DOI: 10.1002/zaac.200700151

Pt4S4 Clusters with Functionalized Thiosemicarbazones derived from5-Acetylbarbituric Acid

Elena Bermejoa, Alfonso Castineirasa,*, Isabel Garcıa-Santosa, Lourdes Gomez-Rodrigueza, and PalomaSevillanob

a Santiago de Compostela/Spain, Universidad de Santiago de Compostela, Departamento de Quımica Inorganicab Karlsruhe/Germany, Forschungszentrum Karlsruhe, Institut für Nanotechnologie

Received March 28th, 2007.

Dedicated to Professor Dieter Fenske on the Occasion of his 65th Birthday

Abstract. Reaction of K2[PtCl4] with thiosemicarbazones derivedfrom 5-acetylbarbituric acid led to the isolation of the tetranuclearspecies [Pt(AcbM)]4 · 2/2DMSO·2DMSO·5H2O (1) and[Pt(AcbE)]4 · 4DMSO·2H2O (2) (H2AcbM � 5-acetylbarbituric-4N-methyl thiosemicarbazone and H2AcbE � 5-acetylbarbituric-4N-ethyl thiosemicarbazone). Both of these compounds feature aPt4S4 cluster in which some of the Pt�Pt distances suggest theexistence of weak metal-metal interactions. Crystals of these tetra-nuclear species are stabilized by intermolecular π-π stacking inter-actions. The two compounds have almost equivalent molecular

Introduction

There is growing interest in the coordination chemistry of2�-heterocycle thiosemicarbazones and this is driven by thewide-ranging chemical-therapeutic properties shown bysome of these compounds [1], including antibacterial, anti-microbial, antifungal and anti-HIV activities [2]. The bio-logical activity is partly due to the ability of these systemsto form chelates with metal ions that are essential to life.Bonding occurs through the sulfur atom [3], sulfur and ni-trogen atoms [4], or with the ligand acting in a tridentateNNS manner [5], or through one oxygen, one nitrogen andone sulfur atom as an ONS system [6].

In a similar way, the chemistry of metal complexes withbiologically important ligands continues to be of interestbecause this area contributes to our understanding of therole played by the ligand in biological systems and couldprovide additional knowledge that would enable the devel-opment of novel therapeutic agents based on metals [7].

Barbituric acid derivatives represent one such class ofbiologically active compounds and their coordinationchemistry has been investigated in depth because the metal

* Prof. Dr. A. CastineirasDepartamento de Quımica InorganicaFacultad de FarmaciaUniversidad de Santiago de CompostelaE-15706 Santiago de CompostelaFax: �34 981 547163E-mail: qiac01@usc.es

Z. Anorg. Allg. Chem. 2007, 633, 2255�2261 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2255

structures, differing only in the orientation of the substituent onthe amine nitrogen atom of the thiosemicarbazone. The two tetra-nuclear complexes contain the thiosemicarbazone bonded as a terd-entate ligand to the platinum atom through the thiolate sulfuratom, the azomethine nitrogen atom and the alcoholate oxygenatom of the 5-acetylbarbiturate function.

Keywords: Platinum; Cluster compounds; Thiosemicarbazonatecomplexes; 5-Acetylbarbituric derivatives; Crystal structures

complexes are important in the detection and identificationof barbiturate pharmaceuticals. This importance stemsfrom the fact that barbituric acid and its derivatives are aclass of psycho-therapeutic agents that are widely used fortheir tranquilising, sedation and hypnotic properties andalso because barbiturates are amongst the most commoncomponents in pharmaceuticals.

Barbituric acids can coordinate through the depro-tonated nitrogen atoms, the carbonyl oxygen atoms and thedeprotonated CH2 group (pKa � 4), giving a wide rangeof metal complexes that can range from mononuclear topolynuclear [8].

As part of a broad-ranging research project of thiosemi-carbazones [9], we have recently undertaken the synthesisand structural study of thiosemicarbazones derived frombarbituric acids and have investigated their metal com-plexes. This work was carried out with the aim of obtainingbifunctional molecules that, in a similar way to certain anti-biotics [10], would be capable of binding deoxyribonucleicacids and forming complexes with transition metals thatcarry out some essential functions such as, for example, theactivation of molecular oxygen [11]. In an analogous wayto the proposed mode of action of bleomicyn, such com-pounds could show some sorts of antitumor activity by in-ducing splitting of the single and double strands of DNA.

In the work described here, the reactions between 5-acetyl-barbituric-4N-methyl thiosemicarbazone (H2AcbM) and5-acetylbarbituric-4N-ethyl thiosemicarbazone (H2AcbE)(Figure 1) with K2[PtCl4] were carried out. The productsof these reactions, after slow crystallization from DMSO,

E. Bermejo, A. Castineiras, I. Garcıa-Santos, L. Gomez-Rodriguez, P. Sevillano

Fig. 1 5-acetylbarbituric-4N-methyl thiosemicarbazone(H2AcbM) and 5-acetylbarbituric-4N-ethyl thiosemicarbazone(H2AcbE).

gave rise to the complexes [Pt(AcbM)]4 ·2/2DMSO ·2DMSO ·5H2O (1) and [Pt(AcbE)]4 ·4DMSO ·2H2O (2),respectively, both of which contain a Pt4S4 cluster.

