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Crystal structure and synchrotron X-ray powder reference pattern for the porous pillared cyanonickelate, Ni(3-amino-4,4′-bipyridine)[Ni(CN)4]

Published online by Cambridge University Press:  29 February 2024

W. Wong-Ng Open the ORCID record for W. Wong-Ng [Opens in a new window] ,
J. Culp ,
J.A. Kaduk Open the ORCID record for J.A. Kaduk [Opens in a new window] ,
Y.S. Chen  and
S. Lapidus
W. Wong-Ng*
Affiliation:
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
J. Culp
Affiliation:
United States Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA United States Department of Energy, NETL Support Contractor, P.O. Box 10940, Pittsburgh, PA 15236-0940, USA
J.A. Kaduk
Affiliation:
Illinois Institute of Technology, Chicago, IL 60616, USA North Central College, Naperville, IL 64540, USA
Y.S. Chen
Affiliation:
ChemMatCARS, University of Chicago, Argonne, IL 60439, USA
S. Lapidus
Affiliation:
Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA
*
a)Author to whom correspondence should be addressed. Electronic mail: [email protected]
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Abstract

The structure of Ni(3-amino-4,4′-bipyridine)[Ni(CN)4] (or known as Ni-BpyNH2) in powder form was determined using synchrotron X-ray diffraction and refined using the Rietveld refinement technique (R = 8.8%). The orthorhombic (Cmca) cell parameters were determined to be a = 14.7218(3) Å, b = 22.6615(3) Å, c = 12.3833(3) Å, V = 4131.29(9) Å3, and Z = 8. Ni-BpyNH2 forms a 3-D network, with a 2-D Ni(CN)4 net connecting to each other via the BpyNH2 ligands. There are two independent Ni sites on the net. The 2-D nets are connected to each other via the bonding of the pyridine “N” atom to Ni2. The Ni2 site is of six-fold coordination to N with relatively long Ni2–N distances (average of 2.118 Å) as compared to the four-fold coordinated Ni1–C distances (average of 1.850 Å). The Ni(CN)4 net is arranged in a wave-like fashion. The functional group, –NH2, is disordered and was found to be in the m-position relative to the N atom of the pyridine ring. Instead of having a unique position, N has ¼ site occupancy in each of the four m-positions. The powder reference diffraction pattern for Ni-BpyNH2 was prepared and submitted to the Powder Diffraction File (PDF) at the International Centre of Diffraction Data (ICDD).

Keywords

Ni(3-amino-4,4′-bipyridine)[Ni(CN)4])metal-organic framework (MOF)synchrotron powder X-ray studiesdisordered Ni-Bpy-NH2 crystal structure
Type
New Diffraction Data
Information
Powder Diffraction , Volume 39 , Issue 1 , March 2024 , pp. 20 - 28
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Copyright
Copyright © The Author(s), 2024. Published by Cambridge University Press on behalf of International Centre for Diffraction Data

I. INTRODUCTION

The continual rise in anthropogenic CO2 concentration since the dawn of the industrial revolution and its effect on climate change underlie the urgent need for the implementation of carbon mitigation approaches to stabilize the CO2 concentration in the atmosphere (Gammon et al., Reference Gammon, Sundquist, Fraser and Trabalka1985; Etheridge et al., Reference Etheridge, Steele, Langenfelds, Francey, Barnola and Morgan1996). In the past decades, a great number of possible solid sorbents have been reported throughout the literature. For example, a vast number of metal organic framework (MOF) or coordination polymer compounds that show diverse properties and applications at different pressure and temperature have been developed (Espinal et al., Reference Espinal, Poster, Wong-Ng, Allen and Green2009, Reference Espinal, Wong-Ng, Kaduk, Allen, Snyder, Chiu, Siderius, Li, Cockayne, Espinal and Snyder2012; Kauffman et al., Reference Kauffman, Culp, Allen, Espinal-Thielen, Wong-Ng, Brown, Goodman, Bernardo, Pancoast, Chirdon and Matranga2011; Liu et al., Reference Liu, Wang and Zhou2012; Wong-Ng et al., Reference Wong-Ng, Kaduk, Wu and Suchomel2012, Reference Wong-Ng, Culp, Chen, Zavalij, Espinal, Siderius, Allen, Scheins and Matranga2013, Reference Wong-Ng, Kaduk, Siderius, Allen, Espinal, Boyerinas, Levin, Suchomel, Ilavsky, Li, Williamson, Cockayne and Wu2015; Furukawa et al., Reference Furukawa, O'Keeffe and Yaghi2013; Gao et al., Reference Gao, Chrzanowski and Ma2014; Brown and Long, Reference Brown and Long2014; Queen et al., Reference Queen, Hudson, Bloch, Mason, Gonzalez, Lee, Gygi, Howe, Lee, Darwish, James, Peterson, Teat, Smit, Neaton, Long and Brown2014; Zhou and Kitagawa, Reference Zhou and Kitagawa2014; Freund et al., Reference Freund, Zaremba, Arnauts, Ameloot, Skorupskii, Dinca, Bavykina, Gascon, Ejsmont, Goscianska, Kalmutzki, Lächelt, Ploetz, Diercks and Wuttke2021; Unnikrishnan et al., Reference Unnikrishnan, Zabihi, Ahmadi, Li, Blanchard, Kiziltasb and Naebe2021).

