research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 72| Part 3| March 2016| Pages 424-427

Crystal structure of trans-di­chlorido­(1,4,8,11-tetra­aza­undecane-κ4N)chromium(III) perchlorate determined from synchrotron data

CROSSMARK_Color_square_no_text.svg

aPohang Accelerator Laboratory, POSTECH, Pohang 37673, Republic of Korea, and bDepartment of Chemistry, Andong National University, Andong 36729, Republic of Korea
*Correspondence e-mail: jhchoi@anu.ac.kr

Edited by M. Weil, Vienna University of Technology, Austria (Received 26 January 2016; accepted 18 February 2016; online 24 February 2016)

The structure of the title complex, [CrCl2(2,3,2-tet)]ClO4 (2,3,2-tet is 1,4,8,11-tetra­aza­undecane, C7H20N4), has been determined from synchrotron data. The CrIII ion is coordinated by the four N atoms of the 1,4,8,11-tetra­aza­undecane ligand in the equatorial plane and two chloride ions in an axial arrangement, displaying a slightly distorted octa­hedral coordination environment. The two H atoms of the secondary amines are grouped on the same side of the equatorial N4 plane (meso-RS conformation). The Cr—N bond lengths range from 2.069 (2) to 2.084 (2) Å, while the mean Cr—Cl bond length is 2.325 (2) Å. The crystal structure is stabilized by inter­molecular hydrogen-bonding inter­actions between the primary and secondary amine groups of the 2,3,2-tet ligands, the Cl ligands and the O atoms of the perchlorate counter-anion, forming corrugated layers parallel to (010).

1. Chemical context

Geometric and conformational isomerism in chromium(III) complexes of linear flexible tetra­dentate ligands is an inter­esting field because it has played an important role in extending the concept of stereochemistry. The 1,4,8,11-tetra­aza­undecane ligand (2,3,2-tet) is a structural isomer of 1,4,7,11-tetra­aza­undecane (2,2,3-tet). These two ligands have four nitro­gen atoms as donor groups and can adopt three different configurations in chromium(III) complexes with two additional Cl ligands (Choi et al., 2008a[Choi, J.-H., Choi, S. Y., Hong, Y. P., Ko, S.-O., Ryoo, K. S., Lee, S. H. & Park, Y. C. (2008a). Spectrochim. Acta Part A, 70, 619-625.],b[Choi, J.-H., Kim, H.-S. & Habibi, M. H. (2008b). Bull. Korean Chem. Soc. 29, 1399-1402.]). Two conformations of meso-RS or racemic-RR/SS isomers with respect to the orientation of the secondary amine hydrogen atoms in the trans isomer are also possible (Fig. 1[link]). The two hydrogen atoms of the conformers may be on the same side (RS) of the equatorial N4 plane or on opposite sides (RR/SS) of this plane.

[Scheme 1]
[Figure 1]
Figure 1
Schematic representation of the 2,3,2-tet and 2,2,3-tet ligands, and two possible conformational isomers of trans-[CrCl2(2,3,2-tet)]+.

The different symmetries of transition metal complexes allow the determination of their stereochemistry from electronic absorption and infrared spectra. Indeed, infrared and electronic spectroscopic properties often are useful in determining the geometric isomers of chromium(III) complexes with linear tetra­dentate ligands (House & Garner; 1966[House, D. A. & Garner, C. S. (1966). J. Am. Chem. Soc. 88, 2156-2162.]; Kutal & Adamson, 1973[Kutal, C. & Adamson, A. W. (1973). Inorg. Chem. 12, 1990-1994.]; House & Yang, 1983[House, D. A. & Yang, D. (1983). Inorg. Chim. Acta, 74, 179-189.]; Kirk & Fernando, 1994[Kirk, A. D. & Fernando, S. R. L. (1994). Inorg. Chem. 33, 4401-4047.]). However, it should be noted that the geometric assignments based on spectroscopic studies alone are less conclusive. Both trans and cis isomers of [CrCl2(2,3,2-tet)]ClO4 have been isolated (House & Yang, 1983[House, D. A. & Yang, D. (1983). Inorg. Chim. Acta, 74, 179-189.]; Kirk & Fernando, 1994[Kirk, A. D. & Fernando, S. R. L. (1994). Inorg. Chem. 33, 4401-4047.]). Whereas the crystal structure and spectroscopic properties of the cis-β-di­chlorido­chromium(III) complexes containing the 2,3,2-tet ligand were reported (Choi et al., 2008b[Choi, J.-H., Kim, H.-S. & Habibi, M. H. (2008b). Bull. Korean Chem. Soc. 29, 1399-1402.]), the trans isomers with any anion have so far not been structurally characterized. The orientation of the secondary amine hydrogen atoms in the metal complexes is also highly relevant for medical application and likely to be a major factor in determining the anti­viral activity (Ronconi & Sadler, 2007[Ronconi, L. & Sadler, P. J. (2007). Coord. Chem. Rev. 251, 1633-1648.]; Ross et al., 2012[Ross, A., Choi, J.-H., Hunter, T. M., Pannecouque, C., Moggach, S. A., Parsons, S., De Clercq, E. & Sadler, P. J. (2012). Dalton Trans. 41, 6408-6418.]). In order to confirm the orientation of the secondary N—H hydrogen atoms of the Cr(III) complex with 2,3,2-tet and additional Cl ligands, we report the structure of the title compound, trans-[CrCl2(2,3,2-tet)]ClO4, (I)[link], in this communication.

2. Structural commentary

Fig. 2[link] displays the mol­ecular components of compound (I)[link]. In the distorted octa­hedral complex chromium(III) cation, the four N atoms of the 2,3,2-tet ligand occupy the equatorial sites and the two chlorine atoms coordinate axially to the metal. The two hydrogen atoms of the secondary amine groups are grouped on the same side (meso-RS type) of the equatorial N4 plane. Such a conformation is consistent with those of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978[Bang, E. & Pedersen, E. (1978). Acta Chem. Scand. Ser. A, 32, 833-836.]) and trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982[Mäcke, H. R., Mentzen, B. F., Puaux, J. P. & Adamson, A. W. (1982). Inorg. Chem. 21, 3080-3082.]). The meso-RS conformation may be compared with rac-RR/SS types of trans-[CrF2(2,2,3-tet)]ClO4 (Choi & Moon, 2014[Choi, J.-H. & Moon, D. (2014). J. Mol. Struct. 1059, 325-331.]) and trans-[CrF(3,2,3-tet)(H2O)](ClO4)2·H2O (Choi & Lee, 2008[Choi, J.-H. & Lee, U. (2008). Acta Cryst. E64, m1186.]).

