The title compound, [Dy
2(C
2H
3O
2)
6(H
2O)
4]·4H
2O, crystallizes in the form of dimeric units related by an inversion centre. Each cation is nine-coordinate, binding to two water molecules and three acetate groups, two of which are bidentate and the third tridentate. This last acetate group acts as a bridge between neighbouring metal atoms, leading to an intradimer Dy
Dy separation of 4.170 (1) Å.
Supporting information
CCDC reference: 197315
Dysprosium carbonate (0.20 g) was dissolved in a water-acetic acid solution (25 ml; 1:1 v/v) and boiled under reflux for 1 h. After one week,
colourless crystals of (I) suitable for X-ray diffraction were isolated and
dried in air. Analysis calculated for C12H34O20Dy2: C 17.50, H 4.15%;
found: C 17.45, H 4.15%. Spectroscopic analysis, IR (KBr, cm-1): 1540
(versus), 1455 (versus), 1417 (versus), 1385
(versus), 1315 (m), 1050 (m), 1025 (m), 965
(m), 944 (m), 680 (s, br), 610 (w), 475 (w). The
thermo-gravimetric analysis diagram shows a weight loss of 16% in the
temperature range 83.7 to 146.5 °C, which corresponds to the simultaneous
loss of all the water of crystallization and coordination (calculated 15.5%).
H atoms attached to C atoms were added in their expected positions and not
refined, but were allowed to ride. Terminal methyl H atoms in the acetato
groups were allowed to rotate as well. H atoms pertaining to the water
molecules were found in the difference Fourier maps, and included subject to
mild restraints so as to avoid undesirable drifting, with final values of
O—H = 0.83 (5) Å and H···H 1.66(O—H). A scheme of riding isotropic
displacement parameters was used, with Uiso(H) = 1.5Ueq of
the parent atom.
Data collection: SMART-NT (Bruker, 2001); cell refinement: SMART-NT; data reduction: SAINT-NT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL/PC (Sheldrick, 1991); software used to prepare material for publication: SHELXL97.
Bis(µ-acetato-
κ3O,
O':
O')bis[bis(acetato-
κ2O,
O')diaquadysprosium(III)] tetrahydrate
top
Crystal data top
[Dy2(C2H3O2)6(H2O)4]·4H2O | Z = 1 |
Mr = 823.39 | F(000) = 398 |
Triclinic, P1 | Dx = 2.054 Mg m−3 |
Hall symbol: -P1 | Mo Kα radiation, λ = 0.71073 Å |
a = 8.872 (1) Å | Cell parameters from 112 reflections |
b = 9.249 (1) Å | θ = 3.7–24.1° |
c = 10.456 (1) Å | µ = 5.65 mm−1 |
α = 91.71 (1)° | T = 293 K |
β = 114.11 (1)° | Block, colourless |
γ = 117.88 (1)° | 0.34 × 0.28 × 0.20 mm |
V = 665.8 (2) Å3 | |
Data collection top
Make, Model CCD area-detector diffractometer | 2797 independent reflections |
Radiation source: fine-focus sealed tube | 2746 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.043 |