Results and Discussion

The solids obtained in the reactions between K2[PtCl4] andH2AcbM or H2AcbE were recrystallized form DMSO togive [Pt(AcbM)]4 ·2/2DMSO ·2DMSO ·5H2O (1) and[Pt(AcbE)]4 ·4DMSO ·2H2O (2), respectively, where AcbMand AcbE represent the doubly deprotonated forms of theligands H2AcbM and H2AcbE.

It is known that the displacement of a halide ligand by adonor solvent molecule is a relatively easy process, as isthe corresponding deprotonation of a thiosemicarbazone incomplexes containing these ligands. Furthermore, DMSOand other donor solvents, such as dimethylformamide, favorthe aggregation of monomers � as observed in other poly-nuclear complexes with thiosemicarbazones, e.g.[Pd(Ap3Pr)]3 ·DMF (Ap3Pr � N(3)-propylthiosemicarba-zone [12] and [Pd(TSDO)]4 ·4H2O ·2DMF (TSDO � 6-am-ino-5-formyl-1,3-dimethyluracil thiosemicarbazone [13]. Asa result, the structures of the mononuclear platinum(II)complexes [Pt(HAcbTSC)Cl] and [Pt(AcbTSC)(DMSO)],where H2AcbTSC represents the neutral thiosemicarba-zone, can be considered as potential intermediates in theformation of tetranuclear species’ such as those reportedhere. The process for the formation of these tetranuclearspecies’ can be represented as follows:

H2AcbTSC � K2[PtCl4] � [Pt(HAcbTSC)Cl] � 2KCl � HCl

[Pt(HAcbTSC)Cl] � DMSO � [Pt(AcbTSC)(DMSO)] � HCl

4[Pt(AcbTSC)(DMSO)] � [Pt(AcbTSC)]4 � 4DMSO

The formation of tetranuclear species with metals from thesame group as nickel � especially palladium(II) and plati-num(II) � is well documented for systems with sulfur do-nor ligands [14], but particularly with bridging thiolates[15�17]. More recently, a number of tetranuclear pal-ladium(II) and platinum(II) complexes have been synthe-sized with a range of tridentate thiosemicarbazones, either

www.zaac.wiley-vch.de 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2007, 2255�22612256

Fig. 2 Molecular structure of [Pt(AcbM)]4.

through a cyclometallation [18�20] or through the presenceof an additional donor group [13]. To the best of ourknowledge, the complexes reported here represent the firsttetranuclear structures that contain platinum(II) with func-tionalized doubly deprotonated tridentate thiosemicarba-zones.

Structural analysis of[Pt(AcbM)]4 · 2/2DMSO · 2DMSO · 5H2O (1) and[Pt(AcbE)]4 · 4DMSO · 2H2O (2)

If we ignore for a moment the molecules of crystallization,both complexes have a similar molecular structure, which isrepresented in Figure 2 for the complex with N(4)-methylthiosemicarbazone. This structure consists of square planarPtNOS2 units in which each metal atom is tetracoordinatedby the enolate oxygen atoms, the azomethine nitrogen andthe thiolate sulfur atoms, the latter of which acts as a bridgebetween each pair of platinum(II) atoms. These four unitscombine to form an eight-membered Pt4S4 ring which hasa boat conformation (Figure 3) with alternate platinum andsulfur atoms. The torsion angles for this ring in the twocomplexes are given in Table 1.

The molecule [Pt(Ab4E)]4 is represented in Figure 4. Itcan be seen that the Pt4S4 cluster can be described in termsof the interpenetration of a quasi-square plane of sulfuratoms into a tetrahedron of platinum atoms. This occurs insuch a way that the platinum atoms alternate � with twoabove and two below the aforementioned plane. In a regulartetrahedron the value of each of the three angles aroundeach vertex is 60°, whereas in an ideal square plane there isone angle of 90° and two of 45°. In the structures described

Pt4S4 Clusters with Functionalized Thiosemicarbazones

Fig. 3 View of the Pt4S4 ring in the complexes.

Table 1 Torsion angles/° for the Pt4S4 ring in the complexes.

[Pt(AcbM)]4 [Pt(AcbE)]4

Pt(1)�S(1)�Pt(4)�S(4) �37.47 Pt(1)�S(1)�Pt(4)�S(4) 55.75S(1)�Pt(4)�S(4)�Pt(3) �50.11 S(1)�Pt(4)�S(4)�Pt(2) 65.76Pt(4)�S(4)�Pt(3)�S(3) 57.63 Pt(4)�S(4)�Pt(2)�S(2) �52.12S(4)�Pt(3)�S(3)�Pt(2) 58.17 S(4)�Pt(2)�S(2)�Pt(3) �70.83Pt(3)�S(3)�Pt(2)�S(2) �60.17 Pt(2)�S(2)�Pt(3)�S(3) 44.16S(3)�Pt(2)�S(2)�Pt(1) �70.37 S(2)�Pt(3)�S(3)�Pt(1) 61.60Pt(2)�S(2)�Pt(1)�S(1) 50.54 Pt(3)�S(3)�Pt(1)�S(1) �47.33S(2)�Pt(1)�S(1)�Pt(4) 70.90 S(3)�Pt(1)�S(1)�Pt(4) �58.83

here, the Pt�Pt�Pt bond angles around each metal atomin the Pt4 polyhedron have average values of 63.97, 64.91and 51.17° in 1 and 64.55, 64.97 and 50.59° in 2. On theother hand, the average values for the S�S�S angles in theS4 square are 89.91, 45.03 and 45.16° in 1 and 89.62, 44.63and 45.76° in 2. These values provide an idea of the levelof distortion in the nucleus of these complexes.

