Palladium(II) and platinum(II) chloro complexes of novel water‐soluble cage‐like phosphane CAP (1,4,7‐triaza‐9‐phosphatricyclo[5.3.2.14,9]tridecane) have been synthesized and characterized in comparison with their counterparts bearing well known PTA (1,3,5‐triaza‐7‐phosphaadamantane) ligand. A peculiar structural feature of studied cis‐[MCl2L2] complexes is the occurrence of interligand C−Hσ+⋅⋅⋅σ+H−C interactions (hydrogen‐hydrogen bonds) between the phosphane cages: the first case encountered so far among metal‐phosphane complexes. Due to substantial stabilizing contribution to the net molecular energy of the complexes (∼ 20 kcal mol−1), hydrogen‐hydrogen bonding is sufficient to maintain sterically overcrowded cis conformations of the complexes. The interplay between protonation stage of the ligands and their conformations can be a reason of significant differences in in‐vitro cytotoxicity between CAP complexes and their PTA‐bearing counterparts.