Synthesis and structure of di­aqua­bis­(nicotinamide-κO)bis­(nitrato-κ2O,O′)calcium(II)

Djumanazarova, Z.; Kadirova, S.; Kattaev, N.; Ibragimov, B.; Meldebekova, S.; Ashurov, J.

doi:10.1107/S2056989025006759

research communications

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 81| Part 9| September 2025| Pages 792-796

https://doi.org/10.1107/S2056989025006759

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Synthesis and structure of diaquabis(nicotinamide-κO)bis(nitrato-κ²O,O′)calcium(II)

Zulfiya Djumanazarova,^a Shakhnoza Kadirova,^b Nuritdin Kattaev,^b Bakhtiyar Ibragimov,^c Saule Meldebekova ^d and Jamshid Ashurov ^c ^*

^aKarakalpak State University named after Berdakh, Republic of Karakalpakstan, Abdirova Street 1, Nukus 742012, Karakalpakstan, ^bNational University of Uzbekistan named after Mirzo Ulugbek, University Street, 4, Tashkent 100174, Uzbekistan, ^cInstitute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, 100125, M., Ulugbek Str 83, Tashkent, Uzbekistan, and ^dKarakalpakstan Medical Institute, 106 A. Dosnazarov Street, 230105 Nukus City, Uzbekistan
^*Correspondence e-mail: [email protected]

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 7 July 2025; accepted 29 July 2025; online 5 August 2025)

The title complex, [Ca(NO₃)₂(C₆H₆N₂O)₂(H₂O)₂], crystallizes with an eight-coordinate Ca²⁺ ion in a distorted trigonal–dodecahedral coordination environment. The metal ion is coordinated to two nicotinamide ligands via their carbonyl O atoms, two bidentate nitrate anions and two water molecules. The nicotinamide ligands adopt a nearly trans geometry, while the nitrate anions and aqua ligands are arranged in a pseudo-trans fashion. In the crystal, a three-dimensional supramolecular framework is constructed through N—H⋯O and O—H⋯O hydrogen bonds involving water, nitrate, and nicotinamide functional groups, reinforced by offset π–π stacking interactions between nearly parallel pyridine rings [centroid-to-centroid distance = 3.783 (2) Å]. A Hirshfeld surface analysis revealed that the intermolecular interactions are dominated by O⋯H/H⋯O (42.3%) and H⋯H (26.2%) contacts, corresponding to classical hydrogen bonding and van der Waals forces, respectively.

Keywords: calcium complex; nicotinamide; hydrogen bonding; crystal structure.

CCDC reference: 2476945

1. Chemical context

Nicotinamide (niacinamide), a water-soluble form of vitamin B3, plays a pivotal role in human metabolism. It serves as a precursor to the essential coenzymes NAD⁺ and NADP⁺, which are involved in a wide array of redox reactions. NAD⁺/NADH participates in over 400 biochemical processes, while NADP⁺/NADPH is involved in approximately 30 reactions, particularly in cytochrome P450-mediated xenobiotic metabolism (Meyer-Ficca et al., 2016 ; Isin et al., 2007 ). Beyond its metabolic functions, nicotinamide exhibits versatile coordination behavior due to its ability to donate electron pairs through the pyridine nitrogen atom and the amide oxygen or nitrogen atoms. It typically acts as a monodentate ligand via the pyridine N atom, but bidentate and bridging coordination modes have also been observed (Pricop et al., 2022 ; Sun et al., 2018 ). Mixed-ligand complexes involving nicotinamide and 1,10-phenanthroline with Co^II, Ni^II, Cu^II, and Zn^II have demonstrated various coordination geometries and potential antimicrobial properties (Drzewiecka et al., 2013 ). Similarly, cadmium(II) complexes with nicotinamide, nitrate, and oxalate ligands have shown promising pharmacological activity (Pricop et al., 2025 ). In coordination chemistry, the nitrate anion can function as a counter-ion, auxiliary ligand, or redox-active participant. Its inclusion in metal–nicotinamide complexes, such as with calcium(II), may enhance reactivity through NO-release pathways. For instance, recent work by Zhang et al. (2024 ) shows intracellular NO release from nitrate-containing metal complexes, indicating their potential as therapeutic NO donors. Calcium is a biologically essential element involved in diverse physiological roles including bone mineralization, muscle contraction, nerve transmission, and blood coagulation. Emerging research has highlighted calcium's regulatory function in intracellular signaling, gene expression, and metabolic control. Calcium(II)–nicotinamide complexes have garnered interest for their structural variety and bioactivity (Braga et al., 2014 ; Parsekar et al., 2022 ). These include mononuclear species with two nicotinamide and two water ligands and polymeric frameworks where nicotinamide bridges calcium centers (Braga et al., 2011 ; Xue et al., 2015 ). Mixed-ligand systems incorporating additional donors, such as trinitrophenolates, further demonstrate nicotinamide's coordination flexibility (Parsekar et al., 2022). In this study, we report the synthesis and crystal structure of the title complex, [Ca(H₂O)₂(C₆H₆N₂O)₂(NO₃)₂], (I).

