Crystal structure of poly[[hexa-aqua-tris-(μ-3,6-di-oxo-cyclo-hexa-1,4-diene-1,4-diolato)dierbium(III)] octa-deca-hydrate].

The title lanthanide complex, [Er2(C6H2O4)3(H2O)6]·18H2O, is isostructural with its La, Gd, Yb and Lu analogues. The Er3+ ion, located on a threefold rotation axis, is nine-coordinated in a distorted tricapped trigonal-prismatic geometry, which is completed by six oxygen atoms from three dhbq2- ligands and three oxygen atoms from coordinated water mol-ecules. Each dhbq2- ligand acts in a μ2-bis-(bidentate) bridging mode to connect two Er3+ ions to form honeycomb (6,3) two-dimensional sheets extending in the ab plane, having an Er⋯Er separation of 8.7261 (2) Å. In the crystal, extensive O-H⋯O hydrogen-bonding inter-actions involving the coordinated water mol-ecules and the water mol-ecules of crystallization, as well as the oxygen atoms of the dhbq2- ligands, generate an overall three-dimensional supra-molecular network.

Chemical context

Over the past few decades, lanthanide-based coordination polymers (LnCPs) have attracted significant attention because their high photoluminescence efficiency and long luminescence lifetime in lighting and full-colour displays (Parker, 2000 ▸; Bünzli & Piguet, 2005 ▸; Cui et al., 2018 ▸). Besides transition metal ions, lanthanide ions feature high coordination numbers and flexible coordination geometries, which facilitate the formation of diverse extended structures. Since lanthanide(III) ions have a high affinity to hard donor atoms, ligands containing oxygen atoms such as carb­oxy­lic acids (Xu et al., 2016 ▸), phospho­ric acids (Mao, 2007 ▸), calixarenes (Ovsyannikov et al., 2017 ▸) and β-diketones (Vigato et al., 2009 ▸) have been used extensively in the synthesis of new types of LnCPs. On the basis of the above considerations, we selected 2,5-dihy­droxy-1,4-benzo­quinone (H2dhbq) as the ligand to react with erbium(III) nitrate hexa­hydrate under solvothermal conditions to construct a new erbium(III)-based CP, [Er2(dhbq)3(H2O)6]·18H2O, (I), which is isotypic with its La, Gd, Yb and Lu analogues (Abrahams et al., 2002 ▸). Herein, we report its structure.

Structural commentary

The asymmetric unit of (I) contains one third of an Er3+ ion, half of a dhbq2− ligand, one coordinated water mol­ecule and three water mol­ecules of crystallization. The Er3+ ion is located on a threefold rotation axis, whereas the complete dhbq2− anion is generated by a crystallographic inversion center. As can be seen from Fig. 1 ▸, the Er3+ ion is nine-coordinated by six oxygen atoms from three different dhbq2− ligands and three other oxygen atoms from three coordinated water mol­ecules. The coordination polyhedron of the central Er3+ ion can best be described as having a distorted tricapped trigonal–prismatic geometry, as depicted in Fig. 2 ▸, in which the O—Er—O bond angles range from 65.01 (5) to 139.97 (7)°. The Er—O bond lengths in the title complex lie between 2.3577 (15) and 2.4567 (15) Å, mean 2.393 Å. The whole dhbq2− anion is nearly planar: the r.m.s. deviation from the mean plane through all of the non-H atoms is 0.021 Å, with a maximum displacement from this plane of 0.033 (2) Å for atom C2. As can be seen from Fig. 3 ▸, the dhbq2− ligand acts in a μ2-bis(bidentate) bridging mode, connecting two Er3+ ions to form a honeycomb (6,3) sheet extending in the ab plane, having a Er⋯Er separation of 8.7261 (2) Å.

Figure 1

The mol­ecular structure of the title complex, showing selected atom labels. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) 1 + y − x, 1 − x, z; (ii) 1 − y, x − y, z.

