ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Strontium nitrite monohydrate [Sr(NO2)2⋅H2O] has been studied at 294, 100, and 20 K by neutron diffraction. Integrated intensities of 2958 (294 K), 4239 (100 K), and 2154 (20 K) reflections were measured at the Brookhaven National Laboratory high flux beam reactor, resulting in 2068 (294 K), 2030 (100 K), and 1934 (20 K) independent structure factors. Structural refinement in monoclinic space group P21 led to R(F)=0.029 (294 K), 0.019 (100 K), and 0.034 (20 K). Lattice constants at 295 K are a=12.5831(4), b=8.94941(15), c=4.4860(2) A(ring), β=99.111(4)°; at 100 K, a=12.539(2), b=8.909(1), c=4.475(1) A(ring), β=99.086(20)°; and at 20 K, a=12.542(2), b=8.901(1), c=4.472(1) A(ring), β=99.030(20)°.The expansivity of all four lattice parameters is nonlinear, with α1=32.8×10−6 K−1, β1=76×10−9 K−2; α2=31.6×10−6 K−1, β2=44×10−9 K−2; α3=15.6×10−6 K−1, β3=15×10−9 K−2; α4=−2.8×10−6 K−1, β4=−21×10−9 K−2 for αTi =α295i [1+αiΔT+βi(ΔT)2], ΔT=T−295 K. The mean-square amplitude of Sr varies linearly with temperature between 20 and 294 K, and extrapolates to a zero-point value of 0.0010(2) A(ring)2. A survey shows that atoms with masses greater than about 80 have similar zero-point amplitudes which increase toward the maximum exhibited by H, with its zero-point amplitude of about 0.023 A(ring)2, as the atomic mass decreases. The coordination (9 and 10) of the two independent Sr2+ ions remains unchanged with temperature: the coordination shell radius decreases on average by 0.012 A(ring) from 294 to 20 K. Comparison with previous x-ray structural results on Sr(NO2)2⋅H2O shows the latter are influenced by scattering from the nitrogen atom lone-electron pair. Small but significant differences in N–O distances among the four independent NO−2 ions are detected at 294 K (0.020 A(ring)) and at 20 K (0.017 A(ring)). The mean N–O distance at 20 K for all four ions is identical at 1.253–1.254 A(ring). The maximum atomic displacement between 294 and 20 K is that by a nitrite ion oxygen, of 0.045 A(ring).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.449288
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