Self-assembly of a cobalt(II)-based metal–organic framework as an effective water-splitting heterogeneous catalyst for light-driven hydrogen production

The solar photocatalysis of water splitting represents a significant branch of enzymatic simulation by efficient chemical conversion and the generation of hydrogen as green energy provides a feasible way for the replacement of fossil fuels to solve energy and environmental issues. We report herein the self-assembly of a Co^II-based metal–organic framework (MOF) constructed from 4,4′,4′′,4′′′-(ethene-1,1,2,2-tetra­yl)tetra­benzoic acid [or tetra­kis­(4-carb­oxy­phen­yl)ethyl­ene, H₄TCPE] and 4,4′-bipyridyl (bpy) as four-point- and two-point-con­nected nodes, respectively. This material, namely, poly[(μ-4,4′-bipyrid­yl)[μ₈-4,4′,4′′,4′′′-(ethene-1,1,2,2-tetra­yl)tetra­benzoato]cobalt(II)], [Co(C₃₀H₁₆O₈)(C₁₀H₈N₂)]_n, crystallized as dark-red block-shaped crystals with high crystallinity and was fully characterized by single-crystal X-ray diffraction, PXRD, IR, solid-state UV–Vis and cyclic voltammetry (CV) measurements. The redox-active Co^II atoms in the structure could be used as the catalytic sites for hydrogen production via water splitting. The application of this new MOF as a heterogeneous catalyst for light-driven H₂ production has been explored in a three-component system with fluorescein as photosensitizer and tri­methyl­amine as the sacrificial electron donor, and the initial volume of H₂ production is about 360 µmol after 12 h irradiation.

Computing details

Data collection: SMART (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b) and OLEX2 (Dolomanov et al., 2009); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Poly[(µ-4,4'-bipyridyl)[µ₈-4,4',4'',4'''-(ethene-1,1,2,2-tetrayl)tetrabenzoato]cobalt(II)]

Crystal data

[Co(C30H16O8)(C10H8N2)]	Dx = 1.215 Mg m^−3
Mr = 778.48	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pmma	Cell parameters from 9.0145 reflections
a = 11.857 (3) Å	θ = 2.3–22.1°
b = 12.936 (3) Å	µ = 0.83 mm^−1
c = 13.877 (3) Å	T = 200 K
V = 2128.4 (8) Å^3	Block, colourless
Z = 2	0.13 × 0.11 × 0.1 mm
F(000) = 792

Data collection

Bruker APEXII CCD diffractometer	1448 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.059
φ and ω scans	θmax = 25.0°, θmin = 1.6°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −12→14
Tmin = 0.841, Tmax = 0.969	k = −15→15
10844 measured reflections	l = −16→14
2063 independent reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.057	H-atom parameters constrained
wR(F^2) = 0.177	w = 1/[σ^2(Fo^2) + (0.105P)^2 + 1.8388P] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max < 0.001
2063 reflections	Δρmax = 1.01 e Å^−3
179 parameters	Δρmin = −0.37 e Å^−3

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. Single crystals of 1 for X-ray diffraction analyses with suitable dimensions were mounted on a glass rod, and the X-ray intensity data were measured on a Bruker SMART APEX CCD-based diffractometer (Mo–Kα radiation, λ = 0.71073 Å) using the SMART (Bruker, 2008) and SAINT programs (Bruker, 2008). The crystal data was solved by direct methods and further refined by full-matrix least-squares refinements on F² using the SHELXL-2018/3 and OLEX2 software (Dolomanov et al., 2009), and an absorption correction was performed using the SADABS program (Bruker, 2008). The remaining atoms were found from successive full-matrix least-squares refinements on F² and Fourier syntheses. Non-H atoms were refined with anisotropic displacement parameters.

