The infrared spectra of the weakly-bound dimers OCS-HCCCCH, in the region of the v(1) fundamental band of OCS (2050 cm(-1)), and N2O-HCCCCH, in the region of the v(1) fundamental band of N2O (2200 cm(-1)), were observed in a pulsed supersonic slit jet expansion probed with tunable diode/QCL lasers. Both OCS-HCCCCH and N2O-HCCCCH were found to have planar structure with side-by-side monomer units having nearly parallel axes. These bands have hybrid rotational structure which allows for estimates of the orientation of OCS and N2O in the plane of their respective dimers. Analogous bands for OCS-DCCCCD and N2O-DCCCCD were also observed and found to be consistent with the normal isotopologues. Various levels of ab initio calculations were performed to find stationary points on the potential energy surface, optimized structures and interaction energies. Four stable geometries were found for OCS-HCCCCH and three for N2O-HCCCCH. The rotational parameters at CCSD(T*)-F12c level of theory give results in very good agreement with those obtained from the observed spectra. In both dimers, the experimental structure corresponds to the lowest energy isomer.