research communications
N-tert-butylbenzamidinium) hexachloridozirconate(IV) dichloromethane disolvate
of bis(aInstitute of Applied Chemistry, Shanxi University, Taiyuan 030006, People's Republic of China
*Correspondence e-mail: sdbai@sxu.edu.cn
In the ZrIV complex anion of the title complex salt, [(C4H9)HNC(C6H5)NH2]2[ZrCl6]·2CH2Cl2, the ZrIV cation, located on an inversion centre, is coordinated by six Cl− anions in a distorted octahedral geometry with Zr—Cl distances in the range 2.433 (2)–2.4687 (19) Å; in the amidinium cation, the dihedral angle between the aromatic ring and [NCN] plane is 43.3 (4)°. In the crystal, the amidinium cations and [ZrCl6]2− anions are linked by N—H⋯Cl hydrogen bonds, forming a two-dimensional network extending along the b axis; two dichloromethane solvent molecules are linked by a pair of weak C—H⋯Cl hydrogen bonds, forming a centrosymmetric [CHCl]2 six-membered ring.
Keywords: crystal structure; benzamidinium; zirconate; N—H⋯Cl hydrogen bonds.
CCDC reference: 1454857
1. Chemical context
Amidinates represent an important class in the array of N-centered ligands comparable to the cyclopentadienyl system (Edelmann, 1994; Barker & Kilner, 1994; Collins, 2011). They are four-electron, monoanionic and N-donor bidentate chelates, demonstrating a great diversity by variation of substituents on the conjugated N–C–N backbone. Their steric and electronic properties are easily tunable to meet the requirements of different metal atoms. In the course of extending amidinate chemistry, we have explored a practical synthetic pathway to the alkyl-ended amidinate and ansa-bis(amidinate) ligands (Bai et al., 2013). They have been applied in the synthesis of Group 4 complexes, which are good catalysts for ethylene polymerization (Bai et al., 2010). are convenient precursors for both monoanionic amidinate ligands and bianionic ansa-bis(amidinate) ligands (Coles, 2006). Some could be prepared by Yb complex-catalysed addition reactions of aromatic and (Wang et al., 2008). On the other hand, monoanionic amidinate could be used to prepare amidine and amidinium through acidolysis. Based on the same skeleton, the transformation from amidinate to amidinium will undergo an electrical inversion. Here, we report the synthesis and structural characterization of a bis(N-tert-butyl-benzamidinium) hexachloridozirconate complex derived from the monoanionic amidinate.
2. Structural commentary
The anion in the title compound, (I), is centrosymmetric with the ZrIV cation located on an inversion centre (Fig. 1) and is six-coordinated by Cl− atoms. The corresponding can be described as a distorted octahedron where atoms Cl1, Cl2, Cl1i and Cl2i [symmetry code: (i) −x + 2, −y, −z + 1] define the equatorial plane while atoms Cl3 and Cl3i occupy the axial positions. The equatorial Zr—Cl bond lengths are 2.4674 (18) Å and 2.4687 (19) Å while the axial bond length [2.433 (2) Å] is a little shorter. In the amidinium moiety, the terminal tert-butyl group is disposed in the direction opposite to the phenyl group on the ipso-carbon of the N–C–N backbone, which could minimize between the two groups. The dihedral angle between the aromatic ring and [NCN] plane is 43.3 (4)°. The two C—N bond lengths are equivalent [1.300 (8) and 1.299 (9) Å], composing a typical conjugated N—C—N skeleton. The lengths of the C—N bonds in (I) are shorter than those reported for a similar amidinium cation (1.325 Å; Centore et al., 2003).
