Past exam of the chemistry B course of the University of Cambridge / 2022 / Paper 2 / B9 / e

Table of contents
- Solution e

Solution

A reasonable product is sodium facial trimetaphosphate–molybdenum tricarbonyl, with the anion

[Mo (CO)_{3} (κ^{3} O, O^{'}, O^{''} - P_{3} O_{9})]^{3 -}, gas = 3 CO .

(1)

One terminal O from each phosphorus binds Mo; the three O donors occupy one octahedral face, while the three carbonyls occupy the opposite face. The ring bridges remain P–O–P bridges and are not replaced by Mo–P bonds. Mo remains Mo(0),

d^{6}

, and

6 + 3 (2) + 3 (2) = 18

electrons. Overall,

N a_{3} P_{3} O_{9} + Mo (CO)_{6} ⟶ N a_{3} [Mo (CO)_{3} (P_{3} O_{9})] + 3CO .

(2)

acetonitrile can transiently replace CO during heating, but it is not required in the final six-coordinate proposal. The same anion has been structurally characterized with a different counterion: that primary study independently supports the facial O