[Figure 2]
Figure 2
The structures of the mol­ecular components of complex (I)[link], drawn with displacement ellipsoids at the 30% probability level.

The Cr—N bond lengths to the 2,3,2-tet ligand are in the range 2.069 (2) to 2.084 (2) Å, in good agreement with those observed in the related structures of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978[Bang, E. & Pedersen, E. (1978). Acta Chem. Scand. Ser. A, 32, 833-836.]), trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982[Mäcke, H. R., Mentzen, B. F., Puaux, J. P. & Adamson, A. W. (1982). Inorg. Chem. 21, 3080-3082.]), trans-[CrF2(2,2,3-tet)]ClO4 (Choi & Moon, 2014[Choi, J.-H. & Moon, D. (2014). J. Mol. Struct. 1059, 325-331.]), cis-β-[Cr(ox)(2,3,2-tet)]I (ox = oxalate; Kukina et al., 1990[Kukina, G. A., Porai-Koshits, M. A., Shevchenko, Y. N. & Shchurkina, V. N. (1990). Koord. Khim. 16, 784-792.]) and cis-β-[Cr(N3)2(2,2,3-tet)]Br (Choi et al., 2011[Choi, J.-H., Clegg, W. & Harrington, R. W. (2011). Z. Anorg. Allg. Chem. 637, 562-566.]). The two Cr—Cl distances in (I)[link] average to 2.325 (2) Å and are close to the values found in cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008b[Choi, J.-H., Kim, H.-S. & Habibi, M. H. (2008b). Bull. Korean Chem. Soc. 29, 1399-1402.]) and cis-β-[CrCl2(2,2,3-tet)]ClO4 (Choi et al., 2008a[Choi, J.-H., Choi, S. Y., Hong, Y. P., Ko, S.-O., Ryoo, K. S., Lee, S. H. & Park, Y. C. (2008a). Spectrochim. Acta Part A, 70, 619-625.]). The Cr1A—N1A and Cr1A—N4A bond lengths to the primary amine N atoms are slightly longer than the Cr1A—N2A and Cr1A—N3A bond lengths to the secondary amine N atoms. It is inter­esting to note that the Cr—N bond lengths to the primary amine N atoms in cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008b[Choi, J.-H., Kim, H.-S. & Habibi, M. H. (2008b). Bull. Korean Chem. Soc. 29, 1399-1402.]) are slightly shorter than those to the secondary amine N atoms. Two five-membered and one six-membered chelate rings of the 2,3,2-tet ligand are present in the structure of (I)[link]. They adopt gauche and stable chair conformations, respectively. The bond angles of the five- and six-membered chelate rings around the chromium(III) atom are 83.72 (9) and 93.40 (9)°, respectively. The other N—C and C—C bond lengths and Cr—N—C, N—C—C and C—C—C angles are normal for a 2,3,2-tet ligand in a gauche or chair conformation. The tetra­hedral ClO4 counter anion is distorted due to its involvement in hydrogen-bonding inter­actions.

3. Supra­molecular features

In the crystal, mol­ecules are stacked along [010]. An N—H⋯Cl hydrogen bond (N2A⋯Cl1A) links neighboring cations into rows parallel to [100] while a series of N—H⋯O contacts connect the cations to neighboring anions (Table 1[link]). An extensive array of these contacts generates a two-dimensional network extending parallel to (010) (Figs. 3[link] and 4[link]).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1A—H1A1⋯O2Bi 0.90 2.30 3.187 (4) 167
N1A—H1A2⋯O1B 0.90 2.30 3.180 (4) 164
N2A—H2A⋯Cl1Aii 0.99 2.47 3.332 (2) 146
N3A—H3A⋯O1Biii 0.99 2.28 3.174 (4) 150
N4A—H4A1⋯O2B 0.90 2.21 3.086 (4) 163
N4A—H4A2⋯Cl2Aiv 0.90 2.56 3.405 (2) 157
Symmetry codes: (i) [x+{\script{1\over 2}}, -y+1, z+{\script{1\over 2}}]; (ii) x-1, y, z; (iii) [x-{\script{1\over 2}}, -y+1, z-{\script{1\over 2}}]; (iv) x+1, y, z.
[Figure 3]
Figure 3
The crystal packing of complex (I)[link] viewed perpendicular to (010). Dashed lines represent N—H⋯O (pink) and N—H⋯Cl (green) hydrogen-bonding inter­actions, respectively.
[Figure 4]
Figure 4
The crystal packing of complex (I)[link] viewed approximately along [100]. The colour code is as in Fig. 3[link].

4. Database survey

A search in the Cambridge Structural Database (Version 5.36, last update May 2015; Groom & Allen, 2014[Groom, C. R. & Allen, F. H. (2014). Angew. Chem. Int. Ed. 35, 3103-3111.]) shows that there are four reports for CrIII complexes with a [CrL2(2,3,2-tet)]+ unit. The crystal structures of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978[Bang, E. & Pedersen, E. (1978). Acta Chem. Scand. Ser. A, 32, 833-836.]), trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982[Mäcke, H. R., Mentzen, B. F., Puaux, J. P. & Adamson, A. W. (1982). Inorg. Chem. 21, 3080-3082.]), cis-β-[Cr(ox)(2,3,2-tet)]I (Kukina et al., 1990[Kukina, G. A., Porai-Koshits, M. A., Shevchenko, Y. N. & Shchurkina, V. N. (1990). Koord. Khim. 16, 784-792.]), cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008b[Choi, J.-H., Kim, H.-S. & Habibi, M. H. (2008b). Bull. Korean Chem. Soc. 29, 1399-1402.]) have been reported previously. However, no structures of complexes of trans-[CrCl2(2,3,2-tet)]+ with any anions have been deposited.