Fig. 4 Molecular structure of [Pt(AcbE)]4.

In each Pt4 pseudo-tetrahedron there are two types ofPt···Pt distance. The shortest of these have average valuesof 3.283(1) A in 1 and 3.231(1) A in 2 (Table 2), and theselink pairs of atoms above and below the S4 square. Al-though these bonds are not indicative of a direct Pt···Ptbond, a weak interaction can be postulated between thesetwo atoms on the basis of values found in other polynuclear

Z. Anorg. Allg. Chem. 2007, 2255�2261 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 2257

Table 2 Selected bond lengths/A for the complexes.

[Pt(AcbM)]4 · 2/2DMSO · 2DMSO · 5H2O [Pt(AcbE)]4 · 4DMSO · 2H2O

Pt(1)�N(12) 2.001(9) Pt(1)�N(12) 2.005(14)Pt(1)�O(11) 2.009(7) Pt(1)�O(11) 2.007(11)Pt(1)�S(1) 2.221(3) Pt(1)�S(1) 2.232(4)Pt(1)�S(2) 2.306(3) Pt(1)�S(3) 2.306(4)Pt(1)�Pt(3) 3.259(1) Pt(1)�Pt(2) 3.215(1)Pt(1)�Pt(2) 3.690(1) Pt(1)�Pt(4) 3.781(1)Pt(1)�Pt(4) 3.870(1) Pt(1)�Pt(3) 3.840(1)Pt(2)�N(22) 1.989(9) Pt(2)�N(22) 1.994(14)Pt(2)�O(21) 2.014(8) Pt(2)�O(21) 2.022(10)Pt(2)�S(2) 2.230(3) Pt(2)�S(2) 2.216(4)Pt(2)�S(3) 2.302(3) Pt(2)�S(4) 2.292(4)Pt(2)�Pt(4) 3.307(1) Pt(2)�Pt(4) 3.722(1)Pt(2)�Pt(3) 3.706(1) Pt(2)�Pt(3) 3.810 (1)Pt(3)�N(32) 1.988(9) Pt(3)�N(32) 1.988(15)Pt(3)�O(31) 2.021(8) Pt(3)�O(31) 2.017(11)Pt(3)�S(3) 2.226(3) Pt(3)�S(3) 2.221(4)Pt(3)�S(4) 2.310(3) Pt(3)�S(2) 2.308(5)Pt(3)�Pt(4) 3.932(1) Pt(3)�Pt(4) 3.247(1)Pt(4)�N(42) 1.988(9) Pt(4)�N(42) 1.989(14)Pt(4)�O(41) 2.039(8) Pt(4)�O(41) 2.010(12)Pt(4)�S(4) 2.226(3) Pt(4)�S(4) 2.228(4)Pt(4)�S(1) 2.304(3) Pt(4)�S(1) 2.293(4)

platinum(II) complexes [21, 22]. The other Pt···Pt distanceshave values in the range 3.690(1)�3.932(1) A, and these aresignificantly longer than those found in analagous tetranu-clear complexes [18, 19].

The coordination spheres of the platinum(II) atoms aresimilar in both compounds. Each thiosemicarbazone is bi-deprotonated and occupies three of the coordination posi-tions around each metal atom. The fourth position, whichis trans to the azomethine nitrogen, is occupied by the sul-fur atom of the other coordinated thiosemicarbazone. If weconsider the PtONS2 unit, the Pt�N [1.988(9)�2.005(1) A]and Pt�O [2.007(1)�2.039(8) A] bond lengths in the twocomplexes are similar to those found in other analogouscomplexes [14, 18, 19].

On the other hand, there are two different Pt�S distancesin each complex. The distances involving sulfur atoms ofthe same thiosemicarbazone have values between 2.216(4)and 2.232(4) A, whereas those involving sulfur atoms ofthiosemicarbazone units bonded to the other platinum(II)atom have values in the range 2.292(4)�2.310(4) A. Thesedata show that the thiolate bridges are asymmetrical but itis worth noting that both sets of distances are shorter thanthose found in other platinum thiolate complexes [18, 23],including thiosemicarbazonates [19, 24].

In both complexes the angles around the platinum atoms[84.4(3)�98.5(1)° in 1 and 85.6(3)�97.5(2)° in 2] (Table 3)give an indication of the level of distortion in the coordi-nation geometry. In addition, in each monomeric PtONS2

unit the metal atom deviates by a maximum of only0.068(4) A from the average plane formed by the group offour donor atoms. These coordination planes form anglesof between 1.4(2) and 18.7(3)° in 1 and 2.9(7) and 15.7(5)°in 2. The corresponding thiosemicarbazone chain forms a

E. Bermejo, A. Castineiras, I. Garcıa-Santos, L. Gomez-Rodriguez, P. Sevillano

Table 3 Selected bond angles/° for the complexes.

