On the basis of large-scale coupled-cluster calculations the dissociation energy of the complex Cl-. HCCH is predicted to be D-0=3600 cm(-1), with an uncertainty of the order of 1%. The ground state rotational constant is obtained to be 2053 (10) MHz and the wave number of the hydrogen-bonded CH stretching vibration is 2877+/-10 cm(-1). Anharmonicity constants for the stretching vibrations are discussed in comparison with those calculated earlier for Br-. HCCH and I-. HCCH.