We present a multi-wavelength study of comet C/2016 R2 ( PanSTARRS ) . This comet was observed on 23-24 January 2018 with the IRAM 30m telescope , and in January to March 2018 with the Nançay radio telescope . Visible spectroscopy was performed in December 2017 and February 2018 with small amateur telescopes . We report on measurements of CO , CH _ { 3 } OH , H _ { 2 } CO and HCN production rates , and on the determination of the N _ { 2 } /CO abundance ratio . Several other species , especially OH , were searched for but not detected . The inferred relative abundances , including upper limits for sulfur species , are compared to those measured in other comets at about the same heliocentric distance of \sim 2.8 AU . The coma composition of comet C/2016 R2 is very different from all other comets observed so far , being rich in N _ { 2 } and CO and dust poor . This suggests that this comet might belong to a very rare group of comets formed beyond the N _ { 2 } ice line . Alternatively , comet C/2016 R2 ( PanSTARRS ) could be the fragment of a large and differentiated transneptunian object , with properties characteristic of volatile-enriched layers .