1)ϪS(1)
O(3)ϪZn(1)ϪO(4)
N(1)ϪZn(1)ϪO(4)
S(1)ϪZn(1)ϪO(3)
O(5)ϪZn(1)ϪO(4)
O(5)ϪZn(1)ϪO(3)
O(5)ϪZn(1)ϪN(1)
O(5)ϪZn(1)ϪS(1)
Figure 5. The molecular structure of [Zn(tmtsc)(µ-homophthal-
ate)]2 (6), with all carbon-bound hydrogen atoms omitted for clarity
Figure 4. The solid state structure of [{Zn(tmtsc)(OH2)}2(µ-terephthalate)][terephthalate]·2H2O (5)
Eur. J. Inorg. Chem. 2003, 766Ϫ776
771

A. D. Burrows, R. W. Harrington, M. F. Mahon, S. J. Teat
FULL PAPER
is similar to that previously observed in [Zn{SC(NH2)2}2(µ- atom O(2), in an analogous manner to 3a [graph set R12(6)].
[6]
homophthalate)]2
strongly suggesting that dimer forma- Each molecule provides hydrogen bond donors in one di-
tion is driven by the relative orientation of the carboxylate mension and hydrogen bond acceptors in a second, as
groups in the homophthalate dianion. In contrast to 6, shown schematically in Figure 6 (top). These interactions
[Zn{SC(NH2)2}2(µ-homophthalate)]2 contains η1-coordin- therefore serve to link the molecules into sheets (Figure 6,
ated carboxylate groups, with non-bonded ZnϪO distances bottom). Despite the presence of carboxylate oxygen atoms
˚
of 2.86(3) and 3.05(3) A. The distances across the ring in 6, which are not involved in hydrogen bonding, there are no
as represented by the O(2)···O(2)Ј and O(3)···O(3)Ј separa- hydrogen bond interactions linking the sheets together.
˚
tions, are 5.9 and 3.9 A respectively, hence the dimers are
The reaction between [Zn(tmtsc)2](NO3)2 and acetylene-
somewhat flattened relative to those present in dicarboxylate does not give a compound in which the dicarb-
˚
[Zn{SC(NH2)2}2(µ-homophthalate)]2 (O···O 5.3 and 4.9 A). oxylate is incorporated, either as a ligand or as a hydrogen
Molecules of 6 are linked in the solid state through two bonded anion. Instead, a reaction (Scheme 2) between ace-
NϪH···O hydrogen bonds to a single carboxylate oxygen tylenedicarboxylate and a tmtsc molecule occurs to give a
Figure 6. Intermolecular interactions present in [Zn(tmtsc)(µ-homophthalate)]2 (6); (top) schematic representation of hydrogen bonded
sheets; (bottom) part of the extended structure, with all carbon-bound hydrogen atoms omitted for clarity
772
Eur. J. Inorg. Chem. 2003, 766Ϫ776

Probing the Limits of Crystal Engineering Strategies
FULL PAPER
ucts ranging from coordination polymers (3a, 3b, 4) to hy-
drogen-bonded ionic aggregates (2) via an intermediate
structure (5) in which half the anions are coordinated. This
diversity confirms the initial premise concerning the lability
of tmtsc lying between those of tsc and thiourea. The metal
coordination number varies from 4 to 6, and is not a major
factor in determining the supramolecular structure Ϫ this
is witnessed by the zinc centres in the coordination poly-
mers 3a, 3b and 4 having coordination numbers of 4, 6 and
5 respectively. The products observed are also not affected
by changes in the stoichiometry of [Zn(tmtsc)2](NO3)2 and
dicarboxylate used in the reaction, nor do differences ap-
pear to be related to the basicity of the dicarboxylates or
the pH of the reaction mixture. However, it is possible to
rationalise the structural differences on the basis of the di-
carboxylate shape, specifically the relative orientation of the
two carboxylate groups.
