From a nanoparticular solid-state material to molecular organo-f-element-polyarsenides

A convenient pathway to new molecular organo-lanthanide-polyarsenides in general and to a f-element complex with the largest polyarsenide ligand in detail is reported. For this purpose, the activation of the solid state material As0nano (nanoscale gray arsenic) by the multi electron reducing agents [K(18-crown-6)][(Ln+II)2(μ-η6:η6-C6H6)] (Ln = La, Ce, Cp′′ = 1,3-bis(trimethylsilyl)cyclopentadienyl anion) and [K(18-crown-6)]2[(Ln+II)2(μ-η6:η6-C6H6)] (Ln = Ce, Nd) is shown. These non-classical divalent lanthanide compounds were used as three and four electron reducing agents where the product formation can be directed by variation of the applied reactant. The obtained Zintl anions As33−, As73−, and As144− were previously not accessible in molecular 4f-element chemistry. Additionally, the corresponding compounds with As144−-moieties represent the largest organo-lanthanide-polyarsenides known to date.


Synthesis of [{K(18-crown-6)}2(Cp''2Nd)2(μ4-ɳ 2 :ɳ 2 :ɳ 2 :ɳ 2 -As14)] (3):
Toluene (10 mL) was condensed onto a mixture of B(Nd) (100.0 mg, 0.055 mmol, 1.00 equiv.) and As 0 nano (29.0 mg, 0.39 mmol, 7.00 equiv.). The resulting reaction mixture suspended for 4 h in an ultrasonic bath and afterwards stirred for 96 h at 70 °C. All volatiles were removed under reduced pressure and the remaining solid was extracted with 10 mL benzene. Yellowish crystals of 3 were obtained by slow evaporation of the solvent at ambient temperature and washed with cold benzene. Owing to the paramagnetic nature of Nd(III) and the low stability of the compound 3 upon redissolving its single crystals, no meaningful NMR spectra could be obtained. Toluene (10 mL) was condensed onto a mixture of B(Ce) (100.0 mg, 0.055 mmol, 1.00 equiv.) and As 0 nano (29.1 mg, 0.39 mmol, 7.00 equiv.). The resulting reaction mixture suspended for 4 h in an ultrasonic bath and afterwards stirred for 96 h at 60 °C. All volatiles were removed under reduced pressure and the remaining solid was extracted with 10 mL benzene. A mixture of orange-reddish crystals of 2 and 4 was obtained by slow evaporation of the solvent at ambient temperature. Due to the similar solubility of the compounds, a separation was not possible. Toluene (10 mL) was condensed onto a mixture of B(Nd) (100.0 mg, 0.055 mmol, 1.00 equiv.) and As 0 nano (29.0 mg, 0.39 mmol, 7.00 equiv.). The resulting reaction mixture suspended for 4 h in an ultrasonic bath and afterwards stirred for 96 h at RT. All volatiles were removed under reduced pressure and the remaining solid was extracted with 10 mL benzene. A mixture of orange crystals of 3, 5, 6, and 7 was obtained by slow evaporation of the solvent at ambient temperature. Due to the similar solubility of the compounds, a separation was not possible.

X-ray Crystallographic Studies
Suitable crystals were selected under an optic microscope equipped with polarizing filters, covered in mineral oil (Aldrich) and mounted on a MiTeGen holder. The crystals were transferred directly to the cold stream of a STOE IPDS 2 (150 K) or STOE StadiVari (100 K) diffractometer, equipped with a Mo-sealed tube, MoGenix 3D HF or a Ga-MetalJet X-ray source.
All structures were solved using the programs SHELXS/T and Olex2 1.2.4,5,6. 6-9 The remaining non-hydrogen atoms were located from successive difference Fourier map calculations. The refinements were carried out by using full-matrix least-squares techniques on F2 by using the program SHELXL.
Specific comments on the structures discussed here are given below.  Author Response: The residual electron density is likely caused by untreated twinning. This leads to a second and third set of clearly visible q-Peaks for every heavy in the core structure.
However, the chemical abundance of the twinned/disordered structure is too low, to be treated satisfactorily.

[{K(18-crown-6)}(Cp''2Ce)2(μ3-ɳ 2 :ɳ 2 :ɳ 2 -As7)] (2)
The solid-state structure of compound 2 features a disordered toluene molecule in the asymmetric unit. Moderate ISOR restraints were applied to model the disorder appropriately. Compound 5 exhibits two disordered TMS groups and benzene molecules. The former ones were modelled using SIMU restraints, the latter ones using ISOR restraints. Author Response: The residual electron density is likely caused by untreated twinning. This leads to a second set of clearly visible q-Peaks for every heavy atom in the core structure.

Alert level B
However, the chemical abundance of the twinned/disordered structure is too low, to be modelled satisfactorily. However, the chemical abundance of the twinned/disordered structure is too low, to be modelled satisfactorily.