2. Structural commentary

The asymmetric unit of (I) contains one calcium(II) cation coordinated to eight oxygen atoms: two from O-monodentate nicotinamide ligands, four from two bidentate nitrate anions, and two from aqua ligands (Fig. 1). The resulting coordination environment forms a distorted CaO₈ polyhedron best described as a trigonal dodecahedron (also called snub disphenoid). The Ca—O bond lengths (Table 1) range from 2.3150 (16) Å for Ca1—O1B to 2.5825 (18) Å for Ca1—O4B. These values are comparable to those reported in a similar Ca²⁺–nicotinamide complex (Xue et al., 2015), where O-monodentate coordination via carbonyl oxygen atoms gave a Ca—O distance of 2.2659 (13) Å, and the Ca—O (water) distance was 2.3774 (11) Å. The nicotinamide ligands in (I) are arranged in a nearly trans fashion, with an O1A—Ca1—O1B bond angle of 158.82 (7)°. Similarly, the aqua ligands adopt an approximately trans orientation [O1W—Ca1—O2W = 164.15 (7)°] and the nitrate oxygen pairs (O2A/O2B and O4A/O4B) also exhibit pseudo-trans arrangements with angles of 147.25 (6)° and 151.52 (6)°, respectively. Both nicotinamide ligands (molecules A and B) exhibit the expected near planarity of their aromatic rings, with r.m.s.d. values of 0.003 and 0.002 Å, respectively. The CONH₂ groups are slightly twisted relative to the pyridine rings, with dihedral angles of 15.37 (12) and 13.33 (12)° for molecules A and B, respectively. The pyridine ring planes are roughly parallel, forming an interplanar angle of 7.57 (14)°, whereas the carboxamide planes are more tilted relative to one another, with an interplanar angle of 22.24 (17)°. The nitrate anions show a pronounced non-parallel orientation, forming an interplanar angle of 78.4 (1)°.

Table 1
Selected bond lengths (Å)

Ca1—O4B	2.5825 (18)	Ca1—O1B	2.3150 (16)
Ca1—O2W	2.3820 (16)	Ca1—O1A	2.3359 (15)
Ca1—O2B	2.5752 (17)	Ca1—O4A	2.5362 (19)
Ca1—O1W	2.3459 (18)	Ca1—O2A	2.5537 (18)

Figure 1
The molecular structure of (I) showing 50% probability displacement ellipsoids.

3. Supramolecular features

The supramolecular architecture of (I) is consolidated by a network of hydrogen bonds—including both classical (O—H⋯O, N—H⋯O) and non-classical (C—H⋯O) types—as well as π–π stacking interactions, which collectively reinforce the three-dimensional supramolecular framework. The hydrogen-bonding network involves coordinated water molecules (O1W and O2W), amide –NH₂ groups, pyridyl nitrogen atoms (N1A/N1B), coordinated nitrate oxygen atoms (O2A and O2B) and uncoordinated nitrate oxygen atoms (O3A and O3B) (Table 2 and Fig. 2). Propagation of the network along the [100] direction is mediated by O2W—H2WA⋯O2A and N2B—H2BA⋯N1A bonds, related by an inversion center (symmetry operation: 1 − x, 1 − y, 1 − z), while along [001], O1W—H1WB⋯N1B and N2A—H2AB⋯O3B bonds extend the structure via a screw axis (− $[{1\over 2}]$ + x, $[{1\over 2}]$ − y, − $[{1\over 2}]$ + z). Along [010], O2W—H2WB⋯O3A and a weaker C5B—H5B⋯O3A interaction propagate via inversion/translation symmetry (1 − x, 1 − y, 2 − z). The water molecules serve as pivotal hydrogen-bond donors: O1W links to O3B and N1B, while O2W donates to O2A and O3A. The amide groups contribute significantly, with N2B donating to N1A and O3A and N2A—H2AA⋯O2B, forming an intramolecular contact. The nitrate groups act as hydrogen-bond acceptors: the coordinated oxygen atoms O2A and O2B engage in classical N—H⋯O and O—H⋯O interactions, while the uncoordinated O3A and O3B atoms participate in multiple contacts (six in total), including a notably linear C5A—H5A⋯O3B interaction (174°), further reinforcing the structure via weak C—H⋯O bonding. Graph-set analysis reveals centrosymmetric R₂²(8) rings from O2W—H⋯O2A interactions; C₁¹(6) chains along [010] (O2W—H2WB⋯O3A), and two distinct chains along [001]: C₁¹(6) from O1W—H1WA⋯O3B and C₁¹(8) from O1W—H1WB⋯N1B. Higher-order ring motifs include R₄⁴(12), R₆⁶(16), and R₈⁶(20), reflecting increasing hydrogen-bonding complexity, with water molecules serving as key structural nodes. In addition to hydrogen bonding, π–π stacking interactions are observed between pyridyl rings of nicotinamide ligands, involving centroids Cg1 (C1A–C5A/N1A) and Cg2 (C1B–C5B/N1B), related by the symmetry operations −1 + x, y, −1 + z and 1 + x, y, 1 + z. These interactions feature a centroid-to-centroid distance of 3.783 (2) Å, a dihedral angle of 7.57 (10)°, and a slippage of 1.00–1.17 Å, consistent with a parallel-displaced stacking motif, further consolidating the three-dimensional supramolecular assembly.

