K4Mo6Se25O crystallizes in the monoclinic Cm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one Se(10), one Se(12), one Se(14), one Se(2), one Se(3), one Se(9), and two equivalent Se(5) atoms. In the second K site, K(2) is bonded in a 6-coordinate geometry to one Se(1), one Se(10), one Se(11), one Se(13), one Se(9), and two equivalent Se(6) atoms. There are four inequivalent Mo sites. In the first Mo site, Mo(1) is bonded in a distorted single-bond geometry to one Se(12), one Se(2), two equivalent Se(16), two equivalent Se(3), and one O(1) atom. In the second Mo site, Mo(2) is bonded in a 7-coordinate geometry to one Se(1), one Se(11), one Se(17), two equivalent Se(15), and two equivalent Se(4) atoms. In the third Mo site, Mo(3) is bonded in a distorted single-bond geometry to one Se(13), one Se(16), one Se(3), one Se(6), one Se(7), one Se(9), and one O(1) atom. In the fourth Mo site, Mo(4) is bonded to one Se(10), one Se(14), one Se(15), one Se(17), one Se(4), one Se(5), and one Se(8) atom to form distorted face-sharing MoSe7 pentagonal bipyramids. There are seventeen inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent K(2), one Mo(2), and one Se(11) atom. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mo(1), and one Se(12) atom. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to one K(1), one Mo(1), one Mo(3), and one Se(16) atom. In the fourth Se site, Se(4) is bonded in a 3-coordinate geometry to one Mo(2), one Mo(4), and one Se(15) atom. In the fifth Se site, Se(5) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mo(4), and one Se(10) atom. In the sixth Se site, Se(6) is bonded in a 4-coordinate geometry to two equivalent K(2), one Mo(3), and one Se(9) atom. In the seventh Se site, Se(7) is bonded in a 3-coordinate geometry to two equivalent Mo(3) and one Se(13) atom. In the eighth Se site, Se(8) is bonded in a 3-coordinate geometry to two equivalent Mo(4) and one Se(14) atom. In the ninth Se site, Se(9) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mo(3), and one Se(6) atom. In the tenth Se site, Se(10) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mo(4), and one Se(5) atom. In the eleventh Se site, Se(11) is bonded in a 4-coordinate geometry to two equivalent K(2), one Mo(2), and one Se(1) atom. In the twelfth Se site, Se(12) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mo(1), and one Se(2) atom. In the thirteenth Se site, Se(13) is bonded in a 5-coordinate geometry to two equivalent K(2), two equivalent Mo(3), and one Se(7) atom. In the fourteenth Se site, Se(14) is bonded in a 5-coordinate geometry to two equivalent K(1), two equivalent Mo(4), and one Se(8) atom. In the fifteenth Se site, Se(15) is bonded in a 3-coordinate geometry to one Mo(2), one Mo(4), and one Se(4) atom. In the sixteenth Se site, Se(16) is bonded in a 3-coordinate geometry to one Mo(1), one Mo(3), and one Se(3) atom. In the seventeenth Se site, Se(17) is bonded in a 3-coordinate geometry to one Mo(2) and two equivalent Mo(4) atoms. O(1) is bonded in a trigonal non-coplanar geometry to one Mo(1) and two equivalent Mo(3) atoms.
K4Mo6Se25O crystallizes in the monoclinic Cm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one Se(10), one Se(12), one Se(14), one Se(2), one Se(3), one Se(9), and two equivalent Se(5) atoms. The K(1)-Se(10) bond length is 3.51 Å. The K(1)-Se(12) bond length is 3.48 Å. The K(1)-Se(14) bond length is 3.82 Å. The K(1)-Se(2) bond length is 3.50 Å. The K(1)-Se(3) bond length is 3.97 Å. The K(1)-Se(9) bond length is 3.56 Å. There is one shorter (3.68 Å) and one longer (3.90 Å) K(1)-Se(5) bond length. In the second K site, K(2) is bonded in a 6-coordinate geometry to one Se(1), one Se(10), one Se(11), one Se(13), one Se(9), and two equivalent Se(6) atoms. The K(2)-Se(1) bond length is 3.51 Å. The K(2)-Se(10) bond length is 3.55 Å. The K(2)-Se(11) bond length is 3.51 Å. The K(2)-Se(13) bond length is 3.85 Å. The K(2)-Se(9) bond length is 3.43 Å. There is one shorter (3.55 Å) and one longer (3.90 Å) K(2)-Se(6) bond