Yaghi, OЈKeeffe and co-workers have recently described
the geometry of dicarboxylates in terms of three angles, θ,
ψ and ϕ, and used these angular parameters to help in the
design and preparation of porous metal-organic frame-
works with predictable structures.[13] Starting from the
planar terephthalate anion, θ represents bending in the
centre of the anion with the two carboxylates remaining co-
planar, ψ represents bending of the carboxylates towards
each other, and ϕ represents the relative twisting of the
planes of the carboxylate groups. For terephthalate and fu-
marate in the structures of 5 and 2, θ and ψ are 180° and
ϕ is close to zero, as the carboxylate groups are almost co-
planar and orientated in opposite directions. These com-
pounds consist of ionic structures based on cation···anion
tapes, held together by DD:AA hydrogen bond interactions.
This is consistent with previous structures containing these
anions,[5,7] though the formation of 5, in which half of the
terephthalates are coordinated giving ‘‘extended’’
[{Zn(tmtsc)(OH2)}2(µ-terephthalate)]2ϩ cations is some-
what unexpected, as the nickel compound [Ni(tmtsc)2-
(OH2)2][terephthalate] readily forms in a comparative reac-
tion. The presence of the extended cation in 5 does prevent
unfavourable interactions between the methyl groups on
neighbouring tapes that would occur if simple
[Zn(tmtsc)2]2ϩ cations were incorporated in the orientation
Scheme 2. Conversion of 1,1,4-trimethylthiosemicarbazide into the
anion observed in compound 7
2-hydrazono-4-oxo-1,3-thiazolidineacetate, which is itself
incorporated into the structure as the anion. Thus the iden-
tity of 7, as determined by the crystal structure, is
[Zn(tmtsc)2(OH2)][O2CCHϭCC(O)N(Me)C(ϭ
NNMe2)S]2·H2O (Figure 7). The [Zn(tmtsc)2(OH2)]2ϩ cat-
ion has a distorted square pyramidal geometry (τ ϭ 0.41[9])
with the tmtsc ligands mutually trans as in 2 and 5. Selected
bond lengths and angles are given in Table 2, with hydrogen
bond parameters given in Table 3. Reactions between
thiosemicarbazides and acetylenedicarboxylic acid giving
similar products have been reported previously,[12] and the
observation of such a reaction here provides evidence of the
lability of the tmtsc ligand on zinc, as is also evident from
the structures of 3؊6.
The heterocyclic anion contains a carboxylate group, and
these oxygen atoms are involved in DD:AA hydrogen bonds
with the parallel NH groups of the tmtsc ligands. Thus the
principal hydrogen bonding motif in 7 is the same as that
in both 2 and 5. However, the presence of only one carb-
oxylate group per anion means that extended cation···anion
tapes cannot be formed, and instead the available interac-
tions afford only [cation][anion]2 units as observed for 1.
These units are linked together into the gross structure of 7
via hydrogen bonds involving the coordinated and included
water molecules, where the former acts as a hydrogen bond
donor to both a carboxylate oxygen atom and the included
water, and the latter acts as a hydrogen bond donor to a
carboxylate oxygen atom and a nitrogen atom.
Discussion
Compounds 2؊7 were all isolated in good yield as
the sole products from the reactions between
[Zn(tmtsc)2](NO3)2 and a dicarboxylate under identical
conditions. There is a wide structural diversity in the prod-
Figure 7. Part of the solid state structure of [Zn(tmtsc)2(OH2)][O2CCHϭCC(O)N(Me)C(ϭNNMe2)S]2]·H2O (7)
Eur. J. Inorg. Chem. 2003, 766Ϫ776
773

A. D. Burrows, R. W. Harrington, M. F. Mahon, S. J. Teat
FULL PAPER
adopted. Despite possessing the same angular parameters, placed from [Zn{SC(NH2)2}4]2ϩ leading to coordination
terephthalate and fumarate differ in the distance between polymers or cyclic oligomers, all containing tetrahedral zinc
the carboxylate groups and the fact that for fumarate these centres, whereas thiosemicarbazide is generally retained on
are not co-linear, there being a lateral displacement of the metal leading to structures in which the ions are only
˚
1.07 A.
associated through hydrogen bonds. The tmtsc ligand lies
While isophthalate and camphorate are structurally very between these two extremes confirming our initial premise
different, it is noteworthy that each possesses one of the concerning its lability, and this places [Zn(tmtsc)2]2ϩ on the
angular parameters Ϫ θ for isophthalate and ϕ for cam- borderline between the two main strategies currently em-
phorate Ϫ that has been reduced from the 180° value for ployed in crystal engineering. These observations are im-
terephthalate to 120°, and both of these dicarboxylates portant in helping to define the limits of the different crys-
form coordination polymers with Zn(tmtsc) centres. While tal engineering strategies.
the carboxylate orientations in 3a, 3b and 4 do not preclude
hydrogen bonded structures, they may reduce their likeli-
hood since there are more limited ways in which the result-
ant zig-zag tapes would be able to pack.
