The structure of the six-coordinate title complex, [YbI
3(C
4H
8O)
3], is the first
mer-octahedral form of an LnI
3L3 lanthanide (Ln) compound with neutral
L ligands, and is closely related to that of several of the seven-coordinate Ln
X3L4 series of compounds, where
X = Cl, Br or I and
L = tetrahydrofuran (THF), isopropanol, pyridine or water. A structural
trans effect can be assigned to YbI
3(THF)
3, in contrast to the Ln
X3L4 compounds, where steric and crystal packing effects are significant. The Yb—I bond lengths are 2.9543 (4) and 2.9151 (6) Å for I
trans and
cis to I, respectively, and the Yb—O bond lengths are 2.299 (5) and 2.251 (3) Å for O
trans and
cis to I, respectively. The crystal packing allows for six contact distances as weak C—H
I interactions in the range 3.10–3.24 Å. The title molecule has a crystallographic twofold axis passing through a THF O atom, the
trans I atom and the Yb atom.
Supporting information
CCDC reference: 760057
All syntheses were carried out under ultra pure nitrogen (JWS), using
conventional dry-box or Schlenk techniques. Solvents (Fisher) were refluxed
continuously over molten alkali metals or K/benzophenone and were collected
immediately prior to use. Yb was purchased from Strom. Diphenyl
diselenide (PhSeSePh) was purchased from Aldrich and recrystallized from
hexane. For the synthesis of the title compound, Yb (2.0 mmol), PhSeSePh (2.0 mmol), iodine (1.0 mmol) and Hg (0.25 mmol) were combined in THF (50 ml). The
mixture was stirred until all the metal was consumed. To the resulting yellow
solution, elemental S (2.0 mmol) was added. After 24 h, the yellow solution
was filtered and layered with hexanes (15 ml) to give yellow crystals. This
procedure was originally designed to yield the Yb analog of an Er
`double-cubane' cluster compound, (THF)10Er6S6I6.6(THF) (Kornienko
et al., 2005).
All H atoms were located in difference Fourier maps and then treated as
riding atoms. H atoms bonded to the THF C atoms were allowed to
ride in geometrically idealized positions, with C—H = 0.99Å (CH2), with
Uiso(H) = 1.2Ueq(C).
Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and publCIF (Westrip, 2009).
triiodidotris(tetrahydrofuran-
κO)ytterbium(III)
top
Crystal data top
[YbI3(C4H8O)3] | F(000) = 1396 |
Mr = 770.05 | Dx = 2.614 Mg m−3 |
Orthorhombic, Pbcn | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2n 2ab | Cell parameters from 3829 reflections |
a = 9.3507 (7) Å | θ = 2.6–30.5° |
b = 14.6003 (11) Å | µ = 9.51 mm−1 |
c = 14.3335 (11) Å | T = 100 K |
V = 1956.9 (3) Å3 | Lathe, yellow |
Z = 4 | 0.20 × 0.20 × 0.10 mm |
Data collection top
Bruker SMART CCD area-detector diffractometer | 2402 independent reflections |
Radiation source: fine-focus sealed tube | 1808 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.037 |
