Alaklides

Cesium

We all know about hydrides, but I just read about the existance of species with lithide ions. No lithides have been made, but apparently over "30 alkalides" have been made with 18 of them being natrides.

http://www.iupac.org/publications/pa.../6503x0435.pdf
http://www.uni-mainz.de/FB/Chemie/aa...01966-1970.pdf

Natrides, katrides, rubides, cesides!! How the heck is this possible?