Synthesis, Crystal Structure, Polymorphism, and Magnetism of Eu(CN3H4)2 and First Evidence of EuC(NH)3

Abstract

Abstract:We report the first magnetically coupled guanidinate, α-Eu(CN 3 H 4 ) 2 (monoclinic, P2 1 , a = 5.8494(3) Å, b = 14.0007(8) Å, c = 8.4887(4) Å, β = 91.075(6) • , V = 695.07(6) Å 3 , Z = 4). Its synthesis, polymorphism, crystal structure, and properties are complemented and supported by density-functional theory (DFT) calculations. The α-, β-and γ-polymorphs of Eu(CN 3 H 4 ) 2 differ in powder XRD, while the γ-phase transforms into the β-form over time. In α-Eu(CN 3 H 4 ) 2 , Eu is octahedrally coordinated and sits in one-dimensional chains; the guanidinate anions show a hydrogen-bonding network. The different guanidinate anions are theoretically predicted to adopt syn-, anti-and all-trans-conformations. Magnetic measurements evidence ferromagnetic interactions, presumably along the Eu chains. Finally, EuC(NH) 3 (isostructural to SrC(NH) 3 and YbC(NH) 3 , hexagonal, P6 3 /m, a = 5.1634(7) Å, c = 7.1993(9) Å, V = 166.23(4) Å 3 , Z = 2) is introduced as a possible ferromagnet.

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

“…[7] Calcium amide can also be synthesized in two ways; either by reacting calcium metal with liquid ammonia under pressure at room temperature or by reacting calcium metal with gaseous ammonia at 0°C to form a material dubbed "Ca(NH 3 ) 6 ", which then decomposes at room temperature to form calcium amide. [8] Ca + 2 NH 3 Ǟ Ca(NH 2 ) 2 + H 2 Ca + 6 NH 3 Ǟ "Ca(NH 3 ) 6 " Ǟ Ca(NH 2 ) 2 + 4 NH 3 + H 2 Herein we employed the first method by reacting calcium metal with liquid ammonia in steel autoclaves at 20°C for 7 days. Residual ammonia was then released by a Schlenk line leaving a white powder which was confirmed using XRD analysis to be Ca(NH 2 ) 2 .…”

“…We here used the same synthetic technique for calcium guanidinate starting from calcium amide at 50 °C, and it was Juza and Schumacher who first reported an X‐ray crystallographic study of the latter phase in 1963 . Calcium amide can also be synthesized in two ways; either by reacting calcium metal with liquid ammonia under pressure at room temperature or by reacting calcium metal with gaseous ammonia at 0 °C to form a material dubbed “Ca(NH 3 ) 6 ”, which then decomposes at room temperature to form calcium amide …”

“…Reacting equimolar amounts of calcium amide and guanidine at 50 °C, however, directly yields crystalline CaC(NH) 3 . Thus, this synthetic approach follows the prior work on 4f guanidinates as given by Görne et al, …”

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

“…In addition, the all-trans conformation was predicted for the structure of europium guanidinate. [9] These examples reveal that the imino-hydrogen atoms show a distinct sensitivity towards the chemical environment and the packing of the structure-generating molecular anions; alternatively expressed, the imino-hydrogen orientation determines the efficiency of the crystal packing. In addition, guanidinates with bivalent metal cations such as EuC(NH) 3 , YbC (NH) 3 and SrC(NH) 3 have been introduced containing a doubly deprotonated C(NH) 3 2unit, the nitrogen analogue of the carbonate anion.…”

“…In addition, guanidinates with bivalent metal cations such as EuC(NH) 3 , YbC (NH) 3 and SrC(NH) 3 have been introduced containing a doubly deprotonated C(NH) 3 2unit, the nitrogen analogue of the carbonate anion. [7][8][9] In these salt-like solids, the anion adopts a trinacria motif, and then the amount of hydrogen bonding is insignificant. The chemistry and structural motifs have been recently reviewed.…”