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2A—H2AB⋯O3Bⁱ	0.85 (1)	2.42 (2)	3.180 (3)	149 (3)
N2A—H2AA⋯O2B	0.86 (1)	2.53 (2)	3.284 (3)	146 (3)
N2B—H2BA⋯N1Aⁱⁱ	0.86 (1)	2.21 (2)	3.024 (3)	157 (3)
N2B—H2BB⋯O3Aⁱⁱⁱ	0.86 (1)	2.35 (1)	3.211 (3)	174 (3)
O1W—H1WA⋯O3B^iv	0.84 (1)	2.04 (2)	2.761 (3)	144 (3)
O1W—H1WB⋯N1Bⁱ	0.85 (1)	2.00 (1)	2.833 (3)	164 (3)
O2W—H2WA⋯O2Aⁱⁱ	0.85 (1)	1.97 (1)	2.813 (2)	178 (3)
O2W—H2WB⋯O3A^v	0.84 (1)	2.10 (2)	2.904 (3)	160 (4)
C5A—H5A⋯O3Bⁱ	0.93	2.41	3.336 (3)	174
C5B—H5B⋯O3Aⁱⁱⁱ	0.93	2.49	3.362 (3)	155
Symmetry codes: (i) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (ii) ; (iii) ; (iv) ; (v) .

Figure 2
Crystal packing of (I) viewed along the a-axis direction. Intermolecular hydrogen bonds are shown as dashed lines.

4. Hirshfeld surface analysis

To further investigate the intermolecular interactions present in the title compound, a Hirshfeld surface analysis was performed using CrystalExplorer17 (Spackman et al., 2021 ), and the corresponding two-dimensional fingerprint plots were generated. The three-dimensional Hirshfeld surface of the complex, mapped over normalized contact distance (d_norm), is shown in Fig. 3. Intense red spots are clearly visible near atoms O1W, O2W, O2A, and O3B, indicating close contacts associated with strong hydrogen bonding. These visual cues correspond well with the short O—H⋯O and N—H⋯O hydrogen bonds identified crystallographically. Quantitative surface analysis reveal that O⋯H/H⋯O contacts dominate the intermolecular landscape, contributing 42.3% of the total surface. H⋯H contacts contribute 26.2%, indicative of extensive van der Waals interactions (Fig. 4). Additional contributions are observed from N⋯H/H⋯N (12.0%), C⋯C (7.6%; π–π stacking between aromatic rings), H⋯C/C⋯H (5.1%; weak C—H⋯π and C—H⋯Csp² interactions), C⋯N/N⋯C (3.1%), N⋯O/O⋯N (2.1%), and C⋯O/O⋯C (0.7%) contacts. The fingerprint plot for O⋯H/H⋯O contacts exhibits a prominent symmetric double-spike pattern, characteristic of directional and geometrically well-matched hydrogen bonds. This pattern reflects nearly equal internal and external contact distances (d_i ≃ d_e), consistent with classical hydrogen-bonding geometry. The symmetry of the spikes also supports the occurrence of bifurcated hydrogen bonding, notably where O1W acts as a donor to two acceptors (O2A). These interactions, in combination with π–π stacking, reinforce the stability and cohesion of the three-dimensional supramolecular architecture.

Figure 3
View of the three-dimensional Hirshfeld surface of (I) plotted over d_norm. Hydrogen bonds are indicated by red dotted lines.

Figure 4
The two-dimensional fingerprint plots for (I), showing all interactions and different contact types. The d_i and d_e values represent the closest internal and external distances (in Å) from given points on the Hirshfeld surface.