5. Synthesis and crystallization

The free ligand 1,4,8,11-tetra­aza­undecane was purchased from Strem Chemical Company, USA. All other chemicals were reagent grade materials and were used without further purification. Compound (I)[link] was prepared by a literature method (Kirk & Fernando, 1994[Kirk, A. D. & Fernando, S. R. L. (1994). Inorg. Chem. 33, 4401-4047.]). The crude perchlorate salt (0.35 g) was dissolved in 20 mL of 0.1 M HCl at 333 K. The filtrate was added to 5 mL of 60% HClO4. The resulting solution was left for slow evaporation at room temperature. Green block-like crystals suitable for X-ray structural analysis were isolated after one week. The crystals were washed with small amounts of 2-propanol and dried in air before collecting the synchrotron data.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. The H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H distances of 0.98 Å (C—H2), and N—H distances of 0.90 Å and 0.99 Å (secondary amine and primary amine H atoms, respectively), with Uiso(H) values of 1.2Ueq of the parent atoms.

Table 2
Experimental details

Crystal data
Chemical formula [CrCl2(C7H20N4)]ClO4
Mr 382.62
Crystal system, space group Monoclinic, Pn
Temperature (K) 243
a, b, c (Å) 6.4730 (13), 11.449 (2), 10.385 (2)
β (°) 102.42 (3)
V3) 751.6 (3)
Z 2
Radiation type Synchrotron, λ = 0.620 Å
μ (mm−1) 0.89
Crystal size (mm) 0.13 × 0.13 × 0.05
 
Data collection
Diffractometer ADSC Q210 CCD area-detector
Absorption correction Empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. Academic Press, New York.])
Tmin, Tmax 0.893, 0.958
No. of measured, independent and observed [I > 2σ(I)] reflections 7831, 4422, 4214
Rint 0.023
(sin θ/λ)max−1) 0.707
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.025, 0.066, 1.07
No. of reflections 4422
No. of parameters 172
No. of restraints 2
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.39, −0.62
Absolute structure Flack x determined using 2004 quotients [(I+)−(I)]/[(I+)+(I)] (Parsons et al., 2013[Parsons, S., Flack, H. D. & Wagner, T. (2013). Acta Cryst. B69, 249-259.])
Absolute structure parameter 0.038 (9)
Computer programs: PAL BL2D-SMDC Program (Shin et al., 2016[Shin, J. W., Eom, K. & Moon, D. (2016). J. Synchrotron Rad. 23, 369-373.]), HKL3000sm (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. Academic Press, New York.]), SHELXT (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2014/7 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), DIAMOND (Putz & Brandenburg, 2014[Putz, H. & Brandenburg, K. (2014). DIAMOND. Crystal Impact GbR, Bonn, Germany.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information


Chemical context top

Geometric and conformational isomerism in chromium(III) complexes of linear flexible tetra­dentate ligands is an inter­esting field because it has played an important role in extending the concept of stereochemistry. The 1,4,8,11-tetra­aza­undecane ligand (2,3,2-tet) is a structural isomer of 1,4,7,11-tetra­aza­undecane (2,2,3-tet). The latter ligand has four nitro­gen atoms as donor groups and can adopt three different configurations in chromium(III) complexes with two additional Cl ligands (Choi et al., 2008a,b). Two conformations of meso-RS or racemic-RR/SS isomers with respect to the orientation of the secondary amine hydrogen atoms in the trans isomer are also possible (Fig. 1). The two hydrogen atoms of the conformers may be on the same side (RS) of the equatorial N4 plane or on opposite sides (RR/SS) of this plane.

The different symmetries of transition metal complexes allow the determination of their stereochemistry from electronic absorption and infrared spectra. Indeed, infrared and electronic spectroscopic properties often are useful in determining the geometric isomers of chromium(III) complexes with linear tetra­dentate ligands (House & Garner; 1966; Kutal & Adamson, 1973; House & Yang, 1983; Kirk & Fernando, 1994). However, it should be noted that the geometric assignments based on spectroscopic studies alone are less conclusive. Both trans and cis isomers of [CrCl2(2,3,2-tet)]ClO4 have been isolated (House & Yang, 1983; Kirk & Fernando, 1994). Whereas the crystal structure and spectroscopic properties of the cis-β-dichloridochromium(III) complexes containing the 2,3,2-tet ligand were reported (Choi et al., 2008b), the trans isomers with any anion have so far not been structurally characterized. The orientation of the secondary amine hydrogen atoms in the metal complexes is also highly relevant for medical application and likely to be a major factor in determining the anti­viral activity (Ronconi & Sadler, 2007; Ross et al., 2012). In order to confirm the orientation of the secondary N—H hydrogen atoms of the Cr(III) complex with 2,3,2-tet and additional Cl ligands, we report the structure of the title compound, trans-[CrCl2(2,3,2-tet)]ClO4, (I), in this communication.

Structural commentary top

Fig. 2 displays the molecular components of compound (I). In the distorted o­cta­hedral complex chromium(III) cation, the four N atoms of the 2,3,2-tet ligand occupy the equatorial sites and the two chlorine atoms coordinate axially to the metal. The two hydrogen atoms of the secondary amine groups are grouped on the same side (meso-RS type) of the equatorial N4 plane. Such a conformation is consistent with those of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978) and trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982). The meso-RS conformation may be compared with rac-RR/SS types of trans-[CrF2(2,2,3-tet)]ClO4 (Choi & Moon, 2014) and trans-[CrF(3,2,3-tet)(H2O)](ClO4)2· H2O (Choi & Lee, 2008).

