The present invention relates to metal complexes of formula I, compositions comprising the metal complexes, to recording media comprising the metal complexes or compositions and to the use of the compositions in the production of optical recording media: wherein the substituent are, as defined in the description. Use of the metal complexes formula (I) in combination with oxonol dyes results, surprisingly, in a comparatively weak tendency of the oxonol dyes to aggregate in the solid state so that the absorption curve remains advantageously narrow event in the solid state, as a result of which recording media having high reflectivity as well as high sensitivity and good playback characteristics in the desired spectral range are made available.