TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preparation (Claimed): Preparation of (I) comprises anodization reaction of metallic tungsten, which is carried out with an electrolytic solution comprising a nitrogenated organic compound (at least 25 wt.%), fluoride ions (0.01-3 wt.%) and an oxidizing compound of metallic tungsten (1-50 wt.%) under electrolytic conditions, preferably water. Preferred Components: The nanostructure comprises tungsten oxide domains shaped as winding or branched open swellings having a longitudinal groove. (I) has nitrogen/tungsten atomic ratio of greater than or equal to 0.1 (preferably 0.1-0.3). The oxidizing compound of metallic tungsten is: a peroxide (preferably hydrogen peroxide), which is present at 1-10 wt.% with respect to the total weight of the electrolytic solution; or water, which is present at a concentration of 1-50 (preferably 10-20) wt.% with respect to the total weight of the electrolytic solution. The electrolytic solution comprises: up to 50 (preferably 0-25) wt.% of an organic solvent; hydrofluoric acid, ammonium fluoride, tetraalkylammonium fluoride, sodium fluoride and/or potassium fluoride, preferably hydrofluoric acid or ammonium fluoride at a concentration of 0.03-0.5 wt.%, preferably 0.04-0.1 wt.% of fluoride ions; comprises water (20 wt.%), ammonium fluoride (0.05 wt.%) and remaining amount of N-methyl formamide. Preferred Method: The anodization is: effected by applying a potential difference of 5-60V (preferably 30-40V) to the electrodes; and carried out for 1-72 (preferably 12-72) hours.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred components: The organic solvent is 1-5C alcohol, 1-5C organic acid or 1-4C polar aprotic organic compound having at least one oxygen or halogen (preferably fluorine). The nitrogenated organic compound is: a 1-25C nitrogenated organic compound (preferably 1-10C) with at least one nitrogen atom, preferably an organic amine/amide, where the organic amide is of formula (R1-A-NR2R3); and are those capable of forming homogeneous mixtures with water comprising 3-50 (preferably 10-50) wt.% of water and the remaining percentage of the nitrogenated organic compound.R1 = H, 1-6C alkyl (preferably 1-3C alkyl) or -NR2R3;R2 = H (preferred) or 1-6C alkyl (preferably 1-3C alkyl);R3 = 1-6C alkyl (preferably 1-3C alkyl) or H;A = divalent group, which is CO (preferred), SO2 or POR1a; andR1a = R1. EXAMPLE - No suitable example given.