Altering thermochromic transition temperature in transition metal ethylenediamine complexes by substitutional doping of anionic species

A tunable thermochromic material comprising:

• a first instance of N,N′-diethylethylenediamine operating as a ligand and complexed with a metal salt;
• and two different anions present in a first proportion, wherein the anions are tetrafluoroborate (BF4−) and bromide (Br−);
• and
• a second instance of N,N′-diethylethylenediamine operating as a ligand complexed with the metal salt and the two different anions, wherein the two different anions are present in a second proportion differing from the first proportion,
• wherein, as a consequence of the different proportions, the first instance has a different thermochromic transition temperature from that of the second instance, and
• wherein the thermochromic transition is reversible with a change in temperature.

A method of preparing a tunable thermochromic material, the method comprising:

• providing in a first solvent two different anions present in a first proportion and a metal salt;
• adding an organic ligand to the solvent, thereby causing a first thermochromic material to precipitate;
• providing in a second solvent the two different anions present in a second proportion and the metal salt;
• adding the organic ligand to the second solvent, thereby causing a second thermochromic material to precipitate,
• wherein the first and second thermochromic materials differ only in the proportions of the two different anions,
• wherein the ligand is an N,N′-disubstituted diamine, and
• wherein, as a consequence of the different proportions, the first material has a different thermochromic transition temperature from that of the second material, and
• wherein the thermochromic transition is reversible with a change in temperature.