The complexing properties of the phenylsquarate ligand with Ru(II), Pt(II), Gd(III) and Tb(III) ions

Article abstract of DOI:10.1016/S0020-1693(00)00391-1

Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with Ru(dmso)₄Cl₂ in acetonitrile afforded crystals of the monomeric species Ru(dmso)₃Cl(H₂O)(C₆H₅ C₄O₃)·H₂O (1) in which the ruthenium is in a slightly distorted octahedral geometry with three fac S-bonded dmso ligands. No complexation occurs when Pt(NH₃)₄Cl₂ is reacted with the same ligand in aqueous solution; instead, the hydrogen-bonded salt [Pt(NH₃)₄][C₆H₅C₄ O₃]₂·H₂O (2) is produced. The isomorphous complexes {[M(μ-C₆H₅C₄O₃)(C₆ H₅C₄O₃)₂ (H₂O)₄]·H₂O}_n [M = Tb (3), Gd (4)] formed by the reaction of the phenylsquarate ligand with the respective metal nitrate contain eight-coordinate metal centres surrounded by two μ-1,3-bridged and two pendant phenylsquarate ligands and four aqua ligands. In the solid state, 3 and 4 form interleaved π-stacked and hydrogen-bonded sheets with pronounced hydrophobic and hydrophilic surfaces. In compounds 1-4, the phenylsquarate ligands participate in π-π interactions and exhibit multiple bond localisation, the pattern of bonding being the same in each structure.

Full text of DOI:10.1016/S0020-1693(00)00391-1

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Inorganica Chimica Acta 314 (2001) 117–125
The complexing properties of the phenylsquarate ligand with
Ru(II), Pt(II), Gd(III) and Tb(III) ions
Avril R. Williams a, Lincoln A. Hall a,*1, Andrew J.P. White b, David J. Williams b,*2
a Department of Chemistry, The Uni6ersity of the West Indies, St. Augustine, Trinidad and Tobago, West Indies
b Chemical Crystallography Laboratory, Department of Chemistry, Imperial College of Science, Technology and Medicine,
London, SW7 2AY, UK
Received 11 August 2000; accepted 24 November 2000
Abstract
Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with Ru(dmso)4Cl2 in acetonitrile afforded crystals of
the monomeric species Ru(dmso)3Cl(H2O)(C6H5C4O3)·H2O (1) in which the ruthenium is in a slightly distorted octahedral
geometry with three fac S-bonded dmso ligands. No complexation occurs when Pt(NH3)4Cl2 is reacted with the same ligand in
aqueous solution; instead, the hydrogen-bonded salt [Pt(NH3)4][C6H5C4O3]2·H2O (2) is produced. The isomorphous complexes
{[M(m-C6H5C4O3)(C6H5C4O3)2(H2O)4]·H2O}n [M=Tb (3), Gd (4)] formed by the reaction of the phenylsquarate ligand with the
respective metal nitrate contain eight-coordinate metal centres surrounded by two m-1,3-bridged and two pendant phenylsquarate
ligands and four aqua ligands. In the solid state, 3 and 4 form interleaved p-stacked and hydrogen-bonded sheets with pronounced
hydrophobic and hydrophilic surfaces. In compounds 1–4, the phenylsquarate ligands participate in p–p interactions and exhibit
multiple bond localisation, the pattern of bonding being the same in each structure. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Phenylsquarate; Crystal structures; Transition metal and lanthanide complexes; Polymeric complexes
1. Introduction
Ruthenium was selected because of the potential for
any polymeric ruthenium(II) complex to undergo par-
tial oxidation to produce an Ru(II)/Ru(III) species
[8–10], which should, in turn, have an enhanced poten-
tial for exhibiting conductivity. In view of its ease of
synthesis and stability, we selected RuCl2(dmso)4 as a
starting material; it also has the additional advantage
that the resulting product(s) should also contain ruthe-
nium–sulfoxide and ruthenium–halogen bonds, a char-
acteristic of several antitumour agents [11–15].
