Ultramarines are bright blue pigments based on a zeolite (sodalite) that hosts the colour centres [S2] and
Question:
Ultramarines are bright blue pigments based on a zeolite (sodalite) that hosts the colour centres [S2]‾ and [S3]‾. Ultramarines include lapis lazuli and have been in use for over 5500 years. The UV-VIS spectrum of [S2]‾ exhibits a broad band centred at 370 nm, while [S3]‾ absorbs at 595 nm.
(a) Draw Lewis structures for [S2]‾ and [S3]‾. What shape is the [S3]‾ ion?
(b) Why can EPR spectroscopy be used to study these ions? Suggest a reason why both ions behave isotropically even at low temperatures.
(c) Explain why an ultramarine containing only [S3]‾ colour centres appears violet-blue in colour.
(d) Why does [S2]‾ contribute to the colour of ultramarine pigments even though λmax is 370 nm, i.e. in the UV region?
(e) In synthetic ultramarines, the ratio of [S3]‾ : [S2]‾ can be altered to produce pigments ranging from violet-blue through blues to green. Account for this.
Step by Step Answer:
a Lewis structure is a simple representation of molecule with all its valence electrons lone electron pairs and bonds single or multiple First we need to write ground state configuration for sulfur S ...View the full answer
