Is SCN monodentate or bidentate?
SCN is a monodentate ligand because only one donor atom gets attached to the metal at a time. However it is ambidentate in nature because either of the two atoms S or N can act as the donor atoms.
Please remember that there are instances where SCN- has used both of its donor atoms at the same time but they are attached to different metal atoms, in that case case we can call it a bridging ligand but never bidentate.
[ If any ligand has to be called a bidentate ligand it must be able to attach itself to one metal atom using two of its donor atoms.]