Anion SSNSS

Thermal decomposition of [N(PPh3)2]" -[S4N5] in MeCN yields sequentially the corresponding salts of S3N3 and S4N (50% yield). An X-ray crystallographic analysis of the dark-blue air-stable product [N(PPh3)2] [S4N] revealed the presence of the unique acyclic anion [SSNSS] whose structure is in Fig. 15.42c. The anion is planar with cis-trans configuration. 

NMR and visible spectra have established that a number of S-N anions are present in such solutions.The primary reduction products are polysulfides Sx, which dissociate to polysulfur radical anions, especially the deep blue 83 ion (/Imax 620nm). In a IM solution the major S-N anion detected by NMR spectroscopy is cycZo-[S7N] with smaller amounts of the [SSNSS] ion and a trace of [SSNS]. The formation of the acyclic anion 5.23 from the decomposition of cyclo-Sjl is well established from chemical investigations (Section 5.4.3). The acyclic anions 5.22 and 5.23 have been detected by their characteristic visible and Raman spectra. It has also been suggested that a Raman band at 858 cm and a visible absorption band at 390 nm may be attributed to the [SaN] anion formed by cleavage of a S-S bond in [SSNS]. ° However, this anion cannot be obtained as a stable species when [SsN] is treated with one equivalent of PPhs. 

S4N is a planar chain-like anion of connectivity SSNSS [130]. 

Under snitably controlled conditions, thermal decomposition may be used to prepare certain S N componnds. For example, S2N2 is obtained by the mild thermolysis of a variety of S-N heterocycles (see Section 5.1.3) and heating solntions of SbN3 salts in boiling acetonitrile prodnces the acyclic SSNSS anion (see Section 5.3.4). Bond enthalpies for S-N componnds can be estimated from S-N bond lengths. ... 

The IR and Raman spectra of S4" N4 and S N4 have been assigned in accordance with the Did stracture (1). The method of enrichment has also been used to distinguish S-N from S-S vibrations in, for example, the SSNSS and SNSS anions. The S-S vibration appears as a strong band in the Raman spectrum and this technique can be used to detect transannular S-S interactions in bicyclic or... 

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