The pillared layer is a commonly used motif to build porous coordination polymers or MOFs. Materials based on the pillared cyano-bridged architecture, [Ni’(L)Ni(CN)4]n (L = pillar organic ligands), or known as PICNICs, have been shown to be diverse where pore size and pore functionality can be varied by the choice of pillar organic ligands. Knowing the orientation of these functional groups in the pore structure is important for correlating their effects on guest adsorption. In addition, a number of PICNICs have been discovered which show reversible structural transitions between low-porosity and high-porosity phases during the adsorption and desorption process of guests. Structural flexibility in PICNICs can be affected by relatively minor differences in ligand design. The physical driving force for variations in host–guest behavior in these materials is still not totally known. One key to understanding this diversity is a detailed investigation of their crystal structures.

Cyano-bridged complexes have been shown to form polymeric structures with 3-D Hofmann-like microporous frameworks (Hofmann and Kuspert, Reference Hofmann and Küspert1897), formed by metal–metal or metal–ligand–metal bridge connections in one, two, or three dimensions. National Energy and Technology Laboratory (NETL) has been one of the leading laboratories in the research area of novel Ni(CN)4-based flexible MOFs (Culp et al., Reference Culp, Smith, Bittner and Bockrath2008a, Reference Culp, Natesakhawat, Smith, Bittner, Matranga and Bockrath2008b, Reference Culp, Madden, Kauffman, Shi and Matranga2013; Kauffman et al., Reference Kauffman, Culp, Allen, Espinal-Thielen, Wong-Ng, Brown, Goodman, Bernardo, Pancoast, Chirdon and Matranga2011; Wong-Ng et al., Reference Wong-Ng, Culp, Chen, Zavalij, Espinal, Siderius, Allen, Scheins and Matranga2013). The precursors of these flexible MOFs are typically a cyanometallate complex that acts as a ligand and a transition metal complex with available coordination sites. They are collectively called pillared cyanonickelates, or PICNICs. The size of the pores of the materials can be modified by the lengths of the pillared ligands. We have reported a number of PICNIC compounds previously (Wong-Ng et al., Reference Wong-Ng, Culp, Chen, Zavalij, Espinal, Siderius, Allen, Scheins and Matranga2013, Reference Wong-Ng, Culp, Chen and Matranga2016a, Reference Wong-Ng, Culp, Chen, Deschamps and Marti2016b, Reference Wong-Ng, Williamson, Lawson, Siderus, Culp, Chen and Li2018, Reference Wong-Ng, McCandless, Culp, Lawson, Chen, Siderius and Li2021a, Reference Wong-Ng, Culp, Siderius, Chen, Wang, Allen and Cockayne2021b; Allen et al., Reference Allen, Espinal, Wong-Ng, Queen, Brown, Kline, Kauffman, Culp and Matranga2015, Reference Allen, Wong-Ng, Cockayne, Espinal, Culp and Matranga2019, Reference Allen, Cockayne, Wong-Ng, Culp and Kuzmenko2023; Wong-Ng, Reference Wong-Ng2018; Lawson et al., Reference Lawson, Horn, Wong-Ng, Espinal, Lapidus, Nguyen, Meng, Suib, Kaduk and Li2019; Cockayne et al., Reference Cockayne, Wong-Ng, Chen, Culp and Allen2021).

