Ruthenium thioether chemistry: the synthesis and structure of a host–guest complex [Ru([9]aneS3)2][BPh4]2·2Me2SO, and of [Ru([9]aneS3)2][BPh4]2·2MeNO2 and [Ru([18]aneS6)][BPh4]2([9]aneS3=1,4,7-trithiacyclononane, [18]aneS6= 1,4,7,10,13,16-hexathiacyclo-octadecane)