Publisher Summary A number of recent crystal structure determinations on compounds of the nonmetals have discovered intramolecular distances that are much longer than normal bonds, and intermolecular distances that are much shorter than van der Waals distances. In this chapter, these interactions are examined and a qualitative explanation is attempted. It will become clear that in most of them an approximately linear arrangement is found, Y-A—X where Y-A is a normal bond and A—X is a short intermolecular distance. It is with these approximately linear interactions that we are particularly concerned, and it will be our contention that they are the result of directed forces and that their behavior is sufficiently regular and understandable for the name secondary bond to be appropriate. The only conclusive method of establishing the presence of secondary interactions is by crystal structure determinations. An intermolecular interaction can be recognized as being significant by being shorter than the expected intermolecular (van der Waals) distance, but if it is the result of directed forces— that is, bonds rather than electrostatic or nondirectional van der Waals forces.

Secondary Bonding to Nonmetallic Elements

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the – naturally subjective – “reactive”-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

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Reactive p-block cations stabilized by weakly coordinating anions

Publisher Summary This chapter presents an account of the current preparative and structural aspects of chalcogen-halide chemistry. The chapter focuses on the inorganic chemistry of the binary chlorides, bromides, and iodides as well as on the corresponding hypervalent anionic and cationic halo derivatives; fluorides are referred to in only a few cases. The chapter discusses the variability of the structural and bonding properties of the “inert pair” systems of the chalcogens in their formally lower positive oxidation states that directly influences the reactivity and the nature of the variety of possible reaction products. This field of chemistry may serve as a model for bonding, structure, and the reactive properties of analogous s2 systems of the neighboring elements, such as Sb(III), Bi(III), or I(V). Current investigations, for example, on antimony(III) and arsenic(III) halogen compounds, have indicated quite similar structural principles as in Te(IV) analogues. In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride and of tellurium tetrachloride on twinned crystals were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties, as well as the synthetic potential of the compounds. The chapter discusses the characteristic structural and bonding features of the halogen compounds of the chalcogen(IV) systems, in which the role of the inert pair determines much of the stereochemistry and reactive properties of the whole class of compounds. SCl4, as the only stable tetrahalide of sulfur besides SF4, is known to be easily prepared at temperatures below –34°C from the elements or from the reversible reaction of equimolar amounts of SC12 and chlorine.

Developments in chalcogen-halide chemistry

Kristalle von Te3Cl2, aus der isotypen Reihe Te2X (X Cl, Br, J) von Te2Br und Te2J, sowie von β- und α-TeJ wurden dargestellt und zur Strukturbestimmung nach Einkristallmethoden verwendet



Te3Cl2 kristallisiert monoklin, Raumgruppe P21/n, z = 4, mit a = 10,136(15), b = 8,635(3), c = 7,039(8) A und β = 100,74(6)° Die Struktur besteht aus makromolekularen Bauelementen von Telluratomen, deren Beziehung zur Struktur des elementaren Tellurs behandelt wird



Te2X kristallisiert orthorhombisch, Raumgruppe Pnam, z = 8 Gitterkonstanten fur das Bromid [Jodid] sind: a=14,921(12) [15,295(3)], b=12,843(6) [13,694(4)], c=4,005(3) [4,123(2)] A Die Struktur besteht aus unendlichen Doppelketten, die zu Bandern von Te6-Ringen mit Bootkonformation kondensiert sind, und verbruckenden Halogenatomen an den Randern



β-TeJ kristallisiert monoklin, Raumgruppe C2/m, z = 8, mit Gitterkonstanten a = 15,383(2), b = 4,182(2), c = 11,999(2) A und β = 128,09(1)° Die Struktur besteht aus unendlichen Ketten von Telluratomen, an welchen die Jodatome alternierend verbruckende und terminale Positionen besetzen



α-TeJ kristallisiert triklin, Raumgruppe P1, z = 8, mit Gitterkonstanten a = 9,958(3), b = 7,992(2), c = 8,212(4) A, α = 104,37(11), β = 90,13(4) und γ = 102,89(7)° Der makromolekulare Bauzusammenhang der Subhalogenide des Tellurs ist im α-TeJ zu einem Te4-Ring (dem Te4J4-Molekul) entartet



Die untersuchten Strukturen werden vergleichend und im Zusammenhang mit Strukturen anderer Tellurverbindungen diskutiert



On the Subhalides of Tellurium



Crystals of Te3Cl2, within the isotypic series Te2X (X Cl, Br I) of Te2Br and Te2I, as well as of β-TeI and α-TeI have been prepared and were used for structure determination with single crystal methods