Similarly, it is well documented that platinum(II) in-
variably adopts a square planar geometry, which, if
present in a polymeric complex containing appropri-
ately bridged monosubstituted squarate ligands, should
facilitate extended delocalisation along the polymer
chain and confer an enhanced potential for conductiv-
ity. Additionally, partially oxidised platinum(II) com-
pounds also have the potential for exhibiting
one-dimensional conductivity [16]. We also wanted to
compare the coordination modes observed for the
phenylsquarate ligand with first-row transition metals
After our successful synthesis and structural charac-
terisation of several complexes of first-row transition
and lanthanide metals with monosubstituted squarate
ligands [1,2], we decided to focus our attention on the
complexing properties of these ligands with second- and
third-row transition metals. We were further prompted
by the knowledge that, in spite of the enormous
amount of research conducted on first-row transition
and lanthanide metal complexes of the unsubstituted
squarate ion, only a few second- and third-row com-
plexes have been reported [3–7]. A possible reason for
this paucity of complexes could be the low solubility of
squaric acid and its complexes in non-polar organic
solvents, a problem that we believed could be overcome
by the use of monosubstituted squarate ligands.
1 *Corresponding author. Tel.: +1-868-662-2002; fax: +1-868-
645-3771; e-mail: halllincoln@netscape.net
2 *Corresponding author.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(00)00391-1

118
A.R. Williams et al. / Inorganica Chimica Acta 314 (2001) 117–125
and lanthanides [1g,2] with, for example, representative
second- (Ru) and third-row (Pt) transition metals.
2.3.4. {[Gd(v-C6H5C4O3)(C6H5C4O3)2(H2O)4]·H2O}n
(4)
The procedure is identical to that for the preparation
of
3 except that Gd(NO3)·5H2O (0.25 g, 5.8×
10−4 mol) was used.
2. Experimental
Yellow plates. Yield, 0.18 g (40%). Anal. Found: C,
47.2; H, 3.3; Gd, 19.2. Calc. for C30H25GdO14: C, 47.0;
H, 3.3; Gd, 20.5%.
2.1. Preparation of the ligand
The 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione was
prepared according to the method of Liebeskind et al.
[17].
2.4. Elemental analyses
C, H, N, S and metal analyses were done by
MEDAC Limited, Brunel Science Centre, Egham, Sur-
rey, UK.
2.2. Preparation of Ru(dmso)4Cl2 and [Pt(NH3)4]Cl2
2.5. Crystallographic analyses
Ru(dmso)4Cl2 was prepared according to the method
of Evans et al. [18], and [Pt(NH3)4]Cl2 was prepared
according to the method of Keller [19].
2.5.1. Crystal data for 1
C16H25O7S3ClRu·H2O, M=580.1, monoclinic, space
group P21/n (no. 14), a=10.833(1), b=13.747(1), c=
3
2.3. Preparation of the metal complexes
,
,
15.866(1) A, i=109.19(1)°, V=2231.3(2) A , Z=4,
Dc=1.727 g cm−3, v(Mo Ka)=11.4 cm−1, F(000)=
1184, T=105 K; yellow needles, 0.25×0.10×
0.10 mm3, Nonius CAD-4 diffractometer, ꢀ-scans,
6479 independent reflections. The structure was solved
by direct methods and the non-hydrogen atoms were
refined anisotropically using full-matrix least-squares
based on F2 to give R1=0.036, wR2=0.081 for 5464
independent observed absorption-corrected reflections
[ꢀFoꢀ\4|(ꢀFoꢀ), 2q560°] and 266 parameters. CCDC
156538.
2.3.1. Ru(dmso)3Cl(H2O)(C6H5C4O3)·H2O (1)
60 ml of a solution of Ru(dmso)4Cl2 (0.28 g, 5.8×
10−4 mol) in acetonitrile was added to 30 ml of a
solution of phenylsquarate (0.10 g, 5.8×10−4 mol) in
the same solvent. The mixture was then filtered and left
to evaporate slowly at approximately 28°C until crys-
tallisation was complete.
Yellow plates. Yield, 0.029 g (8.82%). Anal. Found:
C, 32.2; H, 4.7; Cl, 7.3; Ru, 18.4; S, 16.3. Calc. for
C16H27ClO8RuS3: C, 33.1; H, 4.7; Cl, 6.1; Ru, 17.4; S,
16.6%.