The Cr—N bond lengths to the 2,3,2-tet ligand are in the range 2.069 (2) to 2.084 (2) Å, in good agreement with those observed in the related structures of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978), trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982), trans-[CrF2(2,2,3-tet)]ClO4 (Choi & Moon, 2014), cis-β-[Cr(ox)(2,3,2-tet)]I (ox = oxalate; Kukina et al., 1990) and cis-β-[Cr(N3)2(2,2,3-tet)]Br (Choi et al., 2011). The two Cr—Cl distances in (I) average to 2.325 (2) Å and are close to the values found in cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008b) and cis-β-[CrCl2(2,2,3-tet)]ClO4 (Choi et al., 2008a). The Cr1A—N1A and Cr1A—N4A bond lengths to the primary amine N atoms are slightly longer than the Cr1A—N2A and Cr1A—N3A bond lengths to the secondary amine N atoms. It is inter­esting to note that the Cr—N bond lengths to the primary amine N atoms in cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008a) are slightly shorter than those to the secondary amine N atoms. Two five-membered and one six-membered chelate rings of the 2,3,2-tet ligand are present in the structure of (I). They adopt gauche and stable chair conformations, respectively. The bond angles of the five- and six-membered chelate rings around the chromium(III) atom are 83.72 (9) and 93.40 (9)°, respectively. The other N—C and C—C bond lengths and Cr—N—C, N—C—C and C—C—C angles are normal for a 2,3,2-tet ligand in gauche or chair conformations. The tetra­hedral ClO4 counter anion is distorted due to its involvement in hydrogen-bonding inter­actions.

Supra­molecular features top

In the crystal, molecules are stacked along [010]. An N—H···Cl hydrogen bond (N2A···Cl1A) links neighboring cations into rows parallel to [100] while a series of N—H···O contacts connect the cations to neighboring anions (Table 1). An extensive array of these contacts generates a two-dimensional network extending parallel to (010) (Figs. 3 and 4).

Database survey top

A search in the Cambridge Structural Database (Version 5.36, last update February 2015; Groom & Allen, 2014) shows that there are four reports for CrIII complexes with a [CrL2(2,3,2-tet)]+ unit. The crystal structures of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978), trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982), cis-β-[Cr(ox)(2,3,2-tet)]I (Kukina et al., 1990), cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008b) have been reported previously. However, no structures of complexes of trans-[CrCl2(2,3,2-tet)]+ with any anions have been deposited.

Synthesis and crystallization top

The free ligand 1,4,8,11-tetra­aza­undecane was purchased from Strem Chemical Company, USA. All other chemicals were reagent grade materials and were used without further purification. Compound (I) was prepared by a literature method (Kirk & Fernando, 1994). The crude perchlorate salt (0.35 g) was dissolved in 20 ml of 0.1 M HCl at 333 K. The filtrate was added to 5 ml of 60% HClO4. The resulting solution was left for slow evaporation at room temperature. Green block-like crystals suitable for X-ray structural analysis were isolated after one week. The crystals were washed with small amounts of 2-propanol and dried in air before collecting the synchrotron data.

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H distances of 0.98 Å (C—H2), and N—H distances of 0.90 Å and 0.99 Å (secondary amine and primary amine H atoms, respectively), with Uiso(H) values of 1.2Ueq of the parent atoms.

Structure description top

Geometric and conformational isomerism in chromium(III) complexes of linear flexible tetra­dentate ligands is an inter­esting field because it has played an important role in extending the concept of stereochemistry. The 1,4,8,11-tetra­aza­undecane ligand (2,3,2-tet) is a structural isomer of 1,4,7,11-tetra­aza­undecane (2,2,3-tet). The latter ligand has four nitro­gen atoms as donor groups and can adopt three different configurations in chromium(III) complexes with two additional Cl ligands (Choi et al., 2008a,b). Two conformations of meso-RS or racemic-RR/SS isomers with respect to the orientation of the secondary amine hydrogen atoms in the trans isomer are also possible (Fig. 1). The two hydrogen atoms of the conformers may be on the same side (RS) of the equatorial N4 plane or on opposite sides (RR/SS) of this plane.

The different symmetries of transition metal complexes allow the determination of their stereochemistry from electronic absorption and infrared spectra. Indeed, infrared and electronic spectroscopic properties often are useful in determining the geometric isomers of chromium(III) complexes with linear tetra­dentate ligands (House & Garner; 1966; Kutal & Adamson, 1973; House & Yang, 1983; Kirk & Fernando, 1994). However, it should be noted that the geometric assignments based on spectroscopic studies alone are less conclusive. Both trans and cis isomers of [CrCl2(2,3,2-tet)]ClO4 have been isolated (House & Yang, 1983; Kirk & Fernando, 1994). Whereas the crystal structure and spectroscopic properties of the cis-β-dichloridochromium(III) complexes containing the 2,3,2-tet ligand were reported (Choi et al., 2008b), the trans isomers with any anion have so far not been structurally characterized. The orientation of the secondary amine hydrogen atoms in the metal complexes is also highly relevant for medical application and likely to be a major factor in determining the anti­viral activity (Ronconi & Sadler, 2007; Ross et al., 2012). In order to confirm the orientation of the secondary N—H hydrogen atoms of the Cr(III) complex with 2,3,2-tet and additional Cl ligands, we report the structure of the title compound, trans-[CrCl2(2,3,2-tet)]ClO4, (I), in this communication.

Fig. 2 displays the molecular components of compound (I). In the distorted o­cta­hedral complex chromium(III) cation, the four N atoms of the 2,3,2-tet ligand occupy the equatorial sites and the two chlorine atoms coordinate axially to the metal. The two hydrogen atoms of the secondary amine groups are grouped on the same side (meso-RS type) of the equatorial N4 plane. Such a conformation is consistent with those of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978) and trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982). The meso-RS conformation may be compared with rac-RR/SS types of trans-[CrF2(2,2,3-tet)]ClO4 (Choi & Moon, 2014) and trans-[CrF(3,2,3-tet)(H2O)](ClO4)2· H2O (Choi & Lee, 2008).