Te3Cl2 is monoclinic, space group P21/n, z = 4, with a = 10136(15), b = 8635(3), c = 7039(8) A and β = 10074(6)° The structure consists of macromolecular units of tellurium atoms, which relation to the structure of elemental tellurium is discussed



Te2X is orthorhombic with space group Pnam z = 8 Lattic parameters for the bromide [iodide] are: a = 14921(12) [15295(3)], b = l2843(6)[13694(4)], c = 4005(3)[4123(2)] A The structure consists of infinite double chains condensed to ribbons of Te6 rings with boat conformation and bridging halogen atoms at the edges



β-TeI is monoclinic, space group C2/m, z = 8, with cell constants a = 15383(2), b = 4182(2), c = 11999(2) A and β = 12809(1)° The structure consists of endless chains of tellurium atoms along which the iodine atoms occupy alternating bridging and terminal positions



α-TeI is triclinic space group P1, z = 8, with lattice parameters a = 9958(3), b = 7992(2), c = 8212(4) A α = 10437(11), β = 9013(4) and γ = 10289(7)° The macromolecular building principle of the subhalides of tellurium is degenerated in α-TeI to a Te4-ring (the Te4I4 molecule)



The structures studied are compared to each other and discussed in connection with structures of other tellurium compounds

Zur Kenntnis der Subhalogenide des Tellurs

TeBr2 and TeCl2, unstable molecules which have previously been characterized only in the gas phase, are present as ligands in the new cluster compounds Re6Te6Cl6(TeCl2)2 and [Re6Te8(TeBr2)6]Br2. In Re6Te6Cl6(TeCl2)2, the Re6 cluster core is inscribed in a cube constructed of six μ3-Te2- and two μ3-Cl- ligands. The Re3+ cations bonded to four μ3-Te2- anions are also ligated by neutral TeCl2 ligands. In [Re6Te8(TeBr2)6]2+, the Re6 cluster core is inscribed in a cube constructed of eight μ3-Te2- ligands and each Re3+ cation is terminated by a neutral TeBr2 ligand.

The New Inorganic Ligands TeCl2 and TeBr2: Syntheses and Crystal Structures of Re6Te6Cl6(TeCl2)2 and [Re6Te8(TeBr2)6]Br2

Die 1:1-Verbindung TeCl4 · AlCl3 kristallisiert monoklin in der Raumgruppe P21/c mit a = 6,600, b = 12,675, c = 13,578 A, β = 105,72°, Z = 4. Die Rontgenstrukturanalyse ergab eine Schichtenstruktur. Die Schichten werden von TeCl6-Oktaedern gebildet, die jeweils uber drei benachbarte Ecken mit verschiedenen AlCl4-Tetraedern zu einem zweidimensionalen Netz verbunden sind. Die TeCl6-Oktaeder sind stark verzerrt, die mittleren Abstande TeCl (endst.) betragen 2,276 A, wahrend die Abstande TeCl (Brucke) im Mittel mit 3,061 A sehr viel langer sind. Der Art ihrer Verknupfung entsprechend (uber 3 Ecken mit verschiedenen TeCl6-Polyedern) sind die AlCl4-Tetraeder schwach verzerrt: AlCl-Bindungsabstande: 2,138, 2,142, 2,146 A (Brucke), 2,087 A (endst.). Im polaren Grenzfall ist die Struktur in guter Naherung zu beschreiben als Anordnung von trigonal-pyramidalen TeCl-Ionen und AlCl-Ionen, beide im wesentlichen mit C3v-Symmetrie. Diese Formulierung ist in Ubereinstimmung mit schwingungsspektroskopischen Ergebnissen.



The crystal structure of the 1:1 compound TeCl4 · AlCl3 has been determined from three-dimensional X-ray data. The compound crystallizes in space group P21/c with a = 6.600, b = 12.675, c = 13.578 A, β = 105.72°, Z = 4. The structure consists of layers composed of strongly distorted TeCl6 octahedra sharing three neighbouring corners with three different AlCl4 tetrahedra. Mean bond distances are 2.276 A in the TeCl (terminal) bonds and 3.061 A for the TeCl (bridge) bonds. The AlCl tetrahedra, which share one corner with each of three TeCl6 polyhedra, have AlCl distances of 2.087 A (terminal), 2.138, 2.142 and 2.146 A. As a good approximation (in the polar limiting case) the structure can be described as an arrangement of trigonal pyramidal TeCl ions and tetrahedral AlCl ions, both with essentially C3v symmetry. This formulation is in accordance with spectroscopic results.

B. Buss

Papers

Die Kristallstruktur von Trichlorotellur(IV)‐tetrachloroaluminat TeCl 3+AlCl 4−