2.5.2. Crystal data for 2
C20H24N4O7Pt, M=627.5, triclinic, space group P1
(no. 2), a=7.099(1), b=8.708(1), c=17.660(2) A, h=
(
,
2.3.2. [Pt(NH3)4][C6H5C4O3]2·H2O (2)
3
,
90.47(1), i=93.18(1), k=90.20(1)°, V=1090.1(2) A ,
40 ml of a solution of [Pt(NH3)4]Cl2 (0.19 g, 5.8×
10−4 mol) in acetonitrile was mixed with a similar
volume of a solution of phenylsquarate (0.10 g, 5.8×
10−4 mol) in the same solvent. The filtered mixture was
allowed to stand at approximately 28°C until crystalli-
sation was complete.
Orange blocks. Yield, 0.028 g (7.82%). Anal. Found:
C, 38.0; H, 3.8; N, 8.8; Pt, 31.0. Calc. for
C20H24N4O7Pt: C, 38.3; H, 3.9; N, 8.9; Pt, 31.1%.
Z=2, Dc=1.912 g cm−3 v(Mo Ka)=64.9 cm−1
,
,
F(000)=612, T=293 K; yellow prisms, 0.27×0.23×
0.10 mm3, Siemens P4/PC diffractometer, ꢀ-scans, 3861
independent reflections. The structure was solved by
direct methods and the non-hydrogen atoms were
refined anisotropically using full-matrix least-squares
based on F2 to give R1=0.032, wR2=0.072 for 3475
independent observed absorption-corrected reflections
[ꢀFoꢀ\4|(ꢀFoꢀ), 2q550°] and 306 parameters. CCDC
156539.
2.3.3. {[Tb(v-C6H5C4O3)(C6H5C4O3)2(H2O)4]·H2O}n
(3)
2.5.3. Crystal data for 3
20 ml of an aqueous solution of Tb(NO3)·5H2O
(0.26 g, 5.8×10−4 mol) was added to an equal volume
of an aqueous solution of phenylsquarate (0.10 g, 5.8×
10−4 mol). The filtered mixture was allowed to stand at
approximately 28°C until crystallisation was complete.
Yellow plates. Yield, 0.19 g (40%). Anal. Found: C,
47.2; H, 3.3; Tb, 20.1. Calc. for C30H25O14Tb: C, 46.9;
H, 3.3; Tb, 20.7%.
C30H23O13Tb·H2O, M=768.4, triclinic, space group
(
,
P1 (no. 2), a=8.228(1), b=9.861(1), c=19.282(2) A,
h=94.38(1),
i=92.92(1),
k=104.84(1)°,
V=
1503.8(3) A , Z=2, Dc=1.697 g cm−3, v(Cu Ka)=
121.9 cm−1, F(000)=764, T=293 K; yellow scythes,
0.27×0.27×0.05 mm3, Siemens P4/RA diffractometer,
ꢀ-scans, 4734 independent reflections. The structure
was solved by the heavy atom method and the non-hy-
3
,

A.R. Williams et al. / Inorganica Chimica Acta 314 (2001) 117–125
119
,
Fig. 1. The molecular structure of [Ru(dmso)3Cl(C6H5C4O3)(H2O)]·H2O (1). The hydrogen bonding geometries are, O···O, H···O (A), OꢀH···O (°):
(a) 2.71, 1.83, 164; (b) 2.70, 1.81, 167.
drogen atoms were refined anisotropically using full-
matrix least-squares based on F2 to give R1=0.040,
wR2=0.098 for 4298 independent observed absorption-
corrected reflections [ꢀFoꢀ\4|(ꢀFoꢀ), 2q5124°] and 437
parameters. CCDC 156540.
