Amirah Faizah Abdul Muthalib, Ibrahim Baba*, Hamid Khaledi, Hapipah Mohd Ali and Edward R. T. Tiekink* Structural systematics of RSn(S 2 CNR 0 R 00 ) 2 Cl compounds Abstract: Three new organotin(IV) structures of general formula RSn(S 2 CNR 0 R 00 ) 2 Cl, where R 0 6¼ R 00 , namely MeSn $ [S 2 CN(Me)(Cy)] 2 Cl (1), MeSn[S 2 CN(i-Pr)(CH 2 Ph)] 2 Cl (2) and PhSn[S 2 CN(Et)(i-Pr)] 2 Cl (3) are described. Each structure features tin in a distorted octahedral geometry defined by a CClS 4 donor set as a result of two chelating dithio- carbamate ligands. In all cases the tin-bound carbon and chloride atoms are cis. The shorter Sn–S bond lengths in 3 are correlated with the presence of the relatively more electronegative Sn-bound phenyl substituent. The new structures conform to the structural motif adopted by all other compounds with the formula RSn(S 2 CNR 0 R 00 ) 2 Cl, where R 0 ¼ R 00 , suggesting the unsymmetrical substitu- tion pattern of the dithiocarbamate ligands in the present study does not influence the adoption of this structural motif. The homogeneity in the structural motif notwith- standing, non-systematic variations in geometric para- meters are found in these structures indicating an overall influence of crystal packing upon molecular geometry. Keywords: tin, organotin, unsymmetric dithiocarbamate, crystal structure analysis, X-ray diffraction  *Corresponding Authors: Ibrahim Baba, Universiti Kebangsaan Malaysia, School of Chemical Sciences and Food Technology, 43600 Bangi, Selangor, Malaysia, e-mail: aibi@ukm.my (IB); Edward R. T. Tiekink: The University of Malaya, Department of Chemistry, 50603 Kuala Lumpur, Malaysia, e-mail: Edward.Tiekink@gmail.com (ERTT) Amirah Faizah Abdul Muthalib: Universiti Kebangsaan Malaysia, School of Chemical Sciences and Food Technology, 43600 Bangi, Selangor, Malaysia Hamid Khaledi, Hapipah Mohd Ali: The University of Malaya, Department of Chemistry, 50603 Kuala Lumpur, Malaysia Introduction The major motivations for investigating tin and organotin compounds of dithiocarbamate ligands, i.e. – S 2 CNR 0 R 00 , revolve around their utility as synthetic precursors for tin sulphide nanoparticles and their potential as therapeutic agents [1]; work in both endeavours continues [2, 3]. Along with other main group element dithiocarbamates [4–6], these molecules can exhibit significant structural diversity in their crystal structures [1]. Thus, dithiocarba- mate-bound substituents and in the case of organotin(IV) derivatives, tin-bound organic substituents, can influ- ence the ultimate molecular structure adopted in the so- lid-state. Differences in structure can relate to molecular geometry and even coordination number, as well as su- pramolecular aggregation patterns based on secondary interactions [7, 8]. The influence of the dithiocarbamate- bound substituents is steric in origin and may, for exam- ple, preclude supramolecular aggregation via secondary Sn … S interactions. A more complicated situation arises for tin-bound substituents in that over and above steric considerations, these groups may exert an electronic ef- fect by influencing the Lewis acidity of the tin centre [1]. An example of structural diversity observed in organotin dithiocarbamates is found in molecules with the general formula R 2 Sn(S 2 CNR 0 R 00 ) 2 , as outlined briefly below. There are four basic structural motifs for molecules conforming to the general formula R 2 Sn(S 2 CNR 0 R 00 ) 2 ; there are over 80 examples in the Cambridge Structural Database (CSD) [9]. The most predominant motif is illus- trated in Fig. 1a for Me 2 Sn(S 2 CNEt 2 ) 2 , which is known to crystallise in three polymorphs [10–12]. In this motif, I, the tin atom is six-coordinate being chelated by two dithiocarbamate ligands with the coordination geometry completed by two methyl-C atoms. The SnS 4 atoms de- fine a skewed-trapezoidal plane with two Sn–S bond lengths (ca. 2.5 Å) being significantly shorter than the other two (ca. 3.0 Å). The methyl-C atoms lie over the weaker Sn–S interactions so that the coordination geo- metry is best described as skew-trapezoidal bipyramidal. The simple substitution of methyl substituents by phenyl groups can result in a rearrangement of the C 2 S 4 donor set that now defines an octahedral geometry, motif II, with cis-disposed ipso-C atoms, as shown in Fig. 1b for Ph 2 Sn(S 2 CNEt 2 ) 2 ; this structure is found in two poly- morphic forms [13, 14]. Increasing the steric bulk of the tin-bound substituents to t-butyl groups results in a de- crease in coordination number, to five, leading to motif III, illustrated in Fig. 1c for (t-Bu) 2 Sn(S 2 CNMe 2 ) 2 [15], as DOI 10.1515/zkri-2013-1682  Z. Kristallogr. 2014; 229(1): 39 – 46 Brought to you by | California Institute of Technology Authenticated Download Date | 6/19/15 5:38 PM