[Pt(AcbM)]4 · 2/2DMSO · 2DMSO · 5H2O [Pt(AcbE)]4 · 4DMSO · 2H2O

N(12)�Pt(1)�O(11) 93.1(4) N(12)�Pt(1)�O(11) 90.7(5)N(12)�Pt(1)�S(1) 85.4(3) N(12)�Pt(1)�S(1) 86.2(4)O(11)�Pt(1)�S(1) 174.6(3) O(11)�Pt(1)�S(1) 176.5(3)N(12)�Pt(1)�S(2) 177.8(3) N(12)�Pt(1)�S(3) 176.2(4)O(11)�Pt(1)�S(2) 86.7(2) O(11)�Pt(1)�S(3) 85.6(3)S(1)�Pt(1)�S(2) 94.6(1) S(1)�Pt(1)�S(3) 97.5(2)N(22)�Pt(2)�O(21) 92.4(3) N(22)�Pt(2)�O(21) 91.6(5)N(22)�Pt(2)�S(2) 86.9(3) N(22)�Pt(2)�S(2) 86.9(4)O(21)�Pt(2)�S(2) 176.1(2) O(21)�Pt(2)�S(2) 176.3(4)N(22)�Pt(2)�S(3) 177.6(3) N(22)�Pt(2)�S(4) 177.2(4)O(21)�Pt(2)�S(3) 86.1(2) O(21)�Pt(2)�S(4) 88.0(3)S(2)�Pt(2)�S(3) 94.8(1) S(2)�Pt(2)�S(4) 93.4(2)N(32)�Pt(3)�O(31) 91.9(3) N(32)�Pt(3)�O(31) 91.9(5)N(32)�Pt(3)�S(3) 85.9(3) N(32)�Pt(3)�S(3) 86.0(4)O(31)�Pt(3)�S(3) 177.6(2) O(31)�Pt(3)�S(3) 177.3(4)N(32)�Pt(3)�S(4) 177.6(3) N(32)�Pt(3)�S(2) 178.3(4)O(31)�Pt(3)�S(4) 86.9(2) O(31)�Pt(3)�S(2) 86.4(4)S(3)�Pt(3)�S(4) 95.3(1) S(3)�Pt(3)�S(2) 95.8(2)N(42)�Pt(4)�O(41) 91.4(3) N(42)�Pt(4)�O(41) 92.8(5)N(42)�Pt(4)�S(4) 84.4(3) N(42)�Pt(4)�S(4) 86.1(4)O(41)�Pt(4)�S(4) 174.8(2) O(41)�Pt(4)�S(4) 174.5(4)N(42)�Pt(4)�S(1) 176.7(3) N(42)�Pt(4)�S(1) 179.2(4)O(41)�Pt(4)�S(1) 85.6(2) O(41)�Pt(4)�S(1) 86.4(3)S(4)�Pt(4)�S(1) 98.5(1) S(4)�Pt(4)�S(1) 94.6(2)

dihedral angle of between 5.7(8) and 33.9(4)° with the aver-age plane of the barbiturate ring to which it is bonded.

In each thiosemicarbazone the average bond lengths forthe C�S [1.80(2) A] and C�O [1.28(2) A] bonds provideevidence for thiolate and enolate character in the sulfur andoxygen atoms, respectively. The experimental bond anglesdiffer from those expected for the free ligands in a similarway to those described for the monomeric palladium(II)and platinum(II) complexes discussed in the previous pages.

Table 4 Hydrogen bond parameters/A,° in[Pt(Ab4M)]4 ·2/2DMSO ·2DMSO ·5H2O

D�H···A d(D�H) d(H···A) d(D···A) �(DHA)

N(11)�H(11)···O(61) 1 0.86 1.99 2.85(2) 178.5N(14)�H(14)···O(3) 0.86 2.26 2.99(2) 142.0N(15)�H(15)···O(71) 2 0.86 2.05 2.90(2) 170.3N(15)�H(15)···S(7) 2 0.86 2.98 3.74(2) 149.2N(21)�H(21)···O(2) 1 0.86 2.07 2.92(2) 170.7N(24)�H(24)···O(33) 3 0.86 2.27 2.91(1) 131.1N(25)�H(25)···O(45) 4 0.86 2.02 2.84(1) 158.0N(31)�H(31)···O(5) 5 0.86 2.07 2.91(2) 165.0N(34)�H(34)···O(25) 6 0.86 2.22 2.93(1) 139.0N(35)�H(35)···O(1) 2 0.86 2.20 3.01(1) 159.1N(41)�H(41)···O(51) 0.86 1.96 2.81(2) 166.8N(44)�H(44)···O(15) 7 0.86 2.08 2.85(1) 149.3N(45)�H(45)···O(23) 4 0.86 2.06 2.91(1) 169.6

Symmetry transformations used to generate equivalent atoms: 1 x�1,y,z�1;2 x�1,�y�1/2,z�1/2; 3 x,�y�1/2,z�1/2; 4 �x�1,�y,�z; 5 x�1,�y�1/2,z�1/2; 6 �x,�y,�z; 7 x,�y�1/2,z�1/2

In the crystalline network in both complexes the mol-ecules of crystallization act as linkers between the tetranu-clear units through the formation of numerous intermolecu-lar N�H···O hydrogen bonds (Tables 4 and 5), a situationthat reinforces the interactions between the molecules of thetetramer and their nearset neighbors. In addition, the O···Obond distances are in the range 2.71�3.10 A, which sug-

www.zaac.wiley-vch.de 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2007, 2255�22612258

Table 5 Hydrogen bond parameters/A,° in[Pt(Ab4E)]4 ·4DMSO ·2H2O.

