First-order phase transitions with strong and extremely anisotropic ch
anges of the lattice parameters were observed in the ThCr2Si2 structur
e-type compounds EuCo2P2 and SrNi2P2. At room temperature, with increa
sing pressure the phase transition occurs in SrNi2P2 at 4 kbar and in
EuCo2P2 at 30 kbar which is in the latter probably accompanied by a va
lence change of Eu. On the basis of single-crystal data of ACo(2)P(2)
(A = Ca, Sr, La, Ce, Pr, Nd, Eu) at ambient pressure and temperature w
e discuss the pressure dependence of the bond lengths in these compoun
ds.