▁other ▁r hen ium ▁complex es . ▁ ▁Str ucture ▁and ▁physical ▁properties ▁As ▁shown ▁by ▁X - ray ▁cry stal log raph y ▁tri r hen ium ▁non ach lor ide ▁consists ▁of ▁Re 3 Cl 1 2 ▁sub un its ▁that ▁share ▁three ▁ch lor ide ▁brid ges ▁with ▁adjacent ▁clusters . ▁The ▁inter connected ▁network ▁of ▁clusters ▁forms ▁sheets . ▁ ▁Ar ound ▁each ▁Re ▁center ▁are ▁seven ▁lig ands , ▁four ▁brid ging ▁ch lor ides , ▁one ▁terminal ▁ch lor ide , ▁and ▁two ▁Re - Re ▁b onds . ▁ ▁The ▁heat ▁of ▁ox id ation ▁is ▁evaluated ▁according ▁to ▁the ▁equation : ▁ 1 / 3 ▁Re 3 Cl 9 ▁ ▁+ ▁▁ 4 ▁O H − ▁ ▁+ ▁▁ 2 ▁O Cl − ▁▁ ▁→ ▁▁ ▁Re O 4 − ▁ ▁+ ▁▁ 2 ▁H 2 O ▁+ ▁ 5 Cl − ▁The ▁ent hal py ▁for ▁this ▁process ▁is ▁ 1 9 0 . 7 ▁ ± ▁ 0 . 2 ▁k cal / m ol . ▁ ▁Pre par ation ▁and ▁re actions ▁The ▁comp ound ▁was ▁discovered ▁in ▁ 1 9 3 2 , ▁although ▁these ▁workers ▁did ▁not ▁determine ▁its ▁structure , ▁which ▁is ▁unusual ▁for ▁metal ▁ch lor ides . ▁Tri r hen ium ▁non ach lor ide ▁is ▁efficiently ▁prepared ▁by ▁thermal ▁decomposition ▁of ▁r hen ium ▁pent ach lor ide ▁or ▁hex ach lor or hen ic ( IV ) ▁acid : ▁ 3 ▁Re Cl 5 ▁▁