The conformation of the complex is stabilised by an
intramolecular OꢀH···O hydrogen bond between one of
the hydrogen atoms on the aqua ligand and the ketonic
oxygen O(2). The other aqua hydrogen atom links to
the included solvent water molecule [O(50)], which in
turn forms hydrogen bonds to the other ketonic oxygen
atom O(3) and the Cl ligand of symmetry-related
monomers to form extended two-dimensional sheets
3. Results and discussion
,
[O···O, H···O; 2.85, 2.00 A, OꢀH···O 157°; O···Cl, H···Cl
3.37, 2.51 A, OꢀH···Cl 160°]. Within these sheets, Ci-re-
3.1. Ru(dmso)3Cl(H2O)(C6H5C4O3)·H2O (1)
,
lated phenylsquarate ligands are arranged in face-to-
face, head-to-tail pairs (Fig. 2) with a mean interplanar
separation of 3.64 A. This geometry is the same as that
observed between the pendant ligands in the polymeric
europium(III) phenylsquarate complex [1g]. Adjacent
The product of the reaction between Ru(dmso)4Cl2
and phenylsquarate was shown by single-crystal X-ray
analysis to be Ru(dmso)3Cl(C6H5C4O3)(H2O)·H2O (1)
(Fig. 1). The coordination at ruthenium is slightly
distorted octahedral with three fac S-bonded dmso
ligands. The RuꢀS distances are in the range 2.246(1) to
,
Table 1
,
2.265(1) A, the longest bond being that trans to Cl; the
,
Selected bond lengths (A) and angles (°) for Ru(dmso)3Cl(H2O)-
two RuꢀO distances are essentially the same (Table 1).
(C6H5C4O3)·H2O (1)
The RuꢀS distances are comparable to those in, for
example,
cis,fac-RuCl2(dmso)3(NH3)
[12]
and
RuꢀCl
RuꢀS(2)
RuꢀO(1)
O(1)ꢀC(1)
O(3)ꢀC(3)
C(1)ꢀC(2)
C(3)ꢀC(4)
2.422(1)
2.265(1)
2.141(2)
1.254(3)
1.219(3)
1.507(4)
1.448(4)
RuꢀS(1)
RuꢀS(3)
RuꢀO(40)
O(2)ꢀC(2)
C(4)ꢀC(10)
C(2)ꢀC(3)
C(1)ꢀC(4)
2.247(1)
2.246(1)
2.135(2)
1.216(3)
1.461(3)
1.527(4)
1.432(3)
cis,cis,cis-RuCl2(dmso)2(py)(Me3Bzm) [py=pyridine;
Me3Bzm=1,5,6-trimethylbenzimidazole) [14]. The pat-
tern of bonding in the C4-ring of the phenylsquarate
ligand shows the usual pattern [1,2] of two short and
,
two long CꢀC bonds [D(CꢀC):0.08 A], the short
bonds being those adjacent to the phenyl substituent.
The C4-cycle and the phenyl ring are nearly coplanar,
the torsional twist about the C(4)ꢀC(10) bond being
approximately 11°, a geometry that enhances conjuga-
tion between the two ring systems, as evidenced by the
O(40)ꢀRuꢀO(1)
O(1)ꢀRuꢀS(3)
O(1)ꢀRuꢀS(1)
O(40)ꢀRuꢀS(2)
S(3)ꢀRuꢀS(2)
O(40)ꢀRuꢀCl
S(3)ꢀRuꢀCl
90.07(7)
88.66(5)
177.86(5)
91.05(6)
94.18(2)
84.39(6)
90.24(2)
172.39(2)
O(40)ꢀRuꢀS(3)
O(40)ꢀRuꢀS(1)
S(3)ꢀRuꢀS(1)
O(1)ꢀRuꢀS(2)
S(1)ꢀRuꢀS(2)
O(1)ꢀRuꢀCl
174.54(6)
88.38(5)
93.02(2)
86.93(5)
91.63(2)
86.99(5)
94.32(2)
131.1(2)
,
shortening of the C(4)ꢀC(10) bond [1.461(3) A cf. a
S(1)ꢀRuꢀCl
C(1)ꢀO(1)ꢀRu
,
mean value of approximately 1.49 A in, for example,
S(2)ꢀRuꢀCl
biphenyls].

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A.R. Williams et al. / Inorganica Chimica Acta 314 (2001) 117–125
Fig. 2. The face-to-face, head-to-tail stacking of Ci-related pairs of coordinated phenylsquarate ligands in the structure of 1. The mean interplanar
,
separation between the ring systems is 3.64 A, the phenyl and C4-ring systems being inclined by approximately 11° to each other.