5. Database survey

A search of the Cambridge Structural Database (CSD, version 6.00, April 2025; Groom et al., 2016 ) yielded six calcium(II) complexes featuring nicotinamide ligands. In these structures, the nicotinamide molecule is typically coordinated to the calcium atom via its pyridyl nitrogen atom, while the amide moiety remains non-coordinating. Coordinated water molecules and counter-ions such as nitrate or chloride are present and contribute to the formation of extended supramolecular networks through hydrogen bonding. On a broader scale, more than 400 crystal structures involving nicotinamide ligands bound to various metal centers have been reported. These complexes frequently exhibit N—H⋯O and O—H⋯O hydrogen bonding interactions, and in some cases, π–π stacking between pyridine rings. Notable structurally related calcium–nicotinamide complexes include CSD refcode BAFZER, a pyridine-3-carboxamide derivative featuring extended hydrogen bonding (Song et al., 2020 ); KOPBIC and KOPBOI, chain-type and monomeric complexes containing chloride and nicotinamide ligands (Braga et al., 2014); REZWAW and REZWEA, which feature coordinated water molecule and nicotinamide with chloride counter-ions (Braga et al., 2011); and YEKHEF, a bis(pyridine-3-carboxamide) calcium complex incorporating trinitrophenolate ligands (Parsekar et al., 2022). These structures demonstrate the flexible coordination behavior of nicotinamide and its consistent role in participating in metal–organic assemblies through directional non-covalent interactions. In addition, approximately 70 calcium(II) complexes containing nitrate anions are reported in the CSD. In most of these, nitrate acts as a bidentate ligand coordinating in a κ²O,O′ fashion. Bridging coordination modes (μ₂-κ²O,O′), in which the nitrate anion links two calcium atoms, are also observed. Tridentate coordination (κ³O,O′,O′′) is extremely rare. In other structures, nitrate remains as an uncoordinated counter-ion and functions as a hydrogen-bond acceptor in the formation of supramolecular networks.

6. Synthesis and crystallization

The title compound was synthesized by a mechanochemical method using a ball mill operating at 21 Hz. A mixture of calcium nitrate tetrahydrate (2.3619 g, 0.0100 mol) and nicotinamide (2.4426 g, 0.0200 mol) was ground in a ball mill at room temperature for 9–12 minutes. The product yield was 87.0%. The resulting powder was dissolved in ethanol, and colorless prismatic crystals, stable at room temperature, were obtained by slow evaporation in a vacuum desiccator over a saturated CaCl₂ solution after 15 days. Suitable single crystals were selected for X-ray diffraction analysis.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atoms bonded to carbon atoms were placed in geometrically idealized positions, with C—H = 0.93 Å and refined using a riding model with U_iso(H) = 1.2U_eq(C). The hydrogen atoms of the coordinated water molecules and the amino groups were located from difference-Fourier maps and refined with restrained geometry (O—H and N—H distances) and displacement parameters.

Table 3
Experimental details

Crystal data
Chemical formula	[Ca(NO₃)₂(C₆H₆N₂O)₂(H₂O)₂]
M_r	444.39
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	292
a, b, c (Å)	7.5454 (3), 24.8759 (9), 10.7807 (4)
β (°)	108.777 (4)
V (Å³)	1915.83 (13)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	3.44
Crystal size (mm)	0.3 × 0.2 × 0.15

Data collection
Diffractometer	Xcalibur, Ruby
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2022 ).
T_min, T_max	0.695, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	7612, 3862, 3249
R_int	0.029
(sin θ/λ)_max (Å⁻¹)	0.630

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.041, 0.114, 1.03
No. of reflections	3862
No. of parameters	295
No. of restraints	8
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.28, −0.22
Computer programs: CrysAlis PRO (Rigaku OD, 2022), SHELXT2018/2 (Sheldrick, 2015a ), SHELXL2019/3 (Sheldrick, 2015b ), OLEX2 (Dolomanov et al., 2009 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 2476945

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989025006759/hb8147sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989025006759/hb8147Isup2.hkl

checkCIF report

Computing details top

Diaquabis(nicotinamide-κO)bis(nitrato-κ²O,O')calcium(II) top

Crystal data top

[Ca(NO₃)₂(C₆H₆N₂O)₂(H₂O)₂]	F(000) = 920
M_r = 444.39	D_x = 1.541 Mg m⁻³
Monoclinic, P2₁/n	Cu Kα radiation, λ = 1.54184 Å
a = 7.5454 (3) Å	Cell parameters from 3138 reflections
b = 24.8759 (9) Å	θ = 4.3–75.6°
c = 10.7807 (4) Å	µ = 3.44 mm⁻¹
β = 108.777 (4)°	T = 292 K
V = 1915.83 (13) Å³	Block, colourless
Z = 4	0.3 × 0.2 × 0.15 mm

Data collection top

Xcalibur, Ruby diffractometer	3862 independent reflections
Radiation source: Enhance (Cu) X-ray Source	3249 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.029
Detector resolution: 10.2576 pixels mm^-1	θ_max = 76.1°, θ_min = 3.6°
ω scans	h = −9→4
Absorption correction: multi-scan (CrysAlisPro; Rigaku OD, 2022).	k = −21→30
T_min = 0.695, T_max = 1.000	l = −12→13
7612 measured reflections

