Glucose Sodium Chloride

Trigonal co-crystal of glucose and sodium chloride: 2C₆H₁₂O₆·NaCl·H₂O Glucose (grape sugar) and sodium chloride (table salt) do not react, but can crystallize together, forming a single compound where there are 2 molecules of glucose per one formal molecule of NaCl. Such compounds, formed by crystallization without chemical interaction, are called cocrystals.

It is well soluble in water (my estimate is 90..110g per 100ml at room temperature) and forms crystals that are different both from pure glucose and from table salt. One of the photos shows the biggest crystal along its order-3 symmetry axis.

Growth time around 1 month, using slow evaporation method.

Properties

Crystal system: trigonal. This means that their base shape is cube, stretched along main diagonal.
Air stability: stable.

Preparation

This compound easily crystallizes from a solution, containing glucose and NaCl in equimolar proportion.

Make mother solution by dissolving 100g of glucose and 15g of NaCl in 90...100g of hot water. Let it cool and put into open container to allow slow evaporation. When small rhombic seed crystal appear on the container walls or solution surface, take few best ones, attach then to a thread and proceed to growing (see this gallery).

Recrystallization improves purity of the compound and clarity of crystals.

I used food-grade glucose and table salt as source materials.

Growing

Because of high solubility and noticeable viscosity of the saturated solution, evaporation rate must be very slow in order to obtain large single crystals. I covered growing container with a paper disc with relatively small hole.