ϕ and ω scans | θmax = 27.9°, θmin = 2.2° |
Absorption correction: part of the refinement model (ΔF) (SADABS in SAINT-NT; Bruker, 2000) | h = −11→9 |
Tmin = 0.17, Tmax = 0.31 | k = −11→11 |
3864 measured reflections | l = 0→13 |
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)] = 0.041 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.095 | H-atom parameters constrained |
S = 1.06 | w = 1/[σ2(Fo2) + (0.0883P)2] where P = (Fo2 + 2Fc2)/3 |
2797 reflections | (Δ/σ)max = 0.003 |
182 parameters | Δρmax = 1.49 e Å−3 |
12 restraints | Δρmin = −1.05 e Å−3 |
Crystal data top
[Dy2(C2H3O2)6(H2O)4]·4H2O | γ = 117.88 (1)° |
Mr = 823.39 | V = 665.8 (2) Å3 |
Triclinic, P1 | Z = 1 |
a = 8.872 (1) Å | Mo Kα radiation |
b = 9.249 (1) Å | µ = 5.65 mm−1 |
c = 10.456 (1) Å | T = 293 K |
α = 91.71 (1)° | 0.34 × 0.28 × 0.20 mm |
β = 114.11 (1)° | |
Data collection top
Make, Model CCD area-detector diffractometer | 2797 independent reflections |
Absorption correction: part of the refinement model (ΔF) (SADABS in SAINT-NT; Bruker, 2000) | 2746 reflections with I > 2σ(I) |
Tmin = 0.17, Tmax = 0.31 | Rint = 0.043 |
3864 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.041 | 12 restraints |
wR(F2) = 0.095 | H-atom parameters constrained |
S = 1.06 | Δρmax = 1.49 e Å−3 |
2797 reflections | Δρmin = −1.05 e Å−3 |
182 parameters | |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Dy | 0.821140 (17) | 0.096282 (15) | 0.910264 (13) | 0.02616 (11) | |
O1W | 0.7210 (5) | −0.0582 (4) | 1.0646 (4) | 0.0419 (7) | |
H1WA | 0.812 (6) | −0.058 (9) | 1.133 (5) | 0.063* | |
H1WB | 0.626 (6) | −0.089 (8) | 1.078 (7) | 0.063* | |
O2W | 0.8589 (5) | 0.2974 (4) | 1.0808 (4) | 0.0436 (7) | |
H2WA | 0.881 (9) | 0.395 (4) | 1.079 (6) | 0.065* | |
H2WB | 0.874 (10) | 0.283 (7) | 1.162 (4) | 0.065* | |
O1A | 0.6424 (4) | 0.1500 (5) | 0.6955 (3) | 0.0470 (7) | |
O2A | 0.4889 (4) | 0.0371 (4) | 0.8161 (3) | 0.0414 (6) | |
C1A | 0.4919 (6) | 0.0928 (5) | 0.7057 (4) | 0.0335 (8) | |
C2A | 0.3168 (8) | 0.0863 (7) | 0.5927 (6) | 0.0479 (11) | |
H2A1 | 0.3550 | 0.1924 | 0.5679 | 0.072* | |
H2A2 | 0.2284 | 0.0665 | 0.6301 | 0.072* | |
H2A3 | 0.2543 | −0.0043 | 0.5074 | 0.072* | |
O1B | 0.6124 (4) | −0.1827 (4) | 0.7326 (4) | 0.0441 (7) | |
O2B | 0.8815 (4) | −0.1477 (4) | 0.9012 (3) | 0.0328 (6) | |
C1B | 0.7202 (5) | −0.2410 (4) | 0.7860 (4) | 0.0298 (7) | |
C2B | 0.6616 (8) | −0.4128 (7) | 0.7183 (7) | 0.0493 (13) | |
H2B1 | 0.5254 | −0.4754 | 0.6498 | 0.074* | |
H2B2 | 0.6869 | −0.4700 | 0.7923 | 0.074* | |
H2B3 | 0.7340 | −0.4053 | 0.6686 | 0.074* | |
O1C | 1.0193 (4) | 0.1552 (3) | 0.7909 (3) | 0.0354 (6) | |
O2C | 1.0502 (5) | 0.3765 (4) | 0.9052 (4) | 0.0400 (7) | |