3. Supramolecular features
The extended structure consists of amidinium cations forming an extended hydrogen-bonded network with the chlorine atoms of the hexachloridozirconate anions. The amidinium cations involving N1 and N2 all serve as hydrogen-bond donors while only the chlorine atoms in the equatorial plane of the hexachloridozirconate anions act as acceptors (Table 1, Fig. 2). With the N—H⋯Cl hydrogen bonds, each amidinium cation connects two adjacent [ZrCl6]2− anions and each [ZrCl6]2− anion links four neighboring amidinium cations. The existence of bifurcated hydrogen bonds enables the formation of a two-dimensional network. Four amidinium cations and four [ZrCl6]2− anions compose a square-like hole. [ZrCl6]2− anions occupy the vertex positions and amidinium cations are on the edge. The corresponding motif obeys the operation of centrosymmetry and the inversion centre is the central point of the square. Moreover, the two-dimensional network extends along the b axis (Fig. 3). In other words, the layered network is parallel to (101) and perpendicular to (010). Besides the N—H⋯Cl hydrogen bonds, a C—H⋯Cl hydrogen bond can be observed between two centrosymmetrically related dichloromethane solvent molecules, leading to the formation of a [CHCl]2 six-membered ring geometry. The angle of the C—H⋯Cl hydrogen bond is 171°, suggesting a closely linear arrangement of the related C, H and Cl atoms, also resulting in a long distance between donor and acceptor atoms [3.70 (2) Å].
4. Database survey
There are 38 structures that incorporate the zirconate anions, including [ZrCl6]2−, [Zr2Cl10]2− and [Zr2Cl9]−. Of those 38 structures, only one has amidinium as the counter-cation (Centore et al., 2003). Its [Zr2Cl10]2− anion has two bridging Cl atoms and its amidinium cation has three substituents attached on the two nitrogen atoms. In contrast to the title compound, no N—H⋯Cl hydrogen bond is observed due to the hindrance of the N-substituents and the lack of an N-bound hydrogen atom.
5. Synthesis and crystallization
General Procedure: All manipulations and reactions were performed under an inert atmosphere of nitrogen using standard Schlenk techniques. Solvents were pre-dried over sodium, distilled from sodium-benzophenone (diethyl ether and dioxane) and stored over molecular sieves (4 Å). CH2Cl2 was purified by distillation over CaH2. HCl was prepared by treating NaCl with concentrated H2SO4 and dissolved in dioxane.
Synthesis of bis(N-tert-butyl-benzamidinium) hexachloridozirconate(IV): The title compound was prepared by a one-pot reaction of tert-butylamine, LiBu, PhCN, HCl (3.6 M in dioxane) and ZrCl4. A solution of LiBun (2.2 M, 2.27 ml, 5.0 mmol) in hexane was slowly added into a solution of tert-butylamine (0.53 ml, 5.0 mmol) in Et2O (30 ml) by syringe at 273 K. The reaction mixture was warmed to room temperature and kept stirring for 3 h. Then benzonitrile (0.51 ml, 5.0 mmol) was added by syringe at 273 K. The reaction mixture was warmed to room temperature and kept stirring for 4 h. HCl (2.78 ml, 10.0 mmol, 3.6 M in dioxane) was added by syringe at 273 K. After stirring at room temperature for 4 h, ZrCl4 (0.583 g, 2.5 mmol) was added at 273 K. The resulting mixture was stirred at room temperature overnight and all volatiles were removed in vacuo. The residue was extracted with dichloromethane and the filtrate was concentrated to give colorless crystals (yield 1.325 g, 64%). The intermediate process involved an of lithium amide and nitrile to yield lithium monoamidinate. Crystals of (I) suitable for single-crystal X-ray investigation were obtained by recrystallization from CH2Cl2.
6. for ethylene polymerization
The to MAO. Therefore, a conclusion could be drawn that the title compound can not catalyse ethylene polymerization.
of the title compound for ethylene polymerization was examined. At normal pressure and in the presence of methylaluminoxane (MAO), it was found to be an inactive catalyst for ethylene polymerization at 303 K or higher temperature. The reaction was then performed at 10 atm in a 250 mL autoclave. However, only a trace to very small amount of polymer formation could be observed, even when heating the reaction system or changing the ratio of (I)7. Refinement
Crystal data, data collection and structure . Hydrogen atoms were included in geometrically calculated positions. For N-bound H atoms, N—H = 0.88 Å and Uiso(H) = 1.2Ueq(N). For methylene H atoms, C—H = 0.99 Å and Uiso(H) = 1.2Ueq(C) and for phenyl H atoms, C—H = 0.95 Å and Uiso(H) = 1.2Ueq(C). Methyl H atoms were constrained to an ideal geometry, with C—H = 0.98 Å and Uiso(H) = 1.5Ueq(C), but each group was allowed to rotate freely along its C—C bond.
