Nickel II Bromide Dihydrate

K The hot mixture disintegrates filter paper the nickel oxide, nickel powder, and fine carbon residues rapidly block a sintered-glass frit or Celite filter bed. 

Thermogravimetric analysis of a sample of the 5 hydrate shows that water evolution occurs between 34.1° and 89.6°, at which latter temperature a dihydrate has formed. This is stable up to 107°, beyond which temperature the remaining two water molecules are slowly lost. Differential thermal analysis shows two dehydration endotherms at 36.4 and 132.8° and a structure transformation (octahedrally coordinated to close-packed hexagonal) endotherm at 151.8°. 

A three-necked, 3-1. flask fitted with a reflux condenser and mechanical stirrer is charged with 327 g. (2.0 moles) of nickel(II) chloride 1.88 hydrate, 550 ml. of absolute ethanol, and 558 g. (4.14moles) of triethyl orthoformate. The cream-colored slurry is stirred at the reflux under an atmosphere of nitrogen for 2 hours, after which time the water content of a 1-ml. sample of the now homogeneous reaction mixture is checked with a 

Karl Fischer titration. The Karl Fischer analysis should indicate that the solution is completely water-free. If water is present the mixture should be refluxed for an additional hour. 

Another Karl Fischer analysis should then be performed, and if water continues to persist, an additional 0.1-0.2 mole of triethyl orthoformate should be added and the refluxing continued for an additional hour. Upon concentration of the solution to a volume of 11., and then cooling it to 0° under nitrogen to exclude moisture, pastel-green hygroscopic needles of the tetrakis-(ethanol) complex (140 g., 22%f) form. These are collected and carefully dried under nitrogen on a Schlenk frit at 23°. Anal. Calcd. for C8H24C104Ni C, 30.61 H, 7.71 Cl, 22.59 O, 20.39 Ni, 18.70. Found C, 27.71 H, 6.95 Cl, 22.97 O, 20.82 Ni, 19.09. 

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Procedures for the preparation of nickel(II) chloride dihydrate and nickel(II) bromide dihydrate follow. From these, the preparation via the orthoformate ester dehydration route of the anhydrous tetrakis(ethanol) and 1,2-dimethoxyethane complexes is described. The preparation of nickel(II) iodide-bis(l,2-dimethoxyethane) from nickel(II) iodide pentahydrate is also given. 

C12H3sBr2N8Ni02Sft, Tetrakis(N,N -dimethylthiourea)nickel(II) bromide dihydrate, 42B, 761... 

Perhaps the most clearly defined example involves the macrocyclic complex of Curtis, Ni(CT)X2. The solid, violet, paramagnetic, anhydrous chloride and bromide must be carefully protected from moisture for they readily revert to yellow, diamagnetic dihydrates. The fact that two molecules of water are taken up to produce a diamagnetic nickel(II) ion is especially interesting for displacement of the halide, and coordination by the water molecules would surely produce a violet, paramagnetic species... 

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