phi and ω scans | θmax = 28.3°, θmin = 2.6° |
Absorption correction: multi-scan (SADABS; Bruker, 2003) | h = −12→8 |
Tmin = 0.22, Tmax = 0.41 | k = −19→19 |
8941 measured reflections | l = −13→19 |
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)] = 0.029 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.066 | H-atom parameters constrained |
S = 1.00 | w = 1/[σ2(Fo2) + (0.030P)2] where P = (Fo2 + 2Fc2)/3 |
2402 reflections | (Δ/σ)max < 0.001 |
88 parameters | Δρmax = 1.35 e Å−3 |
0 restraints | Δρmin = −0.74 e Å−3 |
Crystal data top
[YbI3(C4H8O)3] | V = 1956.9 (3) Å3 |
Mr = 770.05 | Z = 4 |
Orthorhombic, Pbcn | Mo Kα radiation |
a = 9.3507 (7) Å | µ = 9.51 mm−1 |
b = 14.6003 (11) Å | T = 100 K |
c = 14.3335 (11) Å | 0.20 × 0.20 × 0.10 mm |
Data collection top
Bruker SMART CCD area-detector diffractometer | 2402 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2003) | 1808 reflections with I > 2σ(I) |
Tmin = 0.22, Tmax = 0.41 | Rint = 0.037 |
8941 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.029 | 0 restraints |
wR(F2) = 0.066 | H-atom parameters constrained |
S = 1.00 | Δρmax = 1.35 e Å−3 |
2402 reflections | Δρmin = −0.74 e Å−3 |
88 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. |
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 >
σ(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 | Uiso*/Ueq | |
Yb1 | 0.0000 | 0.13361 (2) | 0.2500 | 0.01766 (9) | |
I1 | −0.19169 (4) | 0.12839 (3) | 0.08624 (2) | 0.02774 (10) | |
I2 | 0.0000 | 0.33327 (3) | 0.2500 | 0.02725 (12) | |
O1 | 0.1890 (4) | 0.1150 (3) | 0.1546 (2) | 0.0261 (8) | |
C1 | 0.2094 (6) | 0.1554 (5) | 0.0633 (4) | 0.0371 (16) | |
H1A | 0.2044 | 0.2230 | 0.0672 | 0.045* | |
H1B | 0.1345 | 0.1338 | 0.0196 | 0.045* | |
C2 | 0.3561 (6) | 0.1253 (4) | 0.0299 (4) | 0.0296 (12) | |
H2A | 0.3519 | 0.1036 | −0.0355 | 0.035* | |
H2B | 0.4254 | 0.1764 | 0.0340 | 0.035* | |
C3 | 0.3971 (6) | 0.0498 (5) | 0.0936 (5) | 0.0398 (15) | |
H3A | 0.3761 | −0.0102 | 0.0644 | 0.048* | |
H3B | 0.5006 | 0.0527 | 0.1076 | 0.048* | |
C4 | 0.3156 (8) | 0.0604 (6) | 0.1775 (5) | 0.060 (3) | |
H4A | 0.3735 | 0.0918 | 0.2257 | 0.072* | |
H4B | 0.2867 | −0.0003 | 0.2019 | 0.072* | |
O2 | 0.0000 | −0.0239 (3) | 0.2500 | 0.0302 (12) | |
C5 | 0.0136 (11) | −0.0832 (4) | 0.3306 (4) | 0.065 (3) | |
H5A | 0.1113 | −0.0788 | 0.3568 | 0.078* | |
H5B | −0.0556 | −0.0649 | 0.3794 | 0.078* | |
C6 | −0.0148 (11) | −0.1756 (5) | 0.3001 (6) | 0.068 (3) | |
H6A | −0.1156 | −0.1925 | 0.3124 | 0.081* | |
H6B | 0.0483 | −0.2196 | 0.3329 | 0.081* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Yb1 | 0.02106 (15) | 0.01552 (15) | 0.01640 (14) | 0.000 | 0.00386 (11) | 0.000 |
I1 | 0.02805 (18) | 0.03006 (19) | 0.02512 (17) | −0.00554 (16) | −0.00445 (14) | 0.00095 (16) |
