Ruthenium and osmium are transition metals below iron in Group 8 of the Periodic Table.

1. (a)Two different complex ions, X and Y, can form when anhydrous RuCl3 reacts with water under certain conditions. X and Y have octahedral geometry. Aqueous samples of X and Y react separately with an excess of AgNO3(aq). Different amounts of AgCl are precipitated: • 1 mole of complex ion X produces 2 moles of AgCl • 1 mole of complex ion Y produces 1 mole of AgCl. (i) Complete Table 4.1 to suggest formulae for X and Y. Table 4.1 | | X | Y | |:-------|:--|:--| | formula of complex | | | [2]
2. (a)(ii)Both complexes react with an excess of bipyridine, bipy, to form a mixture of two stereoisomers of [Ru(bipy)3]3+. bipy [Figure 4.1, structure of bipyridine shown with N-N bonds] Bipyridine is a bidentate ligand. Draw three-dimensional diagrams of the two stereoisomers of [Ru(bipy)3]3+. Use N N to represent the bipy ligand in your structures. [2]
3. (b)Fig. 4.1 shows another ruthenium complex. [Figure 4.1, structure of (H3N)5Ru-N(pyrazine)N-Ru(NH3)5]5+ This complex contains the neutral ligand pyrazine. pyrazine [Figure, structure of pyrazine with N=N atoms]
4. (b)(i)Suggest how pyrazine is able to bond to two separate ruthenium ions.[1]
5. (b)(ii)Pyrazine is an aromatic compound. The bonding and structure of pyrazine is similar to that of benzene. Describe and explain the shape of pyrazine. In your answer, include: • the hybridisation of the nitrogen and carbon atoms • how orbital overlap forms π bonds between the atoms in the ring.[2]
6. (b)(iii)Predict the number of peaks seen in the carbon-13 NMR spectrum of pyrazine. Explain your answer.[2]
7. (b)(iv)The overall charge of the ruthenium complex in Fig. 4.1 is 5+. Deduce the possible oxidation states of the two ruthenium ions in the complex.[1]
8. (c)Osmium tetroxide, OsO4, reacts with alkenes in a similar manner to cold dilute acidified MnO4-. Fig. 4.2 shows a proposed synthesis of a condensation polymer G. [Figure 4.2, reaction scheme for polymer G synthesis]
9. (c)(i)Suggest a reagent for step 1.[1]
10. (c)(ii)Draw the structure of exactly one repeat unit of the condensation polymer G. The ester linkage should be shown fully displayed.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.