A member of the PICNIC family, namely, Ni(3-amino-4,4′-bipyridine)[Ni(CN)4], or Ni-BpyNH2(D) has been studied previously using single-crystal diffraction method at the microdiffraction facility of the Advanced Photon Source (APS) of the Argonne National Laboratory. The structure of the single crystal was determined to be orthorhombic Cmca, a = 14.7000(5) Å, b = 22.6879(7) Å, c = 13.8028(4) Å, V = 4603.4(2) Å3, and Z = 8 (Table I). Highly disordered solvent of crystallization, dimethyl sulfoxide (DMSO) molecules, were located inside the pores. As a result, the chemical formula, C18Ni2S2O2N7H21, is designated as Ni-BpyNH2(D), where D stands for DMSO (Wong-Ng et al., Reference Wong-Ng, Culp, Chen and Matranga2016a). Ni-BpyNH2(D) forms a 3-D network, with a 2-D Ni(CN)4 square net connecting to each other via the BpyNH2 ligands.

TABLE I. Lattice parameters of Ni-BpyNH2 with and without the solvent of crystallization DMSO

Both are orthorhombic with space group Cmca. Values inside the brackets are one standard deviation.

This paper describes the structure and provides a reference X-ray (synchrotron) powder pattern for the Ni(3-amino-4,4′-bipyridine)[Ni(CN)4], or Ni-BpyNH2 in the powder form. A brief comparison of the structure of Ni-BpyNH2 with Ni-BpyNH2(D) will also be reported. As X-ray powder reference patterns are critical for material analysis, the diffraction pattern for Ni-BpyNH2 has been submitted to the Powder Diffraction File (PDF) of the International Centre for Diffraction Data (ICDD) (Gates-Rector and Blanton, Reference Gates-Rector and Blanton2019).

II. EXPERIMENTAL

A. Synthesis

We have adopted (with modifications) a procedure originally used by Černák et al. to prepare crystalline 1-D [Ni(CN)4] containing chain compounds (Černák and Abboud, Reference Černák and Abboud2000; Wong-Ng et al., Reference Wong-Ng, Culp, Chen, Zavalij, Espinal, Siderius, Allen, Scheins and Matranga2013, Reference Wong-Ng, Culp, Chen and Matranga2016a) for the crystallization of Ni(L)[Ni(CN)4]. The approach involves the use of NH3 as a blocking agent. When a reaction mixture (0.60 mmol of BpyNH2 with 0.5 mmol Ni2(CN)4 hydrate in a mixture of 6 ml H2O, 6 ml concentrated aqueous NH3, and 18 ml DMSO) is warmed in an open flask, the NH3 will outgas from the solution. Using an H2O/DMSO mixture as the solvent and a reaction temperature of ≈90 °C provided the necessary combination of NH3 out gassing rate and oligomer solubility to produce the targeted 3-D polymeric structure. A good crop of crystals can typically be obtained in 24–48 h. The technique has been found in our laboratory to be adaptable to various organic bridging ligands (L). Extraction of the isolated crystals with warm anhydrous methanol can be used to remove any DMSO guests from the pores. Heating the extracted crystals under vacuum at 90–100 °C is sufficient to remove the methanol from the pores of the crystals and create a “guest-free” sorbent. For powder preparation, the single crystals were simply ground into powder, and packed into a thin capillary tubing for synchrotron data collection.

