Hexakis(urea-κO)zinc(II) dinitrate at 110 and 250 K: uniaxial negative thermal expansion

Abstract

The crystal structure of the title compound, [Zn{CO(NH(2))(2)}(6)](NO(3))(2), has been determined at 110 and 250 K. The structure is stabilized by 12 individual hydrogen bonds, both intra- and intermolecular. Analysis of the thermal expansion tensor, based on unit cells determined over a temperature range of 180 K, shows uniaxial compression in the direction of the b axis during warming. The hydrogen bonds form layers perpendicular to this axis and these layers are connected by coordinative bonds parallel to the axis. As expected, the intermolecular hydrogen bonds expand during warming. Surprisingly, the coordinative bonds contract, accompanied by changes in the O-Zn-O angles. Overall, this behaviour can be described as an accordion-like effect.

Aqueous Solution Processing of Combustible Precursor Compounds into Amorphous Indium Gallium Zinc Oxide (IGZO) Semiconductors for Thin Film Transistor Applications

“…Although, complexes (1), (2)a nd (3)p ossess identical urea/nitrate ratios of 6:3f or (1), (2)a nd 4:2f or (3), they exhibit very differentm ass loss curves( Figure 3a,F igure S2). The residual mass of all the precursors are in good agreement with the expected ceramic yield from the decomposition of the precursors in oxygen ( (1) 18.4 %. Initial mass loss at lower temperatures( < 100 8C) resulting from the releaseo ft he coordinated water molecules in form of vapor is well known for zinc acetates [20] and zinc acetylacetonates [21] and is in good agreement with our observations.…”

“…The decomposition behavior of the indium and zinc precursorsp roceeded as at wo-stepd ecomposition where significant mass loss occursi nt he first step itself. The residual mass of all the precursors are in good agreement with the expected ceramic yield from the decomposition of the precursors in oxygen ( (1) 18.4 %. The differential scanning calorimetry analysiso ft hese precursors also indicate as harpe xothermic decomposition which can be associated with the expected redox reactions between the co-ordinated urea and the nitrate anion.…”

“…The neutralu rea molecule serves as monodentate ligand and coordinates to the central metal atom by its oxygen atom.F or (1)a nd (2)t he trivalent In and Ga metal 2 (3)d rawn at a5 0% probability level. [16] This warrants ar eport herein.A lthough homoleptic urea complexes of the composition M(urea) 6 n + as observed for (1)a nd (2)a re quite common [16,17] and under non aqueous reaction conditions ah omoleptic zinc coordination[ Zn(urea) 6 ][NO 3 ] 2 was reported, [18] ag eneral composition M(urea) 4 (H 2 O) 2 n + as found for (3)i sm uch less common so far. The third nitrate anion is related to the formerb yc rystal symmetry and thereforen ot shown either.…”

“…[15] Although, the molecular structureo ft he divalent zinc compound (3)h as been previously reported, [37] as traight forwardp rocedure to isolate the final product was not established so far. [16] This warrants ar eport herein.A lthough homoleptic urea complexes of the composition M(urea) 6 n + as observed for (1)a nd (2)a re quite common [16,17] and under non aqueous reaction conditions ah omoleptic zinc coordination[ Zn(urea) 6 ][NO 3 ] 2 was reported, [18] ag eneral composition M(urea) 4…”

Investigation of Steric Influences on Hydrogen‐Bonding Motifs in Cyclic Ureas by Using X‐Ray, Neutron, and Computational Methods

“…Since these seminal papers, there have been many reports on the limitations of this pattern7 and of examples of its utilization in other supramolecular systems, such as in gels8 or tethering together two halves of a molecular capsule by virtue of a hydrogen‐bonding belt 9. The ${R_2^2 }$ (8) motif is most notably observed in hexagonal urea‐clathrate materials,10 around κO‐urea complexes (in which the oxygen atoms cannot form the tape motif),11 and in a number of heterocycles. The presence of a disubstituted urea functionality within a heterocyclic molecule is widely observed in species such as the highly polymorphic phenobarbital and other barbiturate derivatives,12 benzimidazolones,13 cyanuric acid (and derivatives thereof),14 and others 15…”