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CuAl2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are eight inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded to four O2- atoms to form CuO4 tetrahedra that share corners with three equivalent CuO6 octahedra and corners with nine AlO6 octahedra. The corner-sharing octahedra tilt angles range from 56–64°. There are a spread of Cu–O bond distances ranging from 1.95–1.97 Å. In the second Cu2+ site, Cu2+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with three equivalent CuO4 tetrahedra, corners with three equivalent AlO4 tetrahedra, and edges with six AlO6 octahedra. There are a spread of Cu–O bond distances ranging from 1.99–2.10 Å. In the third Cu2+ site, Cu2+ is bonded to four O2- atoms to form CuO4 tetrahedra that share corners with three equivalent CuO6 octahedra and corners with nine AlO6 octahedra. The corner-sharing octahedra tilt angles range from 57–64°. There are a spread of Cu–O bond distances ranging from 1.95–1.99 Å. In the fourth Cu2+ site, Cu2+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with three equivalent CuO4 tetrahedra, corners with three equivalent AlO4 tetrahedra, and edges with six AlO6 octahedra. There are a spread of Cu–O bond distances ranging from 2.00–2.12 Å. In the fifth Cu2+ site, Cu2+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with two equivalent AlO4 tetrahedra, corners with four CuO4 tetrahedra, and edges with six AlO6 octahedra. There are a spread of Cu–O bond distances ranging from 1.95–2.15 Å. In the sixth Cu2+ site, Cu2+ is bonded to four O2- atoms to form CuO4 tetrahedra that share a cornercorner with one CuO6 octahedra and corners with eleven AlO6 octahedra. The corner-sharing octahedra tilt angles range from 58–65°. There are a spread of Cu–O bond distances ranging from 1.98–2.02 Å. In the seventh Cu2+ site, Cu2+ is bonded to four O2- atoms to form CuO4 tetrahedra that share a cornercorner with one CuO6 octahedra and corners with eleven AlO6 octahedra. The corner-sharing octahedra tilt angles range from 57–62°. There is one shorter (1.97 Å) and three longer (2.00 Å) Cu–O bond length. In the eighth Cu2+ site, Cu2+ is bonded to four O2- atoms to form CuO4 tetrahedra that share corners with two equivalent CuO6 octahedra and corners with ten AlO6 octahedra. The corner-sharing octahedra tilt angles range from 55–63°. There are a spread of Cu–O bond distances ranging from 1.95–2.04 Å. There are twelve inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with three CuO4 tetrahedra, corners with three AlO4 tetrahedra, edges with two CuO6 octahedra, and edges with four equivalent AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.89–2.00 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with three CuO4 tetrahedra, corners with three AlO4 tetrahedra, edges with two CuO6 octahedra, and edges with four AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.89–2.01 Å. In the third Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two AlO4 tetrahedra, corners with four CuO4 tetrahedra, an edgeedge with one CuO6 octahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.87–2.04 Å. In the fourth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two AlO4 tetrahedra, corners with four CuO4 tetrahedra, an edgeedge with one CuO6 octahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.87–2.05 Å. In the fifth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two equivalent CuO6 octahedra and corners with ten AlO6 octahedra. The corner-sharing octahedra tilt angles range from 53–63°. There are a spread of Al–O bond distances ranging from 1.80–1.85 Å. In the sixth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with three equivalent CuO4 tetrahedra, corners with three equivalent AlO4 tetrahedra, an edgeedge with one CuO6 octahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.90–1.99 Å. In the seventh Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO4 tetrahedra, corners with four CuO4 tetrahedra, edges with two equivalent CuO6 octahedra, and edges with four AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.87–2.05 Å. In the eighth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with three equivalent CuO6 octahedra and corners with nine AlO6 octahedra. The corner-sharing octahedra tilt angles range from 54–62°. There is two shorter (1.83 Å) and two longer (1.84 Å) Al–O bond length. In the ninth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO4 tetrahedra, corners with four CuO4 tetrahedra, an edgeedge with one CuO6 octahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.89–1.98 Å. In the tenth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO4 tetrahedra, corners with four CuO4 tetrahedra, an edgeedge with one CuO6 octahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.88–1.99 Å. In the eleventh Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six CuO4 tetrahedra, an edgeedge with one CuO6 octahedra, and edges with five AlO6 octahedra. There is five shorter (1.92 Å) and one longer (1.95 Å) Al–O bond length. In the twelfth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with three equivalent CuO6 octahedra and corners with nine AlO6 octahedra. The corner-sharing octahedra tilt angles range from 54–61°. There are a spread of Al–O bond distances ranging from 1.81–1.89 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Cu2+ and two Al3+ atoms. In the second O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form distorted corner-sharing OAl3Cu trigonal pyramids. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Cu2+ and two equivalent Al3+ atoms. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Cu2+ and three Al3+ atoms. In the fifth O2- site, O2- is bonded to two Cu2+ and two Al3+ atoms to form distorted OAl2Cu2 trigonal pyramids that share corners with four OAl3Cu tetrahedra, corners with three OAl3Cu trigonal pyramids, and edges with two OAl2Cu2 trigonal pyramids. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Cu2+ and three Al3+ atoms. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the eighth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the ninth O2- site, O2- is bonded to two Cu2+ and two equivalent Al3+ atoms to form distorted OAl2Cu2 trigonal pyramids that share corners with four OAl3Cu tetrahedra, corners with three OAl3Cu trigonal pyramids, and edges with two equivalent OAl2Cu2 trigonal pyramids. In the tenth O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form distorted OAl3Cu tetrahedra that share corners with two equivalent OAl3Cu tetrahedra, corners with four OAl2Cu2 trigonal pyramids, and edges with two equivalent OAl3Cu tetrahedra. In the eleventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Cu2+ and three Al3+ atoms. In the twelfth O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form distorted OAl3Cu tetrahedra that share corners with two OAl3Cu tetrahedra, corners with four OAl2Cu2 trigonal pyramids, and edges with two OAl3Cu tetrahedra. In the thirteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the fourteenth O2- site, O2- is bonded to two Cu2+ and two equivalent Al3+ atoms to form distorted corner-sharing OAl2Cu2 tetrahedra. In the fifteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the sixteenth O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form distorted OAl3Cu trigonal pyramids that share corners with three OAl2Cu2 tetrahedra, corners with three OAl3Cu trigonal pyramids, and edges with three OAl3Cu trigonal pyramids. In the seventeenth O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form distorted OAl3Cu trigonal pyramids that share corners with three OAl2Cu2 tetrahedra and corners with three OAl3Cu trigonal pyramids. In the eighteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Cu2+ and two Al3+ atoms. In the nineteenth O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form a mixture of distorted edge and corner-sharing OAl3Cu trigonal pyramids. In the twentieth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Cu2+ and two equivalent Al3+ atoms. In the twenty-first O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form distorted OAl3Cu trigonal pyramids that share corners with three OAl2Cu2 tetrahedra, corners with three OAl3Cu trigonal pyramids, and edges with three OAl3Cu trigonal pyramids. In the twenty-second O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Cu2+ and three Al3+ atoms. In the twenty-third O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Cu2+ and three Al3+ atoms. In the twenty-fourth O2- site, O2- is bonded to one Cu2+ and three Al3+ atoms to form corner-sharing OAl3Cu tetrahedra.

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