A Hexanuclear Niobium Cluster Compound Crystallizing as Macroscopic Tubes

Abstract

Compounds with ordered structures in one or two dimensions are exciting materials and investigated intensively in many different areas of science. Many activities have been put into the preparation of low‐dimensional nano‐scaled structures and many compounds in this size regime are known. Contrary, the number of known compounds that have low‐dimensional macroscopic sized structures that form directly in a chemical reaction is very limited. Here, we present the synthesis of the niobium cluster compound [(Et2O)2H]2[Nb6Cl18], crystals of which grow in form of large hexagonal empty tubes of several centimeter length and diameters in the range of 2 mm. The single‐crystal X‐ray structure of this compound has been refined. Under warming, the compound readily eliminates diethyl ether molecules and decomposes. From a closer look at the crystallization process a step‐by‐step scheme of the procedure of the tube growth is proposed. The overall conclusion from this proposal is that a crucial balance between the cluster solution concentration, the crystal growth speed and the ether diffusion speed results in the formation of macroscopic crystal tubes.

Cluster Compounds with Oxidised, Hexanuclear [Nb6Cli12Ia6]n− Anions (n=2 or 3)

“…This successful concept of treating [Nb 6 Cl i 12 X a 2 (H 2 O) a 4 ] ⋅ 4H 2 O ( X =Cl or I) with a water scavenger acting as reactant, solvent and oxidiser, and supplying further ligands has been introduced before. [ 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ] All four investigated compounds are obtained in high yield. The experimental conditions for the synthesis of 1 to 4 are summarized in Scheme 1 .…”

“…Because of the presence of two distinct different coordination spheres, inner (i) and outer (a) in [M 6 X i 12 X a 6 ] type cluster compounds, we started to search for preparative procedures for mixed chloride-iodidesupported cluster complexes with only one halide type on each of the two different coordination site types, that is, cluster ) with a water scavenger acting as reactant, solvent and oxidiser, and supplying further ligands has been introduced before. [42][43][44][45][46][47][48][49][50] All four investigated compounds are obtained in high yield. The experimental conditions for the synthesis of 1 to 4 are summarized in Scheme 1.…”

Strong Cluster-Supported Brønsted Acids: Hexanuclear Niobium Cluster Compounds with Protonated Crown Ether Cations: (Crown-H)2[Nb6Cl12iX6a] (X = Cl or Br) and the Intermediate [Nb6Cl16(H2O)2]·4 dioxane

“…This compound forms just on adding the desiccant SOCl 2 to a suspension of [Nb 6 Cl 14 (H 2 O) 4 ]·4H 2 O in a dioxane/petrol ether mixture. Contrary to very similar reaction mixtures but different solvents, complete removal of the water ligands does not happen. ,, Presumably, compound 3 is an intermediate of the multi-step dehydration of the water-containing starting material, which crystallizes in small amounts from the given solvents. In other solvents, the reaction sequence proceeds and compounds with the [Nb 6 Cl 18 ] 2– unit form.…”

“…One example of a niobium cluster-supported acid with diethyl ether-stabilized protons acting as counter cations of the cluster anion, [(Et 2 O) 2 H] 2 [Nb 6 Cl 18 ], has been published recently. When it is crystallized, this compound forms macroscopic tubes …”

Hexanuclear Niobium Cluster Complex Anions with Acetato Ligands on Intramolecular Bridging Sites: [Nb6Cli4(OAc)i8Cla6]2– and [Nb6(OAc)i12Cla6]2–

“…It should be mentioned here, that Nb 6 cluster compounds with exo bonded acetato ligands are accessible as well using very different reaction conditions. [13] A more detailed analysis of the conditions leading to cluster compound with acetato ligands located either on the inner or outer coordination sites seems necessary.…”