NaCaH3 crystallizes in the triclinic P-1 space group. Na(1) is bonded to one H(2), two equivalent H(1), and two equivalent H(3) atoms to form a mixture of distorted edge and corner-sharing NaH5 square pyramids. Ca(1) is bonded in a 7-coordinate geometry to two equivalent H(1), two equivalent H(3), and three equivalent H(2) atoms. There are three inequivalent H sites. In the first H site, H(1) is bonded to two equivalent Na(1) and two equivalent Ca(1) atoms to form HNa2Ca2 tetrahedra that share corners with two equivalent H(1)Na2Ca2 tetrahedra, corners with four equivalent H(3)Na2Ca2 tetrahedra, corners with eight equivalent H(2)NaCa3 trigonal pyramids,  an edgeedge with one H(1)Na2Ca2 tetrahedra, and edges with two equivalent H(3)Na2Ca2 tetrahedra. In the second H site, H(2) is bonded to one Na(1) and three equivalent Ca(1) atoms to form HNaCa3 trigonal pyramids that share corners with four equivalent H(3)Na2Ca2 tetrahedra, corners with eight equivalent H(1)Na2Ca2 tetrahedra, corners with two equivalent H(2)NaCa3 trigonal pyramids, edges with two equivalent H(3)Na2Ca2 tetrahedra, and edges with two equivalent H(2)NaCa3 trigonal pyramids. In the third H site, H(3) is bonded to two equivalent Na(1) and two equivalent Ca(1) atoms to form HNa2Ca2 tetrahedra that share corners with two equivalent H(3)Na2Ca2 tetrahedra, corners with four equivalent H(1)Na2Ca2 tetrahedra, corners with four equivalent H(2)NaCa3 trigonal pyramids,  an edgeedge with one H(3)Na2Ca2 tetrahedra, edges with two equivalent H(1)Na2Ca2 tetrahedra, and edges with two equivalent H(2)NaCa3 trigonal pyramids.
NaCaH3 crystallizes in the triclinic P-1 space group. Na(1) is bonded to one H(2), two equivalent H(1), and two equivalent H(3) atoms to form a mixture of distorted edge and corner-sharing NaH5 square pyramids. The Na(1)-H(2) bond length is 2.36 Å. There is one shorter (2.26 Å) and one longer (2.30 Å) Na(1)-H(1) bond length. There is one shorter (2.26 Å) and one longer (2.33 Å) Na(1)-H(3) bond length. Ca(1) is bonded in a 7-coordinate geometry to two equivalent H(1), two equivalent H(3), and three equivalent H(2) atoms. There is one shorter (2.27 Å) and one longer (2.40 Å) Ca(1)-H(1) bond length. There is one shorter (2.27 Å) and one longer (2.29 Å) Ca(1)-H(3) bond length. There are two shorter (2.36 Å) and one longer (2.40 Å) Ca(1)-H(2) bond length. There are three inequivalent H sites. In the first H site, H(1) is bonded to two equivalent Na(1) and two equivalent Ca(1) atoms to form HNa2Ca2 tetrahedra that share corners with two equivalent H(1)Na2Ca2 tetrahedra, corners with four equivalent H(3)Na2Ca2 tetrahedra, corners with eight equivalent H(2)NaCa3 trigonal pyramids,  an edgeedge with one H(1)Na2Ca2 tetrahedra, and edges with two equivalent H(3)Na2Ca2 tetrahedra. In the second H site, H(2) is bonded to one Na(1) and three equivalent Ca(1) atoms to form HNaCa3 trigonal pyramids that share corners with four equivalent H(3)Na2Ca2 tetrahedra, corners with eight equivalent H(1)Na2Ca2 tetrahedra, corners with two equivalent H(2)NaCa3 trigonal pyramids, edges with two equivalent H(3)Na2Ca2 tetrahedra, and edges with two equivalent H(2)NaCa3 trigonal pyramids. In the third H site, H(3) is bonded to two equivalent Na(1) and two equivalent Ca(1) atoms to form HNa2Ca2 tetrahedra that share corners with two equivalent H(3)Na2Ca2 tetrahedra, corners with four equivalent H(1)Na2Ca2 tetrahedra, corners with four equivalent H(2)NaCa3 trigonal pyramids,  an edgeedge with one H(3)Na2Ca2 tetrahedra, edges with two equivalent H(1)Na2Ca2 tetrahedra, and edges with two equivalent H(2)NaCa3 trigonal pyramids.