I2 | 0.0365 (3) | 0.0165 (2) | 0.0287 (3) | 0.000 | −0.0038 (2) | 0.000 |
O1 | 0.0257 (19) | 0.032 (2) | 0.0209 (18) | 0.0111 (17) | 0.0092 (15) | 0.0063 (16) |
C1 | 0.027 (3) | 0.063 (5) | 0.021 (3) | 0.009 (3) | 0.009 (2) | 0.009 (3) |
C2 | 0.029 (3) | 0.034 (3) | 0.026 (3) | 0.008 (3) | 0.013 (2) | −0.004 (3) |
C3 | 0.024 (3) | 0.047 (4) | 0.048 (4) | 0.008 (3) | 0.008 (3) | 0.014 (3) |
C4 | 0.054 (5) | 0.078 (6) | 0.049 (4) | 0.049 (4) | 0.025 (4) | 0.032 (4) |
O2 | 0.055 (4) | 0.017 (3) | 0.019 (2) | 0.000 | 0.006 (3) | 0.000 |
C5 | 0.147 (8) | 0.025 (3) | 0.022 (3) | −0.009 (4) | −0.001 (4) | 0.005 (2) |
C6 | 0.118 (7) | 0.021 (3) | 0.065 (5) | 0.015 (4) | 0.035 (5) | 0.016 (3) |
Geometric parameters (Å, º) top
Yb1—I1 | 2.9543 (4) | C3—C4 | 1.432 (9) |
Yb1—I2 | 2.9151 (6) | C3—H3A | 0.9900 |
Yb1—O1 | 2.251 (3) | C3—H3B | 0.9900 |
Yb1—O2 | 2.299 (5) | C4—H4A | 0.9900 |
Yb1—O1i | 2.251 (3) | C4—H4B | 0.9900 |
Yb1—I1i | 2.9543 (4) | O2—C5i | 1.449 (7) |
O1—C1 | 1.448 (6) | O2—C5 | 1.449 (7) |
O1—C4 | 1.465 (7) | C5—C6 | 1.443 (10) |
C1—C2 | 1.518 (8) | C5—H5A | 0.9900 |
C1—H1A | 0.9900 | C5—H5B | 0.9900 |
C1—H1B | 0.9900 | C6—C6i | 1.464 (15) |
C2—C3 | 1.482 (8) | C6—H6A | 0.9900 |
C2—H2A | 0.9900 | C6—H6B | 0.9900 |
C2—H2B | 0.9900 | | |
| | | |
I1—Yb1—I1i | 177.044 (18) | H2A—C2—H2B | 108.9 |
I1—Yb1—I2 | 91.478 (9) | C4—C3—C2 | 107.4 (5) |
O2—Yb1—I2 | 180.0 | C4—C3—H3A | 110.2 |
O1i—Yb1—O1 | 166.1 (2) | C2—C3—H3A | 110.2 |
O1i—Yb1—O2 | 83.07 (10) | C4—C3—H3B | 110.2 |
O1—Yb1—O2 | 83.07 (10) | C2—C3—H3B | 110.2 |
O1i—Yb1—I2 | 96.93 (10) | H3A—C3—H3B | 108.5 |
O1—Yb1—I2 | 96.93 (10) | C3—C4—O1 | 107.5 (5) |
O1i—Yb1—I1 | 90.19 (10) | C3—C4—H4A | 110.2 |
O1—Yb1—I1 | 89.46 (10) | O1—C4—H4A | 110.2 |
O2—Yb1—I1 | 88.522 (9) | C3—C4—H4B | 110.2 |
O1i—Yb1—I1i | 89.46 (10) | O1—C4—H4B | 110.2 |
O1—Yb1—I1i | 90.19 (10) | H4A—C4—H4B | 108.5 |
O2—Yb1—I1i | 88.522 (9) | C5i—O2—C5 | 106.6 (6) |
I2—Yb1—I1i | 91.478 (9) | C5i—O2—Yb1 | 126.7 (3) |
C1—O1—C4 | 108.5 (4) | C5—O2—Yb1 | 126.7 (3) |
C1—O1—Yb1 | 127.1 (3) | C6—C5—O2 | 107.6 (6) |
C4—O1—Yb1 | 124.3 (3) | C6—C5—H5A | 110.2 |
O1—C1—C2 | 106.6 (4) | O2—C5—H5A | 110.2 |
O1—C1—H1A | 110.4 | C6—C5—H5B | 110.2 |
C2—C1—H1A | 110.4 | O2—C5—H5B | 110.2 |
O1—C1—H1B | 110.4 | H5A—C5—H5B | 108.5 |
C2—C1—H1B | 110.4 | C5—C6—C6i | 105.2 (4) |
H1A—C1—H1B | 108.6 | C5—C6—H6A | 110.7 |
C3—C2—C1 | 104.7 (5) | C6i—C6—H6A | 110.7 |
C3—C2—H2A | 110.8 | C5—C6—H6B | 110.7 |
C1—C2—H2A | 110.8 | C6i—C6—H6B | 110.7 |
C3—C2—H2B | 110.8 | H6A—C6—H6B | 108.8 |
C1—C2—H2B | 110.8 | | |
| | | |
O1i—Yb1—O1—C1 | 127.3 (5) | C2—C3—C4—O1 | 22.3 (9) |
O2—Yb1—O1—C1 | 127.3 (5) | C1—O1—C4—C3 | −13.1 (9) |
I2—Yb1—O1—C1 | −52.7 (5) | Yb1—O1—C4—C3 | 168.4 (4) |
I1—Yb1—O1—C1 | 38.7 (5) | O1i—Yb1—O2—C5i | 121.4 (5) |
I1i—Yb1—O1—C1 | −144.2 (5) | O1—Yb1—O2—C5i | −58.6 (5) |
