Nitrogen (N) is an important impurity in silicon (Si), which associates with impurities as well as with other defects to form defect complexes. The knowledge of the properties and behavior of defects structures containing carbon (C), N and oxygen (O) are important for the Si–based electronic technology. Here we employ density functional theory (DFT) calculations to investigate the association of nitrogen with carbon and oxygen defects to form the CiN and CiNOi defects. We provide evidence of the formation of these defects and additionally details of their structure, their density of states (DOS) and Bader charges. Therefore, CiN and CiNOi defects are now well characterized.