In the crystals, magnesium atoms, octahedrally
coordinated, join two-dimensional layers of tetrahedral Si[O.sub.4] units (with unshared oxygen atoms facing each other).
As shown in Figure 1, AFt phases are chemically and mineralogically complex, in which columns of [Ca.sub.6]Al[(OH).sub.6]*24[H.sub.2]O are lines of Al[(OH).sub.6.sup.3-] octahedrally
bonded with three calcium polyhedrons, and each calcium polyhedron is with O[H.sup.-] and four water molecules, which presents an orientational column structure on the whole.
Bentonite is composed of two tetrahedrally coordinated sheets of silicon ions surrounding an octahedrally
coordinated sheet of aluminum ions, the isomorphous substitution of [Al.sup.3+] for [Si.sup.4+] in the tetrahedral layer and [Mg.sup.2+] or [Fe.sup.3+] for [Al.sup.3+] in the octahedral layer results in a net negative surface charge on the layer, which makes it hold its physical and chemical properties, i.e., large specific surface area, cation exchange capacity, and adsorptive affinity for organic and inorganic ions [29, 30].
In this complex, the nickel ion is octahedrally
coordinated with the trien ligand bonded through its four nitrogen atoms with the remaining two coordination sites occupied by 1-methylimidazole ligands.
F-NPs are metal oxides with spinel structure with an [AB.sub.2][O.sub.4] formula, where A and B are cations located tetrahedrally (A atom; smaller and two per unit) and octahedrally
(B atom; larger and four per unit) coordinated to oxygen atoms, respectively (Figure 1(b)).
In ruby, [Cr.sup.3+] ions substitute for some [Al.sup.3+] ions, occupying similar octahedrally
coordinated, off-center lattice positions.
(1988) documented substitutions involving F[e.sup.2]+, M[g.sup.2]+, M[n.sup.2]+, F[e.sup.3]+, C[r.sup.3]+, [V.sup.5]+, and S[c.sup.3]+, as well as [V.sup.5]+ and T[i.sup.4]+, for octahedrally
coordinated aluminum, as well as lithium for tetrahedrally coordinated beryllium.
The octahedral alumina sheet consists of close-packed oxygen or hydroxyls between which octahedrally
coordinated aluminum atoms are present.
ZnSn[(OH).sub.6] (ZHS) is a class of perovskite-structured hydroxide, in which the metal atoms are octahedrally
coordinated with oxygen atoms .
ZnO enters the network with Zn[O.sub.4] structural unit as a glass forming oxides while octahedrally
coordinated as network modifier.
Happek, "Luminescence of octahedrally
coordinated [Eu.sup.2+] in [Rb.sub.2]M[P.sub.2][O.sub.7] (M = Ca, Sr)," ECS Transactions, Vol.