Polymetallic Assembly Of Sulfide Complexes Biology Essay

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Heterometallic complexes based on core has always been a fascinating area to explore. This project aims to synthesis complexes with different metal ligands, namely zirconium and zinc.

Complexes with a hinged core are structured like a butterfly with the metal atoms at the wing-tip and sulfur at the hinge positions. Thanks to the flexible hinge angle of the central {Pt2S2} ring as well as the highly pronounced nucleophilicity of the lone pairs on the two μ-sulfide ligands, numerous homo- and hetero-metallic aggregates can be synthesized1.

The chemistry of heteropolynuclear complexes containing diverse metal fragments has drawn intense interest especially relevant to the chemistry of some industrially important catalytic processes. Complexes with bridging sulfide ligands have received widespread attention because of their applications in varied areas, from biological systems, applied catalysis, to the chemistry of novel molecular systems1.

In this project, the assemblies formed from complexes Pt2S2(PPh3)4 and Pt2S2(dppf)2 with metal compound zirconium dichloride oxide (ZrOCl2), zinc chloride (ZnCl2), in different ratios will be studied.

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The synthesis of these assemblies will firstly be observed visually. The detailed analysis will then be carried out by analytical and spectroscopic instruments, such as Electrospray Ionization (ESI) and Nuclear Magnetic Resonance (NMR). Reactions between metal salts and Pt2S2(PPh3)4 and Pt2S2(dppf)2 in pre-determined ratios are discussed.

Experimental Procedures

1.1 Preparation of PtCl2(CH3CN)2

PtCl2 (0.512g, 1.92mmol) was reacted with excess CH3CN, and the mixture was refluxed under nitrogen for two hours. The clear solution was filtered when hot. The solvent of the filtrate was evaporated to dryness. PtCl2(CH3CN)2, a yellow precipitate, was obtained. Yield: 0.493g; Percentage Yield: 74%

1.2 Synthesis of PtCl2(PPh3)2

PtCl2(CH3CN)2 (0.493g, 1.42mmol) was reacted with excess PPh3 (1.500g, 5.73mmol). The mixture was refluxed in CH2Cl2 for three hours. Diethyl ether was used to wash away excess PPh3 remained in the solution. The clear colorless solution was filtered and vacuum dried. PtCl2(PPh3)2 , a white solid, was obtained. Yield: 0.996g; Percentage Yield: 46%

1.3 Synthesis of Pt2(μ2-S)2(PPh3)4

PtCl2(PPh3)2 (0.996g, 1.26mmol) was stirred with excess Na2S·9H2O (3.020g, 12.6mmol) in degassed benzene for four days. The orange suspension was filtered and washed with methanol, distilled water, and ether. The mixture was then been vacuum dried. Pt2(μ2-S)2(PPh3)4, a bright orange solid, was obtained. Yield: 0.868g; Percentage Yield: 95%

1.4 Qualitative analysis of reaction between metallic salts and Pt2(μ-S)2(PPh3)4.

Pt2(μ-S)2(PPh3)4 was added and dissolved in about 2 cm3 methanol. All the metallic salts were also added into about 2 cm3 methanol. All mixtures were heated to promote dissolution, if needed. Solubility was recorded. Pt2(μ-S)2(PPh3)4 solution and metallic salt solutions were then mixed thoroughly to see whether a visible reaction will occur and thus to scale up in the process.

1.5Preparation of polymetallic sulfide complexes in 1:2, 1:4 ratio

Pt2(μ-S)2(PPh3)4 was mixed and stirred with metallic salts: Zr(NO3)2, Zn(NO3)2, ZnCl2, ZrOCl2 (formed when ZrCl4 is exposed to air), AlCl3, in 1:2 and 1:4 ratio in methanol respectively. ZrOCl2 and ZnCl2 were targeted for detailed study based on the ESI result which showed new complex might be produced using these two as well as results from Table 1 (Results and Discussion). The physical changes associated with reactions between ZrOCl2, ZnCl2 and Pt2(μ-S)2 (dppf )2 were also recorded.

1.6 Preparation of polymetallic sulfide complexes with ZrOCl2·8H2O in 1:4, 1:10 ratio

Pt2(μ-S)2(dppf)2 was mixed and stirred with metallic salts ZrOCl2·8H2O in 1:4 and 1:10 ratio respectively in methanol. An excess solid NH4PF6 was added to the clear yellow solution. After stirring for a further 1 h, a yellow solid precipitated. Distilled water (10ml) was then added to the mixture to induce complete precipitation. The yellow solid was then collected on a gine glass frit, washed successively with distilled water, ethanol, ether and dried in vacuo. For 1:4 ratio the product formed is very little and can be neglected. For 1:10 ration, a brown solid product was formed. Percentage Yield: 53%. For 1:4 ratio the product formed is very little and can be neglected. For 1:10 ratio, a brown solid product was formed. Percentage Yield: 53%.

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1.7 Preparation of polymetallic sulfide complexes with ZnCl2 in 1:1 ratio

ZnCl2(0.013 g, 0.1 mmol) was added with stirring to a MeOH (40 cm3) suspension of Pt2(μ-S)2(PPh3)4 (0.15 g, 0.1 mmol). After 6 h, the suspension, which changed gradually from orange to yellow, was filtered. A pale yellow product was obtained. Percentage Yield: 63%. The reaction between Pt2(μ-S)2(dppf)2 and ZnCl­­2 was carried out in the same method. A dark yellow product was formed. Percentage Yield: 39%.