details are summarized in Table 2Supporting information
CCDC reference: 1454857
https://doi.org/10.1107/S2056989016003030/xu5884sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016003030/xu5884Isup2.hkl
Data collection: SMART (Bruker, 2000); cell
SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL/PC (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).(C11H17N2)[ZrCl6]·2CH2Cl2 | F(000) = 840 |
Mr = 828.30 | Dx = 1.498 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 2094 reflections |
a = 10.443 (5) Å | θ = 2.3–22.0° |
b = 16.154 (9) Å | µ = 1.05 mm−1 |
c = 10.891 (6) Å | T = 200 K |
β = 91.259 (10)° | Block, colorless |
V = 1836.9 (17) Å3 | 0.20 × 0.20 × 0.15 mm |
Z = 2 |
Bruker SMART area-detector diffractometer | 3410 independent reflections |
Radiation source: fine-focus sealed tube | 2255 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.061 |
φ and ω scan | θmax = 25.5°, θmin = 2.3° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −10→12 |
Tmin = 0.818, Tmax = 0.859 | k = −19→15 |
10309 measured reflections | l = −12→13 |
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)] = 0.071 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.213 | H-atom parameters constrained |
S = 1.00 | w = 1/[σ2(Fo2) + (0.1176P)2 + 2.835P] where P = (Fo2 + 2Fc2)/3 |
3410 reflections | (Δ/σ)max = 0.001 |
181 parameters | Δρmax = 1.73 e Å−3 |
1 restraint | Δρmin = −0.90 e Å−3 |
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 | ||
Zr1 | 1.0000 | 0.0000 | 0.5000 | 0.0430 (3) | |
Cl1 | 0.79402 (15) | 0.05446 (10) | 0.41944 (16) | 0.0611 (5) | |
Cl2 | 1.08156 (15) | 0.14274 (9) | 0.52270 (16) | 0.0589 (5) | |
Cl3 | 0.91663 (19) | 0.00651 (11) | 0.70660 (16) | 0.0667 (5) | |
N1 | 0.7169 (5) | 0.7997 (3) | 0.7141 (5) | 0.0614 (15) | |
H1 | 0.7742 | 0.8232 | 0.6673 | 0.074* | |
N2 | 0.6913 (6) | 0.7035 (4) | 0.8664 (6) | 0.0803 (19) | |
H2A | 0.6097 | 0.7159 | 0.8731 | 0.096* | |
H2B | 0.7259 | 0.6649 | 0.9135 | 0.096* | |
C1 | 0.5840 (7) | 0.8317 (4) | 0.6987 (8) | 0.0678 (19) | |
C2 | 0.5393 (11) | 0.8666 (7) | 0.8189 (11) | 0.116 (4) | |
H2C | 0.5848 | 0.8390 | 0.8871 | 0.175* | |
H2D | 0.4470 | 0.8573 | 0.8258 | 0.175* | |
H2E | 0.5571 | 0.9261 | 0.8219 | 0.175* | |
C3 | 0.5923 (8) | 0.9014 (6) | 0.6076 (10) | 0.097 (3) | |
H3A | 0.6571 | 0.9413 | 0.6360 | 0.145* | |
