Crystal structure of a homoleptic zinc(II) complex based on bis­(3,5-diiso­propyl­pyrazol-1-yl)acetate

Elsberg, J.G.; Spiropulos, N.G.; Colson, A.C.; Brown, E.C.

doi:10.1107/S2056989018011246

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Volume 74| Part 9| September 2018| Pages 1259-1262

https://doi.org/10.1107/S2056989018011246

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Crystal structure of a homoleptic zinc(II) complex based on bis(3,5-diisopropylpyrazol-1-yl)acetate

Josiah G. Elsberg,^a Nicholas G. Spiropulos,^a Adam C. Colson ^a and Eric C. Brown ^a ^*

^aDepartment of Chemistry and Biochemistry, Boise State University, 1910 University Drive, Boise, ID 83725, USA
^*Correspondence e-mail: ericbrown3@boisestate.edu

Edited by J. Jasinsk, Keene State College, USA (Received 13 July 2018; accepted 6 August 2018; online 16 August 2018)

Deprotonation of the methylene group in bis(3,5-diisopropylpyrazol-1-yl)methane with nBuLi and reaction with carbon dioxide yields lithium bis(3,5-diisopropylpyrazol-1-yl)acetate (1). Treatment of 1 with ZnCl₂ results in the compound bis[bis(3,5-diisopropylpyrazol-1-yl)acetato]zinc(II), [Zn(C₂₀H₃₁N₄O₂)₂] (2), whose structure has monoclinic (P2₁/c) symmetry. The Zn^II ion resides on an inversion center and is coordinated by two bis(3,5-diisopropylpyrazol-1-yl)acetate (bdippza) ligands. Each ligand facially coordinates the zinc center via κ³N,N′,O coordination modes to form a distorted octahedral complex with four pyrazole N atoms in the basal plane and two carboxylate O atoms in the axial sites.

Keywords: crystal structure; zinc; heteroscorpionate ligands.

CCDC reference: 1860544

1. Chemical context

The closely related zinc-containing enzymes thermolysin (Holland et al., 1995 ) and carboxypeptidase A (Rees et al., 1983 ) each contain an active site where a distorted tetrahedral zinc ion is coordinated to two histidine residues, a glutamate residue, and a water molecule. These enzymes catalyze the hydrolysis of peptide bonds containing hydrophobic residues with thermolysin selective for the amide bonds located on the N-terminal side of the polypeptide (Heinrikson, 1977 ), while carboxypeptidase A prefers the amide bonds on the C-terminal side (Lipscomb, 1970 ). However, questions remain concerning the mechanism of amide-bond hydrolysis by thermolysin and carboxypeptidase A. As such, the synthesis and study of model complexes that mimic the active-site structure and reactivity of these biological compounds is necessary to their further understanding.

In an attempt to model the two histidine and glutamate binding motifs present in thermolysin and carboxypeptidase A, the coordination chemistry of bis(3,5-diisopropylpyrazol-1-yl)acetate (bdippza) with zinc chloride was explored to determine if the steric demands of the anionic heteroscorpionate ligand were suitable to form a zinc complex of the form [(bdippza)ZnCl]. However, structural determination of the title compound identified the product not as the target compound but instead as the homoleptic zinc compound [(bdippza)₂Zn] (2). Formation of 2 occurs regardless of the stoichiometric ratio and indicates that the steric environment of the bdippza ligand is too small to prevent complexation of two ligands per zinc ion. Spectroscopic characterization of 2 is consistent with the solid-state structure. For instance, identification of the acetate group is evident by a strong IR absorption at 1687 cm⁻¹ and a ¹³C NMR signal at 165.8 ppm (the carbon peak of the carboxylate was identified by an HMBC experiment that showed a two-bond correlation between the proton of the bridging C atom and the C atom of the carboxylate). Furthermore, the positive-ion ESI–MS spectrum of 2 shows the presence of the [M + Na]⁺ ion, whose isotope pattern is in good agreement with the theoretical isotope pattern of the compound (see supporting information for ESI–MS spectra and 1D and 2D NMR spectra).

2. Structural commentary

The molecular structure of the title complex is shown in Fig. 1. Selected bond lengths and angles are given in Table 1. The Zn^II ion resides on an inversion center and is coordinated by two bdippza ligands to form a six-coordinate complex. The two ligands facially bind the Zn^II ion in a tridentate fashion, with four N atoms making up the basal plane of the distorted octahedron and the two carboxylate oxygens binding the Zn^II at the remaining apical positions in a trans manner (O—Zn—O angle of 180.0°). The Zn—N_pyrazole bond lengths range from 2.1674 (11) to 2.1942 (12) Å and the N—Zn—N angles of the basal plane range from 82.91 (4) to 97.09 (4)°. The apical O atoms are positioned approximately perpendicular to the basal plane, with angles that deviate slightly from 90° [O1—Zn1—N1 = 86.51 (4), O1—Zn1—N1ⁱ = 93.49 (4), O1—Zn1—N4 = 86.40 (4) and O1—Zn1—N4ⁱ = 93.60 (4)°]. The Zn—O bond length is 2.0471 (10) Å. The carbonyl oxygen of the carboxylate donor is tilted away from the zinc carboxylate plane, as indicated by the Zn1—O1—C8—C4 torsion angle of 20.61 (16)°. Complexation of the two bdippza ligands to the Zn^II ion results in the formation of six six-membered metallocycles [Zn1–O1–C8–C4–N2–N1 (A), Zn1–O1–C8–C4–N3–N4 (B), Zn1–N1–N2–C4–N3–N4 (C), Zn1–O1ⁱ–C8ⁱ–C4ⁱ–N2ⁱ–N1ⁱ (D), Zn1–O1ⁱ–C8ⁱ–C4ⁱ–N3ⁱ–N4ⁱ (E), and Zn1–N1ⁱ–N2ⁱ–C4ⁱ–N3ⁱ–N4ⁱ (F)] that are all nonplanar. A ring-puckering analysis [puckering parameters are: Q = 0.9102 (12), θ = 85.76 (8)°, ψ = 346.77 (8)° for A, Q = 0.8809 (11), θ = 96.27 (8)°, ψ = 190.62 (8)° for B, Q = 0.9932 (11), θ = 80.32 (7)°, ψ = 350.91 (7)° for C, Q = 0.9102 (12), θ = 94.24 (8)°, ψ = 166.77 (8)° for D, Q = 0.8809 (11), θ = 83.73 (8)°, ψ = 10.62 (8)° for E, and Q = 0.9932 (11), θ = 99.68 (7)°, ψ = 170.91 (7)° for F] is consistent with each of the metallocycles being described as having a twist-boat conformation (Cremer et al., 1975 ). The dihedral angle between the mean planes of the two five-membered pyrazole rings found on the same bdippza ligand (Cg1 and Cg2) is 118.36°, while the dihedral angle between the mean planes of the imidazole rings Cg1 and Cg2ⁱ, which are on different bdippza ligands, is 61.64°.

Table 1
Selected geometric parameters (Å, °)

Zn1—O1	2.0472 (10)	Zn1—N1	2.1941 (12)
Zn1—N4	2.1674 (11)

O1—Zn1—N4	86.40 (4)	N4—Zn1—N1	82.91 (4)
O1—Zn1—N4ⁱ	93.60 (4)	O1—Zn1—N1ⁱ	93.49 (4)
O1—Zn1—N1	86.51 (4)	N4—Zn1—N1ⁱ	97.09 (4)
Symmetry code: (i) -x, -y, -z+1.

Figure 1
A view of the structure of the title compound, showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level. Symmetry code for generating equivalent atoms: (i) −x, −y, −z + 1.

3. Supramolecular features

Within the crystal, close intermolecular C—H⋯O contacts are present between molecules, which result in the molecules being packed in columns along the a axis. The weak C—H⋯O intermolecular contacts consist of the carboxylate oxygen (O2) at (x, y, z) acting as a hydrogen-bond acceptor to three C—H bonds (C4—H4, C12—H12, and C15—H15) on an adjacent complex at (−1 − x, −y, 1 − z), as shown in Fig. 2. Within each complex, weak π-stacking interactions between the imidazole rings (Cg1⋯Cg2) on the same bdippza ligand are observed. Furthermore, a weak slipped-parallel C—H⋯π (C9—H9⋯Cg2, X—H, π = 60°) interaction is present. Full details of the hydrogen-bonding geometries and π–π interactions are provided in Table 2.

Table 2
Hydrogen-bonding geometry and π–π interactions (Å, °)

Cg1 and Cg2 are the centroids of the N1/N2/C3/C2/C1 and N3/N4/C7/C6/C5 rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C4—H4⋯O2ⁱ	0.95	2.44	3.3883 (18)	172
C12—H12⋯O2ⁱ	0.94	2.34	3.223 (2)	156
C15—H15⋯O2ⁱ	0.94	2.44	3.229 (2)	141
Cg1⋯Cg2			4.2001 (9)
C9—H9⋯Cg2	0.99	2.97	3.9410 (18)	168
Symmetry code: (i) −x − 1, −y, −z + 1.

Figure 2
A partial unit-cell packing diagram, showing the weak C—H⋯O intermolecular interactions (dashed lines). For clarity, only H atoms involved in the C—H⋯O interactions between adjacent molecules have been included.

4. Database survey

Three related homoleptic Zn^II compounds containing different substituted bis(3,5-dialkylpyrazol-1-yl)acetate supporting ligands [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate and bpa^tBu2,Me2 = 3,5-di-tert-butyl-1-(3,5-dimethyl-1H-pyrazol-1-yl)acetate] have been characterized crystallographically (Pockaj et al., 2015 ; Hegelmann et al., 2003 ; Beck et al., 2001 ). The Zn—O bond length in 2 [2.0472 (10) Å] is shorter compared to [(bdmpza)₂Zn]·3H₂O (Beck et al., 2001) and [(bdmpza)₂Zn]·2H₂O (Pockaj et al., 2015), which reported Zn—O bond lengths of 2.119 (3) and 2.100 (2) Å, respectively. The longer Zn—O bond lengths in the hydrated [(bdmpza)₂Zn]·xH₂O complexes are a consequence of O—H⋯H hydrogen-bonding interactions between the carboxylate carbonyl O atoms and cocrystallized water molecules that link adjacent coordination molecules to form infinite chains. Compound 2 does not contain cocrystallized water or solvent. Conversely, the Zn—O distance in 2 is longer by 0.04 Å compared to [(bpa^tBu2,Me2)₂Zn] (Hegelmann et al., 2003), which has a Zn—O bond length of 2.006 (3) Å. The difference in bond lengths arises from [(bpa^tBu2,Me2)₂Zn] having a distorted square-pyramidal environment instead of a distorted octahedral coordination due to one of the 3,5-di-tert-butylpyrazol-1-yl groups having a weak interaction with the zinc ion.

5. Synthesis and crystallization

5.1. General

All reactions were performed using standard Schlenk techniques under a nitrogen atmosphere. The tetrahydrofuran (THF) solvent was distilled from sodium/benzophenone ketyl, while methanol was distilled from CaH₂. NMR spectra were recorded on a Bruker AVANCE III 600 NMR. Chemical shifts are expressed in parts per million (ppm) and referenced to residual solvent as the internal reference for ¹H (CDCl₃; δ = 7.24 ppm) and ¹³C (CDCl₃; δ = 77.16 ppm). IR spectra were measured using a PerkinElmer Spectrum 100 spectrometer. Electrospray mass spectra were recorded on a Bruker HCTultra ETD II mass spectrometer. Bis(3,5-diisopropylpyrazol-1-yl)methane was prepared according to a previously reported procedure (Spiropulos et al., 2011 ).

5.2. Preparation of lithium bis(3,5-diisopropylpyrazol-1-yl)acetate, [Li(bdippza)] (1)

To a solution of bis(3,5-diisopropylpyrazol-1-yl)methane (0.5 g, 1.6 mmol) dissolved in dry THF (40 ml) was added nBuLi (1.6 M, 1.5 ml, 2.4 mmol) in hexane at 195 K. After 1 h of stirring, carbon dioxide was bubbled through the solution at 233 K for 30 min. The solution then was allowed to reach ambient temperature and stirred for 2 h before the volume was reduced to 3 ml under reduced pressure. Addition of hexane (10 ml) resulted in the formation of a white solid, which was filtered off, washed with hexane (2 × 5 ml) and dried under reduced pressure (0.27 g, 47%). ¹H NMR (CDCl₃): δ 6.59 (s, 1H), 5.80 (s, 2H), 3.06 (heptet, J = 6.8 Hz, 2H), 2.83 (heptet, J = 6.9 Hz, 2H), 1.31 (d, J = 6.8 Hz, 6H), 1.23 (d, J = 6.8 Hz, 6H), 1.05 (d, J = 6.9 Hz, 6H), 0.98 (d, J = 6.9 Hz, 6H). FT–IR (ATR, cm⁻¹): 2966 (m), 2930 (m), 2870 (m), 1676 (m), 1643 (s), 1551 (m), 1458 (m), 1408 (m), 1373 (m), 1310 (m), 1284 (m), 1226 (m), 1181 (m), 1104 (m), 1073 (m), 1060 (m), 1012 (m), 912 (m), 861 (m), 792 (s), 771 (m), 738 (m), 723 (m), 686 (m). MS (ESI, neg): m/z found for [C₂₀H₃₁N₄O₂ −Li]⁻, 359; [C₁₉H₃₁N₄ − Li − CO₂]⁻, 315.

5.3. Preparation of [(bdippza)₂Zn]

ZnCl₂ (0.015 g, 0.11 mmol) was added to [Li(bdippza)] (1) (0.083 g, 0.23 mmol) in dry MeOH (15 ml). The reaction was stirred for 24 h, during which time a white solid formed. The solvent was removed under reduced pressure, dichloromethane (15 ml) was added, and the solution filtered through celite. The volume was reduced (∼3 ml) and addition of hexane (10 ml) caused the formation of a white solid. The solid was collected, washed with hexane (2 × 5 ml), and dried under vacuum (0.069 g, 78%). Colorless crystals suitable for crystallographic characterization were obtained by hexane diffusion into THF at room temperature. ¹H NMR (CDCl₃): δ 6.56 (s, 2H, CH), 6.00 (s, 4H, H_pz), 3.59–3.47 (m, 4H, CH-ⁱPr), 3.02 (heptet, J = 6.8 Hz, 4H, CH-ⁱPr), 1.37 (d, J = 6.8 Hz, 12H, CH₃-ⁱPr), 1.30 (d, J = 6.8 Hz, 12H, CH₃-ⁱPr), 1.19 (d, J = 6.9 Hz, 12H, CH₃-ⁱPr), 1.02 (d, J = 6.9 Hz, 12H, CH₃-ⁱPr). ¹³C NMR (CDCl₃): δ 165.8 (CO₂⁻), 163.9 (C_pz), 154.6 (C_pz), 99.6 (C_pz), 67.0 (CH), 27.2 (CH-ⁱPr), 25.9 (CH-ⁱPr), 23.3(CH₃-ⁱPr), 22.8 (CH₃-ⁱPr), 22.4 (CH₃-ⁱPr), 22.1 (CH₃-ⁱPr). FT–IR (ATR, cm⁻¹): 2966 (m), 2932 (m), 2871 (m), 1687 (s, CO₂⁻), 1552 (m, C=N), 1475 (m), 1460 (m), 1409 (m), 1356 (s), 1315 (m), 1292 (m), 1252 (m), 1184 (m), 1088 (m), 1059 (m), 1024 (m), 910 (m), 854 (m), 798 (s), 778 (s), 724 (m), 692 (s). MS (ESI, pos): m/z found for [C₄₀H₆₂N₈O₄Zn + Na]⁺, 805.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3.

Table 3
Experimental details

Crystal data
Chemical formula	[Zn(C₂₀H₃₁N₄O₂)₂]
M_r	784.35
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	150
a, b, c (Å)	10.1806 (1), 16.9578 (3), 12.4534 (2)
β (°)	96.9735 (10)
V (Å³)	2134.06 (6)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	0.62
Crystal size (mm)	0.25 × 0.18 × 0.13

Data collection
Diffractometer	Nonius KappaCCD
Absorption correction	Multi-scan (DENZO-SMN; Otwinowski & Minor, 1997 )
T_min, T_max	0.860, 0.923
No. of measured, independent and observed [I > 2σ(I)] reflections	9825, 5072, 3881
R_int	0.033
(sin θ/λ)_max (Å⁻¹)	0.658

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.033, 0.075, 1.03
No. of reflections	5072
No. of parameters	365
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.28, −0.41
Computer programs: COLLECT (Nonius, 1998 ), DENZO-SMN (Otwinowski & Minor, 1997), SIR97 (Altomare et al., 1999 ), SHELXL97 (Sheldrick, 2008 ) and WinGX and ORTEP-3 (Farrugia, 2012 ).

Supporting information

CCDC reference: 1860544

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989018011246/jj2201sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989018011246/jj2201Isup2.hkl

NMR (1H, 13C{1H}, HMBC, HSQC and COSY) and ESI-MS spectra for the titled compound are provided. DOI: https://doi.org/10.1107/S2056989018011246/jj2201sup3.pdf

checkCIF report

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: WinGX (Farrugia, 2012) and ORTEP-3 (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Bis[bis(3,5-diisopropylpyrazol-1-yl)acetato]zinc(II) top

Crystal data top

[Zn(C₂₀H₃₁N₄O₂)₂]	F(000) = 840
M_r = 784.35	D_x = 1.221 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 8352 reflections
a = 10.1806 (1) Å	θ = 1.0–20.4°
b = 16.9578 (3) Å	µ = 0.62 mm⁻¹
c = 12.4534 (2) Å	T = 150 K
β = 96.9735 (10)°	Prism, colorless
V = 2134.06 (6) Å³	0.25 × 0.18 × 0.13 mm
Z = 2

Data collection top

Nonius KappaCCD diffractometer	5072 independent reflections
Radiation source: fine-focus sealed tube	3881 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.033
Phi and ω scan	θ_max = 27.9°, θ_min = 2.4°
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997)	h = −13→13
T_min = 0.860, T_max = 0.923	k = −22→22
9825 measured reflections	l = −16→16

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.075	All H-atom parameters refined
S = 1.03	w = 1/[σ²(F_o²) + (0.0287P)² + 0.6212P] where P = (F_o² + 2F_c²)/3
5072 reflections	(Δ/σ)_max < 0.001
365 parameters	Δρ_max = 0.28 e Å⁻³
0 restraints	Δρ_min = −0.41 e Å⁻³

Special details top

Experimental. The program Denzo-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm (Fox & Holmes, 1966) which effectively corrects for absorption effects. High redundancy data were used in the scaling program hence the 'multi-scan' code word was used. No transmission coefficients are available from the program (only scale factors for each frame). The scale factors in the experimental table are calculated from the 'size' command in the SHELXL-97 input file.

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. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2sigma(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	U_iso*/U_eq
Zn1	0.0000	0.0000	0.5000	0.01725 (8)
O1	−0.17165 (10)	−0.05936 (6)	0.44996 (8)	0.0209 (2)
O2	−0.39140 (10)	−0.04825 (7)	0.41634 (9)	0.0265 (3)
N1	−0.11682 (11)	0.10849 (7)	0.47319 (9)	0.0176 (3)
N2	−0.23516 (11)	0.10762 (7)	0.51632 (9)	0.0163 (3)
N3	−0.20337 (11)	0.00927 (7)	0.65508 (9)	0.0173 (3)
N4	−0.06882 (11)	0.00496 (7)	0.65787 (9)	0.0182 (3)
C1	−0.10013 (14)	0.18293 (9)	0.44361 (12)	0.0202 (3)
C2	−0.20742 (15)	0.22944 (9)	0.46651 (13)	0.0230 (3)
C3	−0.29170 (14)	0.18053 (9)	0.51367 (12)	0.0184 (3)
C4	−0.28291 (14)	0.03319 (9)	0.55466 (11)	0.0163 (3)
C5	−0.24317 (15)	−0.01243 (9)	0.75104 (11)	0.0201 (3)
C6	−0.12943 (16)	−0.02940 (10)	0.81833 (12)	0.0243 (3)
C7	−0.02332 (15)	−0.01781 (9)	0.75795 (12)	0.0201 (3)
C8	−0.28289 (14)	−0.03104 (9)	0.46471 (11)	0.0168 (3)
C9	0.02168 (16)	0.20845 (10)	0.39572 (14)	0.0283 (4)
C10	−0.0141 (2)	0.26302 (13)	0.29895 (17)	0.0421 (5)
C11	0.11899 (19)	0.24866 (13)	0.48170 (18)	0.0388 (5)
C12	−0.41863 (15)	0.19758 (10)	0.55931 (13)	0.0243 (3)
C13	−0.48545 (18)	0.27096 (11)	0.50744 (18)	0.0360 (4)
C14	−0.3943 (2)	0.20583 (13)	0.68232 (15)	0.0377 (4)
C15	−0.38671 (16)	−0.02061 (11)	0.76703 (13)	0.0267 (4)
C16	−0.4041 (2)	−0.01540 (17)	0.88672 (15)	0.0437 (6)
C17	−0.4420 (2)	−0.09813 (14)	0.71835 (18)	0.0435 (5)
C18	0.12297 (15)	−0.02653 (10)	0.79192 (13)	0.0245 (3)
C19	0.18716 (18)	0.05324 (12)	0.81940 (16)	0.0328 (4)
C20	0.1505 (2)	−0.08334 (12)	0.88676 (16)	0.0361 (4)
H2	−0.2196 (16)	0.2832 (10)	0.4523 (13)	0.024 (4)*
H4	−0.3720 (16)	0.0402 (9)	0.5694 (12)	0.018 (4)*
H6	−0.1259 (16)	−0.0462 (10)	0.8923 (14)	0.027 (4)*
H9	0.0639 (17)	0.1606 (11)	0.3703 (14)	0.031 (5)*
H10A	−0.079 (2)	0.2389 (13)	0.2427 (18)	0.055 (6)*
H10B	0.064 (2)	0.2722 (12)	0.2667 (17)	0.052 (6)*
H10C	−0.0515 (19)	0.3126 (12)	0.3223 (16)	0.043 (6)*
H11A	0.1456 (19)	0.2147 (12)	0.5427 (16)	0.041 (5)*
H11B	0.197 (2)	0.2639 (12)	0.4482 (16)	0.046 (6)*
H11C	0.0797 (19)	0.2952 (11)	0.5102 (15)	0.036 (5)*
H12	−0.4765 (16)	0.1549 (10)	0.5438 (13)	0.019 (4)*
H13A	−0.568 (2)	0.2786 (11)	0.5388 (15)	0.044 (6)*
H13B	−0.504 (2)	0.2641 (13)	0.4277 (18)	0.052 (6)*
H13C	−0.429 (2)	0.3190 (12)	0.5261 (15)	0.044 (5)*
H14A	−0.479 (2)	0.2095 (13)	0.7118 (17)	0.059 (6)*
H14B	−0.344 (2)	0.1589 (12)	0.7184 (15)	0.043 (5)*
H14C	−0.342 (2)	0.2497 (12)	0.7026 (15)	0.039 (5)*
H15	−0.4339 (17)	0.0219 (10)	0.7318 (14)	0.024 (4)*
H16A	−0.498 (2)	−0.0199 (13)	0.8966 (17)	0.054 (6)*
H16C	−0.3739 (19)	0.0372 (12)	0.9114 (15)	0.036 (5)*
H16B	−0.358 (2)	−0.0561 (13)	0.9265 (17)	0.052 (6)*
H17A	−0.432 (2)	−0.0998 (12)	0.6390 (17)	0.051 (6)*
H17B	−0.392 (2)	−0.1428 (12)	0.7557 (16)	0.047 (6)*
H17C	−0.536 (2)	−0.1047 (13)	0.7273 (17)	0.055 (6)*
H18	0.1625 (16)	−0.0474 (10)	0.7325 (13)	0.023 (4)*
H19A	0.1506 (17)	0.0783 (10)	0.8825 (15)	0.032 (5)*
H19B	0.285 (2)	0.0461 (12)	0.8343 (16)	0.050 (6)*
H19C	0.1748 (18)	0.0875 (11)	0.7587 (16)	0.036 (5)*
H20A	0.107 (2)	−0.1343 (13)	0.8722 (16)	0.046 (6)*
H20B	0.117 (2)	−0.0619 (12)	0.9539 (17)	0.049 (6)*
H20C	0.240 (2)	−0.0920 (12)	0.9050 (16)	0.048 (6)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Zn1	0.01007 (11)	0.02354 (14)	0.01834 (12)	0.00096 (10)	0.00251 (9)	−0.00057 (10)
O1	0.0121 (5)	0.0256 (6)	0.0249 (5)	0.0003 (4)	0.0022 (4)	−0.0045 (4)
O2	0.0128 (5)	0.0374 (7)	0.0286 (6)	−0.0035 (5)	0.0005 (5)	−0.0088 (5)
N1	0.0097 (6)	0.0228 (7)	0.0211 (6)	−0.0002 (5)	0.0050 (5)	0.0009 (5)
N2	0.0094 (5)	0.0213 (6)	0.0185 (6)	−0.0001 (5)	0.0031 (5)	−0.0006 (5)
N3	0.0120 (5)	0.0257 (7)	0.0143 (6)	0.0006 (5)	0.0026 (5)	0.0012 (5)
N4	0.0116 (5)	0.0247 (7)	0.0181 (6)	0.0016 (5)	0.0007 (5)	−0.0001 (5)
C1	0.0169 (7)	0.0218 (8)	0.0220 (8)	−0.0037 (6)	0.0027 (6)	−0.0032 (6)
C2	0.0221 (8)	0.0167 (8)	0.0305 (9)	−0.0017 (6)	0.0045 (7)	−0.0029 (6)
C3	0.0141 (7)	0.0205 (8)	0.0198 (7)	0.0004 (6)	−0.0005 (6)	−0.0051 (6)
C4	0.0098 (6)	0.0223 (8)	0.0171 (7)	−0.0004 (6)	0.0027 (6)	0.0023 (6)
C5	0.0194 (7)	0.0265 (9)	0.0148 (7)	−0.0006 (6)	0.0041 (6)	−0.0014 (6)
C6	0.0248 (8)	0.0330 (9)	0.0149 (7)	0.0014 (7)	0.0011 (6)	0.0006 (6)
C7	0.0193 (7)	0.0221 (8)	0.0182 (7)	0.0035 (6)	−0.0005 (6)	−0.0021 (6)
C8	0.0143 (7)	0.0201 (7)	0.0166 (7)	−0.0018 (6)	0.0042 (6)	0.0038 (6)
C9	0.0226 (8)	0.0247 (9)	0.0400 (10)	−0.0060 (7)	0.0139 (8)	0.0004 (7)
C10	0.0447 (12)	0.0462 (13)	0.0372 (11)	−0.0198 (10)	0.0127 (10)	0.0036 (9)
C11	0.0227 (9)	0.0415 (12)	0.0518 (13)	−0.0100 (9)	0.0031 (9)	0.0056 (10)
C12	0.0159 (7)	0.0238 (8)	0.0341 (9)	−0.0004 (7)	0.0064 (7)	−0.0072 (7)
C13	0.0219 (9)	0.0324 (10)	0.0535 (13)	0.0079 (8)	0.0041 (9)	−0.0048 (9)
C14	0.0342 (10)	0.0455 (12)	0.0352 (10)	0.0055 (10)	0.0110 (9)	−0.0117 (9)
C15	0.0202 (8)	0.0436 (11)	0.0174 (7)	−0.0039 (7)	0.0064 (7)	0.0024 (7)
C16	0.0268 (9)	0.0835 (19)	0.0223 (9)	−0.0041 (11)	0.0093 (8)	0.0009 (10)
C17	0.0381 (11)	0.0528 (14)	0.0402 (12)	−0.0201 (10)	0.0079 (10)	0.0006 (10)
C18	0.0205 (8)	0.0310 (9)	0.0206 (8)	0.0072 (7)	−0.0031 (7)	−0.0043 (6)
C19	0.0247 (9)	0.0362 (10)	0.0350 (10)	0.0004 (8)	−0.0066 (8)	−0.0023 (8)
C20	0.0341 (10)	0.0375 (11)	0.0330 (10)	0.0086 (9)	−0.0110 (9)	0.0033 (8)

Geometric parameters (Å, º) top

Zn1—O1ⁱ	2.0471 (10)	C10—H10B	0.94 (2)
Zn1—O1	2.0472 (10)	C10—H10C	0.98 (2)
Zn1—N4	2.1674 (11)	C11—H11A	0.96 (2)
Zn1—N4ⁱ	2.1675 (11)	C11—H11B	0.98 (2)
Zn1—N1	2.1941 (12)	C11—H11C	0.971 (19)
Zn1—N1ⁱ	2.1942 (12)	C12—C13	1.524 (2)
O1—C8	1.2640 (17)	C12—C14	1.528 (2)
O2—C8	1.2275 (17)	C12—H12	0.938 (17)
N1—C1	1.3317 (19)	C13—H13A	0.98 (2)
N1—N2	1.3774 (15)	C13—H13B	0.99 (2)
N2—C3	1.3625 (19)	C13—H13C	1.01 (2)
N2—C4	1.4539 (18)	C14—H14A	0.98 (2)
N3—C5	1.3583 (19)	C14—H14B	1.02 (2)
N3—N4	1.3680 (15)	C14—H14C	0.93 (2)
N3—C4	1.4623 (18)	C15—C16	1.525 (2)
N4—C7	1.3330 (19)	C15—C17	1.526 (3)
C1—C2	1.404 (2)	C15—H15	0.945 (18)
C1—C9	1.503 (2)	C16—H16A	0.98 (2)
C2—C3	1.375 (2)	C16—H16C	0.98 (2)
C2—H2	0.933 (17)	C16—H16B	0.94 (2)
C3—C12	1.5016 (19)	C17—H17A	1.01 (2)
C4—C8	1.562 (2)	C17—H17B	1.00 (2)
C4—H4	0.954 (16)	C17—H17C	0.98 (2)
C5—C6	1.375 (2)	C18—C19	1.523 (2)
C5—C15	1.505 (2)	C18—C20	1.524 (2)
C6—C7	1.403 (2)	C18—H18	0.953 (16)
C6—H6	0.960 (17)	C19—H19A	1.004 (18)
C7—C18	1.505 (2)	C19—H19B	1.00 (2)
C9—C10	1.528 (3)	C19—H19C	0.949 (19)
C9—C11	1.528 (3)	C20—H20A	0.98 (2)
C9—H9	0.988 (18)	C20—H20B	1.01 (2)
C10—H10A	0.99 (2)	C20—H20C	0.93 (2)

O1ⁱ—Zn1—O1	180.0	C9—C10—H10C	110.5 (12)
O1ⁱ—Zn1—N4	93.60 (4)	H10A—C10—H10C	108.5 (18)
O1—Zn1—N4	86.40 (4)	H10B—C10—H10C	111.1 (17)
O1ⁱ—Zn1—N4ⁱ	86.40 (4)	C9—C11—H11A	112.4 (12)
O1—Zn1—N4ⁱ	93.60 (4)	C9—C11—H11B	108.1 (12)
N4—Zn1—N4ⁱ	180.0	H11A—C11—H11B	109.2 (16)
O1ⁱ—Zn1—N1	93.49 (4)	C9—C11—H11C	111.0 (12)
O1—Zn1—N1	86.51 (4)	H11A—C11—H11C	106.6 (16)
N4—Zn1—N1	82.91 (4)	H11B—C11—H11C	109.5 (16)
N4ⁱ—Zn1—N1	97.09 (4)	C3—C12—C13	110.93 (14)
O1ⁱ—Zn1—N1ⁱ	86.51 (4)	C3—C12—C14	110.77 (14)
O1—Zn1—N1ⁱ	93.49 (4)	C13—C12—C14	111.10 (15)
N4—Zn1—N1ⁱ	97.09 (4)	C3—C12—H12	108.8 (9)
N4ⁱ—Zn1—N1ⁱ	82.91 (4)	C13—C12—H12	107.8 (10)
N1—Zn1—N1ⁱ	180.00 (3)	C14—C12—H12	107.4 (10)
C8—O1—Zn1	121.05 (9)	C12—C13—H13A	107.5 (12)
C1—N1—N2	105.37 (11)	C12—C13—H13B	110.4 (12)
C1—N1—Zn1	138.76 (10)	H13A—C13—H13B	110.0 (17)
N2—N1—Zn1	114.54 (9)	C12—C13—H13C	110.5 (12)
C3—N2—N1	111.58 (11)	H13A—C13—H13C	107.2 (15)
C3—N2—C4	129.68 (11)	H13B—C13—H13C	111.1 (16)
N1—N2—C4	118.72 (11)	C12—C14—H14A	109.7 (13)
C5—N3—N4	111.59 (11)	C12—C14—H14B	112.4 (11)
C5—N3—C4	129.36 (12)	H14A—C14—H14B	107.7 (16)
N4—N3—C4	119.03 (11)	C12—C14—H14C	111.3 (12)
C7—N4—N3	105.81 (11)	H14A—C14—H14C	110.2 (17)
C7—N4—Zn1	136.30 (10)	H14B—C14—H14C	105.3 (16)
N3—N4—Zn1	114.33 (8)	C5—C15—C16	110.73 (14)
N1—C1—C2	110.35 (13)	C5—C15—C17	110.12 (15)
N1—C1—C9	121.44 (13)	C16—C15—C17	110.92 (16)
C2—C1—C9	128.20 (14)	C5—C15—H15	108.4 (10)
C3—C2—C1	106.80 (14)	C16—C15—H15	107.3 (10)
C3—C2—H2	126.4 (10)	C17—C15—H15	109.3 (10)
C1—C2—H2	126.8 (10)	C15—C16—H16A	110.4 (13)
N2—C3—C2	105.90 (12)	C15—C16—H16C	106.8 (11)
N2—C3—C12	123.10 (13)	H16A—C16—H16C	107.8 (16)
C2—C3—C12	130.97 (14)	C15—C16—H16B	111.2 (13)
N2—C4—N3	110.44 (11)	H16A—C16—H16B	108.0 (18)
N2—C4—C8	109.91 (11)	H16C—C16—H16B	112.5 (18)
N3—C4—C8	111.81 (12)	C15—C17—H17A	109.8 (12)
N2—C4—H4	108.6 (10)	C15—C17—H17B	108.9 (12)
N3—C4—H4	108.1 (9)	H17A—C17—H17B	109.3 (16)
C8—C4—H4	107.9 (10)	C15—C17—H17C	111.7 (13)
N3—C5—C6	105.89 (13)	H17A—C17—H17C	108.7 (17)
N3—C5—C15	122.65 (13)	H17B—C17—H17C	108.4 (17)
C6—C5—C15	131.26 (14)	C7—C18—C19	111.02 (14)
C5—C6—C7	106.87 (13)	C7—C18—C20	111.26 (14)
C5—C6—H6	125.2 (10)	C19—C18—C20	110.72 (14)
C7—C6—H6	127.9 (10)	C7—C18—H18	108.4 (10)
N4—C7—C6	109.81 (13)	C19—C18—H18	107.1 (10)
N4—C7—C18	120.72 (13)	C20—C18—H18	108.2 (10)
C6—C7—C18	129.46 (14)	C18—C19—H19A	111.2 (10)
O2—C8—O1	127.38 (14)	C18—C19—H19B	109.0 (12)
O2—C8—C4	116.06 (12)	H19A—C19—H19B	111.2 (15)
O1—C8—C4	116.56 (12)	C18—C19—H19C	110.6 (11)
C1—C9—C10	110.96 (15)	H19A—C19—H19C	109.8 (15)
C1—C9—C11	110.26 (14)	H19B—C19—H19C	104.8 (16)
C10—C9—C11	110.77 (15)	C18—C20—H20A	112.2 (12)
C1—C9—H9	107.6 (10)	C18—C20—H20B	111.5 (12)
C10—C9—H9	108.5 (10)	H20A—C20—H20B	106.3 (16)
C11—C9—H9	108.7 (10)	C18—C20—H20C	111.9 (13)
C9—C10—H10A	112.5 (13)	H20A—C20—H20C	108.7 (17)
C9—C10—H10B	107.7 (13)	H20B—C20—H20C	105.9 (17)
H10A—C10—H10B	106.6 (17)

O1ⁱ—Zn1—O1—C8	16 (15)	C1—C2—C3—C12	177.01 (15)
N4—Zn1—O1—C8	53.53 (11)	C3—N2—C4—N3	−109.26 (15)
N4ⁱ—Zn1—O1—C8	−126.47 (11)	N1—N2—C4—N3	72.21 (15)
N1—Zn1—O1—C8	−29.57 (11)	C3—N2—C4—C8	126.92 (15)
N1ⁱ—Zn1—O1—C8	150.43 (11)	N1—N2—C4—C8	−51.62 (16)
O1ⁱ—Zn1—N1—C1	31.57 (15)	C5—N3—C4—N2	128.41 (15)
O1—Zn1—N1—C1	−148.43 (15)	N4—N3—C4—N2	−53.40 (16)
N4—Zn1—N1—C1	124.77 (15)	C5—N3—C4—C8	−108.87 (16)
N4ⁱ—Zn1—N1—C1	−55.23 (15)	N4—N3—C4—C8	69.32 (15)
N1ⁱ—Zn1—N1—C1	−92 (11)	N4—N3—C5—C6	1.46 (17)
O1ⁱ—Zn1—N1—N2	−132.72 (9)	C4—N3—C5—C6	179.76 (14)
O1—Zn1—N1—N2	47.28 (9)	N4—N3—C5—C15	−173.97 (13)
N4—Zn1—N1—N2	−39.52 (9)	C4—N3—C5—C15	4.3 (2)
N4ⁱ—Zn1—N1—N2	140.48 (9)	N3—C5—C6—C7	−0.73 (17)
N1ⁱ—Zn1—N1—N2	104 (11)	C15—C5—C6—C7	174.15 (16)
C1—N1—N2—C3	0.03 (15)	N3—N4—C7—C6	1.08 (16)
Zn1—N1—N2—C3	169.36 (9)	Zn1—N4—C7—C6	−155.28 (12)
C1—N1—N2—C4	178.82 (12)	N3—N4—C7—C18	−178.12 (13)
Zn1—N1—N2—C4	−11.85 (15)	Zn1—N4—C7—C18	25.5 (2)
C5—N3—N4—C7	−1.60 (16)	C5—C6—C7—N4	−0.23 (18)
C4—N3—N4—C7	179.91 (12)	C5—C6—C7—C18	178.88 (15)
C5—N3—N4—Zn1	160.70 (10)	Zn1—O1—C8—O2	159.40 (12)
C4—N3—N4—Zn1	−17.80 (15)	Zn1—O1—C8—C4	−20.61 (16)
O1ⁱ—Zn1—N4—C7	−57.11 (15)	N2—C4—C8—O2	−104.57 (14)
O1—Zn1—N4—C7	122.89 (15)	N3—C4—C8—O2	132.40 (13)
N4ⁱ—Zn1—N4—C7	−160 (6)	N2—C4—C8—O1	75.44 (16)
N1—Zn1—N4—C7	−150.19 (15)	N3—C4—C8—O1	−47.58 (16)
N1ⁱ—Zn1—N4—C7	29.81 (15)	N1—C1—C9—C10	136.65 (16)
O1ⁱ—Zn1—N4—N3	147.94 (9)	C2—C1—C9—C10	−45.1 (2)
O1—Zn1—N4—N3	−32.06 (9)	N1—C1—C9—C11	−100.24 (18)
N4ⁱ—Zn1—N4—N3	45 (6)	C2—C1—C9—C11	78.0 (2)
N1—Zn1—N4—N3	54.86 (9)	N2—C3—C12—C13	−157.28 (15)
N1ⁱ—Zn1—N4—N3	−125.13 (9)	C2—C3—C12—C13	25.2 (2)
N2—N1—C1—C2	−0.58 (16)	N2—C3—C12—C14	78.85 (19)
Zn1—N1—C1—C2	−165.78 (11)	C2—C3—C12—C14	−98.7 (2)
N2—N1—C1—C9	177.97 (13)	N3—C5—C15—C16	−159.12 (17)
Zn1—N1—C1—C9	12.8 (2)	C6—C5—C15—C16	26.7 (3)
N1—C1—C2—C3	0.91 (18)	N3—C5—C15—C17	77.8 (2)
C9—C1—C2—C3	−177.51 (15)	C6—C5—C15—C17	−96.3 (2)
N1—N2—C3—C2	0.52 (16)	N4—C7—C18—C19	79.98 (18)
C4—N2—C3—C2	−178.10 (13)	C6—C7—C18—C19	−99.0 (2)
N1—N2—C3—C12	−177.54 (13)	N4—C7—C18—C20	−156.22 (15)
C4—N2—C3—C12	3.8 (2)	C6—C7—C18—C20	24.8 (2)
C1—C2—C3—N2	−0.84 (16)

Symmetry code: (i) −x, −y, −z+1.

Hydrogen-bonding geometry and π–π interactions (Å, °) top

Cg1 and Cg2 are the centroids of the N1/N2/C3/C2/C1 and N3/N4/C7/C6/C5 rings, respectively.

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4···O2ⁱ	0.95	2.44	3.3883 (18)	172
C12—H12···O2ⁱ	0.94	2.34	3.223 (2)	156
C15—H15···O2ⁱ	0.94	2.44	3.229 (2)	141
Cg1···Cg2			4.2001 (9)
C9—H9···Cg2	0.99	2.97	3.9410 (18)	168

Symmetry code: (i) -x-1, -y, -z+1.

Acknowledgements

We gratefully acknowledge Dr Atta M. Arif at the University of Utah for X-ray structural data collection and refinement. The Boise State University NMR facility instrumentation was purchased through an NSF CRIF-MU/RUI grant and departmental funding.

Funding information

Funding for this research was provided by: NSF CRIF-MU/RUI grant (grant No. 0639251, for the purchase of The Boise State University NMR facility instrumentation); National Science Foundation (grant No. 0923535, for support of mass spectrometry services); Institutional Development Awards (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health (grant Nos. P20GM103408 and P20GM109095).

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