The structures of 6 and [Zn{SC(NH2)2}2(µ-homophthal-
Experimental Section
ate)]2 reflect a clear propensity for homophthalate to form
dimers, despite the dicarboxylates in these complexes
adopting different coordination modes. In the
[Zn{SC(NH2)2}2]2ϩ system this tendency is particularly
marked since homophthalate is the only dicarboxylate out
of 13 structurally characterised compounds not to form a
coordination polymer. A search of the CSD[14] reveals no
examples of homophthalate coordination polymers, and it
is noticeable that dimerisation of Mo2 units has also been
observed with this dicarboxylate.[15]
Microanalyses were carried out by Mr. Alan Carver (University
of Bath Microanalytical Service). 1,1,4-Trimethylthiosemicarbazide
(tmtsc) was prepared from the reaction of N,N-dimethylhydrazine
with methyl isothiocyanate in diethyl ether.[16] Sodium dicarb-
oxylates were either purchased from commercial sources and used
directly (fumarate and terephthalate) or prepared from the appro-
priate dicarboxylic acid and either sodium hydroxide or sodium
hydrogen carbonate.
Synthesis of [Zn(tmtsc)2](NO3)2: 1,1,4-Trimethylthiosemicarbazide
(0.448 g, 3.36 mmol) in ethanol (10 cm3) was added to zinc nitrate
hexahydrate (0.500 g, 1.68 mmol) in ethanol (10 cm3) and the solu-
tion stirred for 1 h. The volume of the solution was reduced to 5
cm3 in vacuo, and the colourless crystals that precipitated overnight
were separated by filtration. Yield 0.75 g (98%). On recrystallis-
ation from water, crystals of [Zn(tmtsc)2(OH2)2](NO3)2 (1) were ob-
tained.
The reaction between [Zn(tmtsc)2](NO3)2 and acetylene-
dicarboxylate gave an unexpected product in 7. The coup-
ling reaction between tmtsc and acetylenedicarboxylate has
generated
a
2-hydrazono-4-oxo-1,3-thiazolidineacetate
anion, and the structure of 7 illustrates the potential for
trapping reaction products in hydrogen bonded networks
through the use of species containing complementary hy-
drogen bonding groups.
Synthesis of 2: Aqueous solutions of sodium fumarate (35 mg,
0.22 mmol) and [Zn(tmtsc)2](NO3)2 (100 mg, 0.22 mmol) were
mixed. After approximately 24 hours colourless crystals formed,
and these were isolated by filtration. Yield 80 mg (79%).
C12H26N6O5S2Zn (463.9): calcd. C 31.1, N 18.1, H 5.65; found C
31.3, N 18.1, H 5.71.
Four of the seven carboxylate-containing structures re-
ported in this paper contain water, either as a ligand (2),
included in the lattice (3b), or both (5 and 7). The tmtsc
ligand has only two hydrogen bond donors whereas a carb-
oxylate group can accept four or even more hydrogen
bonds. Therefore use of tmtsc as a ligand in these systems
leads to a relative deficiency of hydrogen bond donors in
the gross structure which can be overcome by inclusion of
water. This solvent inclusion also affords greater flexibility
in the relative orientations of hydrogen bonding groups.
Synthesis of 3a and 3b: As for 2 using sodium isophthalate (53 mg,
0.25 mmol) and [Zn(tmtsc)2](NO3)2 (115 mg, 0.25 mmol). Yield
81 mg (88%). C12H15N3O4SZn (362.7): calcd. C 39.7, N 11.6, H
4.17; found C 39.6, N 11.5, H 4.22
Synthesis of 4: As for 2 using sodium (1R,3S)-(ϩ)-camphorate
(54 mg, 0.22 mmol) and [Zn(tmtsc)2](NO3)2 (100 mg, 0.22 mmol).
