H.‐Juergen Meyer

Nitridoborates of the Lanthanides: Synthesis, Structure Principles, and Properties of a New Class of Compounds

Investigations of the nitridoborates of lanthanides (Ln) have progressed significantly during the last few years. New compounds have been synthesized and characterized and are presented here together with some of their properties. Currently two distinct methods serve for the preparation of nitridoborate compounds; either hexagonal boron nitride undergoes a fragmentation through the reaction with LnN, or dinitridoborate ions are converted into other nitridoborate ions. Lanthanide nitridoborates contain molecular anions such as [BN]n-, [BN2]3-, [B2N4]8-, [B3N6]9-, and [BN3]6- which may occur in combinations with other nitridoborates or with additional nitride ions. In crystal structures of lanthanide nitridoborates these anions are arranged in layers and are surrounded by metal atoms in a characteristic fashion. Terminal N atoms are capped by metal atoms forming a square-pyramid, and B atoms prefer a trigonal-prismatic environment of metal atoms. Nitridoborates form saltlike as well as metal-rich compounds and have the potential to show a lot of what are considered to be important solid-state properties, thus they have a good chance to establish their position within the group of relevant materials.

Multilateral Solid‐State Metathesis Reactions for the Preparation of Materials with Heteroanions: The [Si(CN2)4]4− Ion

The search for nonoxidic inorganic compounds has led beyond simple metal borides, carbides, nitrides, and silicides to the development of interesting materials in whose structures several nonmetallic elements are combined. For example, in the structures of the well-known compounds Ti(C,N) and Mo2BN, [2] the anions are combined, but are present without bonds between the heteroatoms. An extension to this type of compound comprises metal compounds with element combinations of boron, carbon, nitrogen, and silicon. These elements are bridged to form complex units or ions through heteropolar, covalent bonds. The systematic development of the nitridoborate, nitridosilicate and carbodiimide compound classes has brought about important advances for materials chemistry. These families can be regarded as metal-salt derivatives of the binary nonmetallic materials BN, Si3N4, and C3N4. An extension to these compound types in the form of the cyanamidosilicates is reported herein with the example of the first tetracyanamidosilicates, which can be conceived as metal-salt derivatives of Si(CN2)2. [6] Compounds with this type of heteroanion possess a number of interesting, often unpredictable properties as high-temperature resistant ceramic materials (Si3N4), [7]

Ag8Ca19N7 – Nitrogen Bridged Ca19N7 Superoctahedra surrounded by Silver Tetrahedra

By reacting Ca3N2 and silver powder at a temperature of 1300 K the subnitride Ag8Ca19N7 was obtained. The title compound crystallizes in the space group Fm3m (No. 225) and has the lattice constant a = 1472.0(2) pm at T = 210 K and a = 1474.43(3) pm at T = 295 K. Ag8Ca19N7 combines two very interesting, but rather different structural features, Ag4 tetrahedra and Ca19N7 superoctahedra. An analysis of the bonding situation has been performed by means of Extended-Huckel calculations. Ag8Ca19N7 – Stickstoff-verbruckte Ca19N7-Superoktaeder umgeben von SilberTetraedern Durch die Reaktion von Ca3N2 und Silberpulver bei einer Temperatur von 1300 K wurde das Subnitrid Ag8Ca19N7 erhalten. Die Titelverbindung kristallisiert in der Raumgruppe Fm3m (Nr. 225) mit der Gitterkonstanten a = 1472.0(2) pm (T = 210 K) und a = 1474.43(3) pm (T = 295 K). In Ag8Ca19N7 sind zwei interessante, aber verschiedene Strukturelemente vereint: Ag4-Tetraeder und Ca19N7-Superoktaeder. Eine Analyse der Bindungsverhaltnisse wurde mit der Extended-Huckel-Methode durchgefuhrt.