O1i—Yb1—O1—C4 | −54.5 (6) | I1—Yb1—O2—C5i | 31.1 (5) |
O2—Yb1—O1—C4 | −54.5 (6) | I1i—Yb1—O2—C5i | −148.9 (5) |
I2—Yb1—O1—C4 | 125.5 (6) | O1i—Yb1—O2—C5 | −58.6 (5) |
I1—Yb1—O1—C4 | −143.1 (6) | O1—Yb1—O2—C5 | 121.4 (5) |
I1i—Yb1—O1—C4 | 34.0 (6) | I1—Yb1—O2—C5 | −148.9 (5) |
C4—O1—C1—C2 | −1.0 (7) | I1i—Yb1—O2—C5 | 31.1 (5) |
Yb1—O1—C1—C2 | 177.4 (4) | C5i—O2—C5—C6 | −9.0 (5) |
O1—C1—C2—C3 | 14.1 (7) | Yb1—O2—C5—C6 | 171.0 (5) |
C1—C2—C3—C4 | −22.4 (8) | O2—C5—C6—C6i | 23.3 (13) |
Symmetry code: (i) −x, y, −z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C1—H1A···I1ii | 0.99 | 3.24 | 3.926 (6) | 128 |
C1—H1B···I1 | 0.99 | 3.20 | 3.785 (6) | 120 |
C3—H3B···I1iii | 0.99 | 3.10 | 4.014 (6) | 155 |
C4—H4A···I1i | 0.99 | 3.23 | 3.715 (8) | 112 |
C4—H4B···I2iv | 0.99 | 3.22 | 3.879 (7) | 126 |
C5—H5A···I1i | 0.99 | 3.22 | 3.706 (7) | 112 |
Symmetry codes: (i) −x, y, −z+1/2; (ii) x+1/2, −y+1/2, −z; (iii) x+1, y, z; (iv) x+1/2, y−1/2, −z+1/2. |
Experimental details
Crystal data |
Chemical formula | [YbI3(C4H8O)3] |
Mr | 770.05 |
Crystal system, space group | Orthorhombic, Pbcn |
Temperature (K) | 100 |
a, b, c (Å) | 9.3507 (7), 14.6003 (11), 14.3335 (11) |
V (Å3) | 1956.9 (3) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 9.51 |
Crystal size (mm) | 0.20 × 0.20 × 0.10 |
|
Data collection |
Diffractometer | Bruker SMART CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2003) |
Tmin, Tmax | 0.22, 0.41 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8941, 2402, 1808 |
Rint | 0.037 |
(sin θ/λ)max (Å−1) | 0.667 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.029, 0.066, 1.00 |
No. of reflections | 2402 |
No. of parameters | 88 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 1.35, −0.74 |
Selected geometric parameters (Å, º) topYb1—I1 | 2.9543 (4) | Yb1—O1 | 2.251 (3) |
Yb1—I2 | 2.9151 (6) | Yb1—O2 | 2.299 (5) |
| | | |
I1—Yb1—I1i | 177.044 (18) | O2—Yb1—I2 | 180.0 |
I1—Yb1—I2 | 91.478 (9) | O1i—Yb1—O1 | 166.1 (2) |
Symmetry code: (i) −x, y, −z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C1—H1A···I1ii | 0.99 | 3.24 | 3.926 (6) | 128.0 |
C1—H1B···I1 | 0.99 | 3.20 | 3.785 (6) | 119.6 |
C3—H3B···I1iii | 0.99 | 3.10 | 4.014 (6) | 154.7 |
C4—H4A···I1i | 0.99 | 3.23 | 3.715 (8) | 111.8 |
C4—H4B···I2iv | 0.99 | 3.22 | 3.879 (7) | 125.6 |
C5—H5A···I1i | 0.99 | 3.22 | 3.706 (7) | 111.9 |
Symmetry codes: (i) −x, y, −z+1/2; (ii) x+1/2, −y+1/2, −z; (iii) x+1, y, z; (iv) x+1/2, y−1/2, −z+1/2. |
Average Ln—X and Ln—Y trans to atom X or Y for LnX3L3 and
LnX3L4,
where X=I, Br, Cl; Y=O, N; L=THF, py, i-PrOH, H2O,
O=P[N(Me2)]3. top | ave Ln-(I,Br or Cl) (Å) | | ave Ln-(O or N) (Å) | neutral ligand, L | reference |
7-coordinate compounds | | | | | |
La—I | 3.14/3.19 | La—O | 2.56/2.52 | THF | (Trifonov et al., 1997) |