Yield 56 mg (64%). C14H25N3O4SZn (396.8) calcd. C 42.4, N 10.6,
H 6.35; found C 42.1, N 10.6, H 6.28.
Synthesis of 5: As for 2 using sodium terephthalate (46 mg,
0.22 mmol) and [Zn(tmtsc)2](NO3)2 (100 mg, 0.22 mmol). Yield
63 mg (72%). C24H38N6O12S2Zn2 (797.5): calcd. C 36.2, N 10.5, H
4.80; found C 36.5, N 10.4, H 4.79.
Conclusions
In this paper we have demonstrated that a deceptively
simple series of compounds Ϫ those resulting from the reac-
tion between [Zn(tmtsc)2]2ϩ and a dicarboxylate Ϫ have
widely differing structures, with the relative orientation of
the carboxylate groups a major factor in determining the
type of structure formed. The variety of structural types
obtained from this reaction series contrasts with the prod-
ucts observed from analogous reactions using thiourea or
Synthesis of 6: As for 2 using sodium homophthalate (49 mg,
0.22 mmol) and [Zn(tmtsc)2](NO3)2 (100 mg, 0.22 mmol). Yield
59 mg (71%). C26H34N6O8S2Zn2 (753.5): calcd. C 41.5, N 11.2, H
4.55; found C 41.2, N 10.9, H 4.48.
Synthesis of 7: As for 2 using sodium acetylenedicarboxylate
(35 mg, 0.22 mmol) and [Zn(tmtsc)2](NO3)2 (100 mg, 0.22 mmol).
thiosemicarbazide complexes. Thiourea is invariably dis- Yellow crystals. Yield 74 mg (82% based on tmtsc).
774 Eur. J. Inorg. Chem. 2003, 766Ϫ776

Probing the Limits of Crystal Engineering Strategies
FULL PAPER
Table 6. Crystallographic data for complexes 1, 2, 3a, 3b, 4, 5, 6 and 7
1
2
3a
3b
4
5
6
7
Formula
Mr
T / K
C8H26N8O8S2Zn
491.86
170(2)
C12H26N6O5S2Zn C12H15N3O4SZn
C12H17N3O5SZn
380.72
293(2)
C14H25N3O4SZn
396.80
100(2)
C12H19N3O6SZn
398.73
293(2)
C13H17N3O4SZn
376.73
150(2)
C24H46N12O8S4Zn
824.34
293(2)
463.88
293(2)
362.70
150(2)
Crystal size/mm 0.25 ϫ 0.15 ϫ 0.15 0.30 ϫ 0.20 ϫ 0.20 0.05 ϫ 0.04 ϫ 0.02 0.17 ϫ 0.15 ϫ 0.15 0.30 ϫ 0.13 ϫ 0.10 0.20 ϫ 0.20 ϫ 0.20 0.30 ϫ 0.13 ϫ 0.10 0.23 ϫ 0.20 ϫ 0.20
Crystal system
Space group
monoclinic
P21/c
9.6360(3)
12.4200(4)
9.8170(3)
90
118.4370(16)
90
1033.13(6)
2
triclinic
¯
P1
orthorhombic
Pna21
15.716(2)
11.792(2)
7.603(1)
90
90
90
1409.0(3)
4
monoclinic
P21/c
8.488(1)
14.444(2)
13.675(2)
90
104.92(1)
90
1620.0(4)
4
monoclinic
C2
26.6250(4)
7.5350(1)
18.6840(4)
90
103.7490(7)
90
3640.97(11)
8
triclinic
¯
P1
monoclinic
P21/c
9.6890(2)
12.2920(3)
13.2240(3)
90
94.835(1)
90
1569.34(6)
4
triclinic
¯
P1
˚
a/ A
8.122(1)
8.364(1)
16.247(6)
97.11(2)
101.98(1)
103.200(9)
1034.0(4)
2
7.397(1)
9.384(1)
12.085(2)
98.90(1)
90.80(2)
99.40(1)
817.0(2)
2
9.623(2)
11.844(2)
17.848(5)
102.56(1)
102.69(1)
92.467(10)
1928.2(7)
2
˚
b/ A
˚
c/ A
α/°