C1C | 1.0987 (6) | 0.3131 (5) | 0.8323 (5) | 0.0359 (8) | |
C2C | 1.2533 (9) | 0.4286 (8) | 0.7937 (7) | 0.0603 (13) | |
H2C1 | 1.3498 | 0.3984 | 0.8206 | 0.091* | |
H2C2 | 1.3131 | 0.5446 | 0.8452 | 0.091* | |
H2C3 | 1.1949 | 0.4161 | 0.6907 | 0.091* | |
O3W | 0.7448 (4) | 0.3231 (4) | 0.5045 (4) | 0.0474 (7) | |
H3WA | 0.724 (8) | 0.270 (8) | 0.564 (5) | 0.071* | |
H3WB | 0.641 (5) | 0.298 (8) | 0.433 (5) | 0.071* | |
O4W | 1.0249 (6) | 0.6702 (5) | 0.6294 (4) | 0.0598 (10) | |
H4WA | 1.129 (4) | 0.699 (8) | 0.631 (3) | 0.090* | |
H4WB | 0.936 (7) | 0.571 (5) | 0.581 (8) | 0.090* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Dy | 0.02873 (15) | 0.02685 (15) | 0.02990 (16) | 0.01914 (11) | 0.01435 (11) | 0.01021 (10) |
O1W | 0.0488 (16) | 0.0561 (18) | 0.0521 (17) | 0.0411 (15) | 0.0335 (15) | 0.0286 (15) |
O2W | 0.066 (2) | 0.0359 (14) | 0.0487 (17) | 0.0347 (14) | 0.0341 (16) | 0.0165 (13) |
O1A | 0.0418 (15) | 0.068 (2) | 0.0464 (16) | 0.0356 (14) | 0.0246 (13) | 0.0338 (15) |
O2A | 0.0401 (14) | 0.0591 (17) | 0.0432 (15) | 0.0363 (13) | 0.0225 (12) | 0.0227 (13) |
C1A | 0.0403 (19) | 0.0316 (18) | 0.0360 (19) | 0.0257 (16) | 0.0162 (16) | 0.0113 (15) |
C2A | 0.047 (3) | 0.048 (3) | 0.047 (3) | 0.029 (2) | 0.016 (2) | 0.015 (2) |
O1B | 0.0340 (15) | 0.0444 (17) | 0.0429 (17) | 0.0236 (13) | 0.0062 (13) | 0.0036 (14) |
O2B | 0.0297 (12) | 0.0323 (13) | 0.0325 (13) | 0.0172 (11) | 0.0108 (11) | 0.0052 (11) |
C1B | 0.0286 (15) | 0.0311 (16) | 0.0308 (16) | 0.0183 (13) | 0.0119 (13) | 0.0094 (13) |
C2B | 0.041 (2) | 0.034 (2) | 0.054 (3) | 0.0144 (19) | 0.014 (2) | −0.010 (2) |
O1C | 0.0393 (13) | 0.0366 (13) | 0.0442 (15) | 0.0273 (11) | 0.0226 (12) | 0.0161 (11) |
O2C | 0.0508 (18) | 0.0312 (15) | 0.0484 (18) | 0.0238 (13) | 0.0296 (15) | 0.0132 (13) |
C1C | 0.0377 (18) | 0.0394 (19) | 0.0409 (19) | 0.0239 (16) | 0.0226 (16) | 0.0184 (16) |
C2C | 0.058 (3) | 0.063 (3) | 0.090 (4) | 0.039 (3) | 0.052 (3) | 0.037 (3) |
O3W | 0.0342 (14) | 0.0516 (19) | 0.0408 (16) | 0.0154 (13) | 0.0134 (12) | 0.0130 (14) |
O4W | 0.065 (2) | 0.060 (2) | 0.050 (2) | 0.0259 (19) | 0.0322 (19) | 0.0081 (18) |
Geometric parameters (Å, º) top
Dy—O1W | 2.357 (3) | C2A—H2A3 | 0.9600 |
Dy—O2W | 2.342 (3) | O1B—C1B | 1.257 (5) |
Dy—O1A | 2.387 (3) | O2B—C1B | 1.272 (4) |
Dy—O1B | 2.444 (3) | O2B—Dyi | 2.365 (3) |
Dy—O1C | 2.425 (3) | C1B—C2B | 1.468 (6) |
Dy—O2A | 2.458 (3) | C2B—H2B1 | 0.9600 |
Dy—O2Bi | 2.365 (3) | C2B—H2B2 | 0.9600 |
Dy—O2B | 2.558 (3) | C2B—H2B3 | 0.9600 |
Dy—O2C | 2.453 (4) | O1C—C1C | 1.252 (5) |
O1W—H1WA | 0.83 (5) | O2C—C1C | 1.260 (5) |
O1W—H1WB | 0.83 (5) | C1C—C2C | 1.514 (6) |