Figure 2

View of the distorted tricapped trigonal–prismatic geometry of the central ErIII ion in the title complex. Symmetry codes: (i) 1 + y − x, 1 − x, z; (ii) 1 − y, x − y, z.

Figure 3

View of the honeycomb (6,3) sheet extending normal to the c-axis direction.

Supra­molecular features

In the crystal, extensive O—H⋯O hydrogen-bonding inter­actions (Table 1 ▸) are observed between the oxygen atoms of the coordinated (O3) and lattice (O4 and O5) water mol­ecules as well as between the water (O5 and O6) mol­ecules of crystallization. Other O—H⋯O hydrogen-bonding inter­actions involve O6 and the dhbq2− oxygen atom, and this inter­action further links neighbouring sheets into a three-dimensional supra­molecular structure (Fig. 4 ▸).

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3A⋯O6i	0.83 (1)	1.94 (1)	2.769 (3)	174 (3)
O3—H3B⋯O5ii	0.84 (1)	1.94 (1)	2.758 (3)	165 (3)
O4—H4A⋯O2iii	0.84 (1)	1.92 (1)	2.738 (3)	167 (4)
O4—H4B⋯O4iv	0.84 (1)	1.98 (1)	2.803 (3)	164 (4)
O5—H5A⋯O1v	0.85 (1)	2.09 (3)	2.870 (3)	153 (5)
O5—H5B⋯O6vi	0.84 (1)	1.95 (1)	2.794 (3)	174 (5)
O6—H6A⋯O4vii	0.85 (1)	1.88 (1)	2.725 (3)	174 (4)
O6—H6B⋯O5	0.84 (1)	1.91 (1)	2.747 (3)	169 (5)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

Figure 4

View of the packing in the unit cell of the title complex along the c axis. Hydrogen-bonding inter­actions are shown as dashed lines.

Database survey

A search of the Cambridge Structural Database (Version 5.39 update February 2018; Groom et al., 2016 ▸) for complexes of dhbq2− ligand gave 94 hits. They include the isotypic crystal structures (Abrahams et al., 2002 ▸) with La (MIZXAU), Gd (MIZXEY), Yb (MIZXIC) and Lu (MIZXOI). In most cases, the dhbq2− ligand acts in a μ2-bis­(bidentate) bridging mode to the central metal ions. Comparing the mean Ln—O bond length and the unit-cell volume for the title complex with the La, Gd, Yb and Lu analogues (Abrahams et al., 2002 ▸), the values decrease as the ionic radius of the Ln 3+ ions decreases in the order La [La—O = 2.540 Å, V = 3289.3 (16) Å3] > Gd [Gd—O = 2.438 Å, V = 3162.7 (7) Å3] > Er [Er—O = 2.393 Å, V = 3107.18 (13) Å3] > Yb [Yb—O = 2.377 Å, V = 3087.1 (4) Å3] > Lu [Lu—O = 2.368 Å, V = 3074.2 (4) Å3], which is consistent with the lanthanide contraction effect.

Synthesis and crystallization

A mixture of Er(NO3)3·6H2O (46.2 mg, 0.1 mmol) and H2dhbq (14.2 mg, 0.1 mmol) in distilled H2O (4 ml) and DMF (1 ml) was placed in a 20 ml vial and stirred at room temperature for 10 min. The mixture was sealed tightly, placed in an oven and then heated to 358 K under autogenous pressure for 12 h. After the reactor was cooled to room temperature, block-shaped dark-red crystals were filtered off, washed with deionized H2O and dried in air at room temperature. Yield: 57% based on ErIII source.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. The carbon-bound H atoms were placed in geometrically calculated positions and refined as riding with C—H = 0.93 Å and U iso(H) = 1.2U eq(C). The hydrogen atoms of the water mol­ecules were located from difference-Fourier maps but were refined with distance restraints of O—H = 0.84 Å and U iso(H) = 1.5U eq(O).

