The cooperative effects between pnicogen bond interactions in open-chain clusters of (PH2F)(n) and (PH2Cl)(n) are studied by ab initio calculations, where n = 2-7. These effects are analyzed in terms of geometric and energetic properties of the clusters. The intermolecular distances observed in the PH2F clusters exhibit quite larger bond contractions than those found in the PH2Cl. The contribution of cooperative effects to the interaction energy is quite significant. In order to understand the mechanism of the cooperativity, interaction energy decomposition and molecular electrostatic potential analyses are performed. (C) 2014 Elsevier B.V. All rights reserved.