H3B | 0.5089 | 0.9290 | 0.6000 | 0.145* | |
H3C | 0.6161 | 0.8793 | 0.5275 | 0.145* | |
C4 | 0.4977 (8) | 0.7642 (6) | 0.6490 (11) | 0.105 (3) | |
H4A | 0.5305 | 0.7441 | 0.5708 | 0.157* | |
H4B | 0.4110 | 0.7862 | 0.6360 | 0.157* | |
H4C | 0.4954 | 0.7184 | 0.7079 | 0.157* | |
C5 | 0.7605 (6) | 0.7420 (4) | 0.7870 (7) | 0.0595 (17) | |
C6 | 0.8982 (7) | 0.7194 (4) | 0.7806 (7) | 0.0614 (17) | |
C7 | 0.9913 (7) | 0.7784 (5) | 0.7678 (7) | 0.070 (2) | |
H7 | 0.9687 | 0.8353 | 0.7640 | 0.084* | |
C8 | 1.1165 (8) | 0.7553 (6) | 0.7606 (8) | 0.084 (2) | |
H8 | 1.1813 | 0.7962 | 0.7540 | 0.100* | |
C9 | 1.1485 (9) | 0.6735 (6) | 0.7630 (9) | 0.095 (3) | |
H9 | 1.2358 | 0.6577 | 0.7575 | 0.113* | |
C10 | 1.0578 (9) | 0.6150 (6) | 0.7731 (11) | 0.105 (3) | |
H10 | 1.0814 | 0.5582 | 0.7733 | 0.127* | |
C11 | 0.9321 (9) | 0.6364 (5) | 0.7831 (9) | 0.092 (3) | |
H11 | 0.8684 | 0.5949 | 0.7916 | 0.110* | |
C12 | 0.335 (2) | 0.4738 (14) | 0.5569 (19) | 0.248 (13) | |
H12A | 0.4220 | 0.4533 | 0.5391 | 0.298* | |
H12B | 0.3246 | 0.4692 | 0.6468 | 0.298* | |
Cl4 | 0.2363 (6) | 0.4119 (4) | 0.4939 (5) | 0.232 (3) | |
Cl5 | 0.3316 (6) | 0.5793 (3) | 0.5205 (4) | 0.1913 (19) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Zr1 | 0.0361 (5) | 0.0397 (4) | 0.0535 (5) | −0.0011 (3) | 0.0091 (3) | −0.0003 (3) |
Cl1 | 0.0445 (9) | 0.0580 (9) | 0.0805 (11) | 0.0060 (7) | −0.0031 (8) | −0.0021 (8) |
Cl2 | 0.0490 (9) | 0.0442 (8) | 0.0841 (12) | −0.0066 (6) | 0.0129 (8) | −0.0070 (7) |
Cl3 | 0.0766 (12) | 0.0676 (11) | 0.0566 (10) | 0.0072 (8) | 0.0201 (8) | 0.0021 (8) |
N1 | 0.043 (3) | 0.058 (3) | 0.084 (4) | 0.001 (2) | 0.016 (3) | 0.018 (3) |
N2 | 0.057 (4) | 0.075 (4) | 0.110 (5) | −0.006 (3) | 0.018 (3) | 0.037 (4) |
C1 | 0.045 (4) | 0.056 (4) | 0.102 (6) | 0.002 (3) | 0.015 (4) | 0.015 (4) |
C2 | 0.096 (8) | 0.115 (8) | 0.139 (9) | 0.037 (6) | 0.027 (7) | 0.000 (7) |
C3 | 0.056 (5) | 0.082 (6) | 0.154 (9) | 0.016 (4) | 0.010 (5) | 0.048 (6) |
C4 | 0.057 (5) | 0.091 (6) | 0.166 (10) | −0.006 (5) | −0.006 (6) | 0.011 (6) |
C5 | 0.049 (4) | 0.050 (4) | 0.079 (5) | −0.006 (3) | 0.006 (3) | 0.006 (3) |
C6 | 0.058 (4) | 0.049 (3) | 0.078 (5) | 0.004 (3) | 0.002 (3) | 0.013 (3) |
C7 | 0.053 (4) | 0.061 (4) | 0.095 (5) | −0.008 (3) | 0.004 (4) | 0.022 (4) |
C8 | 0.056 (5) | 0.096 (6) | 0.099 (6) | −0.009 (4) | 0.004 (4) | 0.024 (5) |
