Crystal and molecular structure and substitution reactivity of (.mu.-hydrido)(.mu.-pyridyl)dirhenium octacarbonyl, (.mu.-H)Re2(CO)8(.mu.-NC5H4). Crystal and molecular structure of (.mu.-hydrido)(.mu.-pyridyl)(trimethylamine N-oxide)dirhenium heptacarbonyl, (.mu.-H)Re2(CO)7(.mu.-NC5H4)(ME3NO)