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.041	w = 1/[σ²(F_o²) + (0.0628P)² + 0.3395P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.114	(Δ/σ)_max < 0.001
S = 1.03	Δρ_max = 0.28 e Å⁻³
3862 reflections	Δρ_min = −0.22 e Å⁻³
295 parameters	Extinction correction: SHELXL2019/3 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
8 restraints	Extinction coefficient: 0.0024 (3)
Primary atom site location: dual

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Ca1	0.67003 (6)	0.39970 (2)	0.68777 (4)	0.03229 (14)
O4B	1.0018 (2)	0.37641 (6)	0.68407 (17)	0.0493 (4)
O2W	0.8098 (2)	0.48033 (6)	0.64428 (17)	0.0468 (4)
O2B	0.8417 (2)	0.30884 (6)	0.71333 (18)	0.0499 (4)
O1W	0.4593 (3)	0.33030 (7)	0.6873 (2)	0.0579 (5)
O1B	0.8260 (3)	0.40080 (7)	0.91112 (15)	0.0547 (4)
N3B	0.9890 (2)	0.32726 (7)	0.70013 (18)	0.0392 (4)
O1A	0.6075 (3)	0.37876 (7)	0.46656 (15)	0.0527 (4)
O4A	0.4497 (3)	0.45182 (8)	0.77806 (17)	0.0599 (5)
O3A	0.2005 (2)	0.49445 (8)	0.6654 (2)	0.0627 (5)
O2A	0.3761 (3)	0.45368 (8)	0.56996 (17)	0.0592 (5)
N3A	0.3399 (3)	0.46709 (7)	0.6718 (2)	0.0427 (4)
O3B	1.1193 (2)	0.29668 (7)	0.7045 (2)	0.0696 (6)
N2B	0.7909 (4)	0.46252 (9)	1.0519 (2)	0.0610 (6)
C6B	0.8402 (3)	0.41447 (9)	1.0239 (2)	0.0403 (5)
N1A	0.3231 (3)	0.43303 (9)	0.0959 (2)	0.0570 (5)
C1B	0.9154 (3)	0.37523 (8)	1.1338 (2)	0.0368 (4)
N2A	0.5831 (4)	0.29261 (9)	0.4060 (2)	0.0690 (7)
N1B	0.9965 (3)	0.28306 (8)	1.1918 (3)	0.0623 (6)
C1A	0.4714 (3)	0.36137 (8)	0.24086 (19)	0.0363 (4)
C2A	0.4057 (4)	0.41346 (9)	0.2157 (2)	0.0475 (5)
H2A	0.420138	0.436219	0.286721	0.057*
C6A	0.5592 (3)	0.34461 (9)	0.3802 (2)	0.0410 (5)
C2B	0.9309 (4)	0.32181 (9)	1.1026 (3)	0.0482 (5)
H2B	0.893628	0.312300	1.014492	0.058*
C5A	0.4520 (4)	0.32777 (10)	0.1350 (2)	0.0515 (6)
H5A	0.494550	0.292461	0.147272	0.062*
C5B	0.9718 (4)	0.38893 (9)	1.2648 (2)	0.0513 (6)
H5B	0.963082	0.424312	1.290129	0.062*
C3A	0.3056 (4)	0.39995 (11)	−0.0036 (2)	0.0563 (6)
H3A	0.247755	0.412757	−0.088068	0.068*
C4A	0.3681 (4)	0.34791 (11)	0.0112 (2)	0.0620 (7)
H4A	0.354019	0.326380	−0.061917	0.074*
C4B	1.0411 (5)	0.34951 (12)	1.3576 (3)	0.0655 (8)
H4B	1.080955	0.357922	1.446329	0.079*
C3B	1.0502 (4)	0.29799 (12)	1.3170 (3)	0.0657 (8)
H3B	1.096600	0.271718	1.380608	0.079*
H2BA	0.754 (4)	0.4861 (9)	0.990 (2)	0.067 (9)*
H2AA	0.632 (4)	0.2829 (13)	0.4866 (14)	0.077 (10)*
H2BB	0.800 (5)	0.4726 (14)	1.1305 (16)	0.083 (11)*
H2AB	0.547 (5)	0.2684 (10)	0.347 (2)	0.079 (10)*