O2W—H2WA | 0.83 (5) | C2C—H2C1 | 0.9600 |
O2W—H2WB | 0.83 (5) | C2C—H2C2 | 0.9600 |
O1A—C1A | 1.239 (5) | C2C—H2C3 | 0.9600 |
O2A—C1A | 1.283 (5) | O3W—H3WA | 0.83 (5) |
C1A—C2A | 1.490 (7) | O3W—H3WB | 0.83 (5) |
C2A—H2A1 | 0.9600 | O4W—H4WA | 0.83 (5) |
C2A—H2A2 | 0.9600 | O4W—H4WB | 0.83 (5) |
| | | |
O2W—Dy—O1W | 76.02 (11) | C1A—O1A—Dy | 96.6 (2) |
O2W—Dy—O2Bi | 83.91 (11) | C1A—O2A—Dy | 92.0 (2) |
O1W—Dy—O2Bi | 78.03 (11) | O1A—C1A—O2A | 118.3 (4) |
O2W—Dy—O1A | 97.72 (12) | O1A—C1A—C2A | 121.4 (4) |
O1W—Dy—O1A | 130.67 (10) | O2A—C1A—C2A | 120.2 (4) |
O2Bi—Dy—O1A | 150.94 (10) | C1A—C2A—H2A1 | 109.5 |
O2W—Dy—O1C | 125.62 (10) | C1A—C2A—H2A2 | 109.5 |
O1W—Dy—O1C | 144.35 (9) | H2A1—C2A—H2A2 | 109.5 |
O2Bi—Dy—O1C | 77.03 (10) | C1A—C2A—H2A3 | 109.5 |
O1A—Dy—O1C | 78.63 (9) | H2A1—C2A—H2A3 | 109.5 |
O2W—Dy—O1B | 148.39 (12) | H2A2—C2A—H2A3 | 109.5 |
O1W—Dy—O1B | 83.86 (12) | C1B—O1B—Dy | 98.1 (2) |
O2Bi—Dy—O1B | 115.70 (10) | C1B—O2B—Dyi | 152.1 (3) |
O1A—Dy—O1B | 77.18 (12) | C1B—O2B—Dy | 92.2 (2) |
O1C—Dy—O1B | 84.45 (11) | Dyi—O2B—Dy | 115.69 (10) |
O2W—Dy—O2C | 73.58 (12) | O1B—C1B—O2B | 118.3 (3) |
O1W—Dy—O2C | 143.44 (13) | O1B—C1B—C2B | 121.1 (4) |
O2Bi—Dy—O2C | 79.00 (12) | O2B—C1B—C2B | 120.6 (4) |
O1A—Dy—O2C | 73.76 (12) | C1B—C2B—H2B1 | 109.5 |
O1C—Dy—O2C | 53.07 (10) | C1B—C2B—H2B2 | 109.5 |
O1B—Dy—O2C | 132.02 (12) | H2B1—C2B—H2B2 | 109.5 |
O2W—Dy—O2A | 77.41 (11) | C1B—C2B—H2B3 | 109.5 |
O1W—Dy—O2A | 78.19 (10) | H2B1—C2B—H2B3 | 109.5 |
O2Bi—Dy—O2A | 152.65 (10) | H2B2—C2B—H2B3 | 109.5 |
O1A—Dy—O2A | 53.06 (9) | C1C—O1C—Dy | 94.0 (2) |
O1C—Dy—O2A | 130.22 (9) | C1C—O2C—Dy | 92.5 (3) |
O1B—Dy—O2A | 74.75 (11) | O1C—C1C—O2C | 120.5 (4) |
O2C—Dy—O2A | 113.81 (11) | O1C—C1C—C2C | 119.7 (4) |
O2W—Dy—O2B | 139.43 (10) | O2C—C1C—C2C | 119.8 (4) |
O1W—Dy—O2B | 73.31 (10) | C1C—C2C—H2C1 | 109.5 |
O2Bi—Dy—O2B | 64.31 (11) | C1C—C2C—H2C2 | 109.5 |
O1A—Dy—O2B | 122.42 (11) | H2C1—C2C—H2C2 | 109.5 |
O1C—Dy—O2B | 73.07 (9) | C1C—C2C—H2C3 | 109.5 |
O1B—Dy—O2B | 51.39 (9) | H2C1—C2C—H2C3 | 109.5 |
O2C—Dy—O2B | 120.27 (10) | H2C2—C2C—H2C3 | 109.5 |
O2A—Dy—O2B | 120.47 (10) | H3WA—O3W—H3WB | 111 (6) |
H1WA—O1W—H1WB | 112 (6) | H4WA—O4W—H4WB | 115 (6) |
H2WA—O2W—H2WB | 110 (6) | | |
Symmetry code: (i) −x+2, −y, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O2W—H2WA···O2Cii | 0.83 (5) | 1.88 (5) | 2.715 (5) | 174 (6) |
O2W—H2WB···O4Wii | 0.83 (5) | 1.93 (3) | 2.726 (6) | 161 (6) |
O3W—H3WA···O1A | 0.83 (5) | 1.95 (3) | 2.773 (4) | 171 (6) |
O3W—H3WB···O1Biii | 0.83 (5) | 1.91 (3) | 2.723 (4) | 165 (7) |
O4W—H4WB···O3W | 0.83 (5) | 1.98 (3) | 2.797 (5) | 168 (8) |
O1W—H1WA···O1Ci | 0.83 (5) | 2.00 (5) | 2.751 (4) | 150 (6) |
