Structural Characterization of Phosphorus‐Based Networks and Clusters: ³¹P MAS NMR Spectroscopy and Magnetic Shielding Calculations on Hittorf’s Phosphorus

Abstract

The (31)P MAS NMR spectrum of Hittorf's phosphorus has been measured and assigned to the 21 crystallographically distinct phosphorus atoms based on two-dimensional dipolar correlation spectroscopies. Application of such 2D techniques to phosphorus-based networks is particularly challenging owing to the wide chemical shift dispersions, rapid irreversible decay of transverse magnetization, and extremely slow spin-lattice relaxation in these systems. Nevertheless, a complete assignment was possible by using the combination of correlated spectroscopy (COSY) and radiofrequency-driven dipolar recoupling (RFDR). The assignment is supported further by DFT-based ab initio chemical shift calculations using a cluster-model approach, which gives good agreement between experimental and calculated chemical shift values. The (31)P chemical shifts appear to be strongly correlated with the average P-P bond lengths within the P(P(1/3))(3) coordination environments, whereas no clear dependence on average P-P-P bond angles can be detected. Calculations of localized Kohn-Sham orbitals reveal that this bond-length dependence is reflected in energy variations in the corresponding localized p-p-σ orbitals influencing the paramagnetic deshielding contribution in Ramsey's equation. In contrast, the contributions of the lone pairs to shielding differences are small and/or do not vary in a systematic manner for the different crystallographically distinct phosphorus sites. The combined spectroscopic and quantum chemical approach applied here and the increased theoretical understanding of (31)P chemical shifts will facilitate the structural elucidation of other phosphorus-based clusters and networks.

Gold(I) and Silver(I) Complexes of Diphosphacyclobutadiene Cobaltate Sandwich Anions

“…The resonances at d = + + 27.5 and À43.4 ppm are assigned to the two crystallographically distinct 31 P sites of the diphosphacyclobutadiene ligand which is h 1 -coordinated to Au + (P2, d = 27.5 and P1, d = À43.4 ppm). Due to extremely short transverse relaxation times of the phosphorus nuclei (most probably due to rapid fluctuations occurring in the Zeeman states of the quadrupolar cobalt nuclei in close proximity to the 31 P nuclei), standard 2D MAS NMR spectroscopic techniques for assigning the resonances [29] were unsuccessful. Nevertheless, 31 P SPARTAN (Selective Population Anti-z and Rate of Transfer to Adjacent Nuclei) experiments, by using crossrelaxation effects between spatially close or bonded phosphorus nuclei, [30] clearly confirm the proposed peak assignments since significant spectral spin-diffusion is observed between the P atoms detected at d = 27.5 and À43.4 ppm ( Figure 5).…”

Unexpected Reactivity of Red Phosphorus in Ionic Liquids

“…We observed a broad line centered at about 50 ppm (Figures S1 and S2, Supporting Information) in agreement with the literature, which reports values of 60 to 65 ppm 6. Black phosphorus appears at δ = 22.2 ppm,7 Hittorf's phosphorus exhibits a broader and more complex spectrum ranging from –84.5 to 171.3 ppm,8 and white phosphorus resonates at δ = –527 ppm 9. Crystalline fibrous phosphorus10 has not yet been characterized by NMR spectroscopy, but owing to its structural similarity to Hittorf's phosphorus, one can expect a similarly complex spectrum.…”

Laser ablation synthesis of arsenic–phosphide AsmPn clusters from As–P mixtures. Laser desorption ionisation with quadrupole ion trap time‐of‐flight mass spectrometry: The mass spectrometer as a synthesizer

“…Many structures of phosphorus or arsenic clusters have already been computed. Some of the clusters observed (P 16 ) were also synthesized by classical synthetic methods, e.g.…”