The Co-2(OH)(PO4)(1-x)(AsO4)(x) [0 <= x <= 1] solid solution exhibits a complex magnetic behaviour due to the bond-frustration in its magnetic structure. Heat capacity measurements of the (x=0.1-0.5) phases show a three-dimensional magnetic ordering (lambda anomaly) that shifts to lower temperatures and becomes broader as the AsO43- content increases. For x=0.75, no significant feature was observed whereas for higher arsenate ion content, x=0.9 and 1, a small maximum was detected. The magnetic structures of solid solution are consistent with the existence of predominant antiferromagnetic superexchange interactions through the vertical bar OH vertical bar and vertical bar XO4 vertical bar (X=P and As) groups between the Co+2 ions. The substitution of PO43- by AsO43- anions by more than 90% substantially modifies the magnetic exchange pathways in the solid solution, leading to an incommensurate antiferromagnetic structure in Co-2(OH)(PO4)(1-x)(AsO4)(x) [x=0.9 and 1] phases. (C) 2012 Elsevier Inc. All rights reserved.