An Important Properties of Entanglement: Pairwise Entanglement can Only   be Transferred by Entangled Pair
  Basing on the calculation of all the pairwise entanglement in the $n$ ($n \leq 6$)-qubit Heisenberg XX open chain with system impurity, we find an important result: pairwise entanglement can only be transferred through entangled pair. The non-nearest pairwise entanglement will has the possibility to exist as long as there has even number qubit in their middle. This point means that we can get longer distance entanglement in solid system. 
Xiao-Qiang Xi, W. M. Liu