Theoretical and Experimental Studies on the Ability of Intracrystalline Pores of β-La(SO) To Accommodate Various Gas Species with a Special Focus on Ammonia Insertion Behaviors.

β-La(SO) is a microporous inorganic crystal with one-dimensional perforated pores where HO molecules can be inserted. To evaluate the nature of the pores and extend the application range, we investigate the ability to accommodate various hydrogen compound molecules XH (CH, NH, HF, HS, HCl, and HI) by insertion. The stable structures of the XH molecules in the pores of β-La(SO) and the change in the Gibbs energy for XH insertion Δ () are estimated by first-principles calculations. The guest XH molecules are stabilized by forming H-O and X-La bonds with the β-La(SO) host structure. Based on the values of Δ (), NH, HO, and HF are energetically stable in the crystal even above 0 °C. Correspondingly, thermogravimetry (TG) of β-La(SO) in NH, CH, and CO gases revealed that NH can be inserted into β-La(SO) below 360 °C, but CH and CO cannot. Unlike the case of HO insertion, NH insertion proceeds two steps. The first step is a single-solid-phase reaction of β-La(SO)·NH, where NH molecules are inserted into the host structure with a continuously changing nonstoichiometric value between 0 and 0.1. The second step is a two-solid-phase reaction between β-La(SO)·0.1NH and β'-La(SO)·0.3NH, which is a phase formed after further NH insertion into β-La(SO)·0.1NH with a minor change in the host structure. The fact that both NH and HO can be inserted confirms that the pores of β-La(SO) allow for the insertion of molecules with a strong polarity. This nature is similar to zeolites and metal-organic frameworks (MOFs) with polar surfaces in the pores.