H2WA	0.751 (4)	0.4995 (10)	0.5789 (19)	0.059 (8)*
H1WA	0.3466 (18)	0.3343 (13)	0.682 (3)	0.068 (9)*
H1WB	0.486 (4)	0.2973 (5)	0.682 (3)	0.069 (9)*
H2WB	0.921 (2)	0.4763 (19)	0.646 (4)	0.118 (16)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ca1	0.0386 (2)	0.0279 (2)	0.0297 (2)	0.00102 (16)	0.01011 (16)	−0.00019 (14)
O4B	0.0591 (10)	0.0293 (7)	0.0599 (10)	−0.0019 (7)	0.0198 (8)	0.0047 (7)
O2W	0.0478 (9)	0.0351 (8)	0.0556 (10)	0.0002 (7)	0.0139 (8)	0.0072 (7)
O2B	0.0421 (8)	0.0426 (8)	0.0689 (11)	−0.0012 (7)	0.0235 (8)	0.0038 (8)
O1W	0.0513 (10)	0.0392 (9)	0.0926 (14)	−0.0053 (8)	0.0362 (10)	0.0000 (9)
O1B	0.0630 (11)	0.0628 (11)	0.0319 (8)	0.0128 (9)	0.0065 (7)	−0.0021 (7)
N3B	0.0393 (9)	0.0327 (9)	0.0436 (9)	0.0008 (7)	0.0106 (7)	−0.0003 (7)
O1A	0.0720 (11)	0.0480 (9)	0.0350 (8)	−0.0019 (9)	0.0129 (7)	−0.0094 (7)
O4A	0.0649 (11)	0.0678 (12)	0.0464 (9)	0.0157 (10)	0.0171 (8)	0.0025 (9)
O3A	0.0501 (10)	0.0502 (10)	0.0915 (14)	0.0139 (8)	0.0279 (10)	−0.0030 (9)
O2A	0.0686 (11)	0.0631 (11)	0.0467 (9)	0.0261 (9)	0.0197 (8)	0.0074 (8)
N3A	0.0432 (10)	0.0321 (9)	0.0556 (11)	0.0026 (8)	0.0200 (9)	−0.0001 (8)
O3B	0.0448 (9)	0.0398 (9)	0.1299 (19)	0.0071 (8)	0.0361 (11)	0.0030 (10)
N2B	0.0946 (18)	0.0422 (11)	0.0405 (11)	0.0214 (12)	0.0138 (12)	0.0064 (9)
C6B	0.0443 (12)	0.0404 (11)	0.0321 (9)	0.0045 (9)	0.0065 (9)	0.0005 (8)
N1A	0.0712 (14)	0.0459 (11)	0.0516 (12)	0.0029 (11)	0.0168 (11)	0.0109 (9)
C1B	0.0382 (10)	0.0347 (10)	0.0361 (10)	0.0017 (9)	0.0098 (8)	0.0009 (8)
N2A	0.117 (2)	0.0409 (12)	0.0364 (11)	0.0119 (13)	0.0067 (12)	−0.0006 (9)
N1B	0.0690 (15)	0.0347 (10)	0.0839 (17)	0.0078 (10)	0.0255 (13)	0.0071 (11)
C1A	0.0423 (11)	0.0335 (10)	0.0332 (10)	−0.0040 (9)	0.0124 (8)	−0.0032 (8)
C2A	0.0607 (14)	0.0370 (11)	0.0447 (12)	0.0021 (10)	0.0167 (11)	−0.0025 (9)
C6A	0.0492 (12)	0.0394 (11)	0.0334 (10)	0.0011 (9)	0.0121 (9)	−0.0048 (9)
C2B	0.0536 (13)	0.0367 (11)	0.0543 (13)	0.0052 (10)	0.0176 (11)	−0.0036 (10)
C5A	0.0749 (16)	0.0399 (12)	0.0388 (11)	0.0007 (12)	0.0172 (11)	−0.0051 (9)
C5B	0.0733 (17)	0.0381 (12)	0.0383 (11)	0.0047 (11)	0.0121 (11)	0.0007 (9)
C3A	0.0656 (16)	0.0602 (16)	0.0404 (12)	−0.0086 (13)	0.0132 (11)	0.0098 (11)
C4A	0.091 (2)	0.0587 (16)	0.0339 (11)	−0.0082 (15)	0.0167 (12)	−0.0085 (11)
C4B	0.089 (2)	0.0599 (16)	0.0414 (13)	0.0072 (15)	0.0130 (13)	0.0135 (12)
C3B	0.0740 (18)	0.0491 (15)	0.0721 (19)	0.0097 (14)	0.0211 (15)	0.0280 (14)