The CCDC 1992832 for 1 contains the supplementary crystallographic data for this paper and these data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Co1	0.250000	1.000000	0.18481 (7)	0.0385 (4)
Co2	0.250000	1.000000	0.37986 (7)	0.0399 (4)
O1	0.3696 (3)	0.8910 (3)	0.2019 (2)	0.0784 (12)
O2	0.3688 (3)	0.8902 (3)	0.3611 (2)	0.0721 (10)
N1	0.250000	1.000000	0.0353 (5)	0.0433 (16)
N2	0.250000	1.000000	0.5264 (4)	0.0402 (15)
C1	0.4009 (4)	0.8568 (3)	0.2818 (3)	0.0548 (11)
C2	0.4824 (4)	0.7677 (4)	0.2824 (3)	0.0559 (11)
C3	0.5518 (17)	0.7474 (13)	0.2030 (9)	0.068 (4)	0.52 (2)
H3	0.547768	0.789214	0.148588	0.082*	0.52 (2)
C3A	0.4929 (16)	0.7060 (14)	0.2013 (9)	0.062 (4)	0.48 (2)
H3A	0.449345	0.719186	0.146920	0.075*	0.48 (2)
C4	0.6259 (15)	0.6654 (13)	0.2053 (10)	0.068 (4)	0.52 (2)
H4	0.674355	0.653859	0.153657	0.081*	0.52 (2)
C4A	0.5687 (18)	0.6244 (14)	0.2019 (10)	0.069 (5)	0.48 (2)
H4A	0.579691	0.585834	0.146181	0.082*	0.48 (2)
C5	0.6284 (4)	0.5998 (4)	0.2847 (4)	0.0600 (12)
C6	0.5638 (18)	0.6241 (16)	0.3621 (12)	0.076 (5)	0.52 (2)
H6	0.568757	0.583464	0.417283	0.091*	0.52 (2)
C6A	0.6173 (19)	0.6613 (14)	0.3637 (13)	0.066 (4)	0.48 (2)
H6A	0.659794	0.647237	0.418480	0.080*	0.48 (2)
C7	0.4908 (18)	0.7074 (14)	0.3615 (11)	0.065 (4)	0.52 (2)
H7	0.447356	0.721954	0.415679	0.078*	0.52 (2)
C7A	0.545 (2)	0.7434 (17)	0.3640 (13)	0.072 (5)	0.48 (2)
H7A	0.537123	0.783337	0.419310	0.086*	0.48 (2)
C8	0.6958 (7)	0.500000	0.2846 (6)	0.078 (2)
C9	0.3433 (8)	1.000000	−0.4231 (6)	0.119 (4)
H9	0.411505	1.000000	−0.456240	0.143*
C10	0.3468 (8)	1.000000	−0.3214 (6)	0.116 (4)
H10	0.415778	1.000000	−0.289495	0.139*
C11	0.250000	1.000000	−0.2705 (5)	0.045 (2)
C12	0.250000	1.000000	−0.1635 (6)	0.047 (2)
C13	0.3375 (9)	0.9612 (8)	−0.1115 (6)	0.084 (5)	0.5
H13	0.400916	0.935847	−0.143102	0.100*	0.5
C14	0.3330 (8)	0.9591 (7)	−0.0130 (7)	0.079 (4)	0.5
H14	0.391212	0.927259	0.020658	0.094*	0.5

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0490 (7)	0.0367 (6)	0.0298 (6)	0.000	0.000	0.000
Co2	0.0494 (7)	0.0393 (7)	0.0310 (6)	0.000	0.000	0.000
O1	0.101 (3)	0.088 (3)	0.0466 (19)	0.053 (2)	−0.0028 (18)	−0.0013 (16)
O2	0.089 (3)	0.073 (2)	0.054 (2)	0.040 (2)	0.0085 (18)	0.0002 (17)
N1	0.046 (4)	0.043 (4)	0.041 (4)	0.000	0.000	0.000
N2	0.046 (4)	0.047 (4)	0.027 (3)	0.000	0.000	0.000
C1	0.061 (3)	0.052 (3)	0.051 (3)	0.013 (2)	0.000 (2)	−0.003 (2)
C2	0.063 (3)	0.054 (3)	0.051 (3)	0.017 (2)	0.002 (2)	0.001 (2)
C3	0.079 (11)	0.059 (8)	0.066 (7)	0.025 (8)	0.008 (7)	0.013 (6)
C3A	0.061 (9)	0.070 (9)	0.056 (7)	0.017 (8)	−0.007 (6)	−0.009 (6)
C4	0.059 (8)	0.074 (9)	0.071 (7)	0.011 (7)	0.014 (6)	−0.008 (6)
C4A	0.076 (11)	0.063 (9)	0.067 (7)	0.025 (8)	0.000 (8)	−0.020 (6)
C5	0.061 (3)	0.049 (3)	0.069 (3)	0.014 (2)	−0.002 (3)	0.003 (2)
C6	0.091 (13)	0.072 (11)	0.065 (8)	0.031 (9)	0.014 (9)	0.019 (7)
C6A	0.077 (12)	0.061 (10)	0.060 (7)	0.020 (8)	−0.011 (8)	−0.003 (7)
C7	0.074 (11)	0.071 (10)	0.050 (6)	0.026 (8)	0.012 (7)	0.000 (6)
C7A	0.085 (13)	0.074 (12)	0.055 (7)	0.026 (9)	0.001 (9)	−0.004 (7)
C8	0.068 (4)	0.083 (5)	0.082 (5)	0.000	0.003 (4)	0.000
C9	0.076 (6)	0.233 (12)	0.048 (5)	0.000	0.007 (5)	0.000
C10	0.072 (6)	0.227 (12)	0.048 (5)	0.000	−0.006 (4)	0.000
C11	0.052 (5)	0.057 (5)	0.025 (4)	0.000	0.000	0.000
C12	0.061 (6)	0.049 (5)	0.031 (4)	0.000	0.000	0.000
C13	0.063 (6)	0.143 (14)	0.045 (5)	0.056 (7)	0.004 (4)	−0.002 (5)
C14	0.062 (6)	0.125 (11)	0.048 (5)	0.053 (6)	−0.006 (4)	0.007 (5)

