Crystal structures of complexes between alkali‐metal salts and cyclic polyethers. 12. The complex between sodium bromide and 2,3‐dimethoxybenzo‐15‐crown‐5 {bromo(2,3‐dimethoxy‐6,7,9,10,12,13,15,16‐octahydrobenzo[1,4,7,10,13]pentaoxacyclopentadecene)sodium}