NpB4 crystallizes in the orthorhombic Cmmm space group. There are two inequivalent Np sites. In the first Np site, Np(1) is bonded in a 18-coordinate geometry to two equivalent B(2), four equivalent B(1), four equivalent B(3), four equivalent B(4), and four equivalent B(5) atoms. In the second Np site, Np(2) is bonded in a 18-coordinate geometry to two equivalent B(3), four equivalent B(1), four equivalent B(2), four equivalent B(4), and four equivalent B(5) atoms. There are five inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to two equivalent Np(1), two equivalent Np(2), one B(1), two equivalent B(4), and two equivalent B(5) atoms. In the second B site, B(2) is bonded in a distorted trigonal planar geometry to two equivalent Np(1), four equivalent Np(2), one B(2), and two equivalent B(5) atoms. In the third B site, B(3) is bonded in a distorted trigonal planar geometry to two equivalent Np(2), four equivalent Np(1), one B(3), and two equivalent B(4) atoms. In the fourth B site, B(4) is bonded in a 9-coordinate geometry to two equivalent Np(1), two equivalent Np(2), one B(3), two equivalent B(1), and two equivalent B(5) atoms. In the fifth B site, B(5) is bonded in a 9-coordinate geometry to two equivalent Np(1), two equivalent Np(2), one B(2), two equivalent B(1), and two equivalent B(4) atoms.
NpB4 crystallizes in the orthorhombic Cmmm space group. There are two inequivalent Np sites. In the first Np site, Np(1) is bonded in a 18-coordinate geometry to two equivalent B(2), four equivalent B(1), four equivalent B(3), four equivalent B(4), and four equivalent B(5) atoms. Both Np(1)-B(2) bond lengths are 3.04 Å. All Np(1)-B(1) bond lengths are 2.72 Å. All Np(1)-B(3) bond lengths are 2.89 Å. All Np(1)-B(4) bond lengths are 2.74 Å. All Np(1)-B(5) bond lengths are 2.81 Å. In the second Np site, Np(2) is bonded in a 18-coordinate geometry to two equivalent B(3), four equivalent B(1), four equivalent B(2), four equivalent B(4), and four equivalent B(5) atoms. Both Np(2)-B(3) bond lengths are 3.03 Å. All Np(2)-B(1) bond lengths are 2.72 Å. All Np(2)-B(2) bond lengths are 2.89 Å. All Np(2)-B(4) bond lengths are 2.81 Å. All Np(2)-B(5) bond lengths are 2.75 Å. There are five inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to two equivalent Np(1), two equivalent Np(2), one B(1), two equivalent B(4), and two equivalent B(5) atoms. The B(1)-B(1) bond length is 1.62 Å. Both B(1)-B(4) bond lengths are 1.76 Å. Both B(1)-B(5) bond lengths are 1.76 Å. In the second B site, B(2) is bonded in a distorted trigonal planar geometry to two equivalent Np(1), four equivalent Np(2), one B(2), and two equivalent B(5) atoms. The B(2)-B(2) bond length is 1.76 Å. Both B(2)-B(5) bond lengths are 1.71 Å. In the third B site, B(3) is bonded in a distorted trigonal planar geometry to two equivalent Np(2), four equivalent Np(1), one B(3), and two equivalent B(4) atoms. The B(3)-B(3) bond length is 1.76 Å. Both B(3)-B(4) bond lengths are 1.71 Å. In the fourth B site, B(4) is bonded in a 9-coordinate geometry to two equivalent Np(1), two equivalent Np(2), one B(3), two equivalent B(1), and two equivalent B(5) atoms. Both B(4)-B(5) bond lengths are 1.82 Å. In the fifth B site, B(5) is bonded in a 9-coordinate geometry to two equivalent Np(1), two equivalent Np(2), one B(2), two equivalent B(1), and two equivalent B(4) atoms.