Ce—I | 3.12/3.18 | Ce—O | 2.54/2.50 | THF | (Liddle & Arnold, 2005) |
Pr—I | 3.10/3.16 | Pr—O | 2.51/2.47 | THF | (Izod et al., 2004) |
Nd—I | 3.08/3.15 | Nd—O | 2.50/2.46 | THF | (Balashova et al., 2007) |
La—I | 3.20/3.21 | La—O | 2.51/2.51 | i-PrOH | (Barnhart et al., 1995) |
Ce—I | 3.17/3.19 | Ce—O | 2.48/2.49 | i-PrOH | (Barnhart et al., 1995) |
La—Br | 2.90/2.90 | La—O | 2.55/2.51 | THF | (Deacon et al., 2000) |
Ce—Br | 2.88/2.91 | Ce—O | 2.55/2.50 | THF | (Hitchcock et al., 2004) |
Pr—Br | 2.87/2.90 | Pr—O | 2.53/2.49 | THF | (Petricek, 2004) |
Sm—Br | 2.82/2.86 | Sm—O | 2.49/2.44 | THF | (Petricek, 2004) |
Nd—Br | 2.85/2.83 | Nd—O | 2.52/2.45 | THF,i-PrOH | (Ye Sun Chun, et al., 1994) |
Sm—Br | 2.85/2.80 | Sm—O | 2.49/2.43 | i-PrOH | (Depero et al., 1991) |
Eu—Cl | 2.62/2.64 | Eu—O | 2.47/2.45 | THF | (De-Yuan, et al., 1998) |
Gd—Cl | 2.62/2.66 | Gd—O | 2.46/2.48 | THF | (Willey et al., 1997) |
Sm—Cl | 2.68/2.68 | Sm—O | 2.49/2.45 | THF | (Guan-Yang, et al., 1992) |
Nd—Cl | 2.67/2.67 | Nd—O | 2.52/2.48 | THF | (Wenqi et al., 1987) |
La—Cl | 2.66/2.68 | La—N | 2.62/2.59 | py | (Li et al., 2002) |
Eu—Cl | 2.64/2.67 | Eu—N | 2.61/2.59 | py | (Ning-Hai, et al., 1986) |
Er—Cl | 2.58/2.62 | Er—N | 2.54/2.50 | py | (Li et al., 2002) |
Yb—Cl | 2.56/2.60 | Yb—N | 2.51/2.49 | py | (Deacon et al., 2006) |
Er—Cl | 2.60/2.66 | Er—O | 2.37/2.32 | H2O | (Hines et al., 2008) |
Tm—Cl | 2.64/2.62 | Tm—O | 2.35/2.35 | H2O | (Semenova et al., 2006) |
Yb—Cl | 2.63/2.62 | Yb—O | 2.33/2.26 | H2O | (Semenova et al., 2006) |
Lu—Cl | 2.59/2.60 | Lu—O | 2.35/2.28 | H2O | (Semenova et al., 2006) |
Er—Cl | 2.64/2.63 | Er—O | 2.35/2.29 | H2O | (Semenova et al., 2006) |
6-coordinate compounds | | | | | |
Yb—I | 2.95/2.92 | Yb—O | 2.30/2.25 | THF | current work |
Yb—Br | 2.71/2.66 | Yb—O | 2.33/2.26 | THF | (Deacon et al., 2000) |
Sm—Br | 2.85/2.82 | Sm—O | 2.47/2.28 | THF | (Asakura & Imamoto, 2001) |
Yb—Cl | 2.53/2.51 | Yb—O | 2.36/2.27 | THF | (Chang-Tao, et al., 1993) |
Lu—Cl | 2.53/2.50 | Lu—O | 2.32/2.27 | THF | (Magomedov et al., 1992) |
Dy—Cl | 2.73/2.71 | Dy—O | 2.35/2.35 | i-PrOH | (Radonovich & Glick, 1973) |
Yb—Cl | 2.59/2.58 | Yb—O | 2.22/2.23 | i-PrOH | (Hou et al., 1991) |
The crystal structures of many lanthanide (Ln) halide (X) compounds with one or more neutral ligands (L) are well known. For compounds with X=Cl, Br or I and small to moderate size neutral Lewis base ligands like tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), pyradine (py), hexamethylphosphoramide [O═P(NMe2)3], isopropyl alcohol (i-PrOH) and water (H2O), the most likely species to crystallize is the seven-coordinate LnXnL7-n. This situation is apparently the case whether the lanthanide is di- or tri-valent, where the number of neutral organic ligands is usually 5 or 