Coordination isomers are two or more coordination compounds in which the composition within the coordination sphere (i.e., the metal atom plus the ligands that are bonded to it) is different (i.e., the connectivity between atoms is different).
Not all coordination compounds have coordination isomers.
Coordination isomers have different physical and chemical properties.
Note that the sulfate group is bonded to the Cr atom (via an O atom) and is within the coordination sphere. Note also the octahedral structure. The bromide counterion is needed to maintain charge neutrality with the complex ion (i.e., [Cr(NH3)5(OSO3)]+) and is not shown in the structure.
Note that the bromine atom is bonded to the Cr atom and is within the coordination sphere. Note also the octahedral structure. The sulfate counterion is not shown in the structure.