C9 | 0.060 (5) | 0.097 (7) | 0.127 (8) | 0.012 (5) | −0.002 (5) | 0.027 (6) |
C10 | 0.077 (6) | 0.076 (6) | 0.163 (10) | 0.019 (5) | −0.001 (6) | 0.011 (6) |
C11 | 0.076 (6) | 0.059 (5) | 0.141 (8) | 0.004 (4) | 0.001 (5) | 0.013 (5) |
C12 | 0.25 (2) | 0.30 (3) | 0.191 (18) | −0.16 (2) | −0.103 (18) | 0.103 (18) |
Cl4 | 0.249 (6) | 0.293 (7) | 0.155 (4) | −0.105 (6) | 0.044 (4) | −0.005 (4) |
Cl5 | 0.234 (5) | 0.192 (5) | 0.148 (3) | 0.020 (4) | 0.012 (3) | −0.025 (3) |
Zr1—Cl1 | 2.4674 (18) | C3—H3C | 0.9800 |
Zr1—Cl1i | 2.4674 (18) | C4—H4A | 0.9800 |
Zr1—Cl2i | 2.4687 (19) | C4—H4B | 0.9800 |
Zr1—Cl2 | 2.4687 (19) | C4—H4C | 0.9800 |
Zr1—Cl3i | 2.433 (2) | C5—C6 | 1.487 (10) |
Zr1—Cl3 | 2.433 (2) | C6—C7 | 1.371 (10) |
N1—C5 | 1.300 (8) | C6—C11 | 1.387 (10) |
N1—C1 | 1.487 (9) | C7—C8 | 1.363 (11) |
N1—H1 | 0.8800 | C7—H7 | 0.9500 |
N2—C5 | 1.299 (9) | C8—C9 | 1.364 (12) |
N2—H2A | 0.8800 | C8—H8 | 0.9500 |
N2—H2B | 0.8800 | C9—C10 | 1.345 (13) |
C1—C3 | 1.505 (11) | C9—H9 | 0.9500 |
C1—C4 | 1.508 (12) | C10—C11 | 1.365 (13) |
C1—C2 | 1.509 (13) | C10—H10 | 0.9500 |
C2—H2C | 0.9800 | C11—H11 | 0.9500 |
C2—H2D | 0.9800 | C12—Cl4 | 1.583 (17) |
C2—H2E | 0.9800 | C12—Cl5 | 1.75 (2) |
C3—H3A | 0.9800 | C12—H12A | 0.9900 |
C3—H3B | 0.9800 | C12—H12B | 0.9900 |
Cl3i—Zr1—Cl3 | 180.000 (1) | C1—C3—H3C | 109.5 |
Cl3i—Zr1—Cl1 | 90.77 (7) | H3A—C3—H3C | 109.5 |
Cl3—Zr1—Cl1 | 89.23 (7) | H3B—C3—H3C | 109.5 |
Cl3i—Zr1—Cl1i | 89.23 (7) | C1—C4—H4A | 109.5 |
Cl3—Zr1—Cl1i | 90.77 (7) | C1—C4—H4B | 109.5 |
Cl1—Zr1—Cl1i | 180.00 (8) | H4A—C4—H4B | 109.5 |
Cl3i—Zr1—Cl2i | 89.81 (6) | C1—C4—H4C | 109.5 |
Cl3—Zr1—Cl2i | 90.19 (6) | H4A—C4—H4C | 109.5 |
Cl1—Zr1—Cl2i | 90.07 (6) | H4B—C4—H4C | 109.5 |
Cl1i—Zr1—Cl2i | 89.93 (6) | N2—C5—N1 | 123.9 (6) |
Cl3i—Zr1—Cl2 | 90.19 (6) | N2—C5—C6 | 117.8 (6) |
Cl3—Zr1—Cl2 | 89.81 (6) | N1—C5—C6 | 118.3 (6) |
Cl1—Zr1—Cl2 | 89.93 (6) | C7—C6—C11 | 119.5 (7) |
Cl1i—Zr1—Cl2 | 90.07 (6) | C7—C6—C5 | 121.5 (6) |
Cl2i—Zr1—Cl2 | 180.00 (8) | C11—C6—C5 | 118.9 (7) |
C5—N1—C1 | 129.1 (6) | C8—C7—C6 | 119.9 (7) |
C5—N1—H1 | 115.4 | C8—C7—H7 | 120.1 |
C1—N1—H1 | 115.4 | C6—C7—H7 | 120.1 |
C5—N2—H2A | 120.0 | C7—C8—C9 | 120.0 (8) |
C5—N2—H2B | 120.0 | C7—C8—H8 | 120.0 |
H2A—N2—H2B | 120.0 | C9—C8—H8 | 120.0 |
N1—C1—C3 | 105.5 (6) | C10—C9—C8 | 120.6 (9) |