B. Synchrotron powder X-ray diffractionFootnote 1

The powder pattern of Ni-BpyNH2 was collected from a rotated 0.7 mm capillary specimen, using a wavelength of 0.412817 Å. High-resolution synchrotron X-ray powder diffraction data were collected using beamline 11-BM at the APS, Argonne National Laboratory. Discrete detectors covered a final angular range from 0° to 50°, with data points collected every 0.001° in 2θ at a scan speed of 0.01°/s. The instrumental optics of 11-BM incorporate two platinum-striped mirrors and a double-crystal Si (111) monochromator, where the second crystal has an adjustable sagittal bend (Wang et al., Reference Wang, Toby, Lee, Ribaud, Antao, Kurtz, Ramanathan, Von Dreele and Beno2008). The diffractometer is controlled via EPICS (Dalesio et al., Reference Dalesio, Hill, Kraimer, Lewis, Murray, Hunt, Watson, Clausen and Dalesio1994). A vertical Huber 480 goniometer positions 12 perfect Si (111) analyzers and 12 Oxford-Danfysik LaCl3 scintillators, with a spacing of 2° in 2θ (Lee et al., Reference Lee, Shu, Ramanathan, Preissner, Wang, Beno, Von Dreele, Ribaud, Kurtz, Antao, Jiao and Toby2008). Capillary samples are mounted by a robotic arm and spun at ≈90 Hz. Data are normalized to incident flux and collected while continually scanning the diffractometer 2θ arm. A mixture of National Institute of Standard and Technology standard reference materials, Si (SRM™ 640e) (Walters, Reference Walters2015) and Al2O3 (SRM™ 676) (Walters, Reference Walters2008), was used to calibrate the instrument, where the Si lattice constant determines the wavelength for each detector. Corrections are applied for detector sensitivity, 2θ offset, and small detector wavelength differences, before merging the data into a single set of intensities evenly spaced in 2θ.

C. Rietveld refinements

Rietveld refinements were carried out using General Structure and Analysis System-II (Rietveld, Reference Rietveld1969; Toby and Von Dreele, Reference Toby and Von Dreele2013). The initial model was from the previous single-crystal structure, removing the DMSO solvent. Only the 2.0°–30.0° portion of the pattern was included in the refinement (d min = 0.797 Å). All non-H bond distances and angles were subjected to restraints, based on a Mercury/Mogul Geometry check (Sykes et al., Reference Sykes, McCabe, Allen, Battle, Bruno and Wood2011; Bruno et al., Reference Bruno, Cole, Kessler, Luo, Motherwell, Purkis, Smith, Taylor, Cooper, Harris and Orpen2004). The Mogul average and standard deviation for each quantity were used as the restraint parameters. The Ni1–C2 bonds were restrained to 1.86(1) Å, the Ni2–N1 bonds to 2.07(1) Å, and the Ni2–N6 bonds to 2.11(1) Å. Planar restraints were also applied to the aromatic rings. The restraints contributed 2.5% to the final χ 2. The hydrogen atoms were included in calculated positions, which were recalculated during the refinement using Materials Studio (Dassault Systèmes, 2022). The Uiso of the heavy atoms was fixed. A fourth-order spherical harmonics model for the preferred orientation model was included; the refined texture index was 1.125. The peak profiles were described using the generalized microstrain model (Stephens, Reference Stephens1999). The background was modeled using a three-term shifted Chebyshev polynomial.

D. Powder X-ray pattern for inclusion in PDF

The deposited powder X-ray reference pattern was obtained using a Rietveld pattern decomposition technique (Toby and von Dreele, Reference Toby and Von Dreele2013). Using this technique, the reported peak intensities were derived from the extracted integrated intensities, and positions are calculated from the lattice parameters. When peaks are not resolved at the resolution function, the intensities are summed, and an intensity-weighted d-spacing is reported. The reported d-spacings are corrected for systematic errors via the inclusion of possible instrumental effects in the Rietveld fitting modal.

III. RESULTS AND DISCUSSION

Figure 1 gives the observed (crosses), calculated (solid line), and normalized difference X-ray diffraction (XRD) patterns (bottom) for Ni-BpyNH2 using the Rietveld analysis technique. The vertical lines below the profiles mark the positions of all possible Bragg reflections. The final refinement of 44 variables using 28,045 observations and 33 restraints yielded the residuals R = 0.088, Rwp = 0.2304, and goodness of fit = 4.48. The largest errors in the difference plot (Figure 1) probably indicate the presence of un-model disordered extra-framework species, which were not apparent in a different Fourier map.

Figure 1. Observed (crosses), calculated (solid line), and normalized difference XRD patterns (bottom) for Ni-Bpy-NH2 by the Rietveld analysis technique. The vertical lines below the profiles mark the positions of all possible Bragg reflections.

Since the bond distances and angles were restrained, all of them fall within normal ranges. The root-mean-square Cartesian displacement of the non-H atoms in the solvated single-crystal structure and the unsolvated powder structure is 0.731 Å, indicating that the solvent has a significant effect on the framework.

