Ferroelectric glycine silver nitrate: a single-crystal neutron diffraction study

Protonated crystals of glycine silver nitrate (C₄H₁₀Ag₂N₄O₁₀) undergo a displacive kind of structural phase transition to a ferroelectric phase at 218 K. Glycine silver nitrate (GSN) is a light-sensitive crystal. Single-crystal X-ray diffraction investigations are difficult to perform on these crystals due to the problem of crystal deterioration on prolonged exposure to X-rays. To circumvent this problem, single-crystal neutron diffraction investigations were performed. We report here the crystal structure of GSN in a ferroelectric phase. The final R value for the refined structure at 150 K is 0.059. A comparison of the low-temperature structure with the room-temperature structure throws some light on the mechanism of the structural phase change in this crystal. We have attempted to explain the structural transition in GSN within the framework of the vibronic theory of ferroelectricity, suggesting that the second-order Jahn-Teller (pseudo-Jahn-Teller) behavior of the Ag⁺ ion in GSN leads to structural distortion at low temperature (218 K).

S1. Experimental

S1.1. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1.

S2. Results and discussion

Computing details

For both compounds, data collection: HKLgen; cell refinement: Rafin; data reduction: TriCs_ccl. Program(s) used to solve structure: SHELXL97 (Sheldrick, 1997) for gsnltc; SHELXS97 (Sheldrick, 1990) for gsnrt. For both compounds, program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP; software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

(gsnltc) Glycine Silver Nitrate

Crystal data

C4H10Ag2N2O4·2(NO3)	F(000) = 24
Mr = 489.90	Dx = 2.858 Mg m^−3
Monoclinic, P21	Neutron radiation, λ = 1.17610 Å
a = 5.451 (2) Å	Cell parameters from 25 reflections
b = 19.493 (1) Å	θ = 6.3–30°
c = 5.441 (2) Å	µ = 13.50 mm^−1
β = 100.12 (5)°	T = 150 K
V = 569.1 (3) Å^3	Transparent, transparent
Z = 2	6 × 2 × 1 mm

Data collection

Four circle diffractometer	1090 reflections with I > 2σ(I)
Radiation source: spalation source	Rint = 0.013
Graphite monochromator	θmax = 47.8°, θmin = 6.3°
Absorption correction: integration ?	h = −6→6
Tmin = ?, Tmax = ?	k = −22→0
1116 measured reflections	l = −6→0
1093 independent reflections

