A novel mixed-valent hybrid chiral and polar compound, Fe₇As₃Se₁₂(en)₆(H₂O), has been synthesized by a single-step solvothermal method. The crystal structure consists of 1D [Fe₅Se₉] chains connected via [As₃Se₂]-Se pentagonal linkers and charge-balancing interstitial [Fe(en)₃]²⁺ complexes (en = ethylenediamine). Neutron powder diffraction verified that interstitial water molecules participate in the crystal packing. Magnetic polarizability of the produced compound was confirmed by X-ray magnetic circular dichroism (XMCD) spectroscopy. X-ray absorption spectroscopy (XAS) and ⁵⁷Fe Mössbauer spectroscopy showed the presence of mixed-valent Fe²⁺/Fe³⁺ in the Fe-Se chains. Magnetic susceptibility measurements reveal strong antiferromagnetic nearest neighbor interactions within the chains with no apparent magnetic ordering down to 2 K. Hidden short-range magnetic ordering below 70 K was found by ⁵⁷Fe Mössbauer spectroscopy, showing that a fraction of the Fe³⁺/Fe²⁺ in the chains are magnetically ordered. Nevertheless, complete magnetic ordering is not achieved even at 6 K. Analysis of XAS spectra demonstrates that the fraction of Fe³⁺ in the chain increases with decreasing temperature. Computational analysis points out several competing ferrimagnetic ordered models within a single chain. This competition, together with variation in the Fe oxidation state and additional weak intrachain interactions, is hypothesized to prevent long-range magnetic ordering.