O1W—H1WB···O2Aiv | 0.83 (5) | 1.96 (6) | 2.699 (4) | 148 (7) |
O4W—H4WA···O3Wv | 0.83 (5) | 2.19 (3) | 2.893 (5) | 143 (3) |
Symmetry codes: (i) −x+2, −y, −z+2; (ii) −x+2, −y+1, −z+2; (iii) −x+1, −y, −z+1; (iv) −x+1, −y, −z+2; (v) −x+2, −y+1, −z+1. |
Experimental details
Crystal data |
Chemical formula | [Dy2(C2H3O2)6(H2O)4]·4H2O |
Mr | 823.39 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 293 |
a, b, c (Å) | 8.872 (1), 9.249 (1), 10.456 (1) |
α, β, γ (°) | 91.71 (1), 114.11 (1), 117.88 (1) |
V (Å3) | 665.8 (2) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 5.65 |
Crystal size (mm) | 0.34 × 0.28 × 0.20 |
|
Data collection |
Diffractometer | Make, Model CCD area-detector diffractometer |
Absorption correction | Part of the refinement model (ΔF) (SADABS in SAINT-NT; Bruker, 2000) |
Tmin, Tmax | 0.17, 0.31 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3864, 2797, 2746 |
Rint | 0.043 |
(sin θ/λ)max (Å−1) | 0.658 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.041, 0.095, 1.06 |
No. of reflections | 2797 |
No. of parameters | 182 |
No. of restraints | 12 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 1.49, −1.05 |
Selected bond lengths (Å) topDy—O1W | 2.357 (3) | Dy—O2A | 2.458 (3) |
Dy—O2W | 2.342 (3) | Dy—O2Bi | 2.365 (3) |
Dy—O1A | 2.387 (3) | Dy—O2B | 2.558 (3) |
Dy—O1B | 2.444 (3) | Dy—O2C | 2.453 (4) |
Dy—O1C | 2.425 (3) | | |
Symmetry code: (i) −x+2, −y, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O2W—H2WA···O2Cii | 0.83 (5) | 1.88 (5) | 2.715 (5) | 174 (6) |
O2W—H2WB···O4Wii | 0.83 (5) | 1.93 (3) | 2.726 (6) | 161 (6) |
O3W—H3WA···O1A | 0.83 (5) | 1.95 (3) | 2.773 (4) | 171 (6) |
O3W—H3WB···O1Biii | 0.83 (5) | 1.91 (3) | 2.723 (4) | 165 (7) |
O4W—H4WB···O3W | 0.83 (5) | 1.98 (3) | 2.797 (5) | 168 (8) |
O1W—H1WA···O1Ci | 0.83 (5) | 2.00 (5) | 2.751 (4) | 150 (6) |
O1W—H1WB···O2Aiv | 0.83 (5) | 1.96 (6) | 2.699 (4) | 148 (7) |
O4W—H4WA···O3Wv | 0.83 (5) | 2.19 (3) | 2.893 (5) | 143 (3) |
Symmetry codes: (i) −x+2, −y, −z+2; (ii) −x+2, −y+1, −z+2; (iii) −x+1, −y, −z+1; (iv) −x+1, −y, −z+2; (v) −x+2, −y+1, −z+1. |
The structures of hydrated rare earth acetates are well known, mainly because they can be easily obtained as well shaped crystals by evaporation of aqueous solutions (Gmelin Handbook, 1984). In these crystals, the acetate groups bridge two rare earth cations in a variety of coordination modes, forming dimeric and/or polymeric forms (Ouchi et al., 1988). In addition, water ligands are incorporated in the first coordination sphere of the rare earth cations, leading to coordination numbers in hydrated rare earth acetates of 9 or 10.