4, respectively. Excluding LnX6 ions, there are only 18 six-coordinate monomeric LnX3L3 species with L as described above in the Cambridge Structural Database (CSD) to date (Version 5.30; Allen, 2002). However, the variety of Ln atom is not diminished, and the size of trivalent lanthanide radii appears to play no role in allowing octahedral coordination, as LnX3L3 compounds are observed with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Yb and Lu and X = Cl, except for one X = Br compound, YbBr3(THF)3 (Deacon et al., 2000). Additionally, the organic ligands (L) may be small (e.g. H2O, py or THF) or large (e.g. triphenylarsine oxide; Ryan et al., 1987) and still yield a six-coordinate compound. This group of compounds includes the two LnX3(THF)3 analogs most closely related to the title compound, where Ln, X = Lu, Br (Magomedov et al., 1992) or Yb, Cl (Deacon et al., 1993).
For the six-coordinate LnX3L3 compounds, both fac and mer isomers are found in the CSD for X = Cl, but only mer isomers are found for X = Br, presumably as a result of the increased size of the bromide ion compared with the chloride ion. The title compound is the only six-coordinate triiodo species of this type, and a trans influence on bond geometries is evident, as shown by the data in Table 2. Other mer-octahedral trihalides of this type with significant trans influence are mer-YbBr3(THF)3 (Deacon, et al., 2000) and mer-SmBr3[O═P(NMe2)3]2THF (Asakura & Imamoto, 2001). Of the seven mer isomers, five are LnCl3L3 – mer-YbCl3(THF)3 (Chang-Tao et al., 1993), mer-LuCl3(THF)3 (Magomedov et al., 1992), mer-DyCl3[O═P(NMe2)3]3 (Xing-Wang et al., 1987), mer-PrCl3[O═P(NMe2)3]3 (Radonovich & Glick, 1973) and mer-YbCl3[O═P(NMe2)3]3 (Hou et al., 1991) – and two are LnBr3L3 – mer-YbBr3(THF)3 and mer-SmBr3[O═P(NMe2)3]2THF. The fac isomers of six-coordinate LnX3L3 usually have larger L ligands, as in fac-trichlorido-tris(3-bromo-4-methoxylutidine N-oxide-O)praseodymium (Ban-Oganowska et al., 2002), fac-trichlorido-tris(triphenylarsine oxide)cerium (Ryan et al., 1987), fac-trichlorido-tris(2,6-dimethyl-4-pyrone)gadolinium (Bisi Castellani & Tazzoli, 1984), fac-trichlorido-tris(hexamethylphosphoramide-O)samarium (Petricek et al., 2000), fac-trichlorido-caprolactonato-O–bis(tetrahydrofuran)ytterbium (Evans et al., 1995) and fac-trichlorido-tris[bis(diethylamido)trichloroacetylamidophosphoric acid]praseodymium (Amirkhanov et al., 1995). Instances of fac LnCl3[O═P(NMe2)3]3 are also known, namely, the isostructural series Ln = La, Pr, Sm, Eu, Nd and Gd (Petricek et al. 2000). The only instance of a seven-coordinate Ln3X3 compound approximating a fac isomer is when the sterically constrained tripodal ligand tris(2-pyridylmethyl)amine is used in a Ce triiodo complex (Natrajan et al., 2005).