N1—C1—C4 | 109.8 (6) | C10—C9—H9 | 119.7 |
C3—C1—C4 | 110.3 (8) | C8—C9—H9 | 119.7 |
N1—C1—C2 | 109.7 (7) | C9—C10—C11 | 120.6 (9) |
C3—C1—C2 | 108.4 (8) | C9—C10—H10 | 119.7 |
C4—C1—C2 | 112.8 (8) | C11—C10—H10 | 119.7 |
C1—C2—H2C | 109.5 | C10—C11—C6 | 119.3 (9) |
C1—C2—H2D | 109.5 | C10—C11—H11 | 120.4 |
H2C—C2—H2D | 109.5 | C6—C11—H11 | 120.4 |
C1—C2—H2E | 109.5 | Cl4—C12—Cl5 | 120.5 (12) |
H2C—C2—H2E | 109.5 | Cl4—C12—H12A | 107.2 |
H2D—C2—H2E | 109.5 | Cl5—C12—H12A | 107.2 |
C1—C3—H3A | 109.5 | Cl4—C12—H12B | 107.2 |
C1—C3—H3B | 109.5 | Cl5—C12—H12B | 107.2 |
H3A—C3—H3B | 109.5 | H12A—C12—H12B | 106.8 |
Symmetry code: (i) −x+2, −y, −z+1. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···Cl2ii | 0.88 | 2.64 | 3.491 (6) | 162 |
N2—H2A···Cl2iii | 0.88 | 2.60 | 3.270 (7) | 133 |
N2—H2B···Cl1iii | 0.88 | 2.56 | 3.353 (7) | 150 |
C12—H12A···Cl5iv | 0.99 | 2.72 | 3.70 (2) | 171 |
Symmetry codes: (ii) −x+2, −y+1, −z+1; (iii) −x+3/2, y+1/2, −z+3/2; (iv) −x+1, −y+1, −z+1. |
Acknowledgements
This work was supported by grants from the Natural Science Foundation of China (grant No. 20702029) and the Natural Science Foundation of Shanxi Province, China (grant No. 2008011024).
References
Bai, S.-D., Liu, R.-Q., Guan, F., Wang, T., Tong, H.-B., Guo, J.-P. & Liu, D.-S. (2013). Mendeleev Commun. 23, 265–267. Web of Science CSD CrossRef CAS Google Scholar
Bai, S.-D., Tong, H.-B., Guo, J.-P., Zhou, M.-S., Liu, D.-S. & Yuan, S.-F. (2010). Polyhedron, 29, 262–269. Web of Science CSD CrossRef CAS Google Scholar
Barker, J. & Kilner, M. (1994). Coord. Chem. Rev. 133, 219–300. CrossRef CAS Web of Science Google Scholar
Bruker (2000). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Centore, R., Tuzi, A. & Liguori, D. (2003). Acta Cryst. C59, m241–m242. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Coles, M. P. (2006). Dalton Trans. pp. 985–1001. Web of Science CrossRef Google Scholar
Collins, S. (2011). Coord. Chem. Rev. 255, 118–138. Web of Science CrossRef CAS Google Scholar
Edelmann, F. T. (1994). Coord. Chem. Rev. 137, 403–481. CrossRef Web of Science Google Scholar
Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Wang, J.-F., Xu, F., Cai, T. & Shen, Q. (2008). Org. Lett. 10, 445–448. Web of Science CSD CrossRef PubMed CAS Google Scholar
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