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.059	w = 1/[σ^2(Fo^2) + (0.1358P)^2 + 0.0119P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.157	(Δ/σ)max = 0.001
S = 1.20	Δρmax = 0.16 e Å^−3
1093 reflections	Δρmin = −0.13 e Å^−3
272 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 6.0 (7)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Secondary atom site location: difference Fourier map	Absolute structure parameter: −10 (10)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.4213 (10)	0.4128 (3)	0.9219 (9)	0.0173 (11)
O2	0.6744 (9)	0.4337 (3)	0.6494 (8)	0.0149 (11)
C1	0.6096 (8)	0.4403 (2)	0.8509 (8)	0.0137 (9)
H1C2	0.6658 (16)	0.5161 (6)	1.1435 (17)	0.031 (2)
H2C2	0.891 (2)	0.4495 (6)	1.1705 (19)	0.035 (2)
C2	0.7804 (8)	0.4851 (2)	1.0399 (7)	0.0150 (10)
N1	0.9492 (6)	0.52952 (17)	0.9293 (6)	0.0161 (8)
H1N1	1.0309 (17)	0.5055 (5)	0.800 (2)	0.028 (2)
H2N1	0.855 (2)	0.5710 (6)	0.8394 (18)	0.034 (2)
H3N1	1.0926 (16)	0.5500 (5)	1.0633 (16)	0.027 (2)
N2	−0.4523 (6)	0.21014 (16)	0.1072 (6)	0.0151 (8)
H1N2	−0.5975 (18)	0.1944 (6)	−0.0251 (19)	0.035 (2)
H2N2	−0.526 (2)	0.2357 (6)	0.238 (2)	0.038 (2)
H3N2	−0.3671 (17)	0.1668 (5)	0.196 (2)	0.034 (2)
C4	−0.2702 (7)	0.2534 (2)	−0.0023 (7)	0.0130 (9)
H1C4	−0.377 (2)	0.2865 (6)	−0.137 (2)	0.037 (3)
H2C4	−0.1585 (19)	0.2191 (6)	−0.0988 (18)	0.033 (2)
C3	−0.1033 (7)	0.2961 (2)	0.1868 (8)	0.0119 (9)
O3	−0.1684 (9)	0.3055 (2)	0.3919 (9)	0.0148 (10)
O4	0.0830 (9)	0.3227 (3)	0.1148 (9)	0.0189 (12)
N3	0.1853 (5)	0.18050 (17)	−0.4537 (5)	0.0149 (7)
O5	0.3390 (9)	0.2305 (3)	−0.4465 (10)	0.0208 (11)
O6	0.1381 (10)	0.1557 (3)	−0.2572 (11)	0.0225 (11)
O7	0.0767 (10)	0.1576 (3)	−0.6523 (12)	0.0261 (12)
N4	0.6826 (6)	0.05352 (16)	−0.4977 (6)	0.0161 (7)
O8	0.5817 (9)	0.0744 (3)	−0.7049 (10)	0.0191 (11)
O9	0.8376 (9)	0.0052 (3)	−0.4837 (9)	0.0185 (11)
O10	0.6294 (9)	0.0789 (3)	−0.3088 (10)	0.0236 (13)
Ag1	0.1053 (9)	0.3514 (3)	0.6960 (9)	0.0178 (11)
Ag2	0.4037 (8)	0.3856 (3)	0.3437 (9)	0.0168 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.020 (2)	0.018 (3)	0.015 (2)	−0.0120 (19)	0.0068 (17)	−0.0007 (19)
O2	0.016 (2)	0.020 (3)	0.010 (2)	−0.0082 (19)	0.0079 (16)	−0.0078 (18)
C1	0.0174 (19)	0.011 (2)	0.0106 (18)	−0.0031 (15)	−0.0037 (14)	−0.0012 (15)
H1C2	0.023 (4)	0.046 (7)	0.028 (5)	−0.013 (4)	0.016 (4)	−0.016 (4)
H2C2	0.031 (5)	0.044 (6)	0.027 (5)	−0.001 (4)	−0.006 (4)	0.013 (5)
C2	0.021 (2)	0.019 (2)	0.0040 (17)	−0.0036 (17)	−0.0008 (16)	−0.0039 (17)
N1	0.0241 (16)	0.0108 (17)	0.0127 (15)	−0.0022 (14)	0.0010 (13)	−0.0009 (14)
H1N1	0.029 (5)	0.021 (5)	0.038 (6)	−0.007 (4)	0.014 (4)	−0.006 (4)
H2N1	0.053 (6)	0.025 (5)	0.023 (4)	0.001 (5)	0.006 (4)	0.016 (4)
H3N1	0.026 (4)	0.032 (5)	0.021 (4)	−0.016 (4)	0.001 (3)	−0.012 (4)
N2	0.0150 (14)	0.0128 (17)	0.0179 (16)	−0.0080 (13)	0.0040 (14)	0.0022 (14)
H1N2	0.036 (5)	0.035 (6)	0.028 (5)	−0.008 (4)	−0.011 (4)	0.001 (4)
H2N2	0.048 (6)	0.028 (5)	0.044 (6)	0.004 (5)	0.022 (5)	−0.009 (5)
H3N2	0.033 (5)	0.024 (6)	0.042 (6)	0.001 (4)	−0.002 (4)	0.003 (4)
C4	0.0140 (18)	0.011 (2)	0.0128 (19)	−0.0084 (16)	−0.0006 (15)	0.0011 (17)
H1C4	0.045 (6)	0.032 (6)	0.027 (5)	−0.011 (5)	−0.011 (4)	0.009 (5)
H2C4	0.039 (5)	0.037 (6)	0.023 (4)	−0.005 (5)	0.005 (4)	−0.014 (4)
C3	0.0123 (18)	0.012 (2)	0.0109 (19)	−0.0033 (15)	0.0008 (13)	0.0001 (15)
O3	0.018 (2)	0.011 (2)	0.015 (2)	0.0025 (17)	0.0002 (17)	−0.0043 (18)
O4	0.021 (2)	0.021 (3)	0.013 (2)	−0.007 (2)	−0.0020 (17)	−0.001 (2)
N3	0.0110 (12)	0.0179 (15)	0.0153 (14)	0.0010 (11)	0.0009 (10)	−0.0034 (12)
O5	0.017 (2)	0.019 (3)	0.024 (3)	−0.005 (2)	−0.0023 (17)	0.000 (2)
O6	0.032 (3)	0.020 (3)	0.016 (2)	−0.005 (2)	0.0066 (19)	−0.002 (2)
O7	0.026 (2)	0.023 (3)	0.028 (3)	−0.001 (2)	0.003 (2)	−0.012 (2)
N4	0.0198 (14)	0.0145 (16)	0.0128 (14)	0.0009 (10)	−0.0006 (11)	0.0013 (11)
O8	0.020 (2)	0.014 (2)	0.021 (3)	−0.0015 (18)	−0.0018 (18)	0.0061 (19)
O9	0.020 (2)	0.023 (3)	0.010 (2)	0.005 (2)	−0.0043 (15)	0.0031 (19)
O10	0.017 (2)	0.035 (3)	0.019 (3)	0.000 (2)	0.0038 (19)	−0.003 (2)
Ag1	0.021 (2)	0.021 (3)	0.012 (2)	−0.0084 (19)	0.0027 (18)	−0.0036 (19)
Ag2	0.012 (2)	0.022 (3)	0.016 (2)	−0.0037 (19)	0.0026 (15)	−0.0017 (19)

