Na4Ca2SiAs4 crystallizes in the monoclinic Cc space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one Si(1), one As(1), one As(2), one As(4), and two equivalent As(3) atoms. In the second Na site, Na(2) is bonded in a 4-coordinate geometry to one As(3), one As(4), and two equivalent As(2) atoms. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one As(3), one As(4), and two equivalent As(1) atoms. In the fourth Na site, Na(4) is bonded in a 4-coordinate geometry to one As(1), one As(2), one As(3), and one As(4) atom. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one As(1), one As(2), one As(4), and two equivalent As(3) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one Si(1), two equivalent As(1), two equivalent As(2), and two equivalent As(4) atoms. Si(1) is bonded in a distorted tetrahedral geometry to one Na(1), one Ca(2), one As(1), one As(2), one As(3), and one As(4) atom. There are four inequivalent As sites. In the first As site, As(4) is bonded in a 7-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the second As site, As(1) is bonded in a 8-coordinate geometry to one Na(1), one Na(4), two equivalent Na(3), one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the third As site, As(2) is bonded in a 8-coordinate geometry to one Na(1), one Na(4), two equivalent Na(2), one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the fourth As site, As(3) is bonded in a 8-coordinate geometry to one Na(2), one Na(3), one Na(4), two equivalent Na(1), two equivalent Ca(1), and one Si(1) atom.
Na4Ca2SiAs4 crystallizes in the monoclinic Cc space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one Si(1), one As(1), one As(2), one As(4), and two equivalent As(3) atoms. The Na(1)-Si(1) bond length is 3.27 Å. The Na(1)-As(1) bond length is 3.35 Å. The Na(1)-As(2) bond length is 3.10 Å. The Na(1)-As(4) bond length is 3.03 Å. There is one shorter (3.08 Å) and one longer (3.30 Å) Na(1)-As(3) bond length. In the second Na site, Na(2) is bonded in a 4-coordinate geometry to one As(3), one As(4), and two equivalent As(2) atoms. The Na(2)-As(3) bond length is 2.91 Å. The Na(2)-As(4) bond length is 3.11 Å. There is one shorter (2.94 Å) and one longer (3.02 Å) Na(2)-As(2) bond length. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one As(3), one As(4), and two equivalent As(1) atoms. The Na(3)-As(3) bond length is 2.91 Å. The Na(3)-As(4) bond length is 3.06 Å. There is one shorter (2.94 Å) and one longer (3.09 Å) Na(3)-As(1) bond length. In the fourth Na site, Na(4) is bonded in a 4-coordinate geometry to one As(1), one As(2), one As(3), and one As(4) atom. The Na(4)-As(1) bond length is 3.00 Å. The Na(4)-As(2) bond length is 2.99 Å. The Na(4)-As(3) bond length is 3.03 Å. The Na(4)-As(4) bond length is 3.12 Å. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one As(1), one As(2), one As(4), and two equivalent As(3) atoms. The Ca(1)-As(1) bond length is 3.02 Å. The Ca(1)-As(2) bond length is 3.17 Å. The Ca(1)-As(4) bond length is 3.14 Å. There is one shorter (3.03 Å) and one longer (3.17 Å) Ca(1)-As(3) bond length. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one Si(1), two equivalent As(1), two equivalent As(2), and two equivalent As(4) atoms. The Ca(2)-Si(1) bond length is 3.22 Å. There is one shorter (3.01 Å) and one longer (3.23 Å) Ca(2)-As(1) bond length. There is one shorter (3.03 Å) and one longer (3.16 Å) Ca(2)-As(2) bond length. There is one shorter (3.03 Å) and one longer (3.44 Å) Ca(2)-As(4) bond length. Si(1) is bonded in a distorted tetrahedral geometry to one Na(1), one Ca(2), one As(1), one As(2), one As(3), and one As(4) atom. The Si(1)-As(1) bond length is 2.40 Å. The Si(1)-As(2) bond length is 2.42 Å. The Si(1)-As(3) bond length is 2.38 Å. The Si(1)-As(4) bond length is 2.41 Å. There are four inequivalent As sites. In the first As site, As(4) is bonded in a 7-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the second As site, As(1) is bonded in a 8-coordinate geometry to one Na(1), one Na(4), two equivalent Na(3), one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the third As site, As(2) is bonded in a 8-coordinate geometry to one Na(1), one Na(4), two equivalent Na(2), one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the fourth As site, As(3) is bonded in a 8-coordinate geometry to one Na(2), one Na(3), one Na(4), two equivalent Na(1), two equivalent Ca(1), and one Si(1) atom.