β/°
γ /°
˚
U/ A
Z
dcalcd./g cmϪ3
µ/mmϪ1
θmin, θmax
Reflections
collected
Independent
reflections
Rint
1.555
1.442
2.91, 27.49
12570
1.490
1.423
2.54, 24.97
4023
1.710
1.910
2.10, 29.33
13734
1.561
1.670
2.09, 24.98
3201
1.448
1.485
3.59, 27.49
27784
1.621
1.664
2.23, 24.98
3229
1.594
1.718
3.59, 27.48
37834
1.420
0.912
2.18, 24.97
7485
2369
3618
3894
2840
8071
2857
3580
6764
0.0385
0.0117
257, 6
0.1073
189, 3
0.0167
219, 0
0.0430
447, 5
0.0119
235, 6
0.0959
210, 2
0.0095
486, 8
No. parameters, 144, 5
restraints
Final R1, wR2
[I Ͼ 2σ(I)]
R1, wR2 (all data) 0.0368, 0.1056
0.0287, 0.0955
0.0280, 0.0736
0.0346, 0.0764
0.0667, 0.1473
0.0852, 0.1530
0.0298, 0.0747
0.0423, 0.0781
0.0375, 0.0842
0.0468, 0.0884
0.0272, 0.0841
0.0363, 0.0899
0.0332, 0.0893
0.0476, 0.1018
0.0312, 0.0850
0.0409, 0.0894
[1]
[2]
C24H46N12O8S4Zn (824.3): calcd. C 35.0, N 20.4, H 5.62; found C
34.7, N 20.1, H 5.59.
V. R. Thalladi, B. S. Goud, V. J. Hoy, F. H. Allen, J. A. K.
Howard, G. R. Desiraju, Chem. Commun. 1996, 401Ϫ402.
R. Robson, J. Chem. Soc., Dalton Trans. 2000, 3735Ϫ3744; B.
Moulton, M. J. Zaworotko, Chem. Rev. 2001, 101, 1629Ϫ1658;
A. J. Blake, N. R. Champness, P. Hubberstey, W. S. Li, M. A.
Withersby, M. Schröder, Coord. Chem. Rev. 1999, 183,
117Ϫ138; M. Eddaoudi, D. B. Moler, H. Li, B. Chen, T. M.
Reineke, M. OЈKeeffe, O. M. Yaghi, Acc. Chem. Res. 2001, 34,
319Ϫ330; O. R. Evans, W. Lin, Chem. Mater. 2001, 13,
2705Ϫ2712; M.-L. Tong, S.-L. Zheng, X.-M. Chen, Chem.
Commun. 1999, 561Ϫ562.
V. A. Russell, C. C. Evans, W. Li, M. D. Ward, Science 1997,
276, 575Ϫ579; D. G. Kurth, K. M. Fromm, J.-M. Lehn, Eur.
J. Inorg. Chem. 2001, 1523Ϫ1526; D. Braga, L. Maini, F. Pa-
ganelli, E. Tagliavini, S. Casolari, F. Grepioni, J. Organomet.
Chem. 2001, 637, 609Ϫ615; S. B. Copp, K. T. Holman, J. O. S.
Sangster, S. Subramanian, M. J. Zaworotko, J. Chem. Soc., Dal-
ton Trans. 1995, 2233Ϫ2243; A. D. Burrows, C.-W. Chan, M.
M. Chowdhry, J. E. McGrady, D. M. P. Mingos, Chem. Soc.
Rev. 1995, 24, 329Ϫ339; G. R. Desiraju, Chem. Commun.
1997, 1475Ϫ1482.
C. B. Aakeröy, A. M. Beatty, K. R. Lorimer, J. Chem. Soc.,
Dalton Trans. 2000, 3869Ϫ3872; T. J. Prior, M. J. Rosseinsky,
Chem. Commun. 2001, 1222Ϫ1223.
A. D. Burrows, S. Menzer, D. M. P. Mingos, A. J. P. White, D.
J. Williams, J. Chem. Soc., Dalton Trans. 1997, 4237Ϫ4240.
A. D. Burrows, R. W. Harrington, M. F. Mahon, C. E. Price,
J. Chem. Soc., Dalton Trans. 2000, 3845Ϫ3854.
A. D. Burrows, D. M. P. Mingos, A. J. P. White, D. J. Williams,
Chem. Commun. 1996, 97Ϫ99; M. T. Allen, A. D. Burrows, M.
F. Mahon, J. Chem. Soc., Dalton Trans. 1999, 215Ϫ221.
A. D. Burrows, M. D. Coleman, M. F. Mahon, Polyhedron
1999, 18, 2665Ϫ2671.
A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn, G. C. Ver-
schoor, J. Chem. Soc., Dalton Trans. 1984, 1349Ϫ1356.
J. Bernstein, R. E. Davis, L. Shimoni, N.-L. Chang, Angew.
Chem. Int. Ed. Engl. 1995, 34, 1555Ϫ1573, Angew. Chem. 1995,
107, 1687Ϫ1706.
The syntheses of 2؊7 were repeated on a smaller scale in more
dilute solutions in order to obtain crystals of suitable quality for
the single-crystal X-ray analyses.
For compounds 2, 3b, 5 and 7, data were collected on an
EnrafϪNonius CAD4 automatic four-circle diffractometer and for
compounds 1, 4 and 6 data were collected on a Nonius Kappa
CCD diffractometer, in all cases using Mo-Kα radiation (graphite
[3]
˚
monochromated) with λ ϭ 0.71069 A for 2, 3b, 5 and 7 and 0.71070
˚
A for 1, 4 and 6. Due to small crystal size, data for compound 3a
were collected at Station 9.8 at the SRS, Daresbury using synchro-
˚
tron radiation (silicon 111 monochromated) with λ ϭ 0.68980 A.
Crystallographic data are presented in Table 6. Lorentz and polar-
isation corrections were applied in all analyses and extinction co-
efficients were applied for compounds 2, 3a, 3b and 4. Absorption
corrections (SORTAV[17]) were applied to the data for 1, 4 and 6.
The structures were solved by direct methods (SHELXS-86[18] or
SHELXS-97) with full-matrix least-squares (SHELXL-97[19]) re-
finement based on F2. Non-hydrogen atoms were treated aniso-
tropically. Hydrogen atoms were refined in calculated positions
where relevant on carbon atoms, whereas the NH and OH hydro-
[4]
[5]
[6]
[7]
˚
gen atoms were located and refined at a fixed distance of 0.89 A
from the parent atom throughout. CCDC 191738Ϫ191745 contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)
ϩ44Ϫ1223/336Ϫ033; Email: deposit@ccdc.cam.ac.uk].
[8]
[9]
[10]
Acknowledgments
The EPSRC is thanked for financial support.
Eur. J. Inorg. Chem. 2003, 766Ϫ776
775

A. D. Burrows, R. W. Harrington, M. F. Mahon, S. J. Teat
FULL PAPER
[11]
[16]
[17]
A. D. Burrows, R. W. Harrington, M. F. Mahon, Cryst-
K. A. Jensen, U. Anthoni, B. Kägi, C. Larsen, C. T. Pedersen,
Acta Chem. Scand. 1968, 22, 1.
EngComm 2000, 12.
V. Y. K a u s s, E . E. Liepin’sh, I. Y. Kalvin’sh, E. Lukevits, Chem.
Heterocycl. Compd. 1990, 103.
M. Eddaoudi, J. Kim, D. Vodak, A. Sudik, J. Wachter, M.
OЈKeeffe, O. M. Yaghi, Proc. Natl. Acad. Sci. USA 2002, 99,
4900Ϫ4904.
F. H. Allen, O. Kennard, Chem. Des. Automat. News 1993, 8,
31Ϫ37.
F. A. Cotton, C. Lin, C. A. Murillo, Inorg. Chem. 2001, 40,
472Ϫ477.
[12]
´
´
´
R. H. Blessing, Acta Crystallogr., Sect. A 1995, 51, 33Ϫ38; R.
H. Blessing, J. Appl. Crystallogr. 1997, 30, 421Ϫ426.
G. M. Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467Ϫ473.
G. M. Sheldrick, SHELXL-97, Computer Program for Crystal
Structure Refinement, University of Göttingen, 1997.
Received August 15, 2002
[13]
[18]
[19]
[14]
[15]
[I02462]
776
Eur. J. Inorg. Chem. 2003, 766Ϫ776