Geometric parameters (Å, º) top

Ca1—O4B	2.5825 (18)	N1A—C2A	1.333 (3)
Ca1—O2W	2.3820 (16)	N1A—C3A	1.325 (3)
Ca1—O2B	2.5752 (17)	C1B—C2B	1.385 (3)
Ca1—O1W	2.3459 (18)	C1B—C5B	1.381 (3)
Ca1—O1B	2.3150 (16)	N2A—C6A	1.323 (3)
Ca1—O1A	2.3359 (15)	N2A—H2AA	0.863 (10)
Ca1—O4A	2.5362 (19)	N2A—H2AB	0.852 (10)
Ca1—O2A	2.5537 (18)	N1B—C2B	1.339 (3)
O4B—N3B	1.243 (2)	N1B—C3B	1.332 (4)
O2W—H2WA	0.848 (10)	C1A—C2A	1.383 (3)
O2W—H2WB	0.844 (10)	C1A—C6A	1.493 (3)
O2B—N3B	1.252 (2)	C1A—C5A	1.384 (3)
O1W—H1WA	0.839 (10)	C2A—H2A	0.9300
O1W—H1WB	0.852 (10)	C2B—H2B	0.9300
O1B—C6B	1.234 (3)	C5A—H5A	0.9300
N3B—O3B	1.232 (2)	C5A—C4A	1.374 (3)
O1A—C6A	1.226 (3)	C5B—H5B	0.9300
O4A—N3A	1.238 (3)	C5B—C4B	1.378 (3)
O3A—N3A	1.236 (2)	C3A—H3A	0.9300
O2A—N3A	1.258 (2)	C3A—C4A	1.370 (4)
N2B—C6B	1.315 (3)	C4A—H4A	0.9300
N2B—H2BA	0.862 (10)	C4B—H4B	0.9300
N2B—H2BB	0.864 (10)	C4B—C3B	1.363 (4)
C6B—C1B	1.498 (3)	C3B—H3B	0.9300

O2W—Ca1—O4B	72.13 (5)	O3A—N3A—O2A	121.1 (2)
O2W—Ca1—O2B	121.39 (6)	C6B—N2B—H2BA	119 (2)
O2W—Ca1—O4A	91.80 (6)	C6B—N2B—H2BB	123 (2)
O2W—Ca1—O2A	80.09 (6)	H2BA—N2B—H2BB	117 (3)
O2B—Ca1—O4B	49.31 (5)	O1B—C6B—N2B	122.4 (2)
O1W—Ca1—O4B	119.65 (6)	O1B—C6B—C1B	119.3 (2)
O1W—Ca1—O2W	164.15 (7)	N2B—C6B—C1B	118.29 (19)
O1W—Ca1—O2B	70.83 (6)	C3A—N1A—C2A	116.8 (2)
O1W—Ca1—O4A	81.35 (7)	C2B—C1B—C6B	118.3 (2)
O1W—Ca1—O2A	84.63 (7)	C5B—C1B—C6B	124.2 (2)
O1B—Ca1—O4B	81.25 (6)	C5B—C1B—C2B	117.6 (2)
O1B—Ca1—O2W	94.91 (7)	C6A—N2A—H2AA	118 (2)
O1B—Ca1—O2B	80.17 (6)	C6A—N2A—H2AB	123 (2)
O1B—Ca1—O1W	97.38 (7)	H2AA—N2A—H2AB	119 (3)
O1B—Ca1—O1A	158.82 (7)	C3B—N1B—C2B	116.7 (2)
O1B—Ca1—O4A	76.78 (6)	C2A—C1A—C6A	118.31 (19)
O1B—Ca1—O2A	125.48 (6)	C2A—C1A—C5A	117.9 (2)
O1A—Ca1—O4B	79.19 (6)	C5A—C1A—C6A	123.8 (2)
O1A—Ca1—O2W	86.77 (6)	N1A—C2A—C1A	124.0 (2)
O1A—Ca1—O2B	80.96 (6)	N1A—C2A—H2A	118.0
O1A—Ca1—O1W	85.39 (7)	C1A—C2A—H2A	118.0
O1A—Ca1—O4A	124.32 (6)	O1A—C6A—N2A	122.0 (2)
O1A—Ca1—O2A	75.63 (6)	O1A—C6A—C1A	119.9 (2)
O4A—Ca1—O4B	151.52 (6)	N2A—C6A—C1A	118.10 (19)
O4A—Ca1—O2B	140.96 (6)	C1B—C2B—H2B	118.1
O4A—Ca1—O2A	49.50 (5)	N1B—C2B—C1B	123.9 (2)
O2A—Ca1—O4B	143.26 (6)	N1B—C2B—H2B	118.1
O2A—Ca1—O2B	147.25 (6)	C1A—C5A—H5A	120.8
N3B—O4B—Ca1	95.69 (12)	C4A—C5A—C1A	118.3 (2)
Ca1—O2W—H2WA	119 (2)	C4A—C5A—H5A	120.8
Ca1—O2W—H2WB	113 (3)	C1B—C5B—H5B	120.4
H2WA—O2W—H2WB	109 (4)	C4B—C5B—C1B	119.1 (2)
N3B—O2B—Ca1	95.80 (12)	C4B—C5B—H5B	120.4
Ca1—O1W—H1WA	126 (2)	N1A—C3A—H3A	118.2
Ca1—O1W—H1WB	122 (2)	N1A—C3A—C4A	123.5 (2)
H1WA—O1W—H1WB	112 (3)	C4A—C3A—H3A	118.2
C6B—O1B—Ca1	151.91 (16)	C5A—C4A—H4A	120.3
O4B—N3B—O2B	119.18 (18)	C3A—C4A—C5A	119.4 (2)
O3B—N3B—O4B	121.04 (19)	C3A—C4A—H4A	120.3
O3B—N3B—O2B	119.77 (18)	C5B—C4B—H4B	120.6
C6A—O1A—Ca1	147.46 (16)	C3B—C4B—C5B	118.9 (3)
N3A—O4A—Ca1	97.34 (13)	C3B—C4B—H4B	120.6
N3A—O2A—Ca1	95.91 (13)	N1B—C3B—C4B	123.8 (2)
O4A—N3A—O2A	117.23 (19)	N1B—C3B—H3B	118.1
O3A—N3A—O4A	121.7 (2)	C4B—C3B—H3B	118.1