Geometric parameters (Å, º)

Co1—Co2	2.7067 (15)	C3A—C4A	1.387 (17)
Co1—O1^i	2.014 (3)	C4—H4	0.9300
Co1—O1^ii	2.014 (3)	C4—C5	1.391 (14)
Co1—O1^iii	2.014 (3)	C4A—H4A	0.9300
Co1—O1	2.014 (3)	C4A—C5	1.386 (15)
Co1—N1	2.074 (7)	C5—C6	1.357 (17)
Co2—O2^i	2.018 (3)	C5—C6A	1.362 (17)
Co2—O2^ii	2.018 (3)	C5—C8	1.518 (6)
Co2—O2	2.018 (3)	C6—H6	0.9300
Co2—O2^iii	2.018 (3)	C6—C7	1.38 (2)
Co2—N2	2.034 (6)	C6A—H6A	0.9300
O1—C1	1.251 (5)	C6A—C7A	1.37 (2)
O2—C1	1.241 (5)	C7—H7	0.9300
N1—C14	1.303 (9)	C7A—H7A	0.9300
N2—C9^iv	1.310 (9)	C8—C8^vi	1.285 (16)
N2—C9^v	1.310 (9)	C9—H9	0.9300
C1—C2	1.504 (6)	C9—C10	1.412 (12)
C2—C3	1.400 (13)	C10—H10	0.9300
C2—C3A	1.386 (13)	C10—C11	1.347 (10)
C2—C7	1.350 (17)	C11—C12	1.485 (11)
C2—C7A	1.388 (19)	C12—C13	1.360 (10)
C3—H3	0.9300	C13—H13	0.9300
C3—C4	1.378 (16)	C13—C14	1.367 (13)
C3A—H3A	0.9300	C14—H14	0.9300
O1—Co1—Co2	83.25 (9)	C4—C3—H3	120.0
O1^iii—Co1—Co2	83.25 (9)	C2—C3A—H3A	120.3
O1^ii—Co1—Co2	83.25 (9)	C2—C3A—C4A	119.4 (10)
O1^i—Co1—Co2	83.25 (9)	C4A—C3A—H3A	120.3
O1—Co1—O1^iii	88.9 (3)	C3—C4—H4	120.0
O1^ii—Co1—O1^i	88.9 (3)	C3—C4—C5	120.1 (10)
O1—Co1—O1^ii	89.5 (3)	C5—C4—H4	120.0
O1—Co1—O1^i	166.50 (18)	C3A—C4A—H4A	119.6
O1^iii—Co1—O1^i	89.6 (3)	C5—C4A—C3A	120.8 (10)
O1^iii—Co1—O1^ii	166.50 (18)	C5—C4A—H4A	119.6
O1—Co1—N1	96.75 (9)	C4—C5—C8	122.0 (7)
O1^i—Co1—N1	96.75 (9)	C4A—C5—C8	117.7 (7)
O1^iii—Co1—N1	96.75 (9)	C6—C5—C4	118.3 (9)
O1^ii—Co1—N1	96.75 (9)	C6—C5—C8	119.6 (8)
N1—Co1—Co2	180.0	C6A—C5—C4A	118.9 (10)
O2^ii—Co2—Co1	82.57 (10)	C6A—C5—C8	123.3 (8)
O2^iii—Co2—Co1	82.57 (10)	C5—C6—H6	119.0
O2—Co2—Co1	82.57 (10)	C5—C6—C7	122.0 (13)
O2^i—Co2—Co1	82.57 (10)	C7—C6—H6	119.0
O2^ii—Co2—O2^i	89.5 (2)	C5—C6A—H6A	119.4
O2—Co2—O2^ii	88.6 (2)	C5—C6A—C7A	121.2 (14)
O2—Co2—O2^iii	89.5 (2)	C7A—C6A—H6A	119.4
O2—Co2—O2^i	165.15 (19)	C2—C7—C6	120.1 (13)
O2^ii—Co2—O2^iii	165.15 (19)	C2—C7—H7	120.0
O2^iii—Co2—O2^i	88.6 (2)	C6—C7—H7	120.0
O2^ii—Co2—N2	97.43 (10)	C2—C7A—H7A	119.7
O2^i—Co2—N2	97.43 (10)	C6A—C7A—C2	120.6 (15)
O2^iii—Co2—N2	97.43 (10)	C6A—C7A—H7A	119.7
