The role that the supporting anion has on the stability, structure, and catalytic performance, in solid-state molecular organometallic systems (SMOM) based upon [Rh-(Cy 2 PCH 2 CH 2 PCy 2)(η 2 η 2-NBD)][BAr X 4 ], [1-NBD][BAr X 4 ], is reported (X = Cl, F, H; NBD = norbornadiene). The tetra-aryl borate anion is systematically varied at the 3,5-position, Ar X = 3,5-X 2 C 6 H 3 , and the stability and structure in the solid-state compared with the previously reported [1-NBD][BAr CF3 4 ] complex. Single-crystal X-ray crystallography shows that the three complexes have different packing motifs, in which the cation sits on the shared face of two parallelepipeds for [1-NBD][BAr Cl 4 ], is surrounded by eight anions in a gyrobifastigium arrangement for [1-NBD][BAr F 4 ], or the six anions show an octahedral cage arrangement in [1-NBD][BAr H 4 ], similar to that of [1-NBD][BAr CF3 4 ]. C−X•••X−C contacts, commonly encountered in crystal-engineering, are suggested to be important in determining structure. Addition of H 2 in a solid/gas reaction affords the resulting σ-alkane complexes, [Rh(Cy 2 PCH 2 CH 2 PCy 2)(η 2 η 2-NBA)][BAr X 4 ] [1-NBA][BAr X 4 ] (NBA = norbornane), which can then proceed to lose the alkane and form the zwitterionic, anion-coordinated, complexes. The relative rates at which hydrogenation and then decomposition of σ-alkane complexes proceed are shown to be anion dependent. [BAr CF3 4 ] − promotes fast hydrogenation and an indefinitely stable σ-alkane complex. With [BAr H 4 ] − hydrogenation is slow and the σ-alkane complex so unstable it is not observed. [BAr Cl 4 ] − and [BAr F 4 ] − promote intermediate reactivity profiles, and for [BAr Cl 4 ] − , a single-crystal to single-crystal hydrogenation results in [1-NBA][BAr Cl 4 ]. The molecular structure derived from X-ray diffraction reveals a σalkane complex in which the NBA fragment is bound through two exo Rh•••H−C interactions-different from the endo selective binding observed with [1-NBA][BAr CF3 4 ]. Periodic DFT calculations demonstrate that this selectivity is driven by the microenvironment dictated by the surrounding anions. [1-NBA][BAr X 4 ] are catalysts for gas/solid 1-butene isomerization (298 K, 1 atm), and their activity can be directly correlated to the stability of the σ-alkane complex compared to the anion-coordinated decomposition products.