Table 2

Experimental details

Crystal data
Chemical formula	[Er2(C6H2O4)3(H2O)6]·18H2O
M r	1181.13
Crystal system, space group	Trigonal, R
Temperature (K)	296
a, c (Å)	14.0947 (3), 18.0603 (5)
V (Å3)	3107.18 (13)
Z	3
Radiation type	Mo Kα
μ (mm−1)	4.13
Crystal size (mm)	0.28 × 0.22 × 0.2
Data collection
Diffractometer	Bruker D8 QUEST CMOS
Absorption correction	Multi-scan (SADABS; Bruker, 2016 ▸)
T min, T max	0.677, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	32360, 2522, 2108
R int	0.065
(sin θ/λ)max (Å−1)	0.758
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.023, 0.042, 1.08
No. of reflections	2522
No. of parameters	118
No. of restraints	8
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	1.67, −1.39

Computer programs: APEX3 and SAINT (Bruker, 2016 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL (Sheldrick, 2015b ▸) and OLEX2 (Dolomanov et al., 2009 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989018017516/hb7788sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989018017516/hb7788Isup2.hkl

Click here for additional data file.

Supporting information file. DOI: 10.1107/S2056989018017516/hb7788Isup3.cdx

CCDC reference: 1884389

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

[Er2(C6H2O4)3(H2O)6]·18H2O	Dx = 1.894 Mg m−3
Mr = 1181.13	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3	Cell parameters from 8655 reflections
a = 14.0947 (3) Å	θ = 2.8–31.7°
c = 18.0603 (5) Å	µ = 4.13 mm−1
V = 3107.18 (13) Å3	T = 296 K
Z = 3	Hexagonal prism, dark red
F(000) = 1758	0.28 × 0.22 × 0.2 mm

Bruker D8 QUEST CMOS diffractometer	2522 independent reflections
Radiation source: microfocus sealed x-ray tube, Incoatec Iµus	2108 reflections with I > 2σ(I)
GraphiteDouble Bounce Multilayer Mirror monochromator	Rint = 0.065
Detector resolution: 10.5 pixels mm-1	θmax = 32.6°, θmin = 2.8°
φ and ω scans	h = −21→21
Absorption correction: multi-scan (SADABS; Bruker, 2016)	k = −19→21
Tmin = 0.677, Tmax = 0.746	l = −27→27
32360 measured reflections

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.023	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.042	w = 1/[σ2(Fo2) + (0.0042P)2 + 10.2637P] where P = (Fo2 + 2Fc2)/3
S = 1.08	(Δ/σ)max = 0.001
2522 reflections	Δρmax = 1.67 e Å−3
118 parameters	Δρmin = −1.39 e Å−3
8 restraints	Extinction correction: SHELXL (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: dual	Extinction coefficient: 0.00020 (2)

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.

	x	y	z	Uiso*/Ueq
Er1	0.6667	0.3333	0.587213 (10)	0.01773 (5)
O1	0.65928 (12)	0.50374 (13)	0.58327 (9)	0.0236 (3)
O2	0.54678 (13)	0.33698 (13)	0.49769 (9)	0.0247 (3)
O3	0.54011 (16)	0.33067 (15)	0.67424 (11)	0.0355 (4)
H3A	0.557 (3)	0.3878 (16)	0.6975 (16)	0.055 (10)*
H3B	0.4856 (17)	0.2781 (17)	0.6941 (15)	0.046 (9)*
O4	0.7266 (2)	0.52214 (19)	0.37540 (12)	0.0455 (5)
H4A	0.736 (3)	0.494 (3)	0.4136 (13)	0.075 (13)*
H4B	0.6643 (16)	0.489 (3)	0.356 (2)	0.079 (14)*
O5	0.29245 (18)	0.15371 (19)	0.57009 (14)	0.0452 (5)
H5A	0.354 (2)	0.167 (5)	0.587 (3)	0.15 (2)*
H5B	0.285 (4)	0.138 (4)	0.5247 (8)	0.103 (17)*
O6	0.18028 (19)	0.2663 (2)	0.57759 (14)	0.0470 (5)
H6A	0.213 (3)	0.3315 (15)	0.594 (2)	0.091 (16)*
H6B	0.222 (3)	0.240 (4)	0.576 (2)	0.104 (18)*
C1	0.58618 (18)	0.50816 (18)	0.54547 (12)	0.0212 (4)
C2	0.51755 (18)	0.40906 (18)	0.49646 (12)	0.0216 (4)
C3	0.43354 (19)	0.40401 (19)	0.45415 (13)	0.0256 (5)
H3	0.3902	0.3424	0.4255	0.031*