The Nitrido Borates Ln3B2N4 (Ln = La-Nd) and La5B4N9: Syntheses, Structures, and Properties

Single crystals of the lanthanoide nitrido borates Ln3B2N4 (Ln = La–Nd) and La5B4N9 have been obtained from reactions of lanthanoide metal powder, lanthanoide nitride powder, and hexagonal boron nitride in calcium chloride melts. The isotypic compounds Ln3B2N4 belong to the space group Immm (#71), Z = 2, with the lattice parameters for La3B2N4: a = 362.94(3), b = 641.25(6), c = 1097.20(8) pm; Ce3B2N4: a = 356.20(3), b = 631.90(6), c = 1071.91(8) pm; Pr3B2N4: a = 353.46(4), b = 630.04(13), c = 1079.04(23) pm and Nd3B2N4: a = 351.52(4), b = 627.01(15), c = 1075.59(23) pm. The structure of La5B4N9 has been determined in the space group Pbcm (#57), Z = 4, with a = 988.25(5); b = 1263.48(7), c = 770.33(4) pm. These two structure types resemble three kinds of nitrido borate anions, the oxalate analogue B2N4 of Ln3B2N4, and the carbonate analogue BN3 together with the six-membered ring system B3N6 of La5(BN3)(B3N6). In contrast to the valence compound La5B4N9 the compounds (Ln3+)3(B2N4)8–(e–) contain one electron in the conduction band, yielding temperature independent paramagnetism for La3B2N4. The calculated electronic structure is developed through the formation of B2N48– ions by dimerisation of two BN2 units. Die Nitridoborate Ln3B2N4 (Ln = La–Nd) und La5B4N9: Synthesen, Strukturen und Eigenschaften Einkristalle der Lanthanoidnitrodoborate Ln3B2N4 (Ln = La–Nd) und La5B4N9 wurden durch Reaktionen von Lanthanoid-Metallpulver, Lanthanoidnitrid-Pulver mit hexagonalem Bornitrid in Schmelzen aus Calciumchlorid dargestellt. Die isotypen Verbindungen Ln3B2N4 kristallisieren in der Raumgruppe Immm (Nr. 71), Z = 2, mit den Gitterkonstanten fur La3B2N4: a = 362.94(3), b = 641.25(6), c = 1097.20(8) pm; Ce3B2N4: a = 356.20(3), b = 631.90(6), c = 1071.91(8) pm; Pr3B2N4: a = 353.46(4), b = 630.04(13), c = 1079.04(23) pm und Nd3B2N4: a = 351.54(2), b = 627.01(15), c = 1075.59(23) pm. La5B4N9 kristallisiert in der Raumgruppe Pbcm (Nr. 57), Z = 4, mit a = 988,25(5); b = 1263,48(7), c = 770,33(4) pm. Diese zwei Strukturtypen enthalten drei verschiedene Nitridoborat Anionen, das Oxalat-analoge B2N4 von Ln3B2N4 und das Carbonat-analoge BN3 zusammen mit dem sechsgliedrigen Ringsystem B3N6 von La5(BN3)(B3N6). Anders als die Valenzverbindung La5B4N9 enthalten die Verbindungen (Ln3+)3(B2N4)8–(e–) ein Elektron im Leitungsband. Fur La3B2N4 resultiert temperaturunabhangiger Paramagnetismus. Die berechnete elektronische Struktur von La3B2N4 wird durch die Bildung von B2N48–-Ionen aus zwei BN2-Einheiten abgeleitet.

