X-ray powder diffraction of the new high-Tc superconducting phase (Hg1−xCux) Ba2CuO4+∞, where × = 0.17 with the onset superconducting transition at 125 K was used to define coordinates, isotropic thermal parameters of the atoms and for interatomic distances calculation. For the first time in the Hg-based cuprate superconductors was observed the occurrence of the optical second harmonic generation (SHG) of YAG-Nd laser, which gives evidence for the appearance the asymmetric electronic density, correlated with an increase of superconducting transition temperature. It is assumed that the increase of Tcassociated with the formation of two (CuO2) layers in the average unit cell at the substitution of the part atoms Cu for Hg and the partial occupancy of the (1/2 0 0) sites by oxygen atoms.