Crystal structure of (dimethylformamide-κ O )(perchlorato-κ 2 O , O′ ){μ 2 -6,6′-((1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis(4-bromo-2-methoxyphenolate)-κ 8 N , N′ , O : O , O′ : O′ , O′′ , O′′′ }sodium(I)nickel(II), C 25 H 23 Br 2 ClN 3 NaNiO 9