,
Fig. 3. The molecular structure of the hydrogen-bonded salt 2. The hydrogen-bonding geometries are, N···O, H···O (A), NꢀH···O (°): (a) 2.97, 2.08,
173; (b) 3.01, 2.15, 159; (c) 2.89, 2.17, 137; (d) 3.02, 2.18, 156. (e) 3.01, 2.19, 150; (f) 3.19, 2.40, 147.
hydrogen-bonded sheets are cross-linked weakly by
CꢀH···O hydrogen bonds between one of the methyl
hydrogen atoms attached to C(13) in one layer and the
sulfoxide oxygen O(31) in the next [C···O, H···O; 3.23,
3.2. [Pt(NH3)4][C6H5C4O3]2·H2O (2)
Instead of the desired platinum phenylsquarate com-
plex being formed when a solution of [Pt(NH3)4]Cl2 in
acetonitrile was mixed with phenylsquarate in the same
,
2.35 A, CꢀH···O 151°].

A.R. Williams et al. / Inorganica Chimica Acta 314 (2001) 117–125
121
Table 2
is essentially maximum conjugation between the phenyl
and C4-rings, the delocalisation in the latter ring is
incomplete (i.e. it does not extend to include all four
CꢀC bonds). This pattern is in striking contrast to the
bonding observed in the manganese(II) aminosquarate
salt [1c], where all of the CꢀC bonds in the C4 ring are
the same. Despite the overlap between the p systems in
the phenylsquarate ligand, the absence of mobile elec-
tron density in the substituent, which is present on the
nitrogen atom in the case of the aminosquarate ion, is,
we believe, responsible for the lack of complete delocal-
isation in the former.
The cations and anions are linked by NꢀH···O hydro-
gen bonds. However, the pattern of bonding to the two
independent phenylsquarate units differs. In one case
there is a pair of hydrogen bonds from two cis ammine
groups to the carbonyl trans to the phenyl substituent
(a and b in Fig. 3). The other pair of ammine groups
form one hydrogen bond each (c and f in Fig. 3) to
adjacent carbonyl groups on the other phenylsquarate
anion. This hydrogen-bonded unit is then linked via the
included solvent water molecule to its centrosymmetri-
cally related neighbours by NꢀH···O and OꢀH···O hy-
drogen bonds to form tapes (Fig. 4). Adjacent tapes are
linked both from above and below by further NꢀH···O
and OꢀH···O hydrogen bonds, using all of the remain-
ing non-utilised donors to form continuous cross-linked
,
Selected bond lengths (A) and angles (°) for [Pt(NH3)4]-
[C6H5C4O3]2·H2O (2)
PtꢀN(1)
PtꢀN(3)
2.063(5)
2.064(5)
1.247(8)
1.222(7)
1.514(8)
1.461(8)
1.250(8)
1.236(8)
1.513(8)
1.428(8)
PtꢀN(2)
PtꢀN(4)
2.055(5)
2.047(5)
1.215(8)
1.461(8)
1.511(8)
1.427(8)
1.210(9)
1.442(8)
1.529(9)
1.433(8)
O(1)ꢀC(1)
C(3)ꢀO(3)
C(1)ꢀC(2)
C(3)ꢀC(4)
O(1%)ꢀC(1%)
C(3%)ꢀO(3%)
C(1%)ꢀC(2%)
C(3%)ꢀC(4%)
C(2)ꢀO(2)
C(4)ꢀC(5)
C(2)ꢀC(3)
C(1)ꢀC(4)
C(2%)ꢀO(2%)
C(4%)ꢀC(5%)
C(2%)ꢀC(3%)
C(1%)ꢀC(4%)
N(1)ꢀPtꢀN(2)
N(1)ꢀPtꢀN(4)
N(2)ꢀPtꢀN(4)
91.6(2)
85.8(2)
177.4(2)
N(1)ꢀPtꢀN(3)
N(2)ꢀPtꢀN(3)
N(3)ꢀPtꢀN(4)
179.0(2)
89.2(2)
93.3(2)
solvent, the hydrated hydrogen-bonded salt [Pt(NH3)4]-
[C6H5C4O3]2·H2O was produced (Fig. 3). The two
phenylsquarate moieties have essentially identical ge-
ometries, with both exhibiting delocalisation that ex-
tends from the deprotonated oxygen atom O(1) via
C(4) to O(3) (Table 2). The bond linking the C4- and
C6-rings is the same as that observed in 1. There is,
however, a small difference in the torsional twist about
this bond in the two independent molecules [approxi-
mately 8° about C(4)ꢀC(5), cf. approximately 1° about
C(4%)ꢀC(5%)]. It is interesting to note that although there