Rare earth acetates are used as starting materials in a wide range of applications in materials science, including superconductors, magnetic materials, catalysts etc. (Parker & Williams, 1996; Segal, 1989; Wang et al., 1994). We report here the crystal structure for the title dysprosium acetate, [Dy2(CH3COO)6(H2O)4]·4H2O, (I), for which geometric data could not be found. A search of the October 2001 release of the Cambridge Structural Database (Allen & Kennard, 1993) showed that the compound is isostructural with those reported for the dimeric acetates of lanthanides of medium to small atomic radius, namely Gd (Favas et al., 1980), (II), Eu (Yansheng et al., 1988), (III), Ho (Bats et al., 1979), (IV) and Er (Sawase et al., 1984), (V), as well as the as yet unreported Tb analogue (Baggio et al., 2002), (VI). \sch
The molecular diagram of (I) (Fig. 1) shows dimeric units related by an inversion centre [at (1,0,1) in the reported coordinates]. The two DyIII metal ions are linked by two bridging tridentate carboxylate groups; one of the carboxylate O atoms in the acetate anion is bound to two Dy atoms, whereas the second O atom is bound only to one. As a result, atoms O2B and O2B' bind in a µ2-bridging manner to both metal centres, forming a monoatomic bridge. Due to the inversion centre, the Dy—O2B—Dy'-O2B' loop is perfectly planar.
The two DyO9 coordination polyhedra are best described as distorted TCTP Please expand. The Dy—Oaqua distances are 2.342 (3) and 2.357 (3) Å, the shortest in the polyhedra, whereas the Dy—Ocarboxylate distances display a rather broad span, from 2.365 (3) to 2.558 (3) Å. The resulting Dy···Dy interdimer separation is 4.170 (1) Å, and the next shortest distance between Dy centres is 6.213 (1) Å.
The interaction between dimers is through medium to weak hydrogen bonds (Table 2), in which all the water H atoms are involved, including an O1W—H1WA···O1C(2 - x, -y, 2 - z) intradimer interaction. The resulting packing is a sequence of broad two-dimensional structures parallel to the crystallographic (001) plane, alternately composed of the dimeric entities (at z ~0 and z ~1 in Fig. 2) and of the hydrate water molecules (at z ~0.5). A transverse-cut view of this spatial set-up is shown in Fig. 2, where the hydrogen-bond interactions can be clearly seen; further details are given in the figure caption.
It should be noted that the size of the lanthanide cations seems to have a negligible effect on the geometric parameters of the dimeric entities; the least-squares fit (Sheldrick, 1991) of the LnO9 coordination polyhedra in (I) with those in compounds (II)-(VI) gave the following maximum deviations: Gd 0.042 (4), Eu 0.038 (4), Ho 0.023 (2), Er 0.053 (5) and Tb 0.022 (2) Å. This family of lanthanide dimers, with essentially the same structure, should be of interest for comparative studies of their different electronic and magnetic properties, in particular superexchange between the lanthanide atoms, which may occur through the bridging O atoms.