Azidoberyllate mit Adamantanstruktur: Synthese, IR‐Spektren und Kristallstrukturen von (Ph₄P)₂[Be₄X₄(μ‐N₃)₆] (X = Cl, Br)

Abstract

Azido Beryllates with Adamantan‐like Structures: Synthesis, IR Spectra, and Crystal Structures of (Ph4P)2[Be4X4(μ‐N3)6] (X = Cl, Br)The azido beryllates (Ph4P)2[Be4X4(μ‐N3)6] (X = Cl 1a, X = Br 1b) have been prepared by the reaction of Me3SiN3 with the halogeno beryllates (Ph4P)2[Be2Cl6] and (Ph4P)2[Be2Br6], respectively, in CH2Cl2 and CH2Br2 solution, respectively. Both complexes form moisture sensitive, colourless crystals, which are nonexplosive with respect to mechanical or thermal stress. They are characterized by IR spectroscopy and by crystal structure determinations. 1a and 1b crystallize isotypically in the space group C2/c with 12 formula units per unit cell. Whereas 1a was only refined to R1 = 0.13, which is caused by disordering, 1b could be refined to R1 = 0.066. The structures contain adamantanlike dianions [Be4X4(μ‐N3)6]2— with two symmetry nonequivalent individuals which differ only slightly from one another. The Be4N6 core is formed by bridging function of the α‐nitrogen atoms of the azide groups with BeN bond lengths of 172.5 and bond lengths Nα—Nβ = 123.2 pm and Nβ—Nγ = 113.1 pm on average in the structure of 1b.

Synthesis, Solid‐State Structure, and Bonding Analysis of a Homoleptic Beryllium Azide

“…[10] TheI R spectra of donor-stabilized beryllium diazides (L) 2 Be(N 3 ) 2 (L = THF,p yridine) only show the antisymmetric stretching vibration (2150 cm À1 (THF), 2137 cm À1 (pyridine)), while heteroleptic complexes [Ph 4 P] 2 [Be 4 X 4 (m-N 3 ) 6 ]( X = Cl, Br) with bridging azide groups show the antisymmetric (Cl: 2141 cm À1 ;B r: 2132 cm À1 )a nd symmetric azide stretching vibrations (Cl:1297 cm À1 ;Br: 1299 cm À1 ), pointing to acovalent bonding contribution. [3] BeÀNs tretching vibrations (Cl: 800 cm À1 ;B r: 790 cm À1 )w ere observed for heteroleptic beryllium azides. 9 Be NMR spectra of 1 and 2 in [D 6 ]DMSO solution show singlet resonances at 0.05 ppm (1)a nd 0.04 ppm (2), which support the symmetric tetrahedral coordination mode of the Be atom.…”

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Beryllium azides tend to form predominantly ionic bonds, but are also expected to show covalent bonding contributions owing to the small size of the Be 2+ ion and its high charge density.However,even though Be(N 3 ) 2[1] and solvent-coordinated beryllium azide complexes L 2 Be(N 3 ) 2 (L = THF,p yridine) [2] 6 ]( X = Cl, Br) differ significantly as is typical for covalently bonded azides (type B in Scheme 1), [3] while those of the terminal azides are almost identical, indicating ah igh degree of ionic bonding (type C).

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“…[1] and solvent-coordinated beryllium azide complexes L 2 Be(N 3 ) 2 (L = THF,p yridine) [2] 6 ]( X = Cl, Br) differ significantly as is typical for covalently bonded azides (type B in Scheme 1), [3] while those of the terminal azides are almost identical, indicating ah igh degree of ionic bonding (type C).…”

“…Only two heteroleptic beryllium azides [Ph 4 P] 2 -[Be 4 X 4 (m-N 3 ) 6 ]( X = Cl, Br) with bridging azides and two complexes with terminal azide groups ([Ph 4 P] 2 [Be-(m-OSiMe 3 )(N 3 ) 2 ] 2 and (R,R,S N ,S N' )-[(C 12 H 26 N 2 )BeCl(N 3 )]) have been structurally characterized. [3][4][5] TheN a ÀN b and N b ÀN g bond lengths within the bridging azides in [Ph 4 P] 2 -[Be 4 X 4 -(m-N 3 ) 6 ]( X = Cl, Br) differ significantly as is typical for covalently bonded azides (type B in Scheme 1), [3] while those of the terminal azides are almost identical, indicating ah igh degree of ionic bonding (type C). [4,5] Unfortunately,q uantum-chemical calculations were not provided, and their bonding situation still has not been finally clarified.…”

“…Moreover,t he titration of 2 with [PNP]N 3 ,which was followed by 14 N(Figures S40-S58) and 9 Be NMR spectroscopy ( Figure 2), also confirmed the existence of an equilibrium between two major species. 3 Be À N 3 À Be(N 3 ) 3 ] À (D2). Resonances that are due to free azide N 3 À were observed at ambient temperature,a nd their (Tables S9 and S10).…”