The Cr—N bond lengths to the 2,3,2-tet ligand are in the range 2.069 (2) to 2.084 (2) Å, in good agreement with those observed in the related structures of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978), trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982), trans-[CrF2(2,2,3-tet)]ClO4 (Choi & Moon, 2014), cis-β-[Cr(ox)(2,3,2-tet)]I (ox = oxalate; Kukina et al., 1990) and cis-β-[Cr(N3)2(2,2,3-tet)]Br (Choi et al., 2011). The two Cr—Cl distances in (I) average to 2.325 (2) Å and are close to the values found in cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008b) and cis-β-[CrCl2(2,2,3-tet)]ClO4 (Choi et al., 2008a). The Cr1A—N1A and Cr1A—N4A bond lengths to the primary amine N atoms are slightly longer than the Cr1A—N2A and Cr1A—N3A bond lengths to the secondary amine N atoms. It is inter­esting to note that the Cr—N bond lengths to the primary amine N atoms in cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008a) are slightly shorter than those to the secondary amine N atoms. Two five-membered and one six-membered chelate rings of the 2,3,2-tet ligand are present in the structure of (I). They adopt gauche and stable chair conformations, respectively. The bond angles of the five- and six-membered chelate rings around the chromium(III) atom are 83.72 (9) and 93.40 (9)°, respectively. The other N—C and C—C bond lengths and Cr—N—C, N—C—C and C—C—C angles are normal for a 2,3,2-tet ligand in gauche or chair conformations. The tetra­hedral ClO4 counter anion is distorted due to its involvement in hydrogen-bonding inter­actions.

In the crystal, molecules are stacked along [010]. An N—H···Cl hydrogen bond (N2A···Cl1A) links neighboring cations into rows parallel to [100] while a series of N—H···O contacts connect the cations to neighboring anions (Table 1). An extensive array of these contacts generates a two-dimensional network extending parallel to (010) (Figs. 3 and 4).

A search in the Cambridge Structural Database (Version 5.36, last update February 2015; Groom & Allen, 2014) shows that there are four reports for CrIII complexes with a [CrL2(2,3,2-tet)]+ unit. The crystal structures of trans-[CrF2(2,3,2-tet)]ClO4 (Bang & Pedersen, 1978), trans-[Cr(NCS)2(2,3,2-tet)]NCS (Mäcke et al., 1982), cis-β-[Cr(ox)(2,3,2-tet)]I (Kukina et al., 1990), cis-β-[CrCl2(2,3,2-tet)]ClO4 (Choi et al., 2008b) have been reported previously. However, no structures of complexes of trans-[CrCl2(2,3,2-tet)]+ with any anions have been deposited.

Synthesis and crystallization top

The free ligand 1,4,8,11-tetra­aza­undecane was purchased from Strem Chemical Company, USA. All other chemicals were reagent grade materials and were used without further purification. Compound (I) was prepared by a literature method (Kirk & Fernando, 1994). The crude perchlorate salt (0.35 g) was dissolved in 20 ml of 0.1 M HCl at 333 K. The filtrate was added to 5 ml of 60% HClO4. The resulting solution was left for slow evaporation at room temperature. Green block-like crystals suitable for X-ray structural analysis were isolated after one week. The crystals were washed with small amounts of 2-propanol and dried in air before collecting the synchrotron data.

Refinement details top

Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H distances of 0.98 Å (C—H2), and N—H distances of 0.90 Å and 0.99 Å (secondary amine and primary amine H atoms, respectively), with Uiso(H) values of 1.2Ueq of the parent atoms.

