Ammonothermal Synthesis, X‐Ray and Time‐of‐Flight Neutron Crystal‐Structure Determination, and Vibrational Properties of Barium Guanidinate, Ba(CN₃H₄)₂

Abstract

We report the crystal structure of Ba(CN 3 H 4 ) 2 as synthesized from liquid ammonia. Structure solution based on X‐ray diffraction data suffers from a severe pseudo‐tetragonal problem due to extreme scattering contrast, so the true monoclinic symmetry is detectable only from neutron powder diffraction patterns, and structure solution and refinement was greatly aided by density‐functional theory. The symmetry lowering is due to slight deviations of the guanidinate anion from the mirror plane in space group P b 2, a necessity of hydrogen bonding. At 300 K, barium guanidinate crystallizes in P 2 1 / c with a =6.26439(2) Å, b =16.58527(5) Å, c =6.25960(2) Å, and a monoclinic angle of β=90.000(1)°. To improve the data‐to‐parameter ratio, anisotropic displacement parameters from first‐principles theory were incorporated in the neutron refinement. Given the correct structural model, the positional parameters of the heavy atoms were also refinable from X‐ray diffraction of a twinned crystal. The two independent guanidinate anions adopt the all‐ trans ‐ and the anti ‐shape. The Ba cation is coordinated by eight imino nitrogens in a square antiprism with Ba−N contacts between 2.81 and 3.04 Å. The IR and Raman spectra of barium guanidinate were compared with DFT‐calculated phonon spectra to identify the vibrational modes.

Ammonothermal Synthesis, Crystal Structure, and Vibrational Properties of the Doubly Deprotonated Calcium Guanidinate, CaC(NH)3

“…Hence, YbC(NH) 3 served as the structural model in the Rietveld refinement performed using GSAS II . All N–C–N planes, N–C–N angles, and C–N bond lengths were restrained to sensible values as known from the literature, just like for the U iso parameters. In order to allow for greater accuracy and also locate the exact positions of the hydrogen atoms, neutron powder‐diffraction data were collected on the POWGEN neutron powder diffractometer in the Oak Ridge National Laboratory.…”

Stabilization of Guanidinate Anions [CN3]5− in Calcite‐Type SbCN3

“…A straightforward approach to synthesizing guanidinates involves the deprotonation of guanidine, which can be performed by strong bases like alkali metal hydrides or amides (Table S1) [16–24] . This method allowed achieving the double‐deprotonated guanidinates with the chemical formula MC(NH) 3 (M=Ca, Ba, Sr, Eu, Yb) [17,20,24,25] .…”

“…[16][17][18][19][20][21][22][23][24] This method allowed achieving the double-deprotonated guanidinates with the chemical formula MC(NH) 3 (M=Ca, Ba, Sr, Eu, Yb). [17,20,24,25] However, achieving full deprotonation of guanidine proves impossible due to guanidine's inherent properties as a very strong base itself.…”

“…[13][14][15] A straightforward approach to synthesizing guanidinates involves the deprotonation of guanidine, which can be performed by strong bases like alkali metal hydrides or amides (Table S1). [16][17][18][19][20][21][22][23][24] This method allowed achieving the double-deprotonated guanidinates with the chemical formula MC(NH) 3 (M=Ca, Ba, Sr, Eu, Yb). [17,20,24,25] However, achieving full deprotonation of guanidine proves impossible due to guanidine's inherent properties as a very strong base itself.…”