Splitting up talkative neighbors is an effective way to decrease disruption. However, children sometimes know what you are doing and are unwilling to move!
To avoid this problem, when two friends start chatting, simply ask the whole class to shut their eyes.
Tell them that you will tap two children on the shoulder. These two (only) will open their eyes and swap places with each other. Everyone else must keep their eyes shut.
Once the two have swapped, the class then opens their eyes and has to identify who has moved. This way it becomes a game.
Obviously one of the children you move will be one of the previously chatting neighbors.