Synthesis and characterisation of cobalt and nickel compounds with phosphinothiol ligands. Crystal and molecular structures of [Co{ {2- (Ph2P)-6- (Me3Si)C6H3S)} }3], [Ni{ {2- (Ph2P)-6- (Me3Si)C6H3S)} }2] and [Co{ {2- (Ph2PO)-6- (Me3Si)C6H3S} }2]