The binary alkaline-earth aluminides AEAl2 (AE = Ca and Sr) and AEAl4 (AE = Ca–Ba) have been synthesized from the elements and investigated via powder X-ray diffraction experiments. CaAl2 adopts the cubic MgCu2-type structure (Fd3̅m), while SrAl2 crystallizes in the orthorhombic KHg2-type (Imma). LT-CaAl4 crystallizes with the monoclinic CaGa4-type (C2/m), while HT-CaAl4, SrAl4, and BaAl4 adopt the tetragonal BaAl4-type structure (I4/mmm). The close structural relation of the two CaAl4 polymorphs was established using a group–subgroup relation in the Bärnighausen formalism. In addition to the room-temperature and normal pressure phase of SrAl2, a high-pressure/high-temperature phase has been prepared using multianvil techniques, and its structural and spectroscopic parameters were determined. Elemental analysis by inductively coupled plasma mass spectrometry showed that no significant impurities with other elements besides the weighed ones are present and the chemical compositions match the synthesized ones. The title compounds have been furthermore investigated by 27Al solid-state magic angle spinning NMR experiments to validate the crystal structure and to gain information about the influence of the composition on the electron transfer and the NMR characteristics. This has also been investigated from a quantum chemical point of view using Bader charges, while the stabilities of the binary compounds in the three phase diagrams (Ca−Al, Sr−Al and Ba−Al) have been studied by calculations of formation energies per atom.

The cubic Laves-phase aluminides REAl2 with RE = Sc, Y, La, Yb and Lu were prepared from the elements by arc-melting or using refractory metal ampoules and induction heating. They...

Several ternary rare-earth metals containing titanium aluminum intermetallics in the RE2TiAl3 series (RE = Y, Gd–Lu) have been synthesized from the elements using arc-melting techniques. All compounds crystallize in the trigonal crystal system with rhombohedral space group R3-m (Z = 3) and lattice parameters ranging between a = 582–570 and c = 1353–1358 pm. They adopt the Mg2Ni3Si-type structure, which is an ordered superstructure of the cubic Laves phase MgCu2 and has been observed for Al intermetallics for the first time. Tetrahedral [TiAl3] entities that are connected over all corners form a network where the empty [TiAl3] tetrahedra exhibit a full Ti/Al ordering based on the single crystal results. The Al atoms are arranged into 63 Kagomé nets, while the Ti atoms connect these nets over the triangular units. In the cavities of this three-dimensional arrangement, the RE cations can be found forming a distorted diamond-type substructure. Magnetic measurements revealed that Y2TiAl3 and Lu2TiAl3 are Pauli paramagnetic substances, in line with the metallic character. The other compounds exhibit paramagnetism with antiferromagnetic ordering at a maximum Néel temperature of TN = 26.1(1) K for Gd2TiAl3.

In most intermetallic europium compounds, the Eu atoms exhibit a divalent oxidation state with a high effective magnetic moment since Eu2+ is isoelectronic with Gd3+. Trivalent intermetallic Eu compounds, in contrast, are extremely scarce and under 20 examples are known to literature. This mini-review summarizes the known binary and ternary examples along with their crystal-chemical peculiarities as well as their magnetic and 151Eu Mössbauer spectroscopic behavior. Additionally, compounds that exhibit valence phase transitions are summarized.

During attempts to synthesize new platinides in the ternary system Sr–Al–Pt, single crystals of SrAl5Pt3 and Sr2Al16Pt9 were obtained from a reaction of the elements with the nominal composition Sr4Al13Pt9. Both orthorhombic structures were refined based on single crystal x-ray diffraction data (SrAl5Pt3: Pnma, Wyckoff sequence c 9, a = 2065.04(7), b = 413.74(1), c = 738.98(3) pm, wR2 = 0.0310, 867 F 2 values, 56 variables; Sr2Al16Pt9: Immm, Wyckoff sequence l 4 j 2 ihga, a = 416.69(2), b = 1193.53(6), c = 1832.38(9) pm, wR2 = 0.0517, 671 F 2 values, 49 variables); full atomic ordering was observed in both cases. In order to analyze the bonding situation of these new platinides, quantum-chemical calculations were conducted. According to density functional theory both compounds are polar intermetallics with high negative charges on the Pt atoms and covalently bonded [Al5Pt3]/[Al16Pt9] networks showing strong Pt–Al alongside of weak Al–Al and Pt–Pt bonding.