Antibiotic resistance is one of the biggest health problems of the twenty-first century. In order to cope with this global problem, alternative preventive strategies such as quorum sensing interruption are needed. Therefore, it is very important to develop new compounds with anti-quorum sensing activity. Here we present the synthesis and structural characterization of two new Co (II) complexes; [Co(btmpp)(NCO)(2)], 1 and [Co(btmpp)(NCSe)(2)], 2 (where btmpp is: 2,6-bis(3,4,5-trimethylpyrazolyl) pyridine). The crystal structures of both complexes is determined using single-crystal X-ray diffraction. The coordination environment of Co(II) atoms can be described as a distorted square pyramidal geometry. Both complexes is screened for antibacterial activities against Gram-positive (B. substilis) and Gram-negative (P. aeruginosa, S. typhimurium, S. sonnei, Y. enterocolitica) bacterial strains. The effects of these complexes on QS-regulated behaviors of bacteria such as swarming, and biofilm formation is also examined. All bacteria are found to be more sensitive to complex 2 than complex 1. (C) 2019 Elsevier B.V. All rights reserved.