Reactions of the polyhydride complex ReH7(dppe) (dppe = Ph2PCH2CH2PPh2) with pyridine-2-carboxylic acid, 1-isoquinolinecarboxylic acid, 2-hydroxy-6-methylpyridine and 2-mercaptoquinoline. synthesis and structural characterization of seven-coordinate monohydrido complexes of rhenium(iii)