D�H···A d(D�H) d(H···A) d(D···A) �(DHA)

N(11)�H(11)···O(60) 0.86 2.02 2.70(3) 134.7N(14)�H(14)···O(70) 1 0.86 2.13 2.83(3) 139.2N(15)�H(15)···O(25) 2 0.86 2.03 2.872(18) 166.5N(21)�H(21)···O(23) 3 0.86 2.03 2.854(19) 159.4N(25)�H(25)···O(13) 2 0.86 1.95 2.789(17) 164.8N(31)�H(31)···O(80) 0.86 1.84 2.70(3) 173.1N(31)�H(31)···S(8) 0.86 2.82 3.60(2) 152.1N(34)�H(34)···O(2) 4 0.86 2.19 3.03(4) 164.4N(35)�H(35)···O(45) 5 0.86 2.02 2.86(2) 164.1N(41)�H(41)···O(43) 6 0.86 1.95 2.802(19) 168.6N(44)�H(44)···O(50) 7 0.86 1.90 2.76(3) 172.4N(45)�H(45)···O(33) 5 0.86 1.93 2.752(19) 159.9

Symmetry transformations used to generate equivalent atoms: 1 x�1,y�1,z;2 �x�1,�y,�z; 3 �x�2,�y,�z; 4 x,y�1,z; 5 �x�2,�y�1,�z�1;6 �x�2,�y,�z�1; 7 x�1,y�1/2,z

gests the existence of additional hydrogen bonding betweenthe water molecules and the DMSO molecules of crystalli-zation [25]. In this way a strong three-dimensional networkis formed and, in the case of 1, there are additional π-πstacking interactions that further reinforce the crystallinestructure of the complex.

One notable feature in these tetranuclear compounds isthe coplanarity of pairs of thiosemicarbazones in eachtetramer, with dihedral angles between the average planesof 15.5(2)° and 16.1(3)° in 1 and 18.6(6)° and 1.5(8)° in 2.The planes in question are apart by 3.259(1)�3.307(1) Aand 3.215(1)�3.247(1) A, respectively. These parametersare consistent with the existence of antiparallel intramol-ecular π-π stacking, as described by Janiak in copper(II)compounds with heterocyclic nitrogen ligands [26, 27].

In compound 1 the aforementioned intramolecular π-πstacking interactions, as one would expect given the geo-metric parameters, are somewhat different (Table 6). Thoseinteractions that involve the barbiturate rings of the thiose-micarbazone molecules coordinated to Pt(1) and Pt(3),[N(11)�N(31)], are defined by a dihedral angle � of 8.15°and slipping angles of around 20°.

This compound also gives rise to intermolecular π-πstacking interactions through the N(11)�N(31) pair, whichinvolves the reference molecule and that corresponding tothe equivalent position x, 1/2�y, 1/2�z, in such a way thatthe two molecules are related by a twofold screw axis (Fig-ure 5).

The distance between the centroids is 3.656 A, but theother parameters for this interaction (Table 6) show a slightslip in the parallel disposition of the rings. This situationgives rise to an average stacking distance of 3.43 A. In thethree-dimensional network this stacking extends in the [001]direction, as represented in Figure 6.

In tetramer 2 there are also intramolecular π-π stackinginteractions between opposite pairs of barbiturate rings,similar to those in the H2AcbM derivative (Table 6). How-ever, in the three-dimensional packing the molecules aresufficiently far from one another that the possibility of in-termolecular interactions can be ruled out.

Pt4S4 Clusters with Functionalized Thiosemicarbazones

Table 6 Short π-π stacking interactions for the complexes.

Ring d[Cg(I)-Cg(J)] /A d�[Cg(I)-P(J)] /A d�[Cg(J)-P(I)] /A � /° β /° γ /°

[Pt(AcbM)]4N(11)�N(31) 3.894 3.538 3.515 6.09 25.50 24.69N(11)a�N(31) 3.656 3.445 3.410 8.15 21.18 19.11

[Pt(AcbE)]4N(11)�N(21) 3.721 3.384 3.438 6.15 22.51 24.58N(31)�N(41) 3.808 3.323 3,505 9.48 23.01 29.23

a) x, 1/2�y, �1/2�z

Fig. 5 View of 1 showing the π,π-stacking interactions betweenpairs of barbiturate rings from adjacent thiosemicarbazonate li-gands. Hydrogen atoms, molecules 2 and 4, and methyl groups havebeen omitted for clarity.

Fig. 6 View of [Pt(AcbM)]4 along the direction perpendicular tothe {101} showing the intermolecular stacking in the [001] direction.

Experimental Section

General

Elemental analyses were carried out on a Fisons instrumentsEA1108 CHNS-O microanalyser. IR spectra were recorded on a

Z. Anorg. Allg. Chem. 2007, 2255�2261 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 2259

Bruker IFS-66V spectrophotometer as KBr disks (4000�400 cm�1)or polyethylene-sandwiched Nujol mulls (500�100 cm�1).All chemicals and solvents were of analytical grade and were usedas received.

Synthesis and crystallization of the compounds

The ligands, H2AcbM and H2AcbE, were prepared according toliterature procedures by condensation reactions between 5-acetyl-barbituric acid [28] and 4-methyl or 4-ethyl thiosemicarbazides.

