Crystal structure of μ 3 -bromo-μ 3 -hydroxo-tri-μ 2 -chloro-tris(tetramethyl-ethylenediamine- nickel(II)) bromide—di-μ 3 -hydroxo-tri-μ 2 -chloro-tris(tetramethylethylenediamine-nickel(II)) bromide (0.70:0.30), [{Ni 3 Br(OH)Cl 3 (C 6 H 16 N 2 ) 3 }{Br}] 0.70 · [{Ni 3 (OH) 2 Cl 3 (C 6 H 16 N 2 ) 3 }{Br}] 0.30