length. There are four inequivalent Mo sites. In the first Mo site, Mo(1) is bonded in a distorted single-bond geometry to one Se(12), one Se(2), two equivalent Se(16), two equivalent Se(3), and one O(1) atom. The Mo(1)-Se(12) bond length is 2.64 Å. The Mo(1)-Se(2) bond length is 2.58 Å. Both Mo(1)-Se(16) bond lengths are 2.66 Å. Both Mo(1)-Se(3) bond lengths are 2.72 Å. The Mo(1)-O(1) bond length is 2.09 Å. In the second Mo site, Mo(2) is bonded in a 7-coordinate geometry to one Se(1), one Se(11), one Se(17), two equivalent Se(15), and two equivalent Se(4) atoms. The Mo(2)-Se(1) bond length is 2.60 Å. The Mo(2)-Se(11) bond length is 2.64 Å. The Mo(2)-Se(17) bond length is 2.60 Å. Both Mo(2)-Se(15) bond lengths are 2.63 Å. Both Mo(2)-Se(4) bond lengths are 2.69 Å. In the third Mo site, Mo(3) is bonded in a distorted single-bond geometry to one Se(13), one Se(16), one Se(3), one Se(6), one Se(7), one Se(9), and one O(1) atom. The Mo(3)-Se(13) bond length is 2.72 Å. The Mo(3)-Se(16) bond length is 2.66 Å. The Mo(3)-Se(3) bond length is 2.72 Å. The Mo(3)-Se(6) bond length is 2.58 Å. The Mo(3)-Se(7) bond length is 2.66 Å. The Mo(3)-Se(9) bond length is 2.68 Å. The Mo(3)-O(1) bond length is 2.09 Å. In the fourth Mo site, Mo(4) is bonded to one Se(10), one Se(14), one Se(15), one Se(17), one Se(4), one Se(5), and one Se(8) atom to form distorted face-sharing MoSe7 pentagonal bipyramids. The Mo(4)-Se(10) bond length is 2.66 Å. The Mo(4)-Se(14) bond length is 2.67 Å. The Mo(4)-Se(15) bond length is 2.63 Å. The Mo(4)-Se(17) bond length is 2.54 Å. The Mo(4)-Se(4) bond length is 2.69 Å. The Mo(4)-Se(5) bond length is 2.60 Å. The Mo(4)-Se(8) bond length is 2.60 Å. There are seventeen inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent K(2), one Mo(2), and one Se(11) atom. The Se(1)-Se(11) bond length is 2.39 Å. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mo(1), and one Se(12) atom. The Se(2)-Se(12) bond length is 2.41 Å. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to one K(1), one Mo(1), one Mo(3), and one Se(16) atom. The Se(3)-Se(16) bond length is 2.37 Å. In the fourth Se site, Se(4) is bonded in a 3-coordinate geometry to one Mo(2), one Mo(4), and one Se(15) atom. The Se(4)-Se(15) bond length is 2.34 Å. In the fifth Se site, Se(5) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mo(4), and one Se(10) atom. The Se(5)-Se(10) bond length is 2.38 Å. In the sixth Se site, Se(6) is bonded in a 4-coordinate geometry to two equivalent K(2), one Mo(3), and one Se(9) atom. The Se(6)-Se(9) bond length is 2.40 Å. In the seventh Se site, Se(7) is bonded in a 3-coordinate geometry to two equivalent Mo(3) and one Se(13) atom. The Se(7)-Se(13) bond length is 2.37 Å. In the eighth Se site, Se(8) is bonded in a 3-coordinate geometry to two equivalent Mo(4) and one Se(14) atom. The Se(8)-Se(14) bond length is 2.34 Å. In the ninth Se site, Se(9) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mo(3), and one Se(6) atom. In the tenth Se site, Se(10) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mo(4), and one Se(5) atom. In the eleventh Se site, Se(11) is bonded in a 4-coordinate geometry to two equivalent K(2), one Mo(2), and one Se(1) atom. In the twelfth Se site, Se(12) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mo(1), and one Se(2) atom. In the thirteenth Se site, Se(13) is bonded in a 5-coordinate geometry to two equivalent K(2), two equivalent Mo(3), and one Se(7) atom. In the fourteenth Se site, Se(14) is bonded in a 5-coordinate geometry to two equivalent K(1), two equivalent Mo(4), and one Se(8) atom. In the fifteenth Se site, Se(15) is bonded in a 3-coordinate geometry to one Mo(2), one Mo(4), and one Se(4) atom. In the sixteenth Se site, Se(16) is bonded in a 3-coordinate geometry to one Mo(1), one Mo(3), and one Se(3) atom. In the seventeenth Se site, Se(17) is bonded in a 3-coordinate geometry to one Mo(2) and two equivalent Mo(4) atoms. O(1) is bonded in a trigonal non-coplanar geometry to one Mo(1) and two equivalent Mo(3) atoms.