Sodium potassium tris(oxalato) ferrate

Formula: K₅Na[Fe(C₂O₄)₃]₂

One of the most interesting crystals: a double salt of sodium, potassium and ferrioxalate ion that have deep green color, highly symmetric shape and great stability upon exposure to air. Unfortunately, I was not able to prepare aluminium analog: Na and K alumooxalates just crystallized separtely.

Potassium Chloride

Formula: KCl

Potassium chloride is a potassium analog of a table salt. It has the same cubic crystalline structure and shape of crystals. Large crystals are easy to grow, but often get cloudy and badly formed.

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Potassium tris(oxalato) aluminate

Formula: K₃[Al(C₂O₂)₃]·3H₂O

Also known as potassium alumooxalate or potassium oxalatoaluminate. Similar compounds:

Sodium analog that have different structure: sodium tris(oxalato) aluminate.
Iron analog, with the same structure and nice green color: potassium tris(oxalato) ferrate(III).

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Potassium bis(sulfamato) chlorocuprate

Formula: K₂[Cu(SO₃NH₂)₂Cl₂]

An unusual coordination complex of copper, producing lustrous dark violet crystals.

It has bromine analog: potassium bis(sulfamato) bromocuprate. Also, potassium can be replaced with ammonium: ammonium bis(sulfamato) chlorocuprate

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Potassium Sulfamate

Formula: KSO₃NH₂ Potassium salt of sulfamic (amidosulfonic) acid. One of a few well crystallizing salts of this acid that crystallize well. Other salts often have excessive solubility.

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Potassium bis(sulfamato) bromocuprate

Formula: K₂[Cu(SO₃NH₂)₂Br₂]

Bromine analog of Potassium bis(sulfamato) chlorocuprate

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Potassium tris(oxalato) ferrate (III)

Formula: K₃[Fe(C₂O₄)₃]·3H₂O

Potassium salt of a complex acid, formed by Fe(III) and oxalate ions. As all ferrioxalates, has bright green color and is slightly light sensitve.

Potassium Zinc Sulfate

Formula: K₂Zn(SO₄)₂·6H₂O

Potassium twin of ammonium zinc sulfate, visually indistinguishable from it. I suspect that precise measurement could reveal some subtle differences in angles between faces, but for the naked eye these compounds look the same. Similarly, baking soda can be used to improve crystal quality (see "Growing" section).

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