Ca1—O4B—N3B—O2B	−1.3 (2)	N1A—C3A—C4A—C5A	0.8 (5)
Ca1—O4B—N3B—O3B	179.5 (2)	C1B—C5B—C4B—C3B	−0.6 (5)
Ca1—O2B—N3B—O4B	1.3 (2)	C1A—C5A—C4A—C3A	−0.5 (4)
Ca1—O2B—N3B—O3B	−179.44 (19)	C2A—N1A—C3A—C4A	−0.3 (4)
Ca1—O1B—C6B—N2B	−38.9 (5)	C2A—C1A—C6A—O1A	−15.3 (3)
Ca1—O1B—C6B—C1B	140.9 (3)	C2A—C1A—C6A—N2A	164.9 (3)
Ca1—O1A—C6A—N2A	−25.1 (5)	C2A—C1A—C5A—C4A	−0.2 (4)
Ca1—O1A—C6A—C1A	155.2 (2)	C6A—C1A—C2A—N1A	−179.3 (2)
Ca1—O4A—N3A—O3A	178.72 (18)	C6A—C1A—C5A—C4A	179.9 (2)
Ca1—O4A—N3A—O2A	−1.4 (2)	C2B—C1B—C5B—C4B	0.4 (4)
Ca1—O2A—N3A—O4A	1.4 (2)	C2B—N1B—C3B—C4B	0.2 (5)
Ca1—O2A—N3A—O3A	−178.73 (18)	C5A—C1A—C2A—N1A	0.8 (4)
O1B—C6B—C1B—C2B	−12.9 (3)	C5A—C1A—C6A—O1A	164.6 (2)
O1B—C6B—C1B—C5B	166.7 (2)	C5A—C1A—C6A—N2A	−15.2 (4)
N2B—C6B—C1B—C2B	166.9 (2)	C5B—C1B—C2B—N1B	0.2 (4)
N2B—C6B—C1B—C5B	−13.6 (4)	C5B—C4B—C3B—N1B	0.3 (5)
C6B—C1B—C2B—N1B	179.8 (2)	C3A—N1A—C2A—C1A	−0.5 (4)
C6B—C1B—C5B—C4B	−179.2 (2)	C3B—N1B—C2B—C1B	−0.5 (4)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N2A—H2AB···O3Bⁱ	0.85 (1)	2.42 (2)	3.180 (3)	149 (3)
N2A—H2AA···O2B	0.86 (1)	2.53 (2)	3.284 (3)	146 (3)
N2B—H2BA···N1Aⁱⁱ	0.86 (1)	2.21 (2)	3.024 (3)	157 (3)
N2B—H2BB···O3Aⁱⁱⁱ	0.86 (1)	2.35 (1)	3.211 (3)	174 (3)
O1W—H1WA···O3B^iv	0.84 (1)	2.04 (2)	2.761 (3)	144 (3)
O1W—H1WB···N1Bⁱ	0.85 (1)	2.00 (1)	2.833 (3)	164 (3)
O2W—H2WA···O2Aⁱⁱ	0.85 (1)	1.97 (1)	2.813 (2)	178 (3)
O2W—H2WB···O3A^v	0.84 (1)	2.10 (2)	2.904 (3)	160 (4)
C5A—H5A···O3Bⁱ	0.93	2.41	3.336 (3)	174
C5B—H5B···O3Aⁱⁱⁱ	0.93	2.49	3.362 (3)	155

Symmetry codes: (i) x−1/2, −y+1/2, z−1/2; (ii) −x+1, −y+1, −z+1; (iii) −x+1, −y+1, −z+2; (iv) x−1, y, z; (v) x+1, y, z.

Acknowledgements

The authors are grateful to the Laboratory of Complex Compounds, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, for support and access to research facilities.

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