Computing details top

Data collection: PAL BL2D-SMDC Program (Shin et al., 2016); cell refinement: HKL3000sm (Otwinowski & Minor, 1997); data reduction: HKL3000sm (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015b); molecular graphics: DIAMOND (Putz & Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. Schematic representation of the 2,3,2-tet and 2,2,3-tet ligands, and two possible conformational isomers of trans-[CrCl2(2,3,2-tet)]+.
[Figure 2] Fig. 2. The structures of the molecular components of complex (I), drawn with displacement ellipsoids at the 30% probability level.
[Figure 3] Fig. 3. The crystal packing of complex (I) viewed perpendicular to (010). Dashed lines represent N—H···O (pink) and N—H···Cl (green) hydrogen-bonding interactions, respectively.
[Figure 4] Fig. 4. The crystal packing of complex (I) viewed along [100]. The colour code is as in Fig. 3.
trans-Dichlorido(1,4,8,11-tetraazaundecane-κ4N)chromium(III) perchlorate top
Crystal data top
[CrCl2(C7H20N4)]ClO4F(000) = 394
Mr = 382.62Dx = 1.691 Mg m3
Monoclinic, PnSynchrotron radiation, λ = 0.620 Å
a = 6.4730 (13) ÅCell parameters from 22325 reflections
b = 11.449 (2) Åθ = 0.4–33.6°
c = 10.385 (2) ŵ = 0.89 mm1
β = 102.42 (3)°T = 243 K
V = 751.6 (3) Å3Block, green
Z = 20.13 × 0.13 × 0.05 mm
Data collection top
ADSC Q210 CCD area-detector
diffractometer
4214 reflections with I > 2σ(I)
Radiation source: PLSII 2D bending magnetRint = 0.023
ω scanθmax = 26.0°, θmin = 2.3°
Absorption correction: empirical (using intensity measurements)
(HKL3000sm SCALEPACK; Otwinowski & Minor, 1997)
h = 99
Tmin = 0.893, Tmax = 0.958k = 1616
7831 measured reflectionsl = 1414
4422 independent reflections
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-atom parameters constrained
R[F2 > 2σ(F2)] = 0.025 w = 1/[σ2(Fo2) + (0.0435P)2]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.066(Δ/σ)max < 0.001
S = 1.07Δρmax = 0.39 e Å3
4422 reflectionsΔρmin = 0.62 e Å3
172 parametersAbsolute structure: Flack x determined using 2004 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
2 restraintsAbsolute structure parameter: 0.038 (9)
Crystal data top
[CrCl2(C7H20N4)]ClO4V = 751.6 (3) Å3
Mr = 382.62Z = 2
Monoclinic, PnSynchrotron radiation, λ = 0.620 Å
a = 6.4730 (13) ŵ = 0.89 mm1
b = 11.449 (2) ÅT = 243 K
c = 10.385 (2) Å0.13 × 0.13 × 0.05 mm
β = 102.42 (3)°
Data collection top
ADSC Q210 CCD area-detector
diffractometer
4422 independent reflections
Absorption correction: empirical (using intensity measurements)
(HKL3000sm SCALEPACK; Otwinowski & Minor, 1997)
4214 reflections with I > 2σ(I)
Tmin = 0.893, Tmax = 0.958Rint = 0.023
7831 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.025H-atom parameters constrained
wR(F2) = 0.066Δρmax = 0.39 e Å3
S = 1.07Δρmin = 0.62 e Å3
4422 reflectionsAbsolute structure: Flack x determined using 2004 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
172 parametersAbsolute structure parameter: 0.038 (9)
2 restraints
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
xyzUiso*/Ueq
Cr1A0.49958 (5)0.29857 (3)0.49729 (4)0.01583 (8)
Cl1A0.79710 (9)0.18290 (6)0.56558 (7)0.02827 (14)
Cl2A0.20419 (9)0.41841 (5)0.43425 (6)0.02410 (12)
N1A0.5655 (3)0.3816 (2)0.6797 (2)0.0241 (4)
H1A10.69820.36510.72290.029*
H1A20.55350.45950.66900.029*
N2A0.3179 (3)0.18908 (17)0.5865 (2)0.0199 (4)
H2A0.17080.21800.55980.024*
N3A0.4222 (3)0.21127 (19)0.3180 (2)0.0234 (4)
H3A0.28370.24260.27130.028*
N4A0.6689 (3)0.4076 (2)0.3968 (2)0.0249 (4)
H4A10.63680.48280.40870.030*
H4A20.80870.39780.42780.030*
C1A0.4110 (5)0.3385 (3)0.7556 (3)0.0296 (6)
H1A30.27540.37890.72700.036*
H1A40.46360.35330.84990.036*
C2A0.3824 (5)0.2085 (3)0.7308 (3)0.0284 (5)
H2A10.51520.16750.76640.034*
H2A20.27360.17830.77460.034*
C3A0.3107 (4)0.0636 (2)0.5507 (3)0.0284 (5)
H3A10.21280.02300.59550.034*
H3A20.45150.02930.58120.034*
C4A0.2396 (5)0.0455 (3)0.4025 (3)0.0335 (6)
H4A30.20740.03750.38590.040*
H4A40.10810.08920.37130.040*
C5A0.3975 (5)0.0824 (2)0.3219 (3)0.0326 (6)
H5A10.53510.04710.35970.039*
H5A20.35100.05310.23170.039*
C6A0.5783 (5)0.2472 (3)0.2397 (3)0.0333 (6)
H6A10.52580.22690.14670.040*
H6A20.71260.20640.27160.040*
C7A0.6117 (5)0.3775 (3)0.2536 (3)0.0352 (6)
H7A10.72540.40160.21040.042*
H7A20.48210.41870.21130.042*
Cl1B0.50722 (11)0.72486 (5)0.49469 (7)0.02745 (12)
O1B0.5868 (6)0.6499 (3)0.6047 (3)0.0654 (10)
O2B0.5109 (4)0.6627 (3)0.3746 (3)0.0463 (6)
O3B0.2904 (5)0.7539 (3)0.4912 (3)0.0582 (7)
O4B0.6361 (5)0.8276 (2)0.5033 (3)0.0490 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cr1A0.01154 (13)0.01462 (14)0.01988 (14)0.00061 (12)0.00019 (10)0.00054 (13)