O2—Co2—N2	97.43 (10)	C5—C8—C5^vii	116.5 (6)
N2—Co2—Co1	180.0	C8^vi—C8—C5^vii	121.8 (3)
C1—O1—Co1	124.1 (3)	C8^vi—C8—C5	121.8 (3)
C1—O2—Co2	125.0 (3)	N2^viii—C9—H9	118.0
C14—N1—Co1	121.0 (5)	N2^viii—C9—C10	124.0 (8)
C9^iv—N2—Co2	122.3 (4)	C10—C9—H9	118.0
C9^v—N2—Co2	122.3 (4)	C9—C10—H10	120.0
C9^v—N2—C9^iv	115.3 (9)	C11—C10—C9	119.9 (8)
O1—C1—C2	117.8 (4)	C11—C10—H10	120.0
O2—C1—O1	124.9 (4)	C10—C11—C10^i	116.8 (9)
O2—C1—C2	117.3 (4)	C10^i—C11—C12	121.6 (5)
C3—C2—C1	121.1 (6)	C10—C11—C12	121.6 (5)
C3A—C2—C1	119.6 (6)	C13—C12—C11	122.0 (5)
C3A—C2—C7A	119.0 (10)	C12—C13—H13	119.8
C7—C2—C1	119.6 (7)	C12—C13—C14	120.5 (8)
C7—C2—C3	119.2 (9)	C14—C13—H13	119.8
C7A—C2—C1	121.4 (8)	N1—C14—C13	122.4 (8)
C2—C3—H3	120.0	N1—C14—H14	118.8
C4—C3—C2	120.1 (10)	C13—C14—H14	118.8
Co1—O1—C1—O2	−5.5 (8)	C3A—C4A—C5—C6A	−4.5 (19)
Co1—O1—C1—C2	173.8 (3)	C3A—C4A—C5—C8	170.7 (11)
Co1—N1—C14—C13	−177.5 (8)	C4—C5—C6—C7	4.4 (19)
Co2—O2—C1—O1	5.0 (8)	C4—C5—C8—C5^vii	−110.9 (12)
Co2—O2—C1—C2	−174.4 (3)	C4—C5—C8—C8^vi	69.1 (12)
O1—C1—C2—C3	22.5 (13)	C4A—C5—C6A—C7A	3 (2)
O1—C1—C2—C3A	−20.4 (13)	C4A—C5—C8—C5^vii	−69.3 (14)
O1—C1—C2—C7	−158.8 (12)	C4A—C5—C8—C8^vi	110.7 (12)
O1—C1—C2—C7A	162.1 (13)	C5—C6—C7—C2	0 (2)
O2—C1—C2—C3	−158.1 (12)	C5—C6A—C7A—C2	−2 (2)
O2—C1—C2—C3A	159.0 (12)	C6—C5—C8—C5^vii	65.6 (15)
O2—C1—C2—C7	20.6 (13)	C6—C5—C8—C8^vi	−114.3 (13)
O2—C1—C2—C7A	−18.6 (14)	C6A—C5—C8—C5^vii	105.6 (14)
N2^viii—C9—C10—C11	0.000 (1)	C6A—C5—C8—C8^vi	−74.4 (13)
C1—C2—C3—C4	179.9 (10)	C7—C2—C3—C4	1.2 (18)
C1—C2—C3A—C4A	179.5 (11)	C7A—C2—C3A—C4A	−2.8 (19)
C1—C2—C7—C6	178.7 (10)	C8—C5—C6—C7	−172.3 (11)
C1—C2—C7A—C6A	179.1 (11)	C8—C5—C6A—C7A	−171.8 (11)
C2—C3—C4—C5	3.0 (19)	C9—C10—C11—C10^i	0.000 (1)
C2—C3A—C4A—C5	4 (2)	C9—C10—C11—C12	180.000 (1)
C3—C2—C7—C6	−2.6 (18)	C10—C11—C12—C13	−25.8 (6)
C3—C4—C5—C6	−5.7 (17)	C10^i—C11—C12—C13	154.2 (6)
C3—C4—C5—C8	170.9 (10)	C11—C12—C13—C14	−177.7 (7)
C3A—C2—C7A—C6A	1 (2)	C12—C13—C14—N1	−5.0 (16)

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