Geometric parameters (Å, º)

O1—C1	1.276 (7)	O4—Ag2	2.313 (7)
O1—Ag1	2.273 (7)	O4—Ag1^ii	2.370 (7)
O1—Ag2^i	2.373 (6)	N3—O7	1.222 (7)
O2—C1	1.216 (6)	N3—O6	1.241 (7)
O2—Ag2	2.227 (7)	N3—O5	1.281 (7)
C1—C2	1.534 (5)	N4—O10	1.220 (7)
C2—N1	1.467 (5)	N4—O8	1.234 (6)
N2—C4	1.503 (5)	N4—O9	1.258 (6)
C4—C3	1.500 (5)	Ag1—O4^i	2.370 (7)
C3—O3	1.243 (7)	Ag1—Ag2	2.804 (6)
C3—O4	1.262 (7)	Ag2—O1^ii	2.373 (6)
O3—Ag1	2.213 (7)
C1—O1—Ag1	129.1 (4)	O7—N3—O5	121.2 (5)
C1—O1—Ag2^i	123.9 (4)	O6—N3—O5	120.3 (4)
Ag1—O1—Ag2^i	104.5 (3)	O10—N4—O8	120.1 (5)
C1—O2—Ag2	117.3 (4)	O10—N4—O9	120.5 (4)
O2—C1—O1	127.2 (5)	O8—N4—O9	119.3 (4)
O2—C1—C2	115.2 (4)	O3—Ag1—O1	164.7 (3)
O1—C1—C2	117.5 (4)	O3—Ag1—O4^i	118.8 (3)
N1—C2—C1	114.3 (3)	O1—Ag1—O4^i	76.5 (2)
C3—C4—N2	113.7 (3)	O3—Ag1—Ag2	88.9 (2)
O3—C3—O4	126.2 (5)	O1—Ag1—Ag2	76.64 (18)
O3—C3—C4	117.6 (4)	O4^i—Ag1—Ag2	147.9 (2)
O4—C3—C4	116.1 (4)	O2—Ag2—O4	164.7 (3)
C3—O3—Ag1	118.0 (4)	O2—Ag2—O1^ii	119.6 (3)
C3—O4—Ag2	128.6 (4)	O4—Ag2—O1^ii	75.7 (2)
C3—O4—Ag1^ii	125.1 (4)	O2—Ag2—Ag1	88.7 (2)
Ag2—O4—Ag1^ii	103.3 (3)	O4—Ag2—Ag1	76.56 (19)
O7—N3—O6	118.5 (5)	O1^ii—Ag2—Ag1	147.2 (2)

Symmetry codes: (i) x, y, z+1; (ii) x, y, z−1.

