Ca2B8O15 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 1-coordinate geometry to one B(8), one O(1), one O(15), and one O(5) atom. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one B(7), one O(10), one O(11), one O(14), one O(3), and two equivalent O(6) atoms. There are eight inequivalent B sites. In the first B site, B(1) is bonded in a 3-coordinate geometry to one O(13), one O(7), and one O(8) atom. In the second B site, B(2) is bonded in a 3-coordinate geometry to one O(1), one O(14), and one O(2) atom. In the third B site, B(3) is bonded in a distorted trigonal planar geometry to one O(1), one O(3), and one O(4) atom. In the fourth B site, B(4) is bonded in a 3-coordinate geometry to one O(10), one O(8), and one O(9) atom. In the fifth B site, B(5) is bonded in a 3-coordinate geometry to one O(14), one O(15), and one O(4) atom. In the sixth B site, B(6) is bonded in a 3-coordinate geometry to one O(11), one O(15), and one O(7) atom. In the seventh B site, B(7) is bonded in a 2-coordinate geometry to one Ca(2), one O(11), one O(2), one O(3), and one O(6) atom. In the eighth B site, B(8) is bonded in a 5-coordinate geometry to one Ca(1), one O(12), one O(13), one O(5), and one O(9) atom. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1), one B(2), and one B(3) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one B(2) and one B(7) atom. In the third O site, O(3) is bonded in an L-shaped geometry to one Ca(2), one B(3), and one B(7) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one B(3) and one B(5) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Ca(1) and one B(8) atom. In the sixth O site, O(6) is bonded in a 1-coordinate geometry to two equivalent Ca(2) and one B(7) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one B(1) and one B(6) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one B(1) and one B(4) atom. In the ninth O site, O(9) is bonded in a water-like geometry to one B(4) and one B(8) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Ca(2) and one B(4) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ca(2), one B(6), and one B(7) atom. In the twelfth O site, O(12) is bonded in a single-bond geometry to one B(8) atom. In the thirteenth O site, O(13) is bonded in a 2-coordinate geometry to one B(1) and one B(8) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Ca(2), one B(2), and one B(5) atom. In the fifteenth O site, O(15) is bonded in a 3-coordinate geometry to one Ca(1), one B(5), and one B(6) atom.
Ca2B8O15 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 1-coordinate geometry to one B(8), one O(1), one O(15), and one O(5) atom. The Ca(1)-B(8) bond length is 1.88 Å. The Ca(1)-O(1) bond length is 1.54 Å. The Ca(1)-O(15) bond length is 2.50 Å. The Ca(1)-O(5) bond length is 2.05 Å. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one B(7), one O(10), one O(11), one O(14), one O(3), and two equivalent O(6) atoms. The Ca(2)-B(7) bond length is 1.92 Å. The Ca(2)-O(10) bond length is 2.45 Å. The Ca(2)-O(11) bond length is 2.13 Å. The Ca(2)-O(14) bond length is 2.47 Å. The Ca(2)-O(3) bond length is 2.77 Å. There is one shorter (2.54 Å) and one longer (2.68 Å) Ca(2)-O(6) bond length. There are eight inequivalent B sites. In the first B site, B(1) is bonded in a 3-coordinate geometry to one O(13), one O(7), and one O(8) atom. The B(1)-O(13) bond length is 1.63 Å. The B(1)-O(7) bond length is 1.47 Å. The B(1)-O(8) bond length is 1.26 Å. In the second B site, B(2) is bonded in a 3-coordinate geometry to one O(1), one O(14), and one O(2) atom. The B(2)-O(1) bond length is 1.22 Å. The B(2)-O(14) bond length is 1.46 Å. The B(2)-O(2) bond length is 0.91 Å. In the third B site, B(3) is bonded in a distorted trigonal planar geometry to one O(1), one O(3), and one O(4) atom. The B(3)-O(1) bond length is 1.42 Å. The B(3)-O(3) bond length is 0.97 Å. The B(3)-O(4) bond length is 0.98 Å. In the fourth B site, B(4) is bonded in a 3-coordinate geometry to one O(10), one O(8), and one O(9) atom. The B(4)-O(10) bond length is 1.39 Å. The B(4)-O(8) bond length is 2.07 Å. The B(4)-O(9) bond length is 1.64 Å. In the fifth B site, B(5) is bonded in a 3-coordinate geometry to one O(14), one O(15), and one O(4) atom. The B(5)-O(14) bond length is 1.13 Å. The B(5)-O(15) bond length is 1.81 Å. The B(5)-O(4) bond length is 1.49 Å. In the sixth B site, B(6) is bonded in a 3-coordinate geometry to one O(11), one O(15), and one O(7) atom. The B(6)-O(11) bond length is 1.81 Å. The B(6)-O(15) bond length is 1.64 Å. The B(6)-O(7) bond length is 1.36 Å. In the seventh B site, B(7) is bonded in a 2-coordinate geometry to one Ca(2), one O(11), one O(2), one O(3), and one O(6) atom. The B(7)-O(11) bond length is 2.18 Å. The B(7)-O(2) bond length is 1.46 Å. The B(7)-O(3) bond length is 1.14 Å. The B(7)-O(6) bond length is 1.86 Å. In the eighth B site, B(8) is bonded in a 5-coordinate geometry to one Ca(1), one O(12), one O(13), one O(5), and one O(9) atom. The B(8)-O(12) bond length is 1.57 Å. The B(8)-O(13) bond length is 2.09 Å. The B(8)-O(5) bond length is 1.85 Å. The B(8)-O(9) bond length is 1.55 Å. There are fifteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1), one B(2), and one B(3) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one B(2) and one B(7) atom. In the third O site, O(3) is bonded in an L-shaped geometry to one Ca(2), one B(3), and one B(7) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one B(3) and one B(5) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Ca(1) and one B(8) atom. In the sixth O site, O(6) is bonded in a 1-coordinate geometry to two equivalent Ca(2) and one B(7) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one B(1) and one B(6) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one B(1) and one B(4) atom. In the ninth O site, O(9) is bonded in a water-like geometry to one B(4) and one B(8) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Ca(2) and one B(4) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Ca(2), one B(6), and one B(7) atom. In the twelfth O site, O(12) is bonded in a single-bond geometry to one B(8) atom. In the thirteenth O site, O(13) is bonded in a 2-coordinate geometry to one B(1) and one B(8) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Ca(2), one B(2), and one B(5) atom. In the fifteenth O site, O(15) is bonded in a 3-coordinate geometry to one Ca(1), one B(5), and one B(6) atom.