Crystal structure and Hirshfeld surface analysis of tris(acetohydrazide-κ2 N,O)(nitrato-κO)(nitrato-κ2 O,O′)terbium(III) nitrate

The crystal structure and supramolecular interactions of a new terbium(III) complex with an acetohydrazide ligand are reported.

In the title lanthanide(III) compound, [Tb(NO 3 ) 2 (C 2 H 6 N 2 O) 3 ]NO 3 , the asymmetric unit contains one Tb 3+ ion, three acetohydrazide (C 2 H 6 N 2 O) ligands, two coordinated nitrate anions, and an isolated nitrate anion. The Tb 3+ ion is in a ninefold coordinated distorted tricapped trigonal-prismatic geometry formed by three oxygen atoms and three nitrogen atoms from three different acetohydrazide ligands and three oxygen atoms from two nitrate anions. In the crystal, the complex molecules and the non-coordinated nitrate anions are assembled into a three-dimensional supramolecular architecture through extensive N-HÁ Á ÁO hydrogen-bonding interactions between the amine NH groups of the acetohydrazide ligands and the nitrate oxygen atoms. Hirshfeld surface analysis was performed to aid in the visualization of intermolecular contacts.

Chemical context
Over the past two decades, there has been increasing interest in the construction of new lanthanide-based coordination compounds, not only because of their structural diversity but also because of their fascinating potential applications in luminescence, magnetism, adsorption, and similar areas (Roy et al., 2014;Cui et al., 2018;Kuwamura et al., 2021). It is well known that lanthanide(III) ions have a high affinity for and prefer binding to hard donor atoms. Thus, organic ligands with oxygen donor atoms such as aromatic polycarboxylic acids have been used extensively for the formation of these coordination materials (Janicki et al., 2017) whereas organohydrazide ligands have received far less attention. Accordingly, a ConQuest search of the Cambridge Structural Database (CSD, Version 5.42, September 2021 update;Bruno et al., 2002;Groom et al., 2016) reveals only 23 entries for hydrazidecontaining lanthanide complexes. Among them, 15 lanthanide coordination complexes have recently been reported by our groups. Some of these complexes exhibited a high CO 2 uptake ability at high pressure (Theppitak et al., 2021a), and have shown great potential as luminescent sensors for acetone and the Co 2+ ion with good recyclability (Theppitak et al., 2021b). In this work, we present the molecular structure of a new terbium(III) complex, [Tb(C 2 H 6 N 2 O) 3 (NO 3 ) 2 ]NO 3 (1), synthesized with acetohydrazide (C 2 H 6 N 2 O) as the organic ligand. In addition, a Hirshfeld surface analysis and twodimensional fingerprint plots were used to quantify the intermolecular contacts in the crystal structure.

Structural commentary
The molecular structure of 1 is shown in Fig. 1. The asymmetric unit contains one Tb 3+ ion, three acetohydrazide ligands, two coordinated nitrate anions, and a non-coordinated nitrate counter-anion. The Tb 3+ ion is ninefold coordinated (TbN 3 O 6 ) by three nitrogen atoms and three oxygen atoms from three different acetohydrazide ligands, two oxygen atoms from one chelate nitrate anion, and one oxygen atom from another nitrate anion. As can be seen in Fig. 2, the coordination polyhedron of the Tb 3+ ion is best described as having a distorted tricapped trigonal-prismatic geometry, wherein the N3, N5, O1, O3, O4, and O7 atoms form a trigonal prism, while the N1, O2, and O5 atoms act as caps. The Tb-O bond lengths of 2.353 (2)-2.496 (2) Å are slightly shorter than the Tb-N bond lengths [2.553 (2)-2.586 (2) Å ]. The bond angles around the central Tb 3+ ion fall into the range of 50.93 (7)-150.97 (7) . These values are comparable to those reported for other ninefold-coordinated Tb 3+ compounds containing oxygen/nitrogen-donor ligands such as [Tb(C 17 H 13 Chen et al., 2015) and [Tb(C 13 H 22 Long et al., 2018).

Supramolecular features
Extensive hydrogen-bonding interactions involving the three components of the hydrazide group of the acetohydrazide ligand and the coordinated and non-coordinated nitrate ions contribute to the stabilization of the supramolecular structure of 1 (Table 1;   View of the distorted tricapped trigonal-prismatic coordination geometry of the central Tb 3+ atom in 1.

Table 1
Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1; Ày þ 1; Àz þ 1; H3BÁ Á ÁO6 hydrogen bonds involving the amine NH group of the acetohydrazide ligand and the coordinated nitrate oxygen atom, Fig. 3. Notably, the amine NH donor and the coordinated nitrate oxygen acceptor is also involved in an intramolecular N1-H1AÁ Á ÁO8 hydrogen bond. The dimers are further held together through an intermolecular N3-H3AÁ Á ÁO9 hydrogen bond between the amine NH and the coordinated nitrate oxygen (O9), resulting in the formation of a two-dimensional supramolecular layer that propagates in the

Hirshfeld surface analysis
The Hirshfeld surface analysis (McKinnon et al., 2007) and the associated two-dimensional fingerprint plot generation (Spackman & McKinnon, 2002) were carried out using Crys- Dimer formation through N-HÁ Á ÁO hydrogen bonds (dashed lines) in 1 (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).

Figure 4
The two-dimensional hydrogen bonded layer in 1 (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).

Figure 5
The three-dimensional hydrogen-bonded network in 1 (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).

Figure 6
View of 1 approximately along the b-axis direction, showing the N-HÁ Á ÁO hydrogen-bonding interactions involving the non-coordinated nitrate ion and the complex molecules (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).

Figure 8
Quantitative results of different intermolecular contacts contributing to the Hirshfeld surface of 1.
bind the lanthanide(III) ion and the amine NH moiety of the acetohydrazide ligand can act as a donor site for intermolecular hydrogen-bonding interactions, similar to that of the title compound.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were located in difference-Fourier maps. All carbon-bound hydrogen atoms were placed in calculated positions and refined using a ridingmodel approximation with C-H = 0.96 Å and U iso (H) = 1.5U eq (C). All nitrogen-bound hydrogen atoms were refined with a fixed distance N-H = 0.86 AE 0.02 Å .