(gsnrt) Glycine Silver Nitrate

Crystal data

C4H10Ag2N2O4·2(NO3)	F(000) = 19
Mr = 244.95	Dx = 2.861 Mg m^−3
Monoclinic, P21/a	Neutron radiation, λ = 1.17610 Å
a = 5.451 (5) Å	Cell parameters from 25 reflections
b = 19.493 (9) Å	θ = 3.4–28.6°
c = 5.541 (2) Å	µ = 13.38 mm^−1
β = 100.20 (6)°	T = 293 K
V = 579.5 (6) Å^3	Transparent, transparent
Z = 4	6 × 2 × 1 mm

Data collection

Four circle diffractometer	Rint = 0.028
Radiation source: spallation source	θmax = 28.7°, θmin = 3.5°
Graphite monochromator	h = −2→4
333 measured reflections	k = 0→15
224 independent reflections	l = −4→4
210 reflections with I > 2σ(I)

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.158	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.406	w = 1/[σ^2(Fo^2) + (0.2P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 2.17	(Δ/σ)max < 0.001
224 reflections	Δρmax = 0.10 e Å^−3
62 parameters	Δρmin = −0.09 e Å^−3
12 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 11 (6)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ag	0.160 (5)	0.0164 (10)	−0.175 (4)	0.062 (9)*
O1	0.174 (5)	0.0475 (10)	0.390 (4)	0.056 (9)*
O2	0.424 (5)	0.0626 (11)	0.124 (5)	0.073 (10)*
N1	0.687 (3)	0.1603 (6)	0.406 (2)	0.062 (8)*
C1	0.358 (5)	0.0736 (10)	0.323 (4)	0.078 (10)*
C2	0.523 (4)	0.1146 (8)	0.524 (3)	0.055 (8)*
O3	0.164 (7)	0.2098 (12)	0.171 (5)	0.085 (11)*
O4	0.080 (7)	0.2132 (13)	−0.229 (5)	0.100 (11)*
O5	−0.097 (6)	0.1358 (12)	−0.034 (5)	0.083 (10)*
N2	0.051 (5)	0.1851 (8)	−0.033 (4)	0.085 (9)*
H1N	0.615 (15)	0.199 (2)	0.295 (10)	0.14 (2)*
H2N	0.819 (9)	0.1812 (18)	0.538 (8)	0.084 (15)*
H3N	0.795 (7)	0.139 (2)	0.297 (6)	0.079 (14)*
H1C	0.401 (10)	0.138 (3)	0.613 (10)	0.14 (2)*
H2C	0.589 (15)	0.081 (2)	0.657 (9)	0.14 (2)*

Geometric parameters (Å, º)

Ag—O2	2.16 (3)	O2—C1	1.24 (2)
Ag—O1^i	2.32 (3)	N1—C2	1.491 (17)
Ag—O1^ii	2.49 (3)	C1—C2	1.512 (19)
Ag—Ag^i	2.89 (6)	O3—N2	1.269 (18)
O1—C1	1.233 (19)	O4—N2	1.25 (2)
O1—Ag^i	2.32 (3)	O5—N2	1.246 (18)
O1—Ag^iii	2.49 (3)
O2—Ag—O1^i	161.7 (16)	C1—O2—Ag	119 (2)
O2—Ag—O1^ii	119.9 (15)	O1—C1—O2	125 (2)
O1^i—Ag—O1^ii	78.3 (12)	O1—C1—C2	113 (2)
O2—Ag—Ag^i	88.3 (13)	O2—C1—C2	121 (2)
O1^i—Ag—Ag^i	74.0 (11)	C1—C2—N1	107.7 (14)
O1^ii—Ag—Ag^i	146.0 (15)	O5—N2—O4	121 (3)
C1—O1—Ag^i	131.0 (19)	O5—N2—O3	120 (2)
C1—O1—Ag^iii	124.3 (19)	O4—N2—O3	119 (2)
Ag^i—O1—Ag^iii	101.7 (12)

Symmetry codes: (i) −x, −y, −z; (ii) x, y, z−1; (iii) x, y, z+1.