Evolution of the structural, magnetic, and electronic properties of the triple perovskite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ba</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mi>Co</mml:mi><mml:msub><mml:mi>Ir</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>9</mml:mn></mml:msub></mml:mrow></mml:math>

We report a comprehensive investigation of the triple perovskite iridate Ba$_{3}$CoIr$_{2}$O$_{9}$. Stabilizing in hexagonal $P6_{3}/mmc$ symmetry at room temperature, this system transforms to monoclinic $C2/c$ magnetic phase transition. On further reduction partially distorts an even lower ($P2/c$), with both these structurally disparate phases coexisting down lowest measured temperatures. The structure as determined from neutron diffraction data indicates weakly canted antiferromagnetic structure, which is also supported by first-principles calculations. Theory that Ir$^{5+}$ carries finite moment, consistent data. This suggests putative $J=0$ state avoided. Measurements heat capacity, electrical resistance noise and dielectric susceptibility all point towards stabilization highly correlated ground Ba$_{3}$CoIr$_{2}$O$_{9}$ system.