Synthesis and characterisation of neutral and cationic 2,7-dimethyloctadienediylruthenium(IV) complexes. X-Ray crystal structure of cis-bis(acetonitrile)chloro[(1,2,3,6,7,8-η)-2,7-dimethylocta-2,6-diene-1,8-diyl]ruthenium(IV) tetrafluoroborate