Cl1A0.0156 (2)0.0267 (3)0.0401 (3)0.0062 (2)0.0006 (2)0.0027 (2)
Cl2A0.0175 (2)0.0225 (3)0.0308 (3)0.00531 (19)0.00184 (18)0.0056 (2)
N1A0.0234 (9)0.0212 (10)0.0244 (9)0.0001 (8)0.0019 (7)0.0040 (8)
N2A0.0163 (8)0.0153 (9)0.0270 (10)0.0001 (7)0.0018 (7)0.0032 (7)
N3A0.0242 (10)0.0211 (10)0.0237 (10)0.0005 (8)0.0024 (8)0.0044 (8)
N4A0.0186 (9)0.0227 (11)0.0337 (11)0.0008 (7)0.0063 (8)0.0026 (8)
C1A0.0364 (14)0.0305 (15)0.0222 (11)0.0035 (11)0.0071 (10)0.0034 (10)
C2A0.0369 (15)0.0236 (13)0.0248 (12)0.0033 (10)0.0072 (10)0.0056 (9)
C3A0.0293 (12)0.0156 (11)0.0388 (13)0.0013 (9)0.0037 (10)0.0025 (10)
C4A0.0333 (14)0.0204 (12)0.0422 (15)0.0079 (10)0.0023 (11)0.0055 (11)
C5A0.0386 (15)0.0210 (13)0.0358 (13)0.0006 (10)0.0025 (11)0.0097 (10)
C6A0.0362 (15)0.0376 (18)0.0283 (13)0.0012 (12)0.0118 (11)0.0037 (12)
C7A0.0369 (15)0.0399 (18)0.0316 (13)0.0016 (13)0.0133 (11)0.0052 (12)
Cl1B0.0312 (3)0.0245 (3)0.0255 (2)0.0024 (3)0.00349 (19)0.0028 (3)
O1B0.077 (2)0.0510 (16)0.0495 (15)0.0175 (15)0.0279 (14)0.0247 (13)
O2B0.0544 (16)0.0478 (14)0.0396 (12)0.0064 (12)0.0165 (11)0.0106 (10)
O3B0.0421 (14)0.063 (2)0.075 (2)0.0116 (13)0.0243 (13)0.0017 (16)
O4B0.0587 (17)0.0279 (12)0.0574 (15)0.0124 (11)0.0060 (12)0.0005 (10)
Geometric parameters (Å, º) top
Cr1A—N2A2.069 (2)C1A—H1A40.9800
Cr1A—N3A2.078 (2)C2A—H2A10.9800
Cr1A—N1A2.080 (2)C2A—H2A20.9800
Cr1A—N4A2.084 (2)C3A—C4A1.523 (4)
Cr1A—Cl1A2.3191 (8)C3A—H3A10.9800
Cr1A—Cl2A2.3300 (8)C3A—H3A20.9800
N1A—C1A1.484 (4)C4A—C5A1.514 (4)
N1A—H1A10.9000C4A—H4A30.9800
N1A—H1A20.9000C4A—H4A40.9800
N2A—C3A1.482 (3)C5A—H5A10.9800
N2A—C2A1.483 (4)C5A—H5A20.9800
N2A—H2A0.9900C6A—C7A1.510 (5)
N3A—C5A1.485 (3)C6A—H6A10.9800
N3A—C6A1.485 (4)C6A—H6A20.9800
N3A—H3A0.9900C7A—H7A10.9800
N4A—C7A1.493 (4)C7A—H7A20.9800
N4A—H4A10.9000Cl1B—O1B1.433 (3)
N4A—H4A20.9000Cl1B—O4B1.434 (2)
C1A—C2A1.514 (4)Cl1B—O3B1.435 (3)
C1A—H1A30.9800Cl1B—O2B1.441 (3)
N2A—Cr1A—N3A93.40 (9)H1A3—C1A—H1A4108.4
N2A—Cr1A—N1A83.91 (9)N2A—C2A—C1A108.5 (2)
N3A—Cr1A—N1A177.24 (9)N2A—C2A—H2A1110.0
N2A—Cr1A—N4A176.52 (9)C1A—C2A—H2A1110.0
N3A—Cr1A—N4A83.72 (9)N2A—C2A—H2A2110.0
N1A—Cr1A—N4A98.95 (9)C1A—C2A—H2A2110.0
N2A—Cr1A—Cl1A91.81 (6)H2A1—C2A—H2A2108.4
N3A—Cr1A—Cl1A91.36 (7)N2A—C3A—C4A111.8 (2)
N1A—Cr1A—Cl1A89.33 (7)N2A—C3A—H3A1109.3
N4A—Cr1A—Cl1A90.21 (7)C4A—C3A—H3A1109.3
N2A—Cr1A—Cl2A88.37 (6)N2A—C3A—H3A2109.3
N3A—Cr1A—Cl2A90.36 (7)C4A—C3A—H3A2109.3
N1A—Cr1A—Cl2A88.97 (7)H3A1—C3A—H3A2107.9
N4A—Cr1A—Cl2A89.69 (7)C5A—C4A—C3A115.3 (2)
Cl1A—Cr1A—Cl2A178.26 (3)C5A—C4A—H4A3108.5
C1A—N1A—Cr1A107.58 (16)C3A—C4A—H4A3108.5
C1A—N1A—H1A1110.2C5A—C4A—H4A4108.5
Cr1A—N1A—H1A1110.2C3A—C4A—H4A4108.5
C1A—N1A—H1A2110.2H4A3—C4A—H4A4107.5
Cr1A—N1A—H1A2110.2N3A—C5A—C4A112.5 (2)
H1A1—N1A—H1A2108.5N3A—C5A—H5A1109.1
C3A—N2A—C2A112.7 (2)C4A—C5A—H5A1109.1
C3A—N2A—Cr1A117.73 (18)N3A—C5A—H5A2109.1
C2A—N2A—Cr1A107.34 (16)C4A—C5A—H5A2109.1
C3A—N2A—H2A106.1H5A1—C5A—H5A2107.8
C2A—N2A—H2A106.1N3A—C6A—C7A108.8 (2)
Cr1A—N2A—H2A106.1N3A—C6A—H6A1109.9
C5A—N3A—C6A112.4 (2)C7A—C6A—H6A1109.9
C5A—N3A—Cr1A117.36 (17)N3A—C6A—H6A2109.9
C6A—N3A—Cr1A107.22 (17)C7A—C6A—H6A2109.9
C5A—N3A—H3A106.4H6A1—C6A—H6A2108.3
C6A—N3A—H3A106.4N4A—C7A—C6A108.8 (2)
Cr1A—N3A—H3A106.4N4A—C7A—H7A1109.9
C7A—N4A—Cr1A108.43 (17)C6A—C7A—H7A1109.9
C7A—N4A—H4A1110.0N4A—C7A—H7A2109.9
Cr1A—N4A—H4A1110.0C6A—C7A—H7A2109.9
C7A—N4A—H4A2110.0H7A1—C7A—H7A2108.3
Cr1A—N4A—H4A2110.0O1B—Cl1B—O4B109.70 (17)
H4A1—N4A—H4A2108.4O1B—Cl1B—O3B109.9 (2)
N1A—C1A—C2A108.0 (2)O4B—Cl1B—O3B111.3 (2)
N1A—C1A—H1A3110.1O1B—Cl1B—O2B108.91 (19)
C2A—C1A—H1A3110.1O4B—Cl1B—O2B109.98 (17)
N1A—C1A—H1A4110.1O3B—Cl1B—O2B106.93 (19)
C2A—C1A—H1A4110.1
Cr1A—N1A—C1A—C2A40.4 (2)C6A—N3A—C5A—C4A179.6 (2)
C3A—N2A—C2A—C1A173.1 (2)Cr1A—N3A—C5A—C4A54.6 (3)
Cr1A—N2A—C2A—C1A41.9 (3)C3A—C4A—C5A—N3A70.3 (3)
N1A—C1A—C2A—N2A55.7 (3)C5A—N3A—C6A—C7A173.7 (2)
C2A—N2A—C3A—C4A178.8 (2)Cr1A—N3A—C6A—C7A43.3 (3)
Cr1A—N2A—C3A—C4A55.5 (3)Cr1A—N4A—C7A—C6A36.0 (3)
N2A—C3A—C4A—C5A70.5 (3)N3A—C6A—C7A—N4A53.5 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1A—H1A1···O2Bi0.902.303.187 (4)167
N1A—H1A2···O1B0.902.303.180 (4)164
N2A—H2A···Cl1Aii0.992.473.332 (2)146
N3A—H3A···O1Biii0.992.283.174 (4)150
N4A—H4A1···O2B0.902.213.086 (4)163
N4A—H4A2···Cl2Aiv0.902.563.405 (2)157
Symmetry codes: (i) x+1/2, y+1, z+1/2; (ii) x1, y, z; (iii) x1/2, y+1, z1/2; (iv) x+1, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1A—H1A1···O2Bi0.902.303.187 (4)167.0
N1A—H1A2···O1B0.902.303.180 (4)164.3
N2A—H2A···Cl1Aii0.992.473.332 (2)146.0
N3A—H3A···O1Biii0.992.283.174 (4)150.2
N4A—H4A1···O2B0.902.213.086 (4)162.7
N4A—H4A2···Cl2Aiv0.902.563.405 (2)157.2
Symmetry codes: (i) x+1/2, y+1, z+1/2; (ii) x1, y, z; (iii) x1/2, y+1, z1/2; (iv) x+1, y, z.