[Pt(AcbM)]4 ·2/2DMSO·2DMSO·5H2O (1): An ethanolic sus-pension (20 mL) of H2AcbM (0.28 g, 0.78 mmol) was added to astirred solution of K2[PtCl4] (0.32 g, 0.78 mmol) in water (10 mL).The mixture was heated under reflux for 1 h and was then stirredat room temperature for a further 7 d. The resulting suspensionwas filtered off and the solid was washed with ethanol and driedover calcium chloride. A few brown crystals suitable for a single-crystal X-ray analysis were obtained by slow crystallization at roomtemperature of a DMSO solution, and these crystals were easilyseparated. Yield: 34 % (140 mg).Anal. Found: C 20.7, H 2.06, N 13.1, S 10.1 %. Calc. forC38H64N20O20Pt4S7 (2125.81): C 21.5, H 3.03, N 13.2, S 10.6 %.

IR/(KBr, ν/cm�1): 3404m, 3229m, 3045w (NH), 1716s (CO), 1650m δ(NH),1599s, 1565m (CN � CC), 1308w, 1265m, 1235w (CS � CC), 1053w (NN),802m (C�S),469m (Pt�N), 337 (Pt�S).

[Pt(AcbE)]4 ·4DMSO·2H2O (2): An ethanolic suspension(20 mL) of H2AcbE (0.20 g, 0.74 mmol) was added to a stirredsolution of K2[PtCl4] (0.30 g, 0.74 mmol) in ethanol (10 mL). Themixture was heated under reflux for 1 h and the suspension wasfiltered. Slow evaporation of the solvent in air at room temperatureafforded micro-crystals, which were filtered off and the solid waswashed with ethanol and dried over calcium chloride. Crystalliza-tion of the micro-crystals from DMSO and slow evaporation atroom temperature gave, after several weeks, a few yellow crystalssuitable for X-ray analysis and these were separated by hand. Yield:27 % (110 mg).Anal. Found: C 24.9, H 3.50, N 13.5, S 12.2 %. Calc. forC44H72N20O18Pt4S8 (2206.01): C 24.0, H 3.29, N 12.7, S 11.6 %.

IR/(KBr, ν/cm�1): 3337m, 3217m, 3043w (NH), 1701s (CO), 1638s δ(NH),1606s, 1567s, 1520s (CN � CC), 1303w, 1281m (CS � CC), 1048m (NN),806m (C�S), 465m (Pt�N), 355w (Pt�S).

Crystal structure determinations

Crystals were mounted on glass fibers and these samples were usedfor data collection. Data for 1 and 2 were collected with a BrukerSMART CCD 1000 diffractometer. Cell constants and an orien-tation matrix were obtained from data collection of 2.31 < θ <

E. Bermejo, A. Castineiras, I. Garcıa-Santos, L. Gomez-Rodriguez, P. Sevillano

24.61° for 1, 2.57 < θ < 24.66° for 2. The data were processed withSAINT [29] and corrected for absorption using SADABS [30]. Thestructures were solved by direct methods [31], which revealed thepositions of all non-hydrogen atoms. These atoms were refined onF2 by a full-matrix least-squares procedure using anisotropic dis-placement parameters [32], except for the S, O and C atoms of thesolvent molecules and the ethyl groups of 2 (refined isotropically).In 1, two very disordered DMSO molecules (S7 and S8) were re-fined with an occupancy factor of 0.5. In 2 the contribution of thedensity of the disordered solvent molecules was subtracted fromthe measured structure factors using the SQUEEZE option [33].The hydrogen atoms were placed geometrically and positional par-ameters were refined using a riding model. Isotropic atomic dis-placement parameters for hydrogen atoms were constrained to be1.2 (1.5 for methyl groups). For the compound 1, the largest peaksand valleys in the final difference maps were in the region of thedisordered solvent, and for compound 2, were located close to thePt atoms. Atom scattering factors were taken from the Inter-national Tables for Crystallography [34]. Crystal and refinementdata are listed in Table 7.

Table 7 Crystal data and structure refinement for [Pt(AcbM)]4 ·2/2DMSO ·2DMSO ·5H2O (1) and [Pt(AcbE)]4 ·4DMSO ·2H2O (2).

Compound 1 2

Empirical formula C38H64N20O20Pt4S7 C44H72N20O18Pt4S8

Formula weight 2125.87 2206.06Temperature / K 293(2) 293(2)Wavelength / A 0.71073 0.71073Crystal system monoclinic triclinicSpace group P21/c (No.14) P1 (No.2)Unit cell dimensions

a / A 13.5744(13) 12.123(4)b / A 38.072(4) 12.574(4)c / A 14.0267(14) 24.711(7)� / ° 78.424(5)β / ° 115.239(2) 86.563(5)γ / ° 84.010(5)

