A series of rare earth element (REE) mixed-anion 5,5′azobis(1H-tetrazol-1-ide)-carbonate ([REE 2 (ZT) 2 CO 3 (H 2 O) 10 ]· 2H 2 O; REE = lanthanides plus yttrium) coordination compounds were synthesized, characterized, and analyzed. Syntheses by simple metathesis reactions under a CO 2 atmosphere were carried out at ambient (La-Gd and Ho) and elevated pressures (55 bar; Tb, Dy, Er, Tm, Yb, and Y). The resulting crystalline materials were characterized principally by single-crystal X-ray diffraction and vibrational spectroscopy (infrared and Raman). All materials are structurally isotypic, crystallizing in the space [a]