	U11	U22	U33	U12	U13	U23
Er1	0.01570 (6)	0.01570 (6)	0.02179 (9)	0.00785 (3)	0.000	0.000
O1	0.0218 (8)	0.0214 (8)	0.0293 (8)	0.0121 (7)	−0.0056 (6)	−0.0019 (6)
O2	0.0270 (8)	0.0222 (8)	0.0309 (8)	0.0168 (7)	−0.0069 (7)	−0.0050 (6)
O3	0.0371 (11)	0.0239 (9)	0.0394 (11)	0.0106 (8)	0.0163 (8)	−0.0025 (8)
O4	0.0474 (13)	0.0517 (13)	0.0376 (12)	0.0249 (11)	−0.0043 (10)	0.0091 (10)
O5	0.0335 (11)	0.0505 (13)	0.0505 (14)	0.0202 (10)	0.0094 (10)	0.0035 (11)
O6	0.0434 (13)	0.0436 (14)	0.0534 (14)	0.0212 (11)	0.0057 (10)	0.0082 (11)
C1	0.0202 (10)	0.0208 (10)	0.0221 (10)	0.0099 (9)	0.0003 (8)	0.0004 (8)
C2	0.0215 (10)	0.0217 (10)	0.0226 (10)	0.0115 (9)	0.0011 (8)	0.0015 (8)
C3	0.0259 (11)	0.0216 (11)	0.0318 (12)	0.0137 (10)	−0.0077 (9)	−0.0069 (9)

