Kinetics and mechanism of the oxidation of bis(.mu.-hydroxo)bis[aqua(1,4,7-triazacyclononane)molybdenum(III)](4+) by perchlorate. Acid-base-catalyzed trans .fwdarw. cis isomerization of bis(.mu.-oxo)-trans-dioxobis[(1,4,7-triazacyclononane)molybdenum(V)](2+)