The optimized geometries, infrared spectra and bonding behavior of (XNR)_4 [X = C, Si, Ge, Sn, Pb; R = H, CH_3, C(CH_3)_3, Si(CH_3)_3, C_6H_5] cubic clusters and their fragments (XNR)_2 were investigated using B3LYP(DFT) method at compact effective potential CEP-121G level for the first time. The results show that the structure of (XNR)_4 is not stable as X = C, the stability of (XNH)_4 is the lowest as R = H. For the same substituent R, the order of stability of cubic clusters is that: (PbNR)_4>(SnNR)_4>(GeNR)_4>(SiNR)_4>(CNR)_4.

Key words: CLUSTER COMPOUND, CHEMICAL BONDS, CONFIGURATION, ELECTRONIC STRUCTURE