Er1—O1i	2.4567 (15)	O3—H3B	0.836 (10)
Er1—O1	2.4567 (15)	O4—H4A	0.838 (10)
Er1—O1ii	2.4567 (15)	O4—H4B	0.842 (10)
Er1—O2ii	2.3578 (15)	O5—H5A	0.845 (10)
Er1—O2i	2.3577 (15)	O5—H5B	0.844 (10)
Er1—O2	2.3578 (15)	O6—H6A	0.848 (10)
Er1—O3	2.3636 (18)	O6—H6B	0.843 (10)
Er1—O3i	2.3636 (18)	C1—C2	1.523 (3)
Er1—O3ii	2.3637 (18)	C1—C3iii	1.398 (3)
O1—C1	1.263 (3)	C2—C3	1.381 (3)
O2—C2	1.273 (3)	C3—C1iii	1.398 (3)
O3—H3A	0.831 (10)	C3—H3	0.9300
O1i—Er1—O1	119.917 (4)	O3—Er1—O1ii	139.97 (6)
O1ii—Er1—O1i	119.917 (4)	O3—Er1—O1	68.54 (6)
O1ii—Er1—O1	119.916 (4)	O3ii—Er1—O1ii	68.54 (6)
O2i—Er1—O1i	65.01 (5)	O3i—Er1—O1ii	70.00 (6)
O2ii—Er1—O1	69.91 (5)	O3i—Er1—O1i	68.54 (6)
O2ii—Er1—O1ii	65.01 (5)	O3—Er1—O1i	70.00 (6)
O2—Er1—O1	65.01 (5)	O3i—Er1—O3ii	80.60 (8)
O2—Er1—O1ii	134.93 (5)	O3i—Er1—O3	80.60 (8)
O2i—Er1—O1ii	69.91 (5)	O3—Er1—O3ii	80.60 (8)
O2ii—Er1—O1i	134.93 (5)	C1—O1—Er1	119.88 (14)
O2—Er1—O1i	69.91 (5)	C2—O2—Er1	123.42 (14)
O2i—Er1—O1	134.93 (5)	Er1—O3—H3A	118 (2)
O2i—Er1—O2ii	78.15 (6)	Er1—O3—H3B	131 (2)
O2i—Er1—O2	78.15 (6)	H3A—O3—H3B	109 (3)
O2ii—Er1—O2	78.15 (6)	H4A—O4—H4B	117 (4)
O2ii—Er1—O3ii	85.01 (7)	H5A—O5—H5B	112 (5)
O2—Er1—O3ii	134.96 (6)	H6A—O6—H6B	112 (4)
O2i—Er1—O3ii	138.45 (6)	O1—C1—C2	115.38 (19)
O2i—Er1—O3	134.96 (6)	O1—C1—C3iii	124.7 (2)
O2—Er1—O3	85.01 (7)	C3iii—C1—C2	119.92 (19)
O2ii—Er1—O3	138.45 (6)	O2—C2—C1	114.28 (19)
O2i—Er1—O3i	85.01 (7)	O2—C2—C3	125.4 (2)
O2ii—Er1—O3i	134.96 (6)	C3—C2—C1	120.26 (19)
O2—Er1—O3i	138.46 (6)	C1iii—C3—H3	120.1
O3ii—Er1—O1i	139.97 (7)	C2—C3—C1iii	119.8 (2)
O3i—Er1—O1	139.97 (6)	C2—C3—H3	120.1
O3ii—Er1—O1	70.00 (6)
Er1—O1—C1—C2	−8.1 (2)	O2ii—Er1—O1—C1	96.59 (16)
Er1—O1—C1—C3iii	172.37 (18)	O2ii—Er1—O2—C2	−86.3 (2)
Er1—O2—C2—C1	13.9 (3)	O2i—Er1—O2—C2	−166.47 (17)
Er1—O2—C2—C3	−167.71 (18)	O2—C2—C3—C1iii	−176.2 (2)
O1ii—Er1—O1—C1	139.76 (13)	O3ii—Er1—O1—C1	−171.43 (17)
O1i—Er1—O1—C1	−34.5 (2)	O3i—Er1—O1—C1	−126.15 (16)
O1ii—Er1—O2—C2	−121.30 (16)	O3—Er1—O1—C1	−83.94 (16)
O1—Er1—O2—C2	−13.10 (16)	O3ii—Er1—O2—C2	−15.9 (2)
O1i—Er1—O2—C2	126.04 (18)	O3—Er1—O2—C2	55.53 (17)
O1—C1—C2—O2	−3.1 (3)	O3i—Er1—O2—C2	125.30 (17)
O1—C1—C2—C3	178.4 (2)	C1—C2—C3—C1iii	2.1 (4)
O2i—Er1—O1—C1	48.94 (18)	C3iii—C1—C2—O2	176.4 (2)
O2—Er1—O1—C1	10.65 (15)	C3iii—C1—C2—C3	−2.1 (4)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3A···O6iv	0.83 (1)	1.94 (1)	2.769 (3)	174 (3)
O3—H3B···O5v	0.84 (1)	1.94 (1)	2.758 (3)	165 (3)
O4—H4A···O2ii	0.84 (1)	1.92 (1)	2.738 (3)	167 (4)
O4—H4B···O4vi	0.84 (1)	1.98 (1)	2.803 (3)	164 (4)
O5—H5A···O1i	0.85 (1)	2.09 (3)	2.870 (3)	153 (5)
O5—H5B···O6vii	0.84 (1)	1.95 (1)	2.794 (3)	174 (5)
O6—H6A···O4iii	0.85 (1)	1.88 (1)	2.725 (3)	174 (4)
O6—H6B···O5	0.84 (1)	1.91 (1)	2.747 (3)	169 (5)