Volume / A3 6557.1(11) 3667(2)Z 4 2Calc. density / Mg/m3 2.153 1.998Absorp. coefc. / mm�1 8.811 7.907F(000) 4064 2120Crystal size / mm 0.19 � 0.18 � 0.04 0.25 � 0.07 � 0.05θ range / ° 1.07�24.71 0.84�24.79Limiting indices / h,k,l �14/15, 0/44, �16/0 �14/14, �14/14, 0/29Refl. collect / unique 11155/11155 12566/12566Completeness θ / ° 98.2 99.5Absorp. correct. SADABS SADABSMax. /min. transm. 0.770 / 0.442 0.6932 / 0.2425Data / parameters 11155/709 12566/718Goodness-of-fit on F2 1.061 0.951Final R indices R1 � 0.0431, R1 � 0.0652,

wR2 � 0.1076 wR2 � 0.1679R indices (all data) R1 � 0.0700, R1 � 0.1292,

wR2 � 0.1197 wR2 � 0.1923Largest dif. peak/hole 1.390 / �2.164 3.490 / �2.848

Crystallographic data for the structures reported in this paper (ex-cluding structure factors) have been deposited with the CambridgeCrystallographic Data Centre as Supplementary Publication No.CCDC-637294, [Pt(AcbM)]4 ·2/2DMSO ·2DMSO ·5H2O; CCDC-637295 [Pt(AcbE)]4 ·4DMSO ·2H2O. Copies of the data can beobtained free of charge on application to CCDC, 12 Union Road,Cambridge CB2 1EZ, UK (Fax: � 44-1223/336-033; e-mail:deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).

www.zaac.wiley-vch.de 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2007, 2255�22612260

Acknowledgements. We thank the Xunta de Galicia for continuedfinancial support (Ref. PGIDIT03PXIC20302PN).

References

[1] [a] M. J. M. Campbell, Coord. Chem. Rev. 1975, 15, 279; [b]P. Scovill, D. L. Klayman, C. F. Franchino, J. Med. Chem.1985, 25, 1261.

[2] S. N. Pandeya, D. Siram, G. Nath, E. DeClercq, Eur. J. PharmSci. 1990, 9, 25 and references therein.

[3] E. Lopez-Torres, D. G. Calatayud, M. A. Mendiola, C. J. Pas-tor, J. R. Procopio, Z. Anorg. Allg. Chem. 2006, 632, 2471.

[4] [a] J. P. Jasinski, J. R. Bianchani, J. Cueva, F. A. El-Saied, A.A. El-Asmy, D. X. West, Z. Anorg. Allg. Chem. 2003, 629, 202;[b] L. Adrio, G. Alberdi, A. Amoedo, D. Lata, A. Fernandez,J. Martinez, M. T. Pereira, J. M. Vila, Z. Anorg. Allg. Chem.2005, 631, 1121; [c] L. A. Adrio, A. Amoedo, J. M. Antelo, J.J. Fernandez, J. Martinez, J. M. Ortigueira, M. T. Pereira, J.M. Vila, Z. Anorg. Allg. Chem. 2005, 631, 2204.

[5] [a] A. C. Sartorelli, K. C. Agrawal, A. S. Tsiftsoglou, E. C.More, Adv. Enzyme Reg. 1977, 15, 117; [b] J. S. Casas, E. E.Castellano, J. Ellena, M. S. Garcia-Tasende, A. Sanchez, J.Sordo, E. M. Vazquez-Lopez, M. J. Vidarte, Z. Anorg. Allg.Chem. 2003, 629, 261; [c] V. Lozan, P. G. Lassahn, C. Zhang,B. Wu, C. Janiak, G. Rheinwald, H. Lang, Z. Naturforsch.2003, 58, 1152, 1164; [d] G. Pereiras-Gabian, E. M. Vazquez-Lopez, U. Abram, Z. Anorg. Allg. Chem. 2004, 630, 1665.; [e]A. I. Matesanz, I. Cuadrado, C. Pastor, P. Souza, Z. Anorg.Allg. Chem. 2005, 631, 780.

[6] [a] M. C. Rodriguez-Argüelles, A. Sanchez, M. Belicchi Fer-rari, G. Gasparri Fava, C. Pelizzi, G. Pelosi, R. Alberini, P.Lunghi, S. Pinelli, J. Inorg. Biochem. 1999, 73, 7; [b] E. Labis-bal, A. Sousa-Pedrares, W. Kaminsky, D. X. West, Z. Natur-forsch. 2002, 57, 908; [c] L. Otero, P. Noblia, D. Gambino, H.Cerecetto, M. Gonzalez, R. Sanchez-Delgado, E. E. Castel-lano, O. E. Piro, Z. Anorg. Allg. Chem. 2003, 629, 1033; [d] V.Vrdoljak, M. Cindric, D. Matkovic-Calogovic, B. Prugovecki,P. Novak, B. Kamenar, Z. Anorg. Allg. Chem. 2005, 631, 928;[e] N. I. Dodoff, D. Kovala-Demertzi, M. Kubiak, J. Kuduk-Jaworska, A. Kochel, G. A. Gorneva, Z. Naturforsch. 2006,61, 1110.

[7] [a] T. Bonfada, G. M. de Oliveira, D. F. Back, E. S. Lang, Z.Anorg. Allg. Chem. 2005, 631, 878�881; [b] K. Abu-Shandi,C. Janiak, Z. Naturforsch. 2005, 60b, 1250�1254.

[8] [a] E. Sinn, M. F. Charles Jr, R. B. Martın, J. Am. Chem. Soc.1978, 100, 489; [b] J. M. Moreno, J. Ruız, J. M. Domınguez-Vera, E. Colacio, D. Galisteo, R. Kivekas, Polyhedron 1994,13, 203.