When the DME bidentate ligand is used, the seven-coordinate compound is most likely to be produced, and there are over 80 instances in the CSD of LnX3Y4, where Y is the binding O atom (or N atom for di-, tri- or tetraamine) of a bidentate organic ligand. Unlike the Ce compound mentioned above, about 20 are of the type LnX3(DME)2 with X = Cl or Br only. There is one other LnI3Y4, where Y are O atoms from a multidentate ligand, namely, L = tetraglyme (Vestergren et al., 2004). In a broad sense, the nine compounds in the CSD of the type LnI3L4, where L are not multidentate, approximate the mer conformation (namely, having one nearly linear I—Ln—I angle and two ~90° I—Ln—I angles), even though there is seven-coordinate binding. This situation is presumably also due to the large volume occupied by each iodide ligand and to the fact that two I atoms are axial in the pentagonal–bipyramidal LnI3L4 complexes.
In the search for LnI3(Y = O,N)n species, the CSD revealed no six-coordinate, one nine-coordinate, five eight-coordinate and ten seven-coordinate compounds, with five compounds having tripodal ligands. For LnI3Ln and LnBr3Ln, neither L = py nor L = H2O species are found in the CSD. There are four LnI3(THF)4 compounds in the CSD; their Ln—I and Ln—O distances are compared with those of the title compound in Table 3, which shows a persistent trans influence on the O atom of the two THF ligands furthest from the equatorial I atom (the other two I atoms are trans to each other). However, as seven-coordinate pentagonal–bipyramidal compounds with five equatorial ligands, these LnI3(THF)4 compounds appear to have geometries significantly influenced by steric effects, especially with respect to the equatorial I ligand, such that the cis (e.g. equatorial) Ln—I bond is about 0.06 Å longer than either of the trans Ln—I bonds.
For LnBr3(O,N)n compounds, there are 11 seven-coordinate, one six-coordinate and one eight-coordinate species in the CSD, with five having tripodal ligands. Of these, one is YbBr3(THF)3 (Deacon et al., 2000) and four are LnBr3(THF)4. Details of their lanthanide bond geometries, as well as those of SmBr3(i-PrOH)4 (Depero et al., 1991) and NdBr3(THF)2(i-PrOH)2 (with THF ligands nearly trans to the equatorial Br atom; Ye Sun Chun et al., 1994), are also compared with the Yb—I and Yb—O bonds of the title YbI3(THF)3 compound in Table 3. There are many instances of LnCl3L3 and LnCl3L4, so bond comparisons here will be restricted to only L = THF, py and H2O, the smallest ligands in the series, and these compounds are included in Table 3.
For lanthanides with coordination saturated with halogens, only the LnX6 ions are found in the CSD. For LnX6, the range of Ln—X bonds for any Ln and X is about ±0.02Å from the average, which is not very narrow, even though these compounds are simple octahedra, indicating the likelihood of short-range nonsymmetrical crystal packing effects. There is one reported X = Br species, EuBr6, and the Eu—Br bonds are 2.80 (2) Å (Pellens et al., 2008); there are seven LnI6 [Ln = La, Pr, Nd (three examples), Sm and Er] with La—I bonds of 3.16 (2) Å (Babai & Mudring, 2006a), Pr—I bonds of 3.13 (2) Å (Babai &Mudring, 2005b), Nd—I bonds of 3.11 (2) Å (Babai &Mudring, 2005a; Babai & Mudring, 2006b), Sm—I bonds of 3.09 (2) Å (Babai &Mudring, 2005a) and Er—I bonds of 3.03 (1) Å (Babai &Mudring, 2006a); and there are 35 LnCl6 with an overall average Ln—Cl bond of 2.68 (2) Å and a range of 2.51–2.89 for the entire Ln series, but with a similar 0.01–0.03 Å variation from the mean for any given compound.
In summary, the YbI3(THF)3 complex reported here is the first instance of a six-coordinate triiodolanthanide. In addition, the observed mer conformation allows for the possibility of a trans influence which is rarely seen in six-coordinate lanthanide compounds. The bonds affected are the Yb—I and Yb—O bonds, which are 0.03 and 0.05 Å longer when trans to an I atom. Finally, six H···I contact distances in the range 3.10 to 3.24 Å are observed (Table 1), which are thus of the order of the van der Waals radii sum of 3.18 Å (Bondi, 1964). Although these distances are consistent with weak hydrogen-bond interactions, the THF ligand is traditionally expected to be a poor hydrogen-bond donor.