The atomic coordinates and isotropic displacement factors including hydrogen atoms are shown in Table II. Table III lists the selected pertinent bond distances and Table IV gives the selected bond angles for Ni-BpyNH2.

TABLE II. Atomic coordinates for Ni-BpyNH2

(Space group: orthorhombic Cmca). The value of 0.01 was used as the U iso value for the two Ni sites and 0.03 was used for the rest. Additional coordinates of H4 (0.2259, 0.4008,0.0780) as in C4–H4 and H7 (0.1646, 0.4811, 0.389) as in C7–H7 that are shown in Figure 2(b) are theoretical values each with an occupancy of 0.75, as a result of the disordered NH2 groups. Values inside the brackets are one standard deviation.

TABLE III. Interatomic distances for Ni-BpyNH2 and Ni-BpyNH2(D)

Values inside brackets are one standard deviation.

TABLE IV. Interatomic bond angles for Ni-BpyNH2 and Ni-BpyNH2(D)

Values inside brackets are standard deviations.

A. Powder X-ray pattern for inclusion in PDF

The X-ray powder diffraction pattern for Ni-BpyNH2 has been submitted for inclusion in the PDF and will not be reported here. In the submitted pattern, the symbol “M” refers to peaks containing contributions from two overlapping reflections. The peak that has the strongest intensity in the entire pattern is assigned an intensity of 999 and other lines are scaled relative to this value. In general, the d-spacing values are calculated from refined lattice parameters. The intensity values reported are integrated intensities (rather than peak heights). For resolved overlapped peaks, intensity-weighted calculated d-spacing, along with the observed integrated intensity and the hkl indices of both peaks are used. For peaks that are not resolved at the instrumental resolution, the intensity-weighted average d-spacing and the summed integrated intensity value are used. In the case of a cluster, unconstrained profile fits often reveal the presence of multiple peaks, even when they are closer than the instrumental resolution. In this situation, both d-spacing and intensity values are reported independently.

B. Structure of Ni-BpyNH2

The DMSO solvent of crystallization could not be located in the powdered Ni-BpyNH2 as a result of the methanol extraction procedure. The structure of Ni-BpyNH2 was found to be orthorhombic with a space group of Cmca, a = 14.7218(3) Å, b = 22.6615(3) Å, c = 12.3833(3) Å, V = 4131.29(9) Å3, Z = 8, and Dx = 1.253 g-cm−3 (Table I). Figure 2(a) gives the basic motif of Ni(BpyNH2)[Ni(CN)4] with full atomic labels. In Figure 2(b), a theoretical Ni-BpyNH2 motif with an ordered NH2 group (green – Ni, blue – N, gray – C) showing one NH2 group. Because of the absence of the solvent of crystallization, DMSO, the chemical formula of the compound is Ni2N7C14H9 as compared to Ni2N7C18S2O2H21.

Figure 2. (a) Motif of Ni-BpyNH2 (green – i, blue – N, gray – C) showing disordered NH2 groups. H atoms are omitted for clarity. (b) A theoretical Ni-BpyNH2 motif with ordered NH2 group (green – Ni, blue – N, gray – C) showing one NH2 group.

Ni-BpyNH2 forms a 3-D network, with a sinuous 2-D Ni(CN)4 rectangular net connecting to each other via the BpyNH2 ligands. The b-axis is much longer than that of a- and c- and that is where the long axis of the ligand BpyNH2 aligns. Figure 3 gives the 3-D packing diagram of the structure, viewing along the c-axis. It is clear that the fundamental structure is similar to that of Ni-Bpene (Wong-Ng et al., Reference Wong-Ng, Culp, Chen, Zavalij, Espinal, Siderius, Allen, Scheins and Matranga2013) and Ni-BpyMe (Wong-Ng et al., Reference Wong-Ng, Culp, Siderius, Chen, Wang, Allen and Cockayne2021b) where parallelepiped shape cavities were enclosed by the 2-D Ni(CN)4 net and by the BpyNH2 ligands. The 2-D Ni(CN)4 net is connected to each other via the bonding of the pyridine N3 (and N6) atoms to Ni2. The Ni2 atom is of six-fold coordination to N with relatively long Ni2–N distances (average of 2.118 Å) (Table II) as compared to the much shorter four-fold coordination Ni1–C distances (average of 1.850 Å). Figure 4 gives the “projected view” of the net along the a-axis where the NH2 groups are pointing toward the center of the pores (hydrogen atoms are excluded for clarity). It is also clear that the pertinent bond angles around the 2-D net all deviated substantially from 180° (see Table III), giving rise to the sinuous appearance of the 2-D net.