[9] [a] E. Bermejo, A. Castineiras, L. J. Ackerman, M. D. Owens,D. X. West, Z. Anorg. Allg. Chem. 2001, 627, 1966; [b] E.Bermejo, A. Castineiras, L. M. Fostiak, I. Garcia, A. Llamas-Saiz, J. K. Swearingen, D. X. West, Naturforsch. 2001, 56,1297; [c] A. Castineiras, I. Garcia, E. Bermejo, Z. Anorg. Allg.Chem. 2002, 628, 492; [d] K. A. Ketcham, I. Garcia, E.Bermejo, J. K. Swearingen, A. Castineiras, D. X. West, Z.Anorg. Allg. Chem. 2002, 628, 409; [e] I. G. Santos, U. Abram,Z. Anorg. Allg. Chem. 2004, 630, 697; [f] E. Bermejo, A. Casti-neiras, I. Garcia-Santos, D. X. West, Z. Anorg. Allg. Chem.2004, 630, 1096; [g] E. Bermejo, A. Castineiras, I. Garcia-Santos, L. M. Fostiak, J. K. Swearingen, D. X. West, Z. Anorg.Allg. Chem. 2005, 631, 728; [h] E. Bermejo, A. Castineiras, I.Garcia-Santos, D. X. West, Z. Anorg. Allg. Chem. 2005, 631,2011.

Pt4S4 Clusters with Functionalized Thiosemicarbazones

[10] [a] J. C. Dabrowiak, J. Inorg. Biochem. 1980, 13, 317; [b] P. S.Lin, L. Kwock, K. Hefter, G. Misslbeck, Cancer Res. 1983, 43,1049; [c] L. F. Povirk in S. Neidle, M. J. Waring (eds.) Molecu-lar Aspects of Anti-Cancer Drug Action, VCH, Weinheim,1983; [d] V. J. Basus, N. J. Oppenheimer, Biochem. 1985, 24, 81.

[11] R. D. Jones, D. A. Summerville, F. Basolo, Chem. Rev. 1979,79, 139.

[12] P. N. Yadav, M. A. Demetzis, D. Kovala-Demertzi, A. Casti-neiras, D. X. West, Inorg. Chim. Acta 2002, 332, 204.

[13] F. Hueso-Urena, N. A. Illan-Cabeza, M. N. Moreno-Carret-ero, A. L. Penas-Chamorro, R. Faure, Inorg. Chem. Commun.1999, 2, 323.

[14] H. K. Mahtani, Sh.-Ch. Chang, J. R. Ruble, I. N. L. Black, P.B. Stein, Inorg. Chem. 1993, 32, 4946.

[15] G. Smith, C. H. L. Kennard, P. C. W. Mak, J. Organomet.Chem. 1985, 290, C7.

[16] D. C. Craig, I. Q. Dance, Polyhedron 1987, 6, 1157.[17] K. H. Erbert, W. Massa, H. Donath, J. Lorberth, B.-S. Seo,

E. Herdtweck, J. Organomet. Chem. 1998, 559, 203.[18] T. Kawamoto, I. Nagasawa, H. Kuma, Y. Kushi, Inorg. Chem.

1996, 35, 2427.[19] A. G. Quiroga, J. M. Perez, I. Lopez-Solera, J. R. Masaguer,

A. Luque, P. Roman, A. Edwards, C. Alonso, C. Navarro-Ran-ninger, J. Med. Chem. 1998, 41, 1399.

[20] J. M. Vila, M. T. Pereira, J. M. Ortigueira, M. Grana, D. Lata,A. Suarez, J. J. Fernandez, A. Fernandez, M. Lopez-Torres,H. Adams, J. Chem. Soc., Dalton Trans. 1999, 4193.

Z. Anorg. Allg. Chem. 2007, 2255�2261 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 2261

[21] T. Yamaguchi, A. Shibata, T. A. Ito, J. Chem. Soc., DaltonTrans. 1996, 4031.

[22] D. Gibson, S. J. Lippard, Inorg. Chem. 1986, 25, 219.[23] H.-B. Bürgi, J. D. Dunitz (ed.) Structure Correlation, Vol. 2,

VCH, Weinheim, 1994.[24] A. Castineiras, M. Gil, E. Bermejo, D. X. West, Polyhedron

2001, 20, 449.[25] G. A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford

University Press, Oxford, 1997.[26] C. Janiak, J. Chem. Soc., Dalton Trans. 2000, 3885.[27] H. Suezawa, T. Yoshida, Y. Umezawa, S. Tsuboyama, M.

Nishio, Eur. J. Inorg. Chem. 2002, 3148.[28] H. Biltz, H. Wittek, Chem. Ber. 1921, 54, 1035.[29] Bruker, SMART and SAINT. Area Detector Control Inte-

gration Software, Bruker Analytical X-ray Instruments, Inc.,Madison, Wisconsin, 1999.

[30] G. M. Sheldrick, SADABS, Program for Empirical AbsorptionCorrection of Area Detector Data, University of Göttingen,Germany, 1997.

[31] G. M. Sheldrick, Acta Crystallogr. 1990, A46, 467.[32] G. M. Sheldrick, SHELX-97. Program for the Refinement of

Crystal Structures, University of Göttingen, Germany, 1997.[33] A. L. Spek, PLATON. A Multipurpose Crystalographic Tool.

Utrecht University, The Netherlands, 2004.[34] A. J. C. Wilson (Ed.), International Tables for Crystallography,

Vol. C, Kluwer Academic Publishers, Dordrecht, 1995.