Crystal structure, Hirshfeld analysis and electrochemical properties of poly[di­aqua­bis­[μ6-2-cyano-2-(oxido­imino)­acetato]­copper(II)disodium]

Plutenko, M.O.; Golenya, I.A.; Plavkov, V.M.; Matus, T.; Pap, J.S.; Shova, S.

doi:10.1107/S2056989025008126

research communications

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 81| Part 10| October 2025| Pages 972-976

https://doi.org/10.1107/S2056989025008126

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Crystal structure, Hirshfeld analysis and electrochemical properties of poly[diaquabis[μ₆-2-cyano-2-(oxidoimino)acetato]copper(II)disodium]

Maksym O. Plutenko,^a ^* Irina A. Golenya,^a Vladyslav M. Plavkov,^a Tetiana Matus,^b József S. Pap ^c and Sergiu Shova ^d

^aDepartment of Chemistry, National Taras Shevchenko University, Volodymyrska, Street 64, 01601 Kyiv, Ukraine, ^bInnovation Development Center ABN LLC, Pirogov Str. 2/37, Kyiv, 01030, Ukraine, ^cHUN-REN Centre for Energy Research, Institute for Energy Security and, Environmental Safety, Surface Chemistry and Catalysis Department, H-1121, Budapest, Konkoly-Thege Rd. 29-33, Hungary, and ^dDepartment of Inorganic Polymers, "Petru Poni" Institute of Macromolecular, Chemistry, Romanian Academy of Science, Aleea Grigore Ghica Voda 41-A, Iasi, 700487, Romania
^*Correspondence e-mail: [email protected]

Edited by B. Therrien, University of Neuchâtel, Switzerland (Received 20 August 2025; accepted 12 September 2025; online 19 September 2025)

The title compound, [Na₂Cu(C₃N₂O₃)₂(H₂O)₂]_n, is a three-dimensional coordination polymer composed of divalent copper-centered complex anions, linked by sodium and water molecules. The copper(II) ion adopts a distorted octahedral coordination geometry, defined by two nitrogen atoms from oxime groups and two oxygen atoms from carboxylate groups, originating from two trans-oriented, doubly deprotonated residues of 2-cyano-2-(hydroxyimino)acetic acid. The axial Cu—O bonds are much longer than the equatorial Cu—O and Cu—N bonds due to the Jahn–Teller effect. Each complex anionic unit is linked to four neighboring anions via Cu—O bonds, forming a two-dimensional anionic network parallel to the bc plane.

Keywords: crystal structure; copper(II) complex; oxime-based ligand; Hirshfeld surface analysis; electrochemical properties.

CCDC reference: 2487839

1. Chemical context

Mononuclear 3d-metal complexes often contain non-coordinated donor atoms or chelating functionalities, which can be further employed as binding sites for exo-coordination in the design of homo- and heteropolynuclear architectures. Such systems are employed extensively in bio-inorganic modeling, molecular magnetism, and multi-electron photo- and electrocatalytic processes (Fritsky et al., 2001 , 2003 ; Wörl et al., 2005a ). In particular, multidentate ligands containing mixed donor sets, specifically combinations of oxime groups with either carboxylate or amide functionalities, have attracted considerable attention due to their rich and versatile coordination chemistry. Firstly, the inherent acidic nature of these groups facilitates the formation of negatively charged ligabds or acidoligands, which can readily yield anionic complexes of varying charge states (Fritsky et al., 2004 ; Kanderal et al., 2005 ). Secondly, these functional groups are characterized by diverse coordination modes, ranging from monodentate to bridging interactions (Strotmeyer et al., 2003 ; Wörl et al., 2005b ). Such versatility significantly broadens the spectrum of attainable complex structures and strongly favors the assembly of polynuclear systems exhibiting various types of magnetic interactions.

A particularly noteworthy feature of these donor groups is their ability, in negatively charged forms, to effectively stabilize higher oxidation states of 3d transition metals, driven by their pronounced σ-donor character. Indeed, our earlier studies have demonstrated that ligands featuring a donor set of 2×{N(oxime), N(amide)} effectively stabilize high-valent nickel(III) and copper(III) species (Kanderal et al., 2005; Fritsky et al., 2006 ). These properties underpin considerable interest in such ligand systems and their complexes, particularly as potential catalysts for electrochemical and photochemical water oxidation (Kondo et al., 2021 ; Beil et al., 2022 ). In addition, coordination polymers and metal–organic frameworks (MOFs) featuring such anionic complexes are of particular interest as promising components of hybrid electrode materials. In light of the growing global emphasis on sustainable catalytic technologies, recent decades have seen a marked increase in reports on molecular coordination compounds and MOFs exhibiting relevant catalytic functionality (Singh et al., 2021 ; Liu et al., 2023 ).

Although carboxylate groups generally show a somewhat lower tendency to stabilize high-valent oxidation states compared to amide groups, ligands featuring {N(oxime), O(carboxylate)} donor sets also exhibit significant coordination potential. Notably, coordination compounds based on 2-cyano-2-(hydroxyimino)acetic acid (H₂aaco) have been reported, demonstrating their ability to form anionic complexes with metals such as copper(II), nickel(II), and palladium(II) (Eddings et al., 2004 ; Golenya et al., 2012 ; Opalade, et al., 2019 ). In particular, the deprotonated form of H₂aaco has proven to be an effective chelating ligand for Cu^II and Ni^II ions, forming a variety of mono- and polynuclear complexes depending on the stoichiometry and reaction conditions (Sliva et al., 1998 ; Mokhir et al., 2002 ). Interestingly, some of these complexes were obtained via hydrolysis of the corresponding ethyl ester precursors (Eddings et al., 2004).

This work is part of a broader study aimed at synthesizing polynuclear assemblies, coordination polymers, and MOFs based on mononuclear copper(II) complexes derived from this ligand; investigating their molecular and crystal structures along with their supramolecular organization; and evaluating their electrochemical behavior and potential electrocatalytic activity in water oxidation (Sliva et al., 1998; Golenya et al., 2012).

2. Structural commentary

The title compound, [Na₂Cu(C₃N₂O₃)₂(H₂O)₂]_n, is a three-dimensional coordination polymer composed of Cu^II-centered complex anions, sodium cations and water molecules (Fig. 1). The copper(II) ion adopts a distorted octahedral coordination geometry, defined by two nitrogen atoms from oxime groups and two oxygen atoms from carboxylate groups, originating from two trans-oriented, doubly deprotonated residues of 2-cyano-2-(hydroxyimino)acetic acid. The axial positions are occupied by carboxylate oxygen atoms (O2) from adjacent ligands, which are not involved in chelation via the oxime nitrogen atom.

Figure 1
The [Na₂Cu(C₃N₂O₃)₂(H₂O)₂] complex monomer with displacement ellipsoids shown at the 50% probability level. Symmetry codes: (i1) −x + 1, −y + 1, −z + 1; (i2) −x + 1, y + $[{1\over 2}]$ , −z + $[{3\over 2}]$ ; (i3) x, −y + $[{1\over 2}]$ , z − $[{1\over 2}]$ ; (i4) x, −y + $[{1\over 2}]$ , z + $[{1\over 2}]$ ; (i5) −x + 1, y + $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (i6) −x + 1, y − $[{1\over 2}]$ , −z + $[{3\over 2}]$ ; (i7) x, −y + $[{3\over 2}]$ , z − $[{1\over 2}]$ ; (i8) x − 1, −y + $[{1\over 2}]$ , z − $[{1\over 2}]$ ; (i9) −x + 2, y + $[{1\over 2}]$ , −z + $[{3\over 2}]$ .

The Cu—N and Cu—O bond lengths are consistent with those typically observed in distorted octahedral Cu^II complexes containing deprotonated oxime and carboxylate donors (Sliva et al., 1998; Kanderal et al., 2005). The axial Cu—O2 bonds [2.409 (4) Å] are much longer than equatorial Cu—O3 [1.974 (4) Å] and Cu—N1 [1.972 (5) Å] due to the Jahn–Teller effect. The bite angles around the Cu center deviate slightly from an ideal square-planar arrangement [e.g., O2—Cu1—N1 = 88.87 (16)°], reflecting the constraints imposed by the formation of five-membered chelate rings. Bond distances within the coordinated 2-oximinocarboxylate ligands (C—O, N—O, and C—N) fall within the expected ranges for copper(II) complexes with cyanoxime and carboxylate ligands (Onindo et al., 1995 ; Duda et al., 1997 ; Fritsky et al., 2004).

3. Supramolecular features

In the crystal, the [Cu(C₃N₂O₃)₂]²⁻ complex anions are connected to each other through bridging coordinated carboxylic groups via Cu1—O2 bonds. As a result, each [Cu(C₃N₂O₃)₂]²⁻ unit is linked to four neighboring units, forming a two-dimensional anionic network parallel to the bc plane (Fig. 2). These individual layers are further connected through Na cations via O1—Na1, O3—Na1, and N2—Na1 ionic bonds. The carboxylic group of the ligand thus exhibits a μ₃-coordination mode, binding to two copper ions and one sodium cation. In addition, the carboxylic group is connected to the water molecule via an O4—H4A⋯O2 hydrogen bond (Table 1) in which the water oxygen atom acts as hydrogen-bond donor and the oxygen atom of the carboxylic group acts as acceptor.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O4—H4A⋯O2ⁱ	0.70 (9)	2.10 (9)	2.753 (6)	155 (9)
Symmetry code: (i) .

Figure 2
Crystal packing of the title compound.

The sodium cation adopts a distorted octahedral environment, defined by two oxygen atoms from oxime groups, one oxygen atom from a carboxylic group, one nitrogen atom from a cyano group, and two oxygen atoms from neighboring water molecules. Individual sodium cations are interconnected via bridging oxime groups and water molecules through Na1—O1 and Na1—O4 interactions, forming supramolecular chains along the c-axis direction.

4. Hirshfeld analysis

The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009 ) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007 ) were performed with CrystalExplorer 25 (Spackman et al., 2021 ). The Hirshfeld surfaces of the [Cu(C₃N₂O₃)₂]²⁻ complex anion are color-mapped with the normalized contact distance (d_norm) from red (distances shorter than the sum of the van der Waals radii) through white to blue (distances longer than the sum of the van der Waals radii). According to the Hirshfeld surface (Fig. 3), the most noticeable intermolecular interactions are O1⋯Na1, O2⋯Cu1, O3⋯Na1 and N2⋯Na1 contacts.

Figure 3
The Hirshfeld surfaces of the [Cu(C₃N₂O₃)₂]²⁻ complex anion.

A fingerprint plot delineated into specific interatomic contacts contains information related to specific intermolecular interactions. The blue color refers to the frequency of occurrence of the (d_i, d_e) pair with the full fingerprint plot outlined in gray. Fig. 4 shows the two-dimensional fingerprint plot of the sum of the contacts contributing to the Hirshfeld surface represented in normal mode. The most significant contribution to the Hirshfeld surface is from O⋯Na (14.8%) and O⋯H (12.8%) contacts. In addition, N⋯H (9.3%) is a significant contribution to the total Hirshfeld surface.

Figure 4
(a) Full two-dimensional fingerprint plot of the [Cu(C₃N₂O₃)₂]²⁻ complex anion delineated into (b) O⋯Na (14.8%), (c) O⋯H (12.8%) and (d) N⋯H (19.3%) contacts.

5. Redox Properties

Electrochemical investigations revealed that the complex exhibits no redox activity within the potential range of −1.5 V to +1.5 V (Fig. 5), effectively ruling out its utility as a photo- or electrocatalyst for water oxidation. This redox-inert behavior and the absence of any indication of accessible copper(III) states under these conditions is likely attributed to the strong π-acceptor effect of the nitrile groups. These effects offset the anticipated lowering of the Cu^3+/2+ redox potential by the anionic nature and strong σ-donor capacity of the coordinating nitrogen and oxygen atoms of the oxime and carboxylate functionalities, respectively, thereby disfavoring the stabilization of the trivalent copper state.

Figure 5
Cyclic voltammogram of the 0.1 M phosphate buffer (gray line) and the 0.1 mM title compound in the 0.1 M phosphate buffer (red line). Boron-doped diamond electrode, Ag/AgCl reference electrode (E(Ag/Ag⁺) = 0.210 V versus NHE).

6. Database survey

A search in the Cambridge Structural Database (CSD version 5.45, update of June 2024; Groom et al., 2016 ) resulted in 14 hits dealing with metal complexes including a 2-cyano-2-(oxidoimino)acetate fragment. There are four Cu (CSD refcodes CEFHOM, CEFHOM01, KIXHUX and SOQZIH), four Sb (SURXUB, SURXUB01, SURYAI and SURYAI01), three Ni (KIXJAF, KIXJOT and NEVKIJ), two Ag (YIYPOM and YIYPOM01) and one Pd (SABQES) complex structures.

Two of the four Cu complexes (CEFHOM and CEFHOM01) exhibit a distorted square-pyramidal CuO₃N₂ coordination geometry. One complex (SOQZIH) adopts a distorted octahedral CuO₅N geometry. Another complex (KIXHUX) displays both distorted square-pyramidal and distorted octahedral coordination geometries, with CuO₃N₂ and CuO₆ arrangements, respectively. The geometrical parameters of these complexes are similar to that of the title compound. As in the title compound, the axial Cu—O bonds (2.214–2.495 Å) are longer than the equatorial Cu—O (1.921–1.978 Å) and Cu—N (1.976–2.008 Å) bonds, consistent with the Jahn–Teller effect.

7. Synthesis and crystallization

The title compound was obtained serendipitously during an attempt to synthesize a binuclear copper(II) complex with 2-cyano-2-(oxyimino)acetate anions and 1,4-diazabicyclooctane as a bridging ligand (Petrusenko et al., 1997 ). A solution of copper(II) chloride dihydrate (0.0340 g, 0.2 mmol) in methanol (5 mL) was added to a solution of ethyl 2-cyano-2-(oxyimino)acetate (0.0568 g, 0.4 mmol) in methanol (5 mL). Separately, 1,4-diazabicyclooctane (0.0112 g, 0.1 mmol) was dissolved in methanol (3 mL) and added to the reaction mixture. Then, NaOH solution in methanol (4 ml, 0.1 M, 0.4 mmol) was added. The resulting mixture was stirred and heated (323 K) for 60 minutes, then cooled to room temperature, filtered, and left to stand for crystallization. X-ray quality crystals formed after one week; they were collected by filtration, washed with acetone, and air-dried. Yield: 0.0538 g (73%).

8. Electrochemistry

Cyclic voltammetry (CV) experiments were conducted in aqueous solutions containing 0.1 M phosphate buffer at pH 7.2 as the supporting electrolyte, using a BioLogic SP-150 galvanostat/potentiostat. A three-electrode setup was employed, comprising a boron-doped diamond electrode (3 mm diameter, polished first with a diamond paste, then rinsed it with MilliQ water, next polished with an Al₂O₃ paste before rinsing again and finally, ultrasonicated the electrode in MilliQ water to remove any remaining particles prior to use), a platinum wire counter electrode, and an Ag/AgCl reference electrode. The electrolyte was purged with argon gas before each measurement and maintained under an inert argon atmosphere throughout the experiments. All potentials are reported versus the Ag/Ag⁺ couple, E(Ag/Ag⁺) = 0.210 V vs NHE.

9. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The non-hydrogen atoms were refined anisotropically. The hydrogen atoms were located in a difference-Fourier map, and their positions and isotropic thermal parameters were freely refined.

Table 2
Experimental details

Crystal data
Chemical formula	[Na₂Cu(C₃N₂O₃)₂(H₂O)₂]
M_r	369.65
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	9.1889 (4), 9.1459 (4), 7.1062 (3)
β (°)	99.090 (4)
V (Å³)	589.71 (4)
Z	2
Radiation type	Cu Kα
μ (mm⁻¹)	3.87
Crystal size (mm)	0.15 × 0.10 × 0.02

Data collection
Diffractometer	XtaLAB Synergy, Dualflex, HyPix
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2024 )
T_min, T_max	0.741, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	1044, 1044, 982
R_int	0.67
(sin θ/λ)_max (Å⁻¹)	0.595

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.052, 0.177, 1.22
No. of reflections	1044
No. of parameters	106
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	1.70, −1.55
Computer programs: CrysAlis PRO (Rigaku OD, 2024), SHELXT2018/2 (Sheldrick, 2015a ), SHELXL2018/3 (Sheldrick, 2015b ), DIAMOND (Brandenburg, 2005 ) and OLEX2 (Dolomanov et al., 2009 ).

Supporting information

CCDC reference: 2487839

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989025008126/tx2103sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989025008126/tx2103Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989025008126/tx2103Isup3.cdx

Supporting information file. DOI: https://doi.org/10.1107/S2056989025008126/tx2103Isup4.mol

Supporting information file. DOI: https://doi.org/10.1107/S2056989025008126/tx2103Isup5.cdx

checkCIF report

Computing details top

Poly[diaquabis[µ₆-2-cyano-2-(oxidoimino)acetato]copper(II)disodium] top

Crystal data top

[Na₂Cu(C₃N₂O₃)₂(H₂O)₂]	F(000) = 366
M_r = 369.65	D_x = 2.082 Mg m⁻³
Monoclinic, P2₁/c	Cu Kα radiation, λ = 1.54184 Å
a = 9.1889 (4) Å	Cell parameters from 2721 reflections
b = 9.1459 (4) Å	θ = 4.9–75.2°
c = 7.1062 (3) Å	µ = 3.87 mm⁻¹
β = 99.090 (4)°	T = 100 K
V = 589.71 (4) Å³	Plate, clear light brown
Z = 2	0.15 × 0.10 × 0.02 mm

Data collection top

XtaLAB Synergy, Dualflex, HyPix diffractometer	1044 independent reflections
Radiation source: micro-focus sealed X-ray tube, PhotonJet (Cu) X-ray Source	982 reflections with I > 2σ(I)
Detector resolution: 10.0000 pixels mm^-1	R_int = 0.67
ω scans	θ_max = 66.6°, θ_min = 4.9°
Absorption correction: multi-scan (CrysAlisPro; Rigaku OD, 2024)	h = −10→10
T_min = 0.741, T_max = 1.000	k = −10→10
1044 measured reflections	l = −5→8

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.052	All H-atom parameters refined
wR(F²) = 0.177	w = 1/[σ²(F_o²) + (0.0875P)² + 2.7951P] where P = (F_o² + 2F_c²)/3
S = 1.22	(Δ/σ)_max < 0.001
1044 reflections	Δρ_max = 1.70 e Å⁻³
106 parameters	Δρ_min = −1.55 e Å⁻³

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.

Refinement. Refined as a 2-component twin.

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

	x	y	z	U_iso*/U_eq
Cu1	0.500000	0.500000	0.500000	0.0075 (4)
Na1	0.2083 (2)	0.2433 (2)	0.5468 (3)	0.0106 (6)
N1	0.6935 (5)	0.4743 (5)	0.6615 (7)	0.0096 (10)
N2	0.9401 (5)	0.2608 (6)	0.9596 (7)	0.0160 (11)
O1	0.7992 (4)	0.5681 (4)	0.6968 (6)	0.0115 (9)
O2	0.5888 (4)	0.1131 (4)	0.7338 (5)	0.0110 (9)
O3	0.4627 (4)	0.3009 (4)	0.5884 (5)	0.0087 (8)
O4	0.1809 (5)	0.0760 (5)	0.2858 (6)	0.0149 (9)
H4A	0.235 (9)	0.022 (9)	0.310 (12)	0.02 (2)*
H4B	0.107 (11)	0.039 (12)	0.253 (16)	0.05 (3)*
C1	0.7049 (6)	0.3431 (6)	0.7386 (8)	0.0087 (11)
C2	0.5766 (6)	0.2432 (6)	0.6845 (8)	0.0093 (11)
C3	0.8351 (6)	0.2974 (6)	0.8622 (8)	0.0106 (11)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.0072 (6)	0.0057 (6)	0.0103 (7)	−0.0002 (4)	0.0035 (5)	0.0016 (4)
Na1	0.0094 (10)	0.0102 (11)	0.0132 (11)	−0.0009 (8)	0.0043 (8)	0.0014 (9)
N1	0.009 (2)	0.007 (2)	0.014 (2)	−0.0010 (17)	0.0070 (19)	−0.0015 (19)
N2	0.013 (2)	0.018 (2)	0.019 (2)	−0.002 (2)	0.007 (2)	0.011 (2)
O1	0.0114 (19)	0.0081 (19)	0.016 (2)	−0.0035 (14)	0.0048 (16)	−0.0027 (15)
O2	0.0131 (19)	0.0083 (19)	0.0137 (19)	0.0021 (14)	0.0088 (15)	0.0000 (15)
O3	0.0089 (18)	0.0076 (17)	0.0109 (18)	−0.0004 (14)	0.0058 (15)	0.0007 (14)
O4	0.014 (2)	0.010 (2)	0.020 (2)	0.0036 (19)	0.0051 (18)	0.0002 (17)
C1	0.007 (2)	0.011 (3)	0.010 (2)	0.002 (2)	0.005 (2)	−0.001 (2)
C2	0.009 (2)	0.009 (3)	0.011 (2)	0.001 (2)	0.007 (2)	0.002 (2)
C3	0.012 (3)	0.010 (3)	0.012 (3)	−0.003 (2)	0.008 (2)	0.002 (2)

Geometric parameters (Å, º) top

Cu1—N1ⁱ	1.972 (5)	Na1—N2^vi	2.445 (5)
Cu1—N1	1.972 (5)	Na1—Na1ⁱⁱ	3.5552 (2)
Cu1—O3	1.974 (4)	Na1—Na1^iv	3.5553 (2)
Cu1—O3ⁱ	1.974 (4)	Na1—H4A	2.67 (8)
Cu1—O2ⁱⁱ	2.409 (4)	N1—O1	1.290 (6)
Cu1—O2ⁱⁱⁱ	2.409 (4)	N1—C1	1.316 (7)
Cu1—Na1	3.618 (2)	N2—C3	1.145 (8)
Cu1—Na1ⁱ	3.618 (2)	O2—C2	1.240 (7)
Na1—O3	2.368 (4)	O3—C2	1.271 (7)
Na1—O4	2.387 (5)	O4—H4A	0.70 (9)
Na1—O4^iv	2.412 (5)	O4—H4B	0.76 (10)
Na1—O1^v	2.435 (4)	C1—C3	1.430 (8)
Na1—O1ⁱ	2.437 (4)	C1—C2	1.493 (7)

N1ⁱ—Cu1—N1	180.0	O3—Na1—Na1^iv	91.35 (10)
N1ⁱ—Cu1—O3	96.25 (17)	O4—Na1—Na1^iv	141.45 (15)
N1—Cu1—O3	83.75 (17)	O4^iv—Na1—Na1^iv	41.92 (11)
N1ⁱ—Cu1—O3ⁱ	83.75 (17)	O1^v—Na1—Na1^iv	43.16 (10)
N1—Cu1—O3ⁱ	96.25 (17)	O1ⁱ—Na1—Na1^iv	132.92 (14)
O3—Cu1—O3ⁱ	180.0	N2^vi—Na1—Na1^iv	95.44 (13)
N1ⁱ—Cu1—O2ⁱⁱ	88.87 (16)	Na1ⁱⁱ—Na1—Na1^iv	176.04 (13)
N1—Cu1—O2ⁱⁱ	91.13 (16)	O3—Na1—Cu1	30.26 (9)
O3—Cu1—O2ⁱⁱ	87.20 (13)	O4—Na1—Cu1	109.47 (12)
O3ⁱ—Cu1—O2ⁱⁱ	92.80 (14)	O4^iv—Na1—Cu1	77.37 (13)
N1ⁱ—Cu1—O2ⁱⁱⁱ	91.13 (16)	O1^v—Na1—Cu1	127.21 (11)
N1—Cu1—O2ⁱⁱⁱ	88.87 (16)	O1ⁱ—Na1—Cu1	54.10 (9)
O3—Cu1—O2ⁱⁱⁱ	92.80 (14)	N2^vi—Na1—Cu1	135.92 (15)
O3ⁱ—Cu1—O2ⁱⁱⁱ	87.20 (14)	Na1ⁱⁱ—Na1—Cu1	76.62 (5)
O2ⁱⁱ—Cu1—O2ⁱⁱⁱ	180.0	Na1^iv—Na1—Cu1	100.75 (6)
N1ⁱ—Cu1—Na1	61.17 (14)	O3—Na1—H4A	93.4 (18)
N1—Cu1—Na1	118.83 (14)	O4—Na1—H4A	14.7 (18)
O3—Cu1—Na1	37.20 (11)	O4^iv—Na1—H4A	173.9 (17)
O3ⁱ—Cu1—Na1	142.80 (11)	O1^v—Na1—H4A	89.3 (17)
O2ⁱⁱ—Cu1—Na1	98.13 (9)	O1ⁱ—Na1—H4A	94.9 (17)
O2ⁱⁱⁱ—Cu1—Na1	81.87 (9)	N2^vi—Na1—H4A	91.0 (18)
N1ⁱ—Cu1—Na1ⁱ	118.83 (14)	Na1ⁱⁱ—Na1—H4A	51.8 (17)
N1—Cu1—Na1ⁱ	61.17 (14)	Na1^iv—Na1—H4A	132.1 (17)
O3—Cu1—Na1ⁱ	142.80 (11)	Cu1—Na1—H4A	106.9 (17)
O3ⁱ—Cu1—Na1ⁱ	37.20 (11)	O1—N1—C1	121.2 (5)
O2ⁱⁱ—Cu1—Na1ⁱ	81.87 (9)	O1—N1—Cu1	128.0 (4)
O2ⁱⁱⁱ—Cu1—Na1ⁱ	98.13 (9)	C1—N1—Cu1	110.8 (4)
Na1—Cu1—Na1ⁱ	180.0	C3—N2—Na1^vii	151.3 (4)
O3—Na1—O4	102.74 (16)	N1—O1—Na1ⁱⁱⁱ	118.2 (3)
O3—Na1—O4^iv	88.32 (16)	N1—O1—Na1ⁱ	113.4 (3)
O4—Na1—O4^iv	167.6 (3)	Na1ⁱⁱⁱ—O1—Na1ⁱ	93.72 (13)
O3—Na1—O1^v	101.37 (14)	C2—O2—Cu1^v	127.4 (3)
O4—Na1—O1^v	98.50 (16)	C2—O3—Cu1	112.6 (3)
O4^iv—Na1—O1^v	84.57 (15)	C2—O3—Na1	133.4 (3)
O3—Na1—O1ⁱ	81.24 (14)	Cu1—O3—Na1	112.54 (17)
O4—Na1—O1ⁱ	85.07 (15)	Na1—O4—Na1ⁱⁱ	95.62 (15)
O4^iv—Na1—O1ⁱ	91.19 (15)	Na1—O4—H4A	106 (7)
O1^v—Na1—O1ⁱ	174.92 (17)	Na1ⁱⁱ—O4—H4A	120 (7)
O3—Na1—N2^vi	166.03 (18)	Na1—O4—H4B	120 (8)
O4—Na1—N2^vi	79.32 (18)	Na1ⁱⁱ—O4—H4B	106 (8)
O4^iv—Na1—N2^vi	88.61 (18)	H4A—O4—H4B	109 (10)
O1^v—Na1—N2^vi	91.89 (17)	N1—C1—C3	121.7 (5)
O1ⁱ—Na1—N2^vi	85.20 (16)	N1—C1—C2	116.3 (5)
O3—Na1—Na1ⁱⁱ	87.77 (10)	C3—C1—C2	121.9 (5)
O4—Na1—Na1ⁱⁱ	42.46 (11)	O2—C2—O3	125.5 (5)
O4^iv—Na1—Na1ⁱⁱ	134.16 (15)	O2—C2—C1	118.8 (5)
O1^v—Na1—Na1ⁱⁱ	140.81 (14)	O3—C2—C1	115.7 (5)
O1ⁱ—Na1—Na1ⁱⁱ	43.12 (10)	N2—C3—C1	179.3 (6)
N2^vi—Na1—Na1ⁱⁱ	84.62 (13)

C1—N1—O1—Na1ⁱⁱⁱ	−94.0 (5)	Cu1^v—O2—C2—C1	99.9 (5)
Cu1—N1—O1—Na1ⁱⁱⁱ	84.8 (4)	Cu1—O3—C2—O2	−169.5 (4)
C1—N1—O1—Na1ⁱ	157.8 (4)	Na1—O3—C2—O2	25.6 (8)
Cu1—N1—O1—Na1ⁱ	−23.4 (5)	Cu1—O3—C2—C1	9.9 (5)
O1—N1—C1—C3	−1.0 (8)	Na1—O3—C2—C1	−155.1 (3)
Cu1—N1—C1—C3	180.0 (4)	N1—C1—C2—O2	171.1 (5)
O1—N1—C1—C2	−178.9 (4)	C3—C1—C2—O2	−6.8 (8)
Cu1—N1—C1—C2	2.1 (6)	N1—C1—C2—O3	−8.3 (7)
Cu1^v—O2—C2—O3	−80.7 (6)	C3—C1—C2—O3	173.8 (5)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, −y+1/2, z−1/2; (iii) −x+1, y+1/2, −z+3/2; (iv) x, −y+1/2, z+1/2; (v) −x+1, y−1/2, −z+3/2; (vi) x−1, −y+1/2, z−1/2; (vii) x+1, −y+1/2, z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4A···O2^viii	0.70 (9)	2.10 (9)	2.753 (6)	155 (9)

Symmetry code: (viii) −x+1, −y, −z+1.

Acknowledgements

The authors are grateful to the FAIRE programme provided by the Cambridge Crystallographic Data Centre (CCDC) for the opportunity to use the Cambridge Structural Database (CSD) and associated software

Funding information

This work is supported by the European Union's HORIZON-MSCA-2023-SE-01 under grant agreement No 101183082 - PacemCAT. Funding for this research was also provided by Ministry of Education and Science of Ukraine (grant for the perspective development of the scientific direction "Mathematical sciences and natural sciences" at the Taras Shevchenko National University of Kyiv). JSP thanks the Renewable Energy National Laboratory (Hungary) for support, financed by the RRF-2.3.1–21-2022–00009 project.

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