RESULTS AND DISCUSSION

2.1 Analysis of reactions with Pt2(μ-S)2(PPh3)4

Complexes, Zn(NO­3)2, Zr(NO3)2, ZnCl2 did not exhibit visible reaction with Pt2(μ-S)2(PPh3)4 at room temperature, and Zr(NO3)2 with Pt2(μ-S)2(PPh3)4 did not exhibit visible reaction at high temperature, 62.7oC as well. This could imply that either there is no reaction or the resulting product is soluble in the solution or there is no color difference between the product and reagent mixtures. ESI was done to confirm whether a reaction had taken place. ZrCl2 and AlCl3 with Pt2S2(PPh3)4 exhibited a visible reaction at room temperature; Zn(NO­3)2 and ZnCl2 exhibited a visible reaction at 62.7oC. The solubility of salts in methanol and color changes on mixing with Pt2(μ-S)2(PPh3)4 were displayed in the following table.

Table1: Qualitative analysis of the reactions between metal salts and Pt2(μ-S)2(PPh3)4

Salt

Condition

Solubility

Color change after mixing with Pt2(μ-S)2(Pph3)4

Zn(NO3)2

Room temperature

Partially dissolved

Fromorange suspension into light yellow color suspension

Heating to 62.7oC

Partially dissolved

ZnCl2

Room temperature

Partially dissolved

From orange suspension into light yellowish clear solution

Heating to 62.7oC

Dissolved completely

Zr(NO3)2

Room temperature

Partially dissolved

No significant change

Heating to 62.7oC

Partially dissolved

AlCl3

Room temperature

Dissolved completely

From orange suspension into light yellowish clear solution

ZrOCl2·8H2O

Room temperature

Partially dissolved

From orange suspension solution into light yellowish clear solution.

[Pt2S2(PPh3)3+H+]

[Pt2S2(PPh3)2+H+]

[Pt2S2(PPh3)4+H+]

[Pt2S2(PPh3)4+ZnCl]+

Figure 1.1: ESI MS Spectra of the precipitate of the reaction between Pt2(μ-S)2(PPh3)4 and ZnCl2 in ratio 1:1.

This reaction has been reported in 2003. From the ESI it can be seen that the product formed is [Pt2S2(PPh3)+ZnCl]+ with the zinc bind to the Pt2S2 ring. A chloride atom may have detached from Zn due to the high temperature which required by ESI. Hence the product is suspected to be ZnPt2Cl2(PPh3 )4(μ-S)2.

2.2. Analysis of reactions with Pt2(μ-S)2 (dppf )2

The solubility of salts in methanol and color changes on mixing with Pt2(μ-S)2(dppf )2 were displayed in the following table.

Table 2: Qualitative analysis of the reactions between metal salts and Pt2(μ-S)2(dppf)2

Salt

Condition

Solubility

Color change after mixing with Pt2(μ-S)2 (dppf)2

ZrOCl2·8H2O

Room temperature

Dissolved completely

From orange suspension into dark yellowish clear solution

ZnCl2

Room temperature

Partially dissolved

From orange suspension into yellowish suspension

Figure 2.1: ESI MS Spectra of the precipitate of the reaction between Pt2S2(dppf)2 and ZrOCl2 in ratio 1:10 after 10 min

From the ESI above, the product formed is suspected to be [[Pt­2S2dppf2]2+ZrOCl++Na++H2O+MeOH]2+ with a positive charge of two. As the reaction had only taken place for 10 min, the amount of product formed is little.

[Pt­2S2dppf2]2+

ZrOCl++

Na++H2O+MeOH]]2=

[PtSdppf+H+]

[Pt2S2dppf2+H+]

Figure 2.2: ESI MS Spectra of the precipitate of the reaction between Pt2S2(dppf)2 and ZrOCl2 in ratio 1:10 after 3 hr

Figure 2.3: A zoom in of the ESI MS spectra of the product of the precipitate of the reaction between Pt2S2(dppf)2 and ZrOCl2 in ratio 1:10 after 3hr.

[Pt2S2dppf2+H+]

[PtSdppf+H+]

From the ESI in Figure 2.2, the amount of product formed had increased to a significant amount. This zoom scan is done to confirm the charge which is a positive charge of two.

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Figure 2.4: ESI MS Spectra of the precipitate of the reaction between Pt2S2(dppf)2 and ZrOCl2 in ratio 1:10 after 5 hr

After five hours, the amount of product had decreased almost to zero, which implies that the product is not stable under long period of experimental conditions.

[Pt2S2(dppf)2 + ZnCl]+

[Pt2S2(dppf)2+H+]

Figure 2.5: ESI MS Spectra of the precipitate of the reaction between Pt2S2(dppf)2 and ZnCl2 in ratio 1:1

This reaction is similar to that between Pt2S­­2(PPh3)4 and ZnCl2. The product is formed with ZnCl2 attaching to the Pt2S2 ring.

Our future plan is to isolate pure compound from the product already synthesized and . NMR and EA (elemental analysis) will also be done for deeper analysis of these complexes. Crystals will be grown to carry out further study.