(5-Fluoro-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-1-ido-κN 1)(1,4,8,11-tetraazacyclotetradecane-κ4 N)zinc(II) perchlorate

In the structure of the title complex, the zinc(II) ion forms coordination bonds with the four nitrogen atoms of cyclam as well as with the nitrogen atom of a deprotonated 5-fluorouracil ion. Cyclam adopts a trans-I type conformation within this structure. The coordination structure of the zinc(II) ion is a square pyramid with a distorted base plane formed by the four nitrogen atoms of the cyclam.

In the structure of the title complex, [Zn(C 4 H 2 FN 2 O 2 )(C 10 H 24 N 4 )]ClO 4 , the zinc(II) ion forms coordination bonds with the four nitrogen atoms of cyclam (1,4,8,11-tetraazacyclotetradecane or [14]aneN4) as well as with the nitrogen atom of a deprotonated 5-fluorouracil ion (FU À ).Cyclam adopts a trans-I type conformation within this structure.The coordination structure of the zinc(II) ion is a square pyramid with a distorted base plane formed by the four nitrogen atoms of the cyclam.FU À engages in intermolecular hydrogen bonding with neighboring FU À molecules and with the cyclam molecule.

Structure description
Cyclam (= 1,4,8,11-tetraazacyclotetradecane or [14]aneN4) is a widely recognized macrocyclic polyamine renowned for its strong chelation properties with transition-metal cations, such as cobalt(III) ion (Fang et al., 2024), copper(II) ion (Emsley et al., 1990), and nickel(II) ion (Prasad et al., 1987).We have reported the crystal structure of a zinc(II) ion and a cyclam complex (Zn II -cyclam) (Ichimaru et al., 2022).Cyclen (= 1,4,7,10-tetraazacyclododecane or [12]aneN4) shares similarities with cyclam as a macrocyclic polyamine.Cyclen's chelation properties with metal cations are largely akin to those of cyclam, including its affinity for zinc(II) ions (Ichimaru et al., 2021).Cyclam and cyclen differ in the number of atoms forming their rings.In metal-cyclam complexes, the metal cation and four nitrogen atoms lie within the same plane, allowing for the coordination of two counter-anions perpendicular to the plane; the coordination structure of a central metal is octahedral.Conversely, in metal-cyclen complexes, the metal cation is located above the plane formed by the four nitrogen atoms, enabling the coordination of one counter anion; the coordination structure of a central metal is a square pyramid.We previously reported on the formation of a complex between deprotonated 5-fluorouracil (FU À ) and Zn II -cyclen (Ichimaru et al., 2023).In this study, we attempted to synthesize the aforementioned complex by reacting Zn II -cyclam with FU À at a 1:2 stoichiometry.However, the resulting molecule was identified as the title complex, that is, Zn II -cyclam and FU À formed a complex with 1:1 stoichiometry.Further studies on the reaction conditions for complex formation, including changing the reaction stoichiometry, are expected in the future.
The title complex comprises an FU À bound to a zinc(II) ion chelated by cyclam (Fig. 1).The FU À molecule was formed by deprotonation of the N-H group at the most acidic 3-position of FU.Additionally, one perchlorate ion serves as a counteranion adjacent to the complex.In terms of the cyclam ring's conformation within the title complex, it adopts a trans-I (R, S, R, S) type, while the energetically most stable coordination is the trans-III (R, R, S, S) type (Bosnich et al., 1965;Oakley et al., 2024).In instances where the central metal is a zinc(II) ion, it is noted that two counter-anions can coordinate perpendicular to the plane established by the trans-III type cyclam (Ichimaru et al., 2022).However, in the title complex, contrary to our expectation, only one FU À molecule coordinates with the zinc(II) ion, while the cyclam adopts a trans-I type.In cases where an anion coordinates with the central metal of Ntetramethylcyclam, the trans-I type is often adopted, primarily due to non-bonding interactions (Liang & Sadler, 2004).However, it is uncommon for N-non-substituted cyclam to adopt the trans-I type.The coordination system of zinc(II) ion is shown in Fig. 2. The bond angles formed by N5-Zn1 and the nitrogen atoms of cyclam (N1, N2, N3, and N4) are 108.17(13), 90.91 (13), 115.88 (13), and 100.68 (13) � , respectively.These bond angles were observed to be smaller for the longer bond lengths between Zn1 and the nitrogen atoms of cyclam (N1, N2, N3, and N4).In a typical Zn II -cyclam complex, the corresponding bond angles and bond lengths are approximately 90 � and 2.08 A ˚, respectively (Ichimaru et al., 2022).In the title compound, the bond Z1-N2 is 2.211 (3) A ẘhen the bond angle N5-Zn1-N2 is 90.91 (13) � , and the distance Zn1-N1 equals 2.082 (3) A ˚when the bond angle N5-Zn1-N1 amounts to 108.17 (13) � .The distances between two pairs of N atoms located diagonally across Zn1 are N1� � �N3 = 3.840 (5) and N2� � �N4 = 4.349 (5) A ˚.In a typical Zn II -cyclam complex, the corresponding distance is approximately 4.17 A ˚ (Ichimaru et al., 2022).As discussed earlier, the nitrogen atoms of the cyclam are not situated in the same plane.The coordination structure of the zinc(II) ion is a distorted square pyramid.The zinc(II) ion is located 0.5034 (18) A ˚vertically above the centroid of the mean plane formed by the nitrogen atoms of the cyclam.
FU À molecules engage in intermolecular hydrogen bonding with neighboring FU À molecules (Fig. 3).In addition, there are intramolecular hydrogen bonds between the carbonyl groups and the NH moieties of the cyclam.The perchlorate ion forms hydrogen bonds to two different cyclam rings.Table 1 provides Zn(C 4 H 2 FN 2 O 2 )(C 10 H 24 N 4 )]ClO 4 IUCrData (2024).9, x240431