Experimental details

Crystal data
Chemical formula[CrCl2(C7H20N4)]ClO4
Mr382.62
Crystal system, space groupMonoclinic, Pn
Temperature (K)243
a, b, c (Å)6.4730 (13), 11.449 (2), 10.385 (2)
β (°) 102.42 (3)
V3)751.6 (3)
Z2
Radiation typeSynchrotron, λ = 0.620 Å
µ (mm1)0.89
Crystal size (mm)0.13 × 0.13 × 0.05
Data collection
DiffractometerADSC Q210 CCD area-detector
Absorption correctionEmpirical (using intensity measurements)
(HKL3000sm SCALEPACK; Otwinowski & Minor, 1997)
Tmin, Tmax0.893, 0.958
No. of measured, independent and
observed [I > 2σ(I)] reflections
7831, 4422, 4214
Rint0.023
(sin θ/λ)max1)0.707
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.025, 0.066, 1.07
No. of reflections4422
No. of parameters172
No. of restraints2
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.39, 0.62
Absolute structureFlack x determined using 2004 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
Absolute structure parameter0.038 (9)

Computer programs: PAL BL2D-SMDC Program (Shin et al., 2016), HKL3000sm (Otwinowski & Minor, 1997), SHELXT (Sheldrick, 2015a), SHELXL2014/7 (Sheldrick, 2015b), DIAMOND (Putz & Brandenburg, 2014), publCIF (Westrip, 2010).

 

Acknowledgements

This work was supported by a grant from 2016 Research Funds of Andong National University. The X-ray crystallography experiment at the PLS-II BL2D-SMC beamline was supported in part by MSIP and POSTECH.

References

First citationBang, E. & Pedersen, E. (1978). Acta Chem. Scand. Ser. A, 32, 833–836.  CrossRef Google Scholar
First citationChoi, J.-H., Choi, S. Y., Hong, Y. P., Ko, S.-O., Ryoo, K. S., Lee, S. H. & Park, Y. C. (2008a). Spectrochim. Acta Part A, 70, 619–625.  CrossRef Google Scholar
First citationChoi, J.-H., Clegg, W. & Harrington, R. W. (2011). Z. Anorg. Allg. Chem. 637, 562–566.  CrossRef CAS Google Scholar
First citationChoi, J.-H., Kim, H.-S. & Habibi, M. H. (2008b). Bull. Korean Chem. Soc. 29, 1399–1402.  CAS Google Scholar
First citationChoi, J.-H. & Lee, U. (2008). Acta Cryst. E64, m1186.  Web of Science CSD CrossRef IUCr Journals Google Scholar
First citationChoi, J.-H. & Moon, D. (2014). J. Mol. Struct. 1059, 325–331.  Web of Science CSD CrossRef CAS Google Scholar
First citationGroom, C. R. & Allen, F. H. (2014). Angew. Chem. Int. Ed. 35, 3103–3111.  Google Scholar
First citationHouse, D. A. & Garner, C. S. (1966). J. Am. Chem. Soc. 88, 2156–2162.  CrossRef CAS Google Scholar
First citationHouse, D. A. & Yang, D. (1983). Inorg. Chim. Acta, 74, 179–189.  CrossRef CAS Google Scholar
First citationKirk, A. D. & Fernando, S. R. L. (1994). Inorg. Chem. 33, 4401–4047.  Google Scholar
First citationKukina, G. A., Porai-Koshits, M. A., Shevchenko, Y. N. & Shchurkina, V. N. (1990). Koord. Khim. 16, 784–792.  CAS Google Scholar
First citationKutal, C. & Adamson, A. W. (1973). Inorg. Chem. 12, 1990–1994.  CrossRef CAS Google Scholar
First citationMäcke, H. R., Mentzen, B. F., Puaux, J. P. & Adamson, A. W. (1982). Inorg. Chem. 21, 3080–3082.  Google Scholar
First citationOtwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. Academic Press, New York.  Google Scholar
First citationParsons, S., Flack, H. D. & Wagner, T. (2013). Acta Cryst. B69, 249–259.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationPutz, H. & Brandenburg, K. (2014). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
First citationRonconi, L. & Sadler, P. J. (2007). Coord. Chem. Rev. 251, 1633–1648.  Web of Science CrossRef CAS Google Scholar
First citationRoss, A., Choi, J.-H., Hunter, T. M., Pannecouque, C., Moggach, S. A., Parsons, S., De Clercq, E. & Sadler, P. J. (2012). Dalton Trans. 41, 6408–6418.  Web of Science CSD CrossRef CAS PubMed Google Scholar
First citationSheldrick, G. M. (2015a). Acta Cryst. A71, 3–8.  Web of Science CrossRef IUCr Journals Google Scholar
First citationSheldrick, G. M. (2015b). Acta Cryst. C71, 3–8.  Web of Science CrossRef IUCr Journals Google Scholar
First citationShin, J. W., Eom, K. & Moon, D. (2016). J. Synchrotron Rad. 23, 369–373.  Web of Science CrossRef IUCr Journals Google Scholar
First citationWestrip, S. P. (2010). J. Appl. Cryst. 43, 920–925.  Web of Science CrossRef CAS IUCr Journals Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 72| Part 3| March 2016| Pages 424-427
Follow Acta Cryst. E
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds