Crystal structures of dimetal terephthalate di-hydroxides, M 2(C8H4O4)(OH)2 (M = Co, Ni, Zn) from powder diffraction data and DFT calculations.

The crystal structure of poly[di-hydroxido(μ6-terepthalato)dizinc], [Zn2(C8H4O4)(OH)2] n , was solved and refined using synchrotron powder data, and the structures of the isostructural Co and Ni analogues were refined using laboratory powder X-ray data. The structure of [Co2(C8H4O4)(OH)2] n has been reported previously in space group C2/m, which yields disordered terephthalate anions. Doubling the c-axis of that cell results in an ordered model in space group C2/c. The octa-hedral MO6 coordination polyhedra of the metal cations share edges, forming chains running parallel to the b-axis direction. These chains share corners (hydroxyl groups), forming layers lying perpendicular to the a-axis direction. © Markun et al. 2022.

Chemical context

Dicobalt terephthalate di­hydroxide, Co2(C8H4O4)(OH)2, was first prepared by Sherif (1970 ▸). A powder pattern was reported, but no unit cell or crystal structure were determined. The powder pattern from this reference is included in the Powder Diffraction File (Gates-Rector & Blanton, 2019 ▸) as entry 00-034-1897. A search of the nine peaks of this entry against the PDF-4 Organics 2022 database yielded no additional terephthalate compounds.

Approximately 20 years ago, one of us (JAK) solved and refined the structure of Zn2(C8H4O4)(OH)2 using synchrotron powder data, first in a C2/m cell with disordered terephthalate anions. It then became apparent that if the c-axis were doubled, the systematic absences corresponded to space group C2/c. This doubled unit cell removed the disorder and yielded a more satisfactory refinement. This structure was deposited in the Cambridge Structural Database (Kaduk, 2016 ▸; refcode PUCYAO01), but never otherwise published or discussed. Since that time, another polymorph of Zn2(C8H4O4)(OH)2 (in space group P21/c) has been reported (Carton et al., 2009 ▸; PUCYAO).

Some of our recent attempts to prepare Co and Ni porous metal–organic frameworks (MOFs) yielded instead cobalt and nickel terephthalate hydroxide. We took advantage of the opportunity to re-refine the structures (as well as that of Zn) in what we believe to be the correct space group, and to optimize the structures using density functional techniques.

Structural commentary

Doubling the c-axis of the previously reported disordered C2/m model for Co results in a chemically-reasonable ordered C2/c structure for these compounds. The X-ray powder diffraction patterns show that the three compounds are isostructural (Fig. 1 ▸). The root-mean-square Cartesian displacements of the non-H atoms in the Rietveld-refined and DFT-optimized structures are 0.125, 0.143, and 0.339 Å for Co, Ni, and Zn, respectively (Figs. 2 ▸–4 ▸ ▸). The good agreement provides strong evidence that the structures are correct (van de Streek & Neumann, 2014 ▸). This discussion concentrates on the DFT-optimized structures. The asymmetric unit (with atom numbering) is illustrated in Fig. 5 ▸. The best view of the crystal structure is down the b-axis (Fig. 6 ▸). A view down the c-axis is shown in Fig. 7 ▸.

Figure 1

The X-ray powder diffraction patterns of Co2(C8H4O4)(OH)2 (black), Ni2(C8H4O4)(OH)2 (green), and Zn2(C8H4O4)(OH)2 (red). The Zn pattern (measured using Co radiation) and the Zn pattern (measured using synchrotron radiation) were converted to the Mo wavelength used to measure the Co pattern using JADE Pro (MDI, 2021 ▸).

Figure 2

Comparison of the Rietveld-refined (red) and VASP-optimized (blue) structures of Co2(C8H4O4)(OH)2. The r.m.s. Cartesian displacement is 0.125 Å.

Figure 3

Comparison of the Rietveld-refined (red) and VASP-optimized (blue) structures of Ni2(C8H4O4)(OH)2. The r.m.s. Cartesian displacement is 0.143 Å.

Figure 4

Comparison of the Rietveld-refined (red) and VASP-optimized (blue) structures of Zn2(C8H4O4)(OH)2. The r.m.s. Cartesian displacement is 0.339 Å.

Figure 5

The asymmetric unit of Co2(C8H4O4)(OH)2, with the atom numbering. The atoms are represented by 50% probability spheroids.

Figure 6

The crystal structure of Co2(C8H4O4)(OH)2, viewed down the b-axis direction.

Figure 7

The crystal structure of Co2(C8H4O4)(OH)2, viewed down the c-axis direction.

Almost all of the bond distances, angles, and torsion angles in the terephthalate anions fall within the normal ranges indicated by a Mercury Mogul Geometry check (Macrae et al., 2020 ▸). Only the Ni9—O11 bond distance of 2.187 Å [average = 2.007 (9) Å, Z-score = 20.4] and the Zn14—O16 bond of 1.970 Å [average = 2.122 (47) Å, Z-score = 3.2] are flagged as unusual. The carbox­yl–phenyl torsion angles of 7.5, 9.8, and 6.2° for Co, Ni, and Zn, respectively, correspond to a distortion energy of only ∼2 kJ mol−1 (Kaduk et al., 1999 ▸). This energy penalty can easily be compensated for by coordination to the cations. The closest Miller plane of the phenyl ring is (85 ) for Co and Ni, and (530) for Zn. M9 lies on a center of symmetry, and M10 lies on a twofold axis. For M = Co, Co9 has two shorter Co—O distances of 2.000 Å, and four longer ones ∼2.19–2.20 Å. Co10 has four distances ∼2.11 Å, and two at 2.157 Å. For M = Ni, all six distances to Ni9 are 2.187–2.232 Å, and Ni10 has four shorter distances at 2.03–2.08 Å and two longer at 2.115 Å. For M = Zn, Zn9 has two short distances of 1.969 Å, and four long ones at ∼2.22 Å whereas Zn10 has two distances of 2.095 Å and four at 2.14–2.18 Å. Both Co9 and Co10 exhibit octa­hedral coordination. The coordination sphere of Co9 contains two trans O7 and four equatorial O11 (hydroxyl group), while Co10 has two trans O11 and four equatorial O8. The hydroxyl group bridges three cobalt atoms: one Co9 and two Co10. Atom O7 coordinates to Co10, and O8 bridges two Co9 atoms; as a result each carboxyl group bridges three metal atoms. The bond-valence sums (Brown, 2002 ▸) are 1.90 and 1.84 for Co9 and Co10, respectively, 1.78 and 1.93 for Ni9 and Ni10, and 1.92 and 1.86 for Zn9 and Zn10. All cations are thus slightly under-bonded compared to their expected values of 2.00.

The peak profiles are dominated by microstrain broadening. The generalized microstrain model was used for Co and Zn, but the limited Ni data supported refinement of only an isotropic broadening coefficient. The average microstrain is similar for Co and Zn (21042 and 20094 ppm, respectively), while that for Ni is much larger, at 114830 ppm. Perhaps this greater microstrain indicates that some square-planar Ni coordination also occurs. Analysis of the contributions to the total crystal energy of the structure using the Forcite module of Materials Studio (Dassault Systèmes, 2021 ▸) suggests that for Co and Ni, the bond and angle distortion terms dominate intra­molecular deformation energy, but that torsion terms are also significant. For Zn, the angle distortion terms dominate the intra­molecular deformation energy. The inter­molecular energy in all three compounds is dominated by electrostatic attractions, which represent the M—O bonds.

The Bravais–Friedel–Donnay–Harker (Bravais, 1866 ▸; Friedel, 1907 ▸; Donnay & Harker, 1937 ▸) morphology suggests that we might expect elongated (with [010] as the long axis) or platy (with {200} as the major faces) morphology for these compounds. A 2nd order spherical harmonic model was included in the refinement. The texture indices were 1.003, 1.417, and 1.016 for Co, Ni, and Zn respectively, showing that preferred orientation was significant only for the flat-plate Ni specimen.

Supra­molecular features

The octa­hedral coordination spheres of Co9 share edges, forming chains running parallel to the b-axis direction; the shared edges are parallel the a-axis direction. The octa­hedral coordination spheres of Co10 share edges, forming chains propagating along the b-axis; in this case, the shared edges lie parallel to the c-axis direction. Co9 and Co10 share corners (via O11 = the hydroxyl group), forming layers lying perpendicular to the a-axis direction (Fig. 8 ▸). The hydroxyl group does not participate in hydrogen bonds.

Figure 8

The layers in the crystal structure of Co2(C8H4O4)(OH)2, viewed down the a-axis direction.

Database survey

The crystal structure of the ‘new terephthalate-based cobalt hydroxide Co2(OH)2(C8H4O4)’ was reported by Huang et al. (2000 ▸), and its crystal structure determined [Cambridge Structural Database (Groom et al., 2016 ▸) refcode QASLIF] by ab initio methods using X-ray powder diffraction data. The reported space group is C2/m with a = 19.943 (1), b = 3.2895 (1), c = 6.2896 (3) Å, β = 95.746 (3)°, V = 410.545 Å3, and Z = 2. The structure consists of alternating Co-hydroxide and terephthalate layers, and the terephthalate anions are disordered about an inversion center. Anti­ferromagnetic ordering in this compound was studied using neutron powder diffraction by Feyerherm et al. (2003 ▸), using the same unit cell (QASLIF02). The structure was also determined by Kurmoo et al. (2001 ▸; QASLIF01) in the same unit cell, as well as the structure of cobalt terephthalate dihydrate. The structures of a series of (Co,Fe)2(C8H4O4)(OH)2 solid solutions were refined in the same unit cell by Mesbah et al. (2010 ▸) (UJIMOQ, UJIMOQ01, UJINAD, UJINAD01) using synchrotron and neutron powder data. A reduced cell search in the Cambridge Structural Database yielded in addition the structures of Ni2(C8H4O4)(OH)2 (Mesbah et al., 2014 ▸, NIWQOB; Han et al., 2018 ▸, NIWQOB01).

Synthesis and crystallization

Cobalt(II) nitrate hexa­hydrate (0.0364 g, 0.125 mmol) and terephthalic acid (0.0208 g, 0.125 mmol) were added to a flask followed by 0.125 ml of tri­ethyl­amine and approximately 5 ml of di­methyl­formamide. The reaction was stirred for 10 min until a homogenous mixture was obtained. The reaction was heated using a CEM Discover microwave with power set to 150 W using a ramp time of 2 min to reach 423 K with a hold time of 30 min and inter­nal stirring switched off. The vial remained in the microwave until it cooled to 323 K, and the reaction mixture was filtered using vacuum filtration, washed with DMF and deionized water (10 ml each). The remaining solid was dried in an oven at 343 K under vacuum.

Nickel(II) nitrate hexa­hydrate (0.1948 g, 0.67 mmol) and terephthalic acid (0.2492 g, 1.5 mmol) were dissolved in 10 ml of DMF in a microwave vial. The solution was stirred until homogenous. The solution was then heated using a CEM Mars 6 microwave reactor at 750 W for a total of 85 s, in increments of 25 and 60 s. The resulting green solid was isolated using vacuum filtration, washed with water, methanol, and acetone, and allowed to air dry.

Information on the synthesis of Zn2(C8H4O4)(OH)2 from prior to 1997 is no longer available.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▸.

Table 1

Experimental details

	[Co2(C8H4O4)(OH)2]	[Ni2(C8H4O4)(OH)2]	[Zn2(C8H4O4)(OH)2]
Crystal data
M r	316	315.53	328.89
Crystal system, space group	Monoclinic, C2/c	Monoclinic, C2/c	Monoclinic, C2/c
Temperature (K)	300	300	300
a, b, c (Å)	19.9554 (10), 3.2883 (2), 12.6139 (8)	20.35 (5), 3.364 (6), 12.19 (4)	20.165 (2), 3.3273 (5), 12.5956 (16)
β (°)	96.059 (5)	98.9 (2)	97.431 (10)
V (Å3)	823.08 (6)	824.6 (15)	837.99 (14)
Z	4	4	4
Radiation type	Mo Kα1,2, λ = 0.70932, 0.71361 Å	Co Kα1,2, λ = 1.78892, 1.79278 Å	Synchrotron, λ = 1.15008 Å
Specimen shape, size (mm)	Cylinder, 12 × 0.7	Flat sheet, 16 × 16	Cylinder, ? × ?
Data collection
Diffractometer	PANalytical Empyrean	PANalytical X’Pert	NSLS beamline X3B1
Specimen mounting	Glass capillary	Si zero-background plate with well	Kapton capillary
Data collection mode	Transmission	Reflection	Transmission
Scan method	Step	Step	Step
2θ values (°)	2θmin = 1.002, 2θmax = 49.991, 2θstep = 0.008	2θmin = 4.007, 2θmax = 69.983, 2θstep = 0.017	2θmin = 6.0, 2θmax = 60.0, 2θstep = 0.01
Refinement
R factors and goodness of fit	R p = 0.045, R wp = 0.063, R exp = 0.020, R(F 2) = 0.05751, χ2 = 10.414	R p = 0.084, R wp = 0.107, R exp = 0.070, R(F 2) = 0.14454, χ2 = 2.369	R p = 0.092, R wp = 0.121, R exp = 0.097, R(F 2) = 0.14121, χ2 = 1.573
No. of parameters	42	12	57
No. of restraints	15	0	14
(Δ/σ)max	0.025	97.398	1.459

The same symmetry and lattice parameters were used for the DFT calculations as for each powder diffraction study. Computer programs: GSAS-II (Toby & Von Dreele, 2013 ▸), Mercury (Macrae et al., 2020 ▸), DIAMOND (Crystal Impact, 2015 ▸), and publCIF (Westrip, 2010 ▸).

Rietveld refinements (Figs. 9 ▸–11 ▸ ▸) were carried out using GSAS-II (Toby & Von Dreele, 2013 ▸). All non-H bond distances and angles in the terephthalate anions were subjected to restraints, based on a Mercury Mogul Geometry Check (Sykes et al., 2011 ▸; Bruno et al., 2004 ▸). The Mogul average and standard deviation for each qu­antity were used as the restraint parameters. The restraints contributed 0–2.3% to the final χ2. The U iso were grouped by chemical similarity. The U iso values for the H atoms were fixed at 1.3 × the U iso of the heavy atoms to which they are attached. The peak profiles were described using the generalized microstrain model. The background was modeled using a 3–12-term shifted Chebyshev polynomial.

Figure 9

The Rietveld plot for the refinement of Co2(C8H4O4)(OH)2. The blue crosses represent the observed data points, and the green line is the calculated pattern. The cyan curve is the normalized error plot. The row of tick marks indicates the calculated reflection positions. The vertical scale has been multiplied by a factor of 4× for 2θ > 5.0°, and by a factor of 20× for 2θ > 27.0°.

Figure 10

The Rietveld plot for the refinement of Ni2(C8H4O4)(OH)2. The blue crosses represent the observed data points, and the green line is the calculated pattern. The cyan curve is the normalized error plot. The row of tick marks indicates the calculated reflection positions.

Figure 11

The Rietveld plot for the refinement of Zn2(C8H4O4)(OH)2. The blue crosses represent the observed data points, and the green line is the calculated pattern. The cyan curve is the normalized error plot. The row of tick marks indicates the calculated reflection positions. The vertical scale has been multiplied by a factor of 5× for 2θ > 10.0°, and by a factor of 15× for 2θ > 18.0°.

The structures were optimized with density functional techniques using VASP (Kresse & Furthmüller, 1996 ▸) (fixed experimental unit cells) through the MedeA graphical inter­face (Materials Design, 2016 ▸). The calculations were carried out on 16 2.4 GHz processors (each with 4 Gb RAM) of a 64-processor HP Proliant DL580 Generation 7 Linux cluster at North Central College. The calculations for Co and Ni were spin-polarized magnetic calculations, using the simplified LDSA + U approach, and U j = 3.7 eV for Co and Ni. The calculations used the GGA-PBE functional, a plane wave cutoff energy of 400.0 eV, and a k-point spacing of 0.5 Å−1 leading to an 8 × 8 × 2 mesh.

Crystal structure: contains datablock(s) Co_Riet, Co_DFT, Ni_Riet, Ni_DFT, Zn_Riet, Zn_DFT. DOI: 10.1107/S2056989022005023/hb8022sup1.cif

CCDC references: 2171929, 2171928, 2171927, 2171926, 2171925, 2171924

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Co2(C8H4O4)(OH)2]	V = 823.08 (6) Å3
Mr = 316	Z = 4
Monoclinic, C2/c	Dx = 2.550 Mg m−3
a = 19.9554 (10) Å	Mo Kα1,2 radiation, λ = 0.70932, 0.71361 Å
b = 3.2883 (2) Å	T = 300 K
c = 12.6139 (8) Å	pink
β = 96.059 (5)°	cylinder, 12 × 0.7 mm

PANalytical Empyrean diffractometer	Scan method: step
Specimen mounting: glass capillary	2θmin = 1.002°, 2θmax = 49.991°, 2θstep = 0.008°
Data collection mode: transmission

Least-squares matrix: full	42 parameters
Rp = 0.045	15 restraints
Rwp = 0.063	H-atom parameters not defined?
Rexp = 0.020	Weighting scheme based on measured s.u.'s
R(F2) = 0.05751	(Δ/σ)max = 0.025
5864 data points	Background function: Background function: "chebyschev-1" function with 4 terms: 1063(5), -577(6), 95(4), -25(3), Background peak parameters: pos, int, sig, gam: 11.866, 3892.401, 44425.907, 0.100,
Profile function: Finger-Cox-Jephcoat function parameters U, V, W, X, Y, SH/L: peak variance(Gauss) = Utan(Th)2+Vtan(Th)+W: peak HW(Lorentz) = X/cos(Th)+Ytan(Th); SH/L = S/L+H/L U, V, W in (centideg)2, X & Y in centideg 30.816, 10.768, 0.000, 1.935, 0.000, 0.033, Crystallite size in microns with "isotropic" model: parameters: Size, G/L mix 1.000, 1.000, Microstrain, "generalized" model (106 * delta Q/Q) parameters: S400, S040, S004, S220, S202, S022, S301, S103, S121, G/L mix 2180.060, 4.385767395e6, 5373.300, 103711.383, 724.789, 689333.161, -2196.502, 2609.389, 91248.973, 0.800,	Preferred orientation correction: Simple spherical harmonic correction Order = 2 Coefficients: 0:0:C(2,-2) = -0.0542; 0:0:C(2,0) = -0.1055; 0:0:C(2,2) = -0.0207

	x	y	z	Uiso*/Ueq
C1	0.3140 (2)	0.106 (3)	0.0412 (4)	0.018 (3)*
C2	0.2695 (3)	0.269 (3)	0.1093 (3)	0.0184*
C3	0.2024 (3)	0.368 (4)	0.0686 (4)	0.0184*
H4	0.28873	0.24618	0.19840	0.0220*
H5	0.17120	0.48125	0.13117	0.0220*
C6	0.3837 (3)	−0.024 (5)	0.0845 (5)	0.0200*
O7	0.3988 (3)	−0.007 (7)	0.1799 (5)	0.020000*
O8	0.4268 (3)	−0.031 (5)	0.0168 (5)	0.020000*
Co9	0.50000	0.50000	0.50000	0.0020 (5)*
Co10	0.00000	0.495 (3)	−0.25000	0.0020*
O11	0.0287 (3)	0.030 (7)	0.1569 (7)	0.0200*
H12	0.06922	−0.03114	0.16621	0.0260*

C1—C2	1.406 (6)	O8—C6	1.274 (4)
C1—C3i	1.391 (3)	O8—Co9ii	2.151 (12)
C1—C6	1.501 (5)	Co9—O8iii	2.151 (12)
C2—C1	1.406 (6)	Co9—O8iv	2.151 (12)
C2—C3	1.421 (4)	Co9—O11v	2.004 (8)
C3—C1i	1.391 (3)	Co9—O11vi	2.004 (8)
C3—C2	1.421 (4)	Co10—O7i	2.119 (5)
C6—C1	1.501 (5)	Co10—O7vii	2.119 (5)
C6—O7	1.211 (5)	Co10—O11viii	2.072 (16)
C6—O8	1.274 (4)	Co10—O11ix	2.072 (16)
O7—C6	1.211 (5)	O11—Co9x	2.004 (8)
O7—Co10i	2.119 (5)	O11—Co10viii	2.072 (16)
C2—C1—C3i	119.1 (3)	C1i—C3—C2	119.2 (3)
C2—C1—C6	120.4 (2)	C1—C6—O7	118.2 (4)
C3i—C1—C6	119.5 (3)	C1—C6—O8	115.2 (5)
C1—C2—C3	119.9 (3)	O7—C6—O8	123.5 (6)

C8H6Co2O6	c = 12.59800 Å
Mr = 316	β = 96.33°
Monoclinic, C2/c	V = 828.49 Å3
a = 20.02520 Å	Z = 4
b = 3.30420 Å

h = →	l = →
k = →

	x	y	z	Uiso*/Ueq
C1	0.31569	0.14758	0.04012	0.0184
C2	0.26806	0.23812	0.11006	0.0184
C3	0.20287	0.33955	0.07035	0.0184
H4	0.28329	0.23013	0.19578	0.022
H5	0.16565	0.41266	0.12436	0.022
C6	0.38562	0.03773	0.08352	0.020
O7	0.39861	0.98679	0.18301	0.020
O8	0.42960	0.00198	0.01583	0.020
Co9	0.00000	0.00000	0.00000	0.002
Co10	0.50000	0.97237	0.25000	0.002
O11	0.02838	0.97997	0.15714	0.020
H12	0.07726	0.97414	0.17088	0.026

[Ni2(C8H4O4)(OH)2]	V = 824.6 (15) Å3
Mr = 315.53	Z = 4
Monoclinic, C2/c	Dx = 2.542 Mg m−3
a = 20.35 (5) Å	Co Kα1,2 radiation, λ = 1.78892, 1.79278 Å
b = 3.364 (6) Å	T = 300 K
c = 12.19 (4) Å	pale green
β = 98.9 (2)°	flat_sheet, 16 × 16 mm

PANalytical X'Pert diffractometer	Scan method: step
Specimen mounting: Si zero-background plate with well	2θmin = 4.007°, 2θmax = 69.983°, 2θstep = 0.017°
Data collection mode: reflection

Least-squares matrix: full	12 parameters
Rp = 0.084	0 restraints
Rwp = 0.107	H-atom parameters not defined?
Rexp = 0.070	(Δ/σ)max = 97.398
R(F2) = 0.14454	Background function: Background function: "chebyschev-1" function with 3 terms: 139.3(6), -71.0(8), 7.7(7),
3949 data points	Preferred orientation correction: Simple spherical harmonic correction Order = 2 Coefficients: 0:0:C(2,-2) = -0.91(8); 0:0:C(2,0) = 0.63(8); 0:0:C(2,2) = 0.93(13)
Profile function: Finger-Cox-Jephcoat function parameters U, V, W, X, Y, SH/L: peak variance(Gauss) = Utan(Th)2+Vtan(Th)+W: peak HW(Lorentz) = X/cos(Th)+Ytan(Th); SH/L = S/L+H/L U, V, W in (centideg)2, X & Y in centideg 2.761, 0.000, 1.090, 3.610, 0.000, 0.047,

	x	y	z	Uiso*/Ueq
C1	0.31564	0.11999	0.03425	0.0100*
C2	0.27426	0.26556	0.10759	0.0100*
C3	0.20930	0.40008	0.07333	0.0100*
H4	0.28873	0.24618	0.19840	0.0130*
H5	0.17120	0.48125	0.13117	0.0130*
C6	0.38661	−0.01497	0.07632	0.0100*
O7	0.39933	−0.00110	0.17831	0.0100*
O8	0.43321	−0.00173	0.01302	0.0100*
Ni9	0.50000	0.50000	0.50000	0.0387*
Ni10	0.00000	0.50145	−0.25000	0.0387*
O11	0.02771	0.0007	0.15823	0.0063*
H12	0.06922	−0.03114	0.16621	0.0082*

C1—C2	1.4074	O8—C6	1.3123
C1—C3i	1.3331	Ni9—O11ii	1.9246
C1—C6	1.5251	Ni9—O11iii	1.9246
C2—C1	1.4074	Ni10—O7i	2.0995
C2—C3	1.3985	Ni10—O7iv	2.0995
C3—C1i	1.3331	Ni10—O11v	2.149
C3—C2	1.3985	Ni10—O11vi	2.1377
H5—C3	1.1584	Ni10—O11vii	2.149
C6—C1	1.5251	Ni10—O11viii	2.1377
C6—O7	1.2313	O11—Ni9ix	1.9246
C6—O8	1.3123	O11—Ni10v	2.149
O7—C6	1.2313	O11—Ni10vi	2.1377
O7—Ni10i	2.0995
C2—C1—C3i	117.925	C1i—C3—C2	118.448
C2—C1—C6	121.216	C1—C6—O7	111.649
C3i—C1—C6	120.856	C1—C6—O8	121.645
C1—C2—C3	123.601	O7—C6—O8	122.291

C8H6Ni2O6	c = 12.22464 Å
Mr = 315.53	β = 99.20°
Monoclinic, C2/c	V = 805.74 Å3
a = 20.40719 Å	Z = 4
b = 3.27188 Å

h = →	l = →
k = →

	x	y	z	Uiso*/Ueq
C1	0.31659	0.14671	0.03597	0.010
C2	0.27424	0.23178	0.11288	0.010
C3	0.20831	0.33316	0.07742	0.010
H4	0.29416	0.22005	0.20095	0.013
H5	0.17519	0.40045	0.13678	0.013
C6	0.38690	0.03143	0.07591	0.010
O7	0.90294	0.45891	0.17836	0.010
O8	0.42774	0.00936	0.00489	0.010
Ni9	0.00000	0.00000	0.00000	0.03866
Ni10	0.00000	0.45204	0.25000	0.03866
O11	0.52764	0.45960	0.16035	0.00631
H12	0.57607	0.45471	0.17494	0.00821

[Zn2(C8H4O4)(OH)2]	V = 837.99 (14) Å3
Mr = 328.89	Z = 4
Monoclinic, C2/c	Dx = 2.607 Mg m−3
a = 20.165 (2) Å	Synchrotron radiation, λ = 1.15008 Å
b = 3.3273 (5) Å	T = 300 K
c = 12.5956 (16) Å	white
β = 97.431 (10)°

NSLS beamline X3B1 diffractometer	Scan method: step
Specimen mounting: Kapton capillary	2θmin = 6.0°, 2θmax = 60.0°, 2θstep = 0.01°
Data collection mode: transmission

Least-squares matrix: full	57 parameters
Rp = 0.092	14 restraints
Rwp = 0.121	H-atom parameters not defined?
Rexp = 0.097	(Δ/σ)max = 1.459
R(F2) = 0.14121	Background function: Background function: "chebyschev-1" function with 12 terms: 28.78(11), -16.88(18), 8.18(16), 0.45(16), -2.60(15), -1.04(14), 3.60(13), -1.88(13), 0.46(12), 1.97(12), -1.94(11), 1.26(10),
5400 data points	Preferred orientation correction: Simple spherical harmonic correction Order = 2 Coefficients: 0:0:C(2,-2) = -0.05(4); 0:0:C(2,0) = -0.18(6); 0:0:C(2,2) = -0.21(4)
Profile function: Finger-Cox-Jephcoat function parameters U, V, W, X, Y, SH/L: peak variance(Gauss) = Utan(Th)2+Vtan(Th)+W: peak HW(Lorentz) = X/cos(Th)+Ytan(Th); SH/L = S/L+H/L U, V, W in (centideg)2, X & Y in centideg 6.427, -1.067, 0.000, 0.000, 0.000, 0.022, Crystallite size in microns with "isotropic" model: parameters: Size, G/L mix 1.000, 1.000, Microstrain, "generalized" model (106 * delta Q/Q) parameters: S400, S040, S004, S220, S202, S022, S301, S103, S121, G/L mix 807.414, 6.074702219e6, 12850.425, 116093.843, 1080.871, 214564.056, 1450.184, -4276.159, -164837.348, 0.600,

	x	y	z	Uiso*/Ueq
C1	0.3153 (9)	0.132 (11)	0.038 (2)	0.148 (18)*
C2	0.2801 (13)	0.369 (13)	0.1020 (17)	0.148*
C3	0.2145 (14)	0.477 (16)	0.067 (2)	0.148*
H7	0.29840	0.55800	0.17260	0.192*
H8	0.18320	0.73700	0.09150	0.192*
C11	0.3863 (5)	0.016 (8)	0.0750 (18)	0.0500*
O12	0.4045 (9)	0.025 (16)	0.1743 (18)	0.050000*
O13	0.4201 (7)	−0.156 (9)	0.008 (2)	0.050000*
Zn14	0.50000	0.50000	0.50000	0.078 (4)*
Zn15	0.00000	0.54200	−0.25000	0.078*
O16	0.0318 (13)	0.072 (14)	0.161 (3)	0.0500*
H17	0.06922	−0.03114	0.16621	0.065000*

C1—C2	1.3877 (16)	O13—C11	1.284 (2)
C1—C3i	1.43 (4)	O13—Zn14ii	1.989 (13)
C1—C11	1.498 (3)	Zn14—O13iii	1.989 (13)
C2—C1	1.3877 (16)	Zn14—O13iv	1.989 (13)
C2—C3	1.385 (2)	Zn14—O16v	2.06 (3)
C3—C1i	1.43 (4)	Zn14—O16vi	2.06 (3)
C3—C2	1.385 (2)	Zn15—O12i	2.048 (17)
C11—C1	1.498 (3)	Zn15—O12vii	2.048 (17)
C11—O12	1.2573 (14)	Zn15—O16viii	1.87 (4)
C11—O13	1.284 (2)	Zn15—O16ix	1.87 (4)
O12—C11	1.2573 (14)	O16—Zn14x	2.06 (3)
O12—Zn15i	2.048 (17)	O16—Zn15viii	1.87 (4)
C2—C1—C3i	119.81 (12)	C1—C11—O12	116.6 (2)
C2—C1—C11	120.4 (2)	C1—C11—O13	118.59 (19)
C3i—C1—C11	119.6 (4)	O12—C11—O13	123.42 (15)
C1—C2—C3	120.20 (17)	O16viii—Zn15—O16xi	93 (2)
C1i—C3—C2	119.83 (12)

C8H6O6Zn2	c = 12.59470 Å
Mr = 328.89	β = 97.52°
Monoclinic, C2/c	V = 837.00 Å3
a = 20.15960 Å	Z = 4
b = 3.32510 Å

h = →	l = →
k = →

	x	y	z	Uiso*/Ueq
C1	0.31537	0.14052	0.03973	0.14798
C2	0.26900	0.22410	0.11036	0.14798
C3	0.20398	0.33320	0.07087	0.14798
H7	0.28504	0.20470	0.19624	0.19231
H8	0.16745	0.40076	0.12504	0.19231
C11	0.38529	0.02740	0.08247	0.050
O12	0.39938	0.97473	0.18247	0.050
O13	0.42745	0.99381	0.01434	0.050
O16	0.02778	0.97322	0.15570	0.050
H17	0.07652	0.96489	0.16886	0.065
Zn14	0.00000	0.00000	0.00000	0.07842
Zn15	0.50000	0.96690	0.25000	0.07842