© 2019 Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd. The coupled Λ Λ nn-Ξ- pnn system was studied to investigate whether the inclusion of channel coupling is able to bind the Λ Λ nn-Ξ- system. We use a separable potential three-body model of the coupled Λ Λ nn-Ξ- pnn system and a variational four-body calculation with realistic interactions. Our results exclude the possibility of a Λ Λ nn bound state by a large margin. Instead, we found a Ξ- t quasibound state above the Λ Λ nn threshold.