Spontaneous formation of a chiral (Mo2O2S2)2+-based cluster driven by dimeric {Te2O6}-based templates

Utilization of tellurite anion as template, led to the formation of unprecedented oxothiometalate based building blocks and the spontaneous manifestation of chirality.

Thermogravimetric Analysis: Analysis was performed on a TA Instruments Q500 Thermogravimetric Analyser under nitrogen flow with a typical heating rate of 10° C/min from room temperature up to 800° C, unless otherwise stated Elemental Analysis: Mo, S and Te content were determined by ICP-OES analysis according to the following procedure: 5-10 mg sample material was digested by adding 1 mL deionised water and 2mL conc. HNO3 to the sample in a digestion beaker. The sample solution was warmed until clear before being allowed to cool and a further 5mL deionised water added. The resulting solution was transferred quantitatively with washings to an A class 50mL volumetric flask and made up to the mark with deionised water. A blank sample was also prepared simultaneously to account for any digestion interferences. The samples were transferred to 50mL polypropylene centrifuge tubes and analysed on an Agilent SVDV 5100 ICP-OES using the SVDV mode and appropriate calibration standards.
Carbon and nitrogen content was analysed by the University of Glasgow microanalysis service within the School of Chemistry.
Potassium content was determined using a Corning 410 Flame Photometer using the same samples and calibration standards used in the ICP-OES analysis.
Synthesis of K3[(Mo2O2S2)4(TeO3)(OH)9]·20H2O, 1: Na2TeO3 (0.0501 g, 0.226 mmol) was dissolved in 20 mL distilled water to form a clear, colourless solution. Dimeric [Mo2O2S2] 2+ (5 mL, 0.68 mmol) was added, upon which the colour of the solution transitioned from colourless, through red and cloudy yellow to black. 1M K2CO3(aq) was used to bring the pH to 5.13, with the colour being a cloudy yellow. The reaction mixture was then stirred at room temperature for 1 hour during which time the pH rose to 6.87. The solution was filtered and kept at 18 °C and after 1 week orange, cubic crystals suitable for X-ray diffraction studies were collected (57.8 mg, 20.67 % based on Mo  2+ (0.68 mmol) followed which resulted in a series of colour change from colourless to cloudy orange to black. The pH of the solution was adjusted to 5.48 with 1M K2CO3 after which the reaction mixture turned cloudy yellow. After stirring at room temperature for 1 hour, during which time the pH rose to 7.79, the reaction mixture was filtered and the resulting clear orange solution was stored at 5 °C for 1-2 weeks, after which 64.2 mg orange diamond-shaped plate crystals suitable for X-ray diffraction studies were collected (17.38 % yield based on Mo) Elemental Analysis of H98K8Mo20O93S20Te5 (FW: 5097.47): Theoretical (Found)%: Mo 37.64 (37.17), S 12.58 (13.16), Te 12.52 (12.80), K 6.14 (6.10).

ESI-Mass Spectrometry
We have employed electrospray ionisation mass spectrometry and performed the experiments in ion mobility mode in an effort to de-convolute and identify the species which correspond to the observed envelopes. Not only have we been able to use this technique to comment on the solution stability of each of the three compounds, we have also been able to confirm that they fragment into their fundamental building blocks which is indicative of the building block library stability.
Compound 1 revealed three envelopes tentatively assigned to the intact cluster centred at c.a. 1464.9, 1486.8 and 1502.8 m/z respectively (Table S1). In addition to this there are three further envelopes that we have assigned to the partially fragmented species derived from the loss of just one constituent part, such as a [Mo2O2S2] 2+ dimeric unit or a tellurite anion. Interestingly, there are two additional envelopes that are large enough to correspond to ion pairing of molecular species centred at 1491.9 and 1496.2 m/z which correspond to the dimeric and trimeric aggregates of compound 1.
Finally, it was possible to identify the type A virtual building block which is used to construct the cluster and gave an envelope centred at 802.3 m/z. The building block can fragment further through the loss of [Mo2O2S2] 2+ dimeric units.
The mass spectrum of compound 2 suggests that this molecule is seemingly less stable than compound 1 under the employed ionization conditions (Table S2). There are still two envelopes that were assigned to compound 2 after removal one of the three virtual building blocks (ca. 959.2 m/z) while the other having lost only a single tellurite template (ca. 1347.32 m/z). What is clearer from this spectrum is the presence of the constituent building blocks in this molecule. B type building blocks occur fairly regularly, as do C type building blocks-however these could equally be D type building blocks since C and D give identical m/z values.
The mass spectrum for compound 3 hasn't revealed any envelopes that could be assigned to the intact cluster indicating lack of stability, under the experimental conditions (Table S3). However we were able to detect virtual building blocks or bigger fragments of the cluster.
Interestingly we were able to observe a fragment that can be assigned to a species that is half of the cluster 3 and gives an envelope centered at 1467.9 m/z. This view is further reinforced by the presence of four envelopes that can be assigned to one third of the full molecule. Finally, two envelopes correspond to type A building blocks with an additional dimeric unit.    Figure S9: Ion Mobility ESI mass spectra for compound 3 (upper) and ESI mass spectra (lower)