K2Al2B2O7 crystallizes in the monoclinic C2 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one O(10), one O(11), one O(2), one O(4), one O(5), one O(7), one O(9), and two equivalent O(3) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to one O(11), two equivalent O(2), two equivalent O(4), two equivalent O(6), and two equivalent O(8) atoms. In the third K site, K(3) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(4), two equivalent O(6), and two equivalent O(8) atoms. In the fourth K site, K(4) is bonded in a 2-coordinate geometry to one O(5) and one O(7) atom. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(11), one O(5), one O(6), and one O(7) atom to form corner-sharing AlO4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), one O(10), one O(8), and one O(9) atom to form corner-sharing AlO4 tetrahedra. In the third Al site, Al(3) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing AlO4 tetrahedra. There are three inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(2), one O(5), and one O(8) atom. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(3), one O(6), and one O(9) atom. In the third B site, B(3) is bonded in a trigonal planar geometry to one O(10), one O(4), and one O(7) atom. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to one K(3), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Al(3), and one B(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent K(1), one Al(3), and one B(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one K(1), one K(2), one K(3), one Al(3), and one B(3) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(1), one K(4), one Al(1), and one B(1) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one K(2), one K(3), one Al(1), and one B(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to one K(1), one K(4), one Al(1), and one B(3) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to one K(2), one K(3), one Al(2), and one B(1) atom. In the ninth O site, O(9) is bonded in a 2-coordinate geometry to one K(1), one Al(2), and one B(2) atom. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one K(1), one Al(2), and one B(3) atom. In the eleventh O site, O(11) is bonded in a linear geometry to one K(2), two equivalent K(1), and two equivalent Al(1) atoms.
K2Al2B2O7 crystallizes in the monoclinic C2 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one O(10), one O(11), one O(2), one O(4), one O(5), one O(7), one O(9), and two equivalent O(3) atoms. The K(1)-O(10) bond length is 2.74 Å. The K(1)-O(11) bond length is 3.03 Å. The K(1)-O(2) bond length is 2.69 Å. The K(1)-O(4) bond length is 3.27 Å. The K(1)-O(5) bond length is 3.22 Å. The K(1)-O(7) bond length is 3.20 Å. The K(1)-O(9) bond length is 2.75 Å. There is one shorter (2.68 Å) and one longer (3.28 Å) K(1)-O(3) bond length. In the second K site, K(2) is bonded in a 9-coordinate geometry to one O(11), two equivalent O(2), two equivalent O(4), two equivalent O(6), and two equivalent O(8) atoms. The K(2)-O(11) bond length is 3.07 Å. Both K(2)-O(2) bond lengths are 3.29 Å. Both K(2)-O(4) bond lengths are 2.68 Å. Both K(2)-O(6) bond lengths are 3.19 Å. Both K(2)-O(8) bond lengths are 2.76 Å. In the third K site, K(3) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(4), two equivalent O(6), and two equivalent O(8) atoms. Both K(3)-O(1) bond lengths are 2.95 Å. Both K(3)-O(4) bond lengths are 3.19 Å. Both K(3)-O(6) bond lengths are 2.69 Å. Both K(3)-O(8) bond lengths are 3.03 Å. In the fourth K site, K(4) is bonded in a 2-coordinate geometry to one O(5) and one O(7) atom. The K(4)-O(5) bond length is 2.69 Å. The K(4)-O(7) bond length is 2.69 Å. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(11), one O(5), one O(6), and one O(7) atom to form corner-sharing AlO4 tetrahedra. The Al(1)-O(11) bond length is 1.71 Å. The Al(1)-O(5) bond length is 1.76 Å. The Al(1)-O(6) bond length is 1.76 Å. The Al(1)-O(7) bond length is 1.76 Å. In the second Al site, Al(2) is bonded to one O(1), one O(10), one O(8), and one O(9) atom to form corner-sharing AlO4 tetrahedra. The Al(2)-O(1) bond length is 1.72 Å. The Al(2)-O(10) bond length is 1.75 Å. The Al(2)-O(8) bond length is 1.75 Å. The Al(2)-O(9) bond length is 1.75 Å. In the third Al site, Al(3) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form corner-sharing AlO4 tetrahedra. The Al(3)-O(1) bond length is 1.72 Å. The Al(3)-O(2) bond length is 1.76 Å. The Al(3)-O(3) bond length is 1.75 Å. The Al(3)-O(4) bond length is 1.76 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(2), one O(5), and one O(8) atom. The B(1)-O(2) bond length is 1.38 Å. The B(1)-O(5) bond length is 1.38 Å. The B(1)-O(8) bond length is 1.37 Å. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(3), one O(6), and one O(9) atom. The B(2)-O(3) bond length is 1.38 Å. The B(2)-O(6) bond length is 1.37 Å. The B(2)-O(9) bond length is 1.37 Å. In the third B site, B(3) is bonded in a trigonal planar geometry to one O(10), one O(4), and one O(7) atom. The B(3)-O(10) bond length is 1.37 Å. The B(3)-O(4) bond length is 1.38 Å. The B(3)-O(7) bond length is 1.37 Å. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to one K(3), one Al(2), and one Al(3) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Al(3), and one B(1) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent K(1), one Al(3), and one B(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one K(1), one K(2), one K(3), one Al(3), and one B(3) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(1), one K(4), one Al(1), and one B(1) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one K(2), one K(3), one Al(1), and one B(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to one K(1), one K(4), one Al(1), and one B(3) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to one K(2), one K(3), one Al(2), and one B(1) atom. In the ninth O site, O(9) is bonded in a 2-coordinate geometry to one K(1), one Al(2), and one B(2) atom. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one K(1), one Al(2), and one B(3) atom. In the eleventh O site, O(11) is bonded in a linear geometry to one K(2), two equivalent K(1), and two equivalent Al(1) atoms.