Figure 1
The title complex with displacement ellipsoids drawn at the 50% probability level.C-bound H atoms and a perchlorate ion are omitted for clarity.

Figure 2
The coordination structure of Zn1 showing with displacement ellipsoids drawn at the 50% probability level.Bond angles and bond lengths are shown in red and black, respectively.
N6-H6 group, which is not coordinated with the cyclam, and the oxygen atom (O2) of the carbonyl group adjacent to the N6-H6 group.Similar hydrogen-bond formations are observed in complexes of FU À and zinc(II) ions other than the title complex (Icsel et al., 2022).Even in crystals where a complex has not formed, two FU molecules form a hydrogen bond similar to that in the title compound (Hulme & Tocher, 2004).However, the N-H group participating in this hydrogen bonding is different from that of the title compound, that is, a more acidic N-H is involved in the hydrogen bond.
In the title complex, the highly acidic hydrogen atom is released, allowing another N-H to form a hydrogen bond.In polyamine complexes such as Zn II -cyclen and Zn II -cyclam, the N-H group involved in ring formation can contribute to the hydrogen bonding network with counter anions and/or ligands (Ichimaru et al., 2021;Donaghy et al., 2023).In our previously reported complex of FU À bound to Zn II -cyclen, the carbonyl oxygen of FU À formed hydrogen bonds with the N-H of cyclen and a perchlorate ion (Ichimaru et al., 2023).
The torsion angles between the two carbonyl groups of FU À and the two pairs of nitrogen atoms (N1 and N3, N2, and N4) located diagonally across the zinc(II) ion are O1-O2-N3-N1 = À 25.84 (8) � and O2-O1-N2-N4 = À 76.57 (11) � .This indicates that the two carbonyl groups are not aligned parallel to either of the two pairs of nitrogen atoms situated at opposite angles.A packing diagram is provided in Fig. 4.Besides the aforementioned hydrogen bonding, no other intermolecular interactions were observed.

Synthesis and crystallization
[Zn II -cyclam](ClO 4 ) 2 was synthesized using a previously reported method (Tyson et al., 1990).5-Fluorouracil (60.0 mg, 0.46 mmol) in 4.54 ml of H 2 O, 0.46 ml of 1 mol L À 1 NaOH aq was added to clarify the suspension.After stirring at room temperature for 30 min, a solution of aqueous [Zn IIcyclam](ClO 4 ) 2 (107.1 mg, 0.23 mmol, 2.0 ml) was added dropwise to the reaction mixture; it was then stirred at 323 K for 4 h.Subsequently, the reaction mixture was filtered through a cellulose acetate filter (0.22-mm pore size) and then allowed to stand overnight at room temperature.Colorless crystals suitable for X-ray crystallographic analysis were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Special details
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.All hydrogen atoms were located by a geometrical calculation, and were not refined.

Fractional atomic coordinates and isotropic
a summary of numerical data related to hydrogen bonding.The hydrogen bonding involves the data reports 2 of 4 Ichimaru et al. � [

Figure 3 Figure 4
Figure 3The intermolecular hydrogen-bonding interactions of the title complex with displacement ellipsoids drawn at the 50% probability level.C-bound H atoms are omitted for clarity.Hydrogen-bonding interactions are shown as dotted lines.[Symmetry code: (i) 1 À x, 1 À y, 1 À z.]

Table 2
Experimental details.