Phosphorus-31, nitrogen-15, and nitrogen-14 nuclear magnetic resonance spectra of α-tetraphosphorus trisulphide isothiocyanates

Abstract

Phosphorus-31 n.m.r. spectra of α-P₄S₃(NCS)₂(1), α-P₄S₃(NCS)Cl (2), and α-P₄S₃(NCS)I (3) have been measured both for natural-abundance ¹⁴N isotopomers [(1a), (2a), and (3a)] and completely ¹⁵N-containing isotopomers [(1b), (2b), and (3b)] over a range of temperatures. Assignment and computer fitting of spectra of the ¹⁵N compounds has yielded accurate values of ³¹P–³¹P and ³¹P–¹⁵N coupling constants, and has allowed their variation with temperature to be studied. Measurement of ¹⁵N n.m.r. spectra [compounds (1b) and (3b)] has allowed the signs of the³¹P–¹⁵N couplings to be confirmed. A ¹⁴N T₁ relaxation study of α-P₄S₃(¹⁴NCS)₂(1a) showed a normal relaxation rate, and abnormal broadening in the ³¹P n.m.r. spectra of the ¹⁴N compounds was ascribed instead to the influence of abnormally large ¹J_PN coupling constants in the scalar coupling relaxation mechanism. Large ³¹P–¹⁵N coupling constants are reported for phosphorus(III) isothiocyanates, and for α-P₄S₃ derivatives. Similarly, large values of ¹J(³¹P–¹³C) for α-P₄S₃(¹³CN)(¹²CN), and of the secondary isotope shifts ¹Δ[³¹P(^37/35Cl)] for α-P₄S₃(¹⁵NCS)Cl (2b) and α-P₄S₃Cl₂, are reported.