A cis-IrL(CO) group responds to increasing steric bulk of L by M-L stretching, not M-C-O tilting or bending

The crystal structures of [Ir(2-R-bq)(PPh3)(2)(H)(CO)](+) (bq = benzoquinolinato; R = H, i-Pr, t-Bu) show that steric interference caused by contact between the bulky pendant R groups of the bq and the C of the cis-CO is relieved by Ir-N bond stretching in the Irbq system and bending of the trans-Ph3P-Ir-PPh3 groups, rather than by tilting or bending of the CO. Ir-CO is therefore more rigid than the Ir-N and Ir-P bonds. The Ir-N stretching is aided by the presence of a high trans effect H trans to N.