Electronic Conditions of Diatomic (BN) Anions in the Structure of CaNiBN

CaNiBN was synthesized from Ca, Ni and BN in sealed tantalum containers at 1000 °C. The structure was determined by single-crystal X-ray diffraction (P4/nmm, Z = 2, a = 353.24(3) pm, c = 763.59(9) pm, R1 = 0.019, wR2 = 0.045 for all collected independent reflections). CaPdBN was synthesized after the same method, and a powder pattern was indexed isotypically (P4/nmm, a = 377.38(1) pm, c = 760.95(4) pm). The CaNiBN structure contains (BN) units with B—N bond lengths of 138.1(4) pm. If the (BN) unit in CaMBN (M = Ni, Pd) is replaced by (C2), the structure can be considered as being isotypic with the structure of UCoC2. Crystals of CaNiBN exhibit metallic lustre. According to the calculated band structure an extremely narrow band gap is present. The covalency between Ni and BN is marked by two important σ type interactions. A third type of interaction between (BN) π* and Ni orbitals represents the slightly occupied conduction bands. CaNiBN exhibits temperature independent paramagnetism and no superconducting transition down to 4 K. Die elektronische Situation zweiatomiger (BN)-Anionen in der Struktur von CaNiBN CaNiBN wurde aus Ca, Ni and BN in verschweisten Tantal-Behaltern bei 1000 °C dargestellt. Die Struktur wurde durch Einkristall-Rontgenbeugung aufgeklart (P4/nmm, Z = 2, a = 353, 24(3) pm, c = 763, 59(9) pm, R1 = 0, 019, wR2 = 0, 045 fur alle erfassten unabhangigen Reflexe). Nach der gleichen Synthesemethode wurde CaPdBN dargestellt, dessen Pulverdiagramm isotyp indiziert wurde (P4/nmm, a = 377.38(1) pm, c = 760.95(4) pm). Die Struktur von CaNiBN enthalt (BN)-Einheiten mit B—N-Bindungslangen von 138.1(4) pm. Die Strukturen CaMBN (M = Ni, Pd) konnen als isotyp zur UCoC2-Struktur betrachtet werden, wenn die (BN)-Einheit durch (C2) ersetzt wird. Kristalle von CaNiBN zeigen metallischen Glanz. Aufgrund der berechneten Bandstruktur kann die Prasenz einer sehr kleinen Bandlucke angenommen werden. Kovalente Bindungen zwischen Ni und (BN) heben sich durch zwei wichtige Arten von σ-Wechselwirkungen hervor. Eine dritte Wechselwirkung reprasentiert das geringfugig besetzte Leitungsband aus π*-Fragmentorbitalen der (BN)-Einheiten und Ni-Orbitalen. CaNiBN zeigt temperaturunabhangigen Paramagnetismus und keinen supraleitenden Ubergang oberhalb von 4 K.

AN EXPECTED CALCIUM CARBIDO BORATE CHLORIDE : CA9CL8(BC2)2

Ca9Cl8(BC2)2 was obtained by solid state reaction of a mixture of CaCl2, Ca, B and C. The structure was solved by single crystal X-ray structure determination. Ca9Cl8(BC2)2 crystallizes in the orthorhombic space group Cmcm (No. 63, a = 1162.91(8) pm, b = 1341.59(10) pm and c = 1208.62(9) pm, Z = 4). The most striking element of the title compound is the bent BC25– unit that is surrounded by a bicapped trigonal prismatic arrangement of calcium ions.

Lanthanide Nitrido Borates with Six‐Membered B3N6 Rings: Ln3B3N6

Metal compounds with heteroatomic ring systems of main group elements are a domain of coordination chemistry. However, lanthanide nitrido borates Ln3 B3 N6 (Ln=La or Ce; see structure) are synthesized by the reaction of hexagonal boron nitride with LnN. The compounds contain the six-membered B3 N6 ring, which can be seen as a fragment from one layer of the hexagonal BN structure.

Driving Electrons to Anti-Bonding States: On the Synthesis of New Niobium Cluster Chlorides by Electrochemical Lithium Intercalation

The lithium intercalation chemistry of LiNb 6 Cl 15 , a 16 e − Nb-cluster, has been explored in order to obtain new Nb-cluster compounds. As a result, three different phases have been detected. Full de-intercalation of lithium produces Nb 6 Cl 15 , a new 15 e − Nb-cluster. The oxidation reaction is reversible since lithium can be intercalated again to produce the parent LiNb 6 Cl 15 . On the other hand, intercalation of lithium into LiNb 6 Cl 15 seems to proceed through two single phases with the following stoichiometries: Li 1.5 Nb 6 Cl 15 and Li 3 Nb 6 Cl 15 . For these two compositions the extra electrons (0.5 and 2 respectively/formula) should enter the e g * molecular orbitals arising from Nb-Nb interactions inside the cluster. The reductions of LiNb 6 Cl 15 leading to these two new electron-rich Nb-cluster are reversible as detected by chronopotentiometry.