Synthese, Struktur und Eigenschaften von SrC(NH)₃, einem stickstoffbasierten Carbonatanalogon mit Trinacriamotiv

Abstract

Strontiumguanidinat, SrC(NH) 3 ,d ie erste Verbindung mit zweifach deprotonierter Guanidineinheit, wurdeaus Strontium und Guanidin in flüssigem Ammoniak synthetisiert und mittels Rçntgen-und Neutronenpulverdiffraktion, IR-Spektroskopie und Dichtefunktionaltheorie inklusive harmonischer Phononenrechnungen charakterisiert. Die in der hexagonalen Raumgruppe P6 3 /m kristallisierende Verbindung ist das Stickstoffanalogon des Strontiumcarbonats,S rCO 3 ,u nd dem Motiv nachs chichtartig aus Sr 2+ -Ionen und komplexen Anionen des Typs C(NH) 3 2À aufgebaut;l etztere nehmen die eigentümlicheT rinacriagestalt an. Der Vergleicht heoretischer Phononenrechnungen mit experimentellen IR-Banden sowie quantenchemische Bindungsanalysen erlauben einen ersten Einblickindie Bindungs-und Packungsverhältnisse des bisher unbekannten Anions im Kristall.

Ammonothermal Synthesis, Crystal Structure, and Properties of the Ytterbium(II) and Ytterbium(III) Amides and the First Two Rare-Earth-Metal Guanidinates, YbC(NH)3 and Yb(CN3H4)3

“…The C–N bonds are somewhat elongated with 1.373(5) Å (Figure , left) compared to 1.3528(4) Å in SrC­(NH) 3 . This value falls between those of a single or double C–N bond and agrees with a bond order of 1 1 / 3 , as discussed before . In contrast, the Yb–N bond distance is shorter by 40% and only comprises 2.541(5) Å.…”

“…Related IR measurements show vibrations around 2000 cm –1 , typical for NCN 2– or HNCN – units . This is in line with the general decomposition of guanidinates toward (hydrogen) cyanamides by eliminating ammonia. , …”

“…YbC­(NH) 3 crystallizes isostructurally to SrC­(NH) 3 in space group P 6 3 / m , as derived from PXRD (Figure , right, and Table ). Ytterbium is coordinated antiprismatically by six imine nitrogen atoms at 2.541(3) Å (Figure , right), leading to a bond valence sum of 1.8, in accordance with the expected charge of 2+. − Each nitrogen atom bridges two ytterbium atoms, while the complete trinacria-shaped guanidinate unit is coordinated in a trigonal prism.…”

“…The crystal structure is related to the high-temperature potassium carbonate polymorph α-K 2 CO 3 in space group P 6 3 / mmc . , In α-K 2 CO 3 , the trigonal prisms not occupied by guanidinate/carbonate molecules are filled with additional potassium atoms on the Wyckoff position 2 d . For K 2 CO 3 , a number of lower-symmetry polymorphs are found where the carbonate units are rotated out of the plane. , For the strontium guanidinate, no structural transition could be observed between room temperature and 15 K, possibly due to steric hindrance. YbCO 3 is isostructural to SrCO 3 , which has a structure distinctly different from those of SrC­(NH) 3 and YbC­(NH) 3 , as discussed in detail in ref .…”

“…Building on this work, we have begun to establish a new class of materials, namely, unsubstituted guanidinate salts with deprotonated anions of the strong base guanidine (Figure ). The first examples are given by the alkali-metal guanidinates, 1:1 salts of the alkali metal A + , and the guanidinate anion CN 3 H 4 – . − More recently, the first alkaline-earth-metal guanidinate, SrC­(NH) 3 , was introduced, containing a doubly deprotonated C­(NH) 3 2– unit, the nitrogen analogue of the carbonate anion …”