Figure 3. Packing diagram of Ni-BpyNH2 viewing down the c-axis (green – Ni, blue – N, gray – C). H atoms are omitted for clarity.

Figure 4. Packing diagram of Ni-BpyNH2 viewing down the a-axis. (green – Ni, blue – N, gray – C). H atoms are omitted for clarity.

The amine functional group, NH2, was found in the m-position relative to the N atom of the pyridine ring and was disordered. Instead of having a unique “N” position, the resulting structure gives a total of four positions (two N4 and two N5) per ligand due to disorder, therefore each N4 and N5 only has a site occupancy of ¼ in each of the four m-positions. In other words, the NH2 group has 25% probability of being at one of the four possible m-positions. Figure 2(b) gives the schematic of the ordered theoretical motif of Ni-BpyNH2 where there is only one NH2 group per ligand. The theoretical coordinates of H4 as in C4–H4 and H7 as in C7–H7 (Figure 2(b)) with an occupancy of 0.75 were computed to be (0.2259, 0.4008, 0.0780) and (0.1646, 0.4811, 0.389), respectively. The two pyridine rings in the ligands are not coplanar, they make an angle of approximately 40° to each other to avoid steric hindrance.

C. Comparison of the crystal structure of Ni-BPyNH2 with Ni-BPyNH2(D)

The lattice constants of solvent-free Ni-BPyNH2 are smaller than that with solvent of crystallization, Ni-BPyNH2(D), and were reported to be orthorhombic, space group Cmca. The unit cell dimensions of Ni-BPyNH2(D) were determined to be a = 14.7000(5) Å, b = 22.6879(7) Å, c = 13.8028(4) Å, V = 4603.4(2) Å3, and Z = 8 (Wong-Ng et al., Reference Wong-Ng, Culp, Chen and Matranga2016a) (Table I).

Tables III and IV give bond lengths and bond angles of both the solvated and unsolved compounds for comparison. In the solvated compound, apparently, the bond angles have a higher tendency to be linear than those in the unsolvated compound where they have more degrees of freedom for the movement of atoms, resulting in a structure with a more sinuous character (larger curvature of the net).

Figures 3 and 4 give the packing diagram of Ni-BpyNH2 viewing down the c- and a-axis while Figures 5 and 6 give the packing for Ni-BPyNH2(D) viewing along c- and a-axis, respectively. A comparison of the packing diagrams of Figure 3 with Figure 5, and Figure 4 with Figure 6 revealed that the 2-D net has a much lesser curvature in the structure with DMSO, probably because the solvent DMSO in the cavity prevented a high degree of curvature of the 2-D net. The average distances Ni2–N are somewhat longer in the guest-free structure than that in the DMSO-included sample (2.118 vs. 2.089 Å, respectively), whereas for the average Ni1–C bonds, the opposite situation was observed (1.850 Å in Ni-BPyNH2 vs. the longer 1.860 Å in Ni-BPyNH2(D)).

Figure 5. Packing diagram of Ni-BpyNH2(D) viewing down the c-axis (Wong-Ng et al., Reference Wong-Ng, Culp, Chen and Matranga2016a) (green – Ni, blue – N, gray – C, yellow – S, and red – O). H atoms are omitted for clarity.

Figure 6. Packing diagram of Ni-BpyNH2(D) viewing down the a-axis (Wong-Ng et al., Reference Wong-Ng, Culp, Chen and Matranga2016a) (green – Ni, blue – N, gray – C, yellow – S, and red – O).

The dihedral angles formed between the two pyridine rings are larger in the solvent-free Ni-BPyNH2 than that in Ni-BPyNH2(D), (≈40° vs 25°, respectively). In another PICNIC structure, Ni-BpyMe (Wong-Ng et al., Reference Wong-Ng, Culp, Siderius, Chen, Wang, Allen and Cockayne2021b), where Me stands for the methyl group, it was reported that as a result of the large curvature of the 2-D net (Figure 7), the dispersive forces between the net and the ligands were maximized for achieving a stable structure. The similar situation is observed here in the structure of Ni-BPyNH2.