Fig. 4. One of the hydrogen-bonded tapes formed by the linking via the included water molecule of adjacent hydrogen-bonded salts in
,
[Pt(NH3)4][C6H5C4O3]2·H2O (2). The hydrogen-bonding geometries are, X···O, H···O (A), XꢀH···O (°): (g) 3.00, 2.26, 139; (h) 2.93, 2.09, 154; (i)
2.79, 1.90, 169. There are additional inter-tape hydrogen-bonding interactions that utilise the remaining ammine and water hydrogen atoms. That
from N(1)ꢀH is to O(1%) [j], from N(2)ꢀH is to O(2) [k], from N(3)ꢀH is to O(1), [l], from N(4)ꢀH is to O(1%) [m] and that from the water molecule
O(4)ꢀH to O(1) [n]. The geometries are (j) 3.01, 2.22, 147 (k) 3.01, 2.23, 145 (l) 3.08, 2.20, 165 (m) 2.91, 2.17, 140 and (n) 2.93, 2.20, 138.

122
A.R. Williams et al. / Inorganica Chimica Acta 314 (2001) 117–125
corrugated sheets. These interactions are supplemented
by ‘reverse’ p stacking of the phenylsquarate ring sys-
tems analogous to that observed in the ruthenium
complex 1. The C(1)/C(10)-based phenylsquarate units
overlay their centrosymmetrically related counterparts
atoms, or as distorted square antiprismatic with the
‘upper’ and ‘lower’ faces comprised of O(31) to O(34)
and O(1), O(11), O(21), O(3A) respectively (Fig. 5). In
this latter interpretation it is interesting to note that all
of the phenylsquarate ligands lie on one square face of
the antiprism, a feature also observed in the related
europium phenylsquarate analogue, though in the eu-
ropium structure the opposite face was populated by
two aqua and two methanol ligands [19]. The
TbꢀO(squarate) distances are in the range 2.326(4)–
,
with a mean interplanar separation of 3.38 A. These
p-stacked pairs of phenylsquarate units pack in a
stepped fashion with their lattice-translated neighbours.
The C(1%)/C(10%) phenylsquarate units stack in a similar
,
fashion, with a mean interplanar separation of 3.37 A
,
and with the lattice-translated counterpart also being in
an overlapping geometry with an interplanar separation
2.376(4) A, whereas those to the aqua ligands are in a
,
much wider range [2.347(4)–2.449(4) A]; the angles at
,
of 3.49 A.
the coordinated ketonic oxygen atoms range between
136.4(3)° at O(1) and 146.0(4)° at O(21) (Table 3).
There is no difference in the patterns of bonding in the
three independent phenylsquarate ligands. They all ex-
hibit delocalisation that extends from the coordinated
oxygen via the carbon atom linked to the phenyl sub-
stituent to the trans ketonic oxygen atom regardless of
their coordination mode. The CꢀC bonds to the car-
bonyl carbon trans to the phenyl substituent are, in all
3.3. {[M(v-C6H5C4O3)(C6H5C4O3)2(H2O)4]·H2O}n
[M=Tb (3); M=Gd (4)]
The terbium and gadolinium complexes are iso-
morphous. The terbium complex is seen from the X-ray
structure to be polymeric, with each terbium centre
being coordinated to two pendant and two m-1,3-bridg-
ing phenylsquarate ligands, the remaining coordination
sites being occupied by four aqua ligands. In each case
the phenylsquarate ligands coordinate via oxygen
atoms cis to the phenyl substituent. The geometry at
terbium can be considered as either distorted bicapped
trigonal prismatic with O(31) and O(33) as the capping
,
cases, single in nature [1.505(7)–1.530(7) A]. As in
structures 1 and 2, the bond linking the C4- and C6-
,
rings [range 1.442(8)–1.447(8) A] is, in each case,
shorter than a conventional single bond, reflecting con-
jugation between the two ring systems (the torsional
twists about this bond range between only 2 and 4°).
Fig. 5. The coordination environment of the terbium atom in {[Tb(m-C6H5C4O3)(C6H5C4O3)2(H2O)4]·H2O}n (3), also showing the intramolecular
hydrogen bonds and the linking to the included water molecule [O(35)]. The phenylsquarate ligand coordinated through O(3A) is related by
,
symmetry to that coordinated through O(1). The hydrogen bonding geometries are O···O, H···O (A), OꢀH···O (°): (a) 2.71, 1.89, 151; (b) 2.84, 2.03,
150; (c) 2.75, 1.93, 151; (d) 2.72, 1.86, 159. The CꢀH···p interaction (e) has H···p, 2.81 A, CꢀH···p, 152°.
,

A.R. Williams et al. / Inorganica Chimica Acta 314 (2001) 117–125
123
Table 3
The complex and polymer chain conformations are,
to some extent, controlled by intramolecular OꢀH···O
and CꢀH···p interactions (a to e in Fig. 5), though these
are complemented by additional interchain OꢀH···O (f
and g in Fig. 6) and p–p interactions resulting in the
formation of sheets comprised of interleaved chains
(Fig. 7). A feature of these sheets is that one of their
surfaces is dominated by the phenyl rings of the phenyl-
squarate ligands and is thus hydrophobic, whereas the
other surface is populated entirely by either ketonic
oxygen atoms or aqua ligands, making it hydrophilic.
Adjacent centrosymmetrically related sheets are ar-
ranged back-to-back such that the two hydrophilic
surfaces are adjacent and are cross-linked by additional
OꢀH···O hydrogen bonds. The hydrophobic surfaces
are only in van der Waals contact with their centrosym-
metrically related counterparts. This sheet packing mo-
tif is distinctly different from that seen in the related
europium structure [1g], where adjacent polymer chains
alternate ‘up’ and ‘down’ (i.e. they do not have distinct
hydrophobic and hydrophilic surfaces) and there are no
inter-sheet hydrogen bonds. The included solvent water
molecule [O(35)] in 3 adopts a dual role, forming both
intra- and inter-sheet hydrogen bonds; the intra-sheet
,
Selected bond lengths (A) and angles (°) for {[Tb(m-C6H5C4O3)(C6H5-
C4O3)2(H2O)4]·H2O}n (3)
TbꢀO(1)
2.360(4)
2.376(4)
2.449(4)
2.422(4)
1.239(6)
1.250(7)
1.530(7)
1.421(7)
TbꢀO(3A)
TbꢀO(21)
TbꢀO(32)
TbꢀO(34)
C(2)ꢀO(2)
C(4)ꢀC(5)
C(2)ꢀC(3)
C(1)ꢀC(4)
2.326(4)
2.351(4)
2.347(4)
2.389(4)
1.206(7)
1.447(8)
1.505(7)
1.425(7)
TbꢀO(11)
TbꢀO(31)
TbꢀO(33)
O(1)ꢀC(1)
C(3)ꢀO(3)
C(1)ꢀC(2)
C(3)ꢀC(4)
O(3A)ꢀTbꢀO(32)
O(32)ꢀTbꢀO(21)
O(32)ꢀTbꢀO(1)
O(3A)ꢀTbꢀO(11)
O(21)ꢀTbꢀO(11)
O(3A)ꢀTbꢀO(34)
O(21)ꢀTbꢀO(34)
O(11)ꢀTbꢀO(34)
O(32)ꢀTbꢀO(33)
O(1)ꢀTbꢀO(33)
O(34)ꢀTbꢀO(33)
O(32)ꢀTbꢀO(31)
O(1)ꢀTbꢀO(31)
O(34)ꢀTbꢀO(31)
C(1)ꢀO(1)ꢀTb
143.66(14)
145.02(14)
87.0(2)
74.43(14)
129.14(14)
99.2(2)
77.3(2)
145.00(14)
73.6(2)
140.77(14)
73.1(2)
69.74(13)
72.64(14)
69.7(2)
O(3A)ꢀTbꢀO(21) 70.82(14)
O(3A)ꢀTbꢀO(1) 107.23(13)
O(21)ꢀTbꢀO(1)
O(32)ꢀTbꢀO(11) 79.35(14)
O(1)ꢀTbꢀO(11) 71.00(14)
O(32)ꢀTbꢀO(34) 88.1(2)
O(1)ꢀTbꢀO(34) 141.32(14)
O(3A)ꢀTbꢀO(33) 74.69(14)
O(21)ꢀTbꢀO(33) 129.5(2)
O(11)ꢀTbꢀO(33) 72.1(2)
O(3A)ꢀTbꢀO(31) 146.03(13)
O(21)ꢀTbꢀO(31) 75.38(14)
O(11)ꢀTbꢀO(31) 132.85(14)
O(33)ꢀTbꢀO(31) 127.61(14)
85.1(2)
136.4(3)
137.5(4)
C(3)ꢀO(3)ꢀTb%
C(21)ꢀO(21)ꢀTb 146.0(4)
140.6(3)
C(11)ꢀO(11)ꢀTb
Fig. 6. Part of one of the sheets formed by the interleaving of adjacent lattice-translated polymer chains. The hydrogen-bonding geometries are
,
O···O, H···O (A), OꢀH···O (°): (f) 2.71, 1.83, 164; (g) 2.70, 1.81, 167. The mean interplanar separations between the p-stacked phenylsquarate ring
,
,
systems are 3.55 A and 3.57 A respectively.

124
A.R. Williams et al. / Inorganica Chimica Acta 314 (2001) 117–125
Fig. 7. The back-to-back packing of the interleaved and hydrogen-bonded sheets present in the structure of 3. The sheets are cross-linked by
OꢀH···O hydrogen bonds between O(33) in one sheet and O(35) in the next and between O(34) in one sheet and O(2) in the other [O···O, H···O
,
(A), OꢀH···O (°): 2.79, 1.93, 159 and 2.92, 2.14, 145 respectively] (see Fig. 5 for numbering scheme).
hydrogen bond is to the ketonic oxygen O(13) of an
and explored for their potential as, for example, antitu-
,
adjacent chain [O···O, H···O, 2.84, 1.95 A; OꢀH···O
175°], whilst the inter-sheet linkage is to the ketonic
oxygen O(22) of an adjacent sheet [O···O, H···O, 2.88,
mour agents.
The formation of polymeric species with gadolinium
and terbium suggests that, as observed previously with
europium phenylsquarate [1g], the steric demand of the
phenyl substituent, which is almost invariably coplanar
with the C4-ring, does not hinder polymer formation
with the lanthanides.
,
2.06 A; OꢀH···O 150°].
4. Conclusions
The unpredictability of the complexing behaviour of
monosubstituted squarate ligands has again been
demonstrated with the formation of a simple monomer
with Ru(dmso)4Cl2, and polymers with terbium and
gadolinium, whereas with platinum only a hydrogen-
bonded salt resulted. This study, however, has provided
further insight into the factors that must be taken into
consideration when attempting to engineer specific crys-
tal architectures. The platinum compound described
here shows that monosubstituted squarate ligands that
exist as resonance-stabilised anions in polar solvents
can react to form salts in the presence of stable cationic
species. Additionally, because these ligands appear to
have only medium field strengths, replacement of
stronger ligands from reactants such as Ru(dmso)4Cl2
will tend to be inhibited and polymerisation will be
prevented.
5. Supplementary material
X-ray crystallographic files, in CIF format, contain-
ing data for the structures of 1–3 are available free of
charge on application to the CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336; e-mail:
deposit@ccdc.cam.ac.uk).
Acknowledgements
L.A.H. wishes to thank the St. Augustine Campus
Committee on Graduate Studies, The University of the
West Indies and CARISCIENCE for financial support.
However, in spite of the fact that no polymeric
species were produced with ruthenium(II), the forma-
tion of a monomeric complex with ruthenium–halogen
and ruthenium–sulfoxide linkages provides a useful
prototype for the synthesis of monomers with other
monosubstituted squarate ligands. This result now ex-
pands the range of compounds that can be synthesised
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