Figure 7. Packing diagram of Ni-BpyMe showing the curvature of the 2-D net and the orientations of the Bpy rings (Wong-Ng et al., Reference Wong-Ng, Culp, Siderius, Chen, Wang, Allen and Cockayne2021b) (green – Ni, blue – N, gray – C, off-white – H). Reprinted with permission from Elsevier Ltd.

IV. SUMMARY

The structure of guest-free Ni-BpyNH2 has been determined and the reference powder pattern has been prepared and submitted to the PDF. The lattice parameters of the guest-free structure were found to be smaller than that with DMSO as a solvent of crystallization, as expected. The amine functional group, –NH2, is disordered in both structures. The NH2 group is found in the m-position relative to the N atom of the pyridine ring. Instead of having an unique position, it has ¼ site occupancy in each of the four m-positions. While the two structures are in general similar to each other, there are noticeable differences including a higher degree of curvature in the 2-D net of solvent-free Ni-BpyNH2, presumably due to maximizing the dispersive forces between the ligands and the net (for stabilizing the structure). The dihedral angle between the two pyridine rings is greater in Ni-BpyNH2 (≈40 °) than that in Ni-BpyNH2(D) (≈25 °).

V. DEPOSITION DATA

The powder pattern of guest-free Ni-BpyNH2 from the measured synchrotron data set has been submitted to ICDD for inclusion in the PDF. The Crystallographic Information Framework (CIF) file containing the results of the Rietveld refinement (including raw data) was deposited with the ICDD. The data can be requested from the PDJ managing editor at .”

ACKNOWLEDGEMENTS

The authors acknowledge ChemMatCARS Sector 15 which is principally supported by the National Science Foundation/Department of Energy under grant number NSF/CHE-1834750. Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC0206CH11357. Partial financial support from the ICDD Grant-in-Aid Program #0903 is acknowledged.

CONFLICTS OF INTEREST

The authors declare none.

Footnotes

1 The purpose of identifying the equipment and software in this article is to specify the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology.

References

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Figure 0

TABLE I. Lattice parameters of Ni-BpyNH2 with and without the solvent of crystallization DMSO

Figure 1

Figure 1. Observed (crosses), calculated (solid line), and normalized difference XRD patterns (bottom) for Ni-Bpy-NH2 by the Rietveld analysis technique. The vertical lines below the profiles mark the positions of all possible Bragg reflections.

Figure 2

TABLE II. Atomic coordinates for Ni-BpyNH2

Figure 3

TABLE III. Interatomic distances for Ni-BpyNH2 and Ni-BpyNH2(D)

Figure 4

TABLE IV. Interatomic bond angles for Ni-BpyNH2 and Ni-BpyNH2(D)

Figure 5

Figure 2. (a) Motif of Ni-BpyNH2 (green – i, blue – N, gray – C) showing disordered NH2 groups. H atoms are omitted for clarity. (b) A theoretical Ni-BpyNH2 motif with ordered NH2 group (green – Ni, blue – N, gray – C) showing one NH2 group.

Figure 6

Figure 3. Packing diagram of Ni-BpyNH2 viewing down the c-axis (green – Ni, blue – N, gray – C). H atoms are omitted for clarity.

Figure 7

Figure 4. Packing diagram of Ni-BpyNH2 viewing down the a-axis. (green – Ni, blue – N, gray – C). H atoms are omitted for clarity.

Figure 8

Figure 5. Packing diagram of Ni-BpyNH2(D) viewing down the c-axis (Wong-Ng et al., 2016a) (green – Ni, blue – N, gray – C, yellow – S, and red – O). H atoms are omitted for clarity.

Figure 9

Figure 6. Packing diagram of Ni-BpyNH2(D) viewing down the a-axis (Wong-Ng et al., 2016a) (green – Ni, blue – N, gray – C, yellow – S, and red – O).

Figure 10

Figure 7. Packing diagram of Ni-BpyMe showing the curvature of the 2-D net and the orientations of the Bpy rings (Wong-Ng et al., 2021b) (green – Ni, blue – N, gray – C, off-white – H). Reprinted with permission from Elsevier Ltd.