Literature DB >> 27555961

Crystal structure of non-centrosymmetric bis-(4-meth-oxy-benzyl-ammonium) tetra-chlorido-zincate.

Najla Mahbouli Rhouma1, Ali Rayes2, Francesco Mezzadri3, Gianluca Calestani3, Mohamed Loukil1.   

Abstract

The structure of the title non-centrosymmetric organic-inorganic hybrid salt, (C8H12NO)2[ZnCl4], consists of two 4-meth-oxy-benzyl-ammonium cations sandwiched between anionic layers, formed by isolated tetra-chlorido-zincate tetra-hedra. The double layers extend parallel to the ac plane. The crystal packing is assured by Coulombic inter-actions and by a complex N-H⋯Cl and C-H⋯Cl hydrogen-bonding system mostly involving the positively charged ammonium groups and the chloride ligands of the isolated tetra-hedral [ZnCl4](2-) units. One of the methyl-ene-ammonium groups is disordered over two sets of sites in a 0.48 (2):0.52 (2) ratio. The crystal investigated was twinned by non-merohedry with a twin component ratio of 0.738 (2):0.262 (2).

Entities:  

Keywords:  crystal structure; hydrogen bonds; non-centrosymmetric organic–inorganic hybrid material

Year:  2016        PMID: 27555961      PMCID: PMC4992936          DOI: 10.1107/S2056989016010069

Source DB:  PubMed          Journal:  Acta Crystallogr E Crystallogr Commun


Chemical context

Non-linear optical (NLO) materials have received much attention in different research areas due to their potential applications in high-density optical data storage, electro-optical shutters, optical communication and signal processing (Maury & Le Bozec, 2005 ▸; Green et al., 2011 ▸; Evans & Lin, 2002 ▸). Mostly connected in the past to a few families of inorganic materials, the research was then extended to organic materials, generally salts of amino acids with organic acids, which are expected to have relatively strong NLO properties due to delocalized electrons at π–π* orbitals. More recently, organic–inorganic hybrid materials showing non-centrosymmetric structures started gaining attention in the field, since they are expected to offer enhanced properties, such as second harmonic generation efficiency, by combining the characteristic features of both organic and inorganic moieties. These materials are usually constituted by the crystal packing of inorganic anions (typically halogenidometalates) and organic ammonium cations ensured by hydrogen bonds and Coulombic inter­actions (Brammer et al., 2002 ▸). Herein we report the synthesis and crystal structure of a new organic–inorganic hybrid compound, bis­(4-meth­oxy­benzyl­ammonium) tetra­chlorido­zincate. This salt crystallizes in a non-centrosymmetric space group and hence could be a potential candidate for second order non-linear optical properties.

Structural commentary

The asymmetric unit of the crystal structure consists of an isolated tetra­chlorido­zincate anion, [ZnCl4]2− and two 4-meth­oxy­benzyl­ammonium cations, (C8H12NO)+, as shown in Fig. 1 ▸. One of the cations shows positional disorder of the methyl­ene­ammonium moiety. The lengths of the C—C, C—N and C—O bonds in the two independent 4-meth­oxy­benzyl­ammonium cations are in accordance with corresponding distances found in the literature (Groom et al., 2016 ▸). The ZnII atom is tetra­hedrally coordinated by four chloride ligands with Zn—Cl bond lengths ranging from 2.249 (2) to 2.289 (2) Å and Cl—Zn—Cl bond angles varying between 107.25 (8) and 112.41 (10)°.
Figure 1

The asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level. Only the major component of the disordered methyl­ene­ammonium group is shown for clarity.

Supra­molecular features

The crystal structure consist of 4-meth­oxy­benzyl­ammonium cations sandwiched between tetra­chlorido­zincate layers extending parallel to the ac plane, as shown in Fig. 2 ▸. The cationic units are linked into a two-dimensional network by weak C—H⋯π inter­actions (Table 1 ▸). The crystal packing is assured by a complex hydrogen-bonding system, mostly involving the positively charged ammonium groups and the chloride ligands of the isolated tetra­hedral [ZnCl4]2− units (Table 1 ▸), which reinforce the Coulombic inter­actions, as depicted in Fig. 3 ▸. Whereas the N2 atom is blocked by a very efficient hydrogen-bonding system involving five donor⋯acceptor distances ranging from 3.279 (8) to 3.452 (7) Å, the N1 ammonium group is disordered over two sets of sites as a consequence of a less efficient hydrogen bonding.
Figure 2

Packing diagram of the title compound viewed along the b axis, showing the alternate stacking, along the c axis, of organic and inorganic layers.

Table 1

Hydrogen-bond geometry (Å, °)

Cg1 and Cg2 are the centroids of the C11–C16 and C1–C6 rings, respectively

D—H⋯A D—HH⋯A DA D—H⋯A
N1A—H1A1⋯Cl30.892.323.19 (2)164
N1A—H1A2⋯Cl2i 0.892.753.26 (2)118
N1A—H1A3⋯Cl4i 0.892.643.34 (2)137
C8A—H8A2⋯Cl4ii 0.972.773.72 (2)168
N1B—H1B1⋯Cl4ii 0.892.783.61 (3)154
N1B—H1B2⋯Cl2i 0.892.663.33 (2)133
N1B—H1B3⋯Cl30.892.803.45 (2)131
C8B—H8B2⋯Cl1ii 0.972.823.60 (2)138
N2—H1N⋯Cl1iii 0.892.653.364 (7)138
N2—H1N⋯Cl2iii 0.892.753.336 (7)125
N2—H2N⋯Cl3iv 0.892.453.279 (8)156
N2—H3N⋯Cl1iv 0.892.723.331 (7)127
N2—H3N⋯Cl20.892.713.452 (7)141
C2—H2⋯Cg10.932.623.432 (8)146
C6—H6⋯Cg2i 0.932.863.579 (8)135

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) .

Figure 3

Partial packing diagram of the title compound approximately viewed along the b axis, showing the hydrogen-bonding network (dashed lines).

Database survey

A search of the Cambridge Structural Database (Version 5.37; last update February 2016; Groom et al., 2016 ▸) for related compounds showed the occurrence of the cadmium analogue of formula (C8H12NO)2[CdCl4] (Kefi et al., 2011 ▸), in which the coordination sphere of the metal is octa­hedral, giving rise to the formation of perovskite-like edge-sharing units that built up two-dimensional anionic layers parallel to the bc plane.

Synthesis and crystallization

Single crystals of (C8H12NO)2[ZnCl4] were synthesized starting from 4-meth­oxy­benzyl­amine (Sigma–Aldrich, 98%), zinc chloride (Sigma–Aldrich, 98%) and HCl (37%), which were weighted in the stoichiometric proportion conforming to the equation reaction: 2 C8H11NO + 2 HCl + ZnCl2 → (C8H12NO)2[ZnCl4] After mixing the reagents in 50 ml of water and stirring at room temperature for more 3 h, the resulting solution was placed in a Petri dish and allowed to evaporate slowly. Single crystals suitable for X-ray diffraction were obtained within a week (yield: 75%).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. The crystals of bis­(4-meth­oxy­benzyl­ammonium) tetra­chlorido­zincate were systematically affected by non-merohedral polar twinning. The ratio of the twin components of the crystal selected for X-ray analysis was refined to 0.738 (2):0.262 (2). One methyl­ene­ammonium group was found to be disordered over two sets of sites with a refined occupancy ratio of 0.52 (2):0.48 (2). During the refinement of the disordered group, the C—C and C—N bond lengths were constrained to be 1.50 (2) and 1.47 (1) Å, respectively. EADP and ISOR restraints (Sheldrick, 2015b ▸) were also applied. All H atoms were placed geometrically and refined using a riding-model approximation, with C—H = 0.93–0.97 Å, N—H = 0.89 Å, and with U iso(H) = 1.2U eq(C) or 1.5U eq(C, N) for methyl and ammonium H atoms, for which a rotating model was applied.
Table 2

Experimental details

Crystal data
Chemical formula(C8H12NO)2[ZnCl4]
M r 483.54
Crystal system, space groupMonoclinic, P21
Temperature (K)294
a, b, c (Å)10.6849 (10), 7.4540 (7), 13.3961 (12)
β (°)93.482 (2)
V3)1064.97 (17)
Z 2
Radiation typeMo Kα
μ (mm−1)1.67
Crystal size (mm)0.31 × 0.29 × 0.11
 
Data collection
DiffractometerBruker SMART CCD
Absorption correctionMulti-scan (SADABS; Bruker, 2008)
T min, T max 0.604, 0.827
No. of measured, independent and observed [I > 2σ(I)] reflections2132, 2132, 1932
(sin θ/λ)max−1)0.606
 
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S 0.043, 0.108, 1.08
No. of reflections2132
No. of parameters239
No. of restraints29
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.42, −0.44
Absolute structureNo quotients, so Flack parameter determined by classical intensity fit
Absolute structure parameter0.09 (2)

Computer programs: APEX2 and SAINT (Bruker, 2008 ▸), SHELXT (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸), VESTA (Momma & Izumi, 2011 ▸) and SCHAKAL (Keller, 1999 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989016010069/wm5302sup1.cif Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016010069/wm5302Isup2.hkl CCDC reference: 1486826 Additional supporting information: crystallographic information; 3D view; checkCIF report
(C8H12NO)2[ZnCl4]F(000) = 496
Mr = 483.54Dx = 1.508 Mg m3
Monoclinic, P21Mo Kα radiation, λ = 0.71073 Å
a = 10.6849 (10) ÅCell parameters from 196 reflections
b = 7.4540 (7) Åθ = 7.3–17.5°
c = 13.3961 (12) ŵ = 1.67 mm1
β = 93.482 (2)°T = 294 K
V = 1064.97 (17) Å3Prism, colourless
Z = 20.31 × 0.29 × 0.11 mm
Bruker SMART CCD diffractometer1932 reflections with I > 2σ(I)
ω scanθmax = 25.5°, θmin = 1.5°
Absorption correction: multi-scan (SADABS; Bruker, 2008)h = −12→12
Tmin = 0.604, Tmax = 0.827k = 0→9
2132 measured reflectionsl = 0→16
2132 independent reflections
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-atom parameters constrained
R[F2 > 2σ(F2)] = 0.043w = 1/[σ2(Fo2) + (0.0576P)2 + 0.2617P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.108(Δ/σ)max < 0.001
S = 1.08Δρmax = 0.42 e Å3
2132 reflectionsΔρmin = −0.44 e Å3
239 parametersAbsolute structure: No quotients, so Flack parameter determined by classical intensity fit
29 restraintsAbsolute structure parameter: 0.09 (2)
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refined as a 2-component twin.
xyzUiso*/UeqOcc. (<1)
Zn10.23731 (7)0.06114 (12)−0.04066 (6)0.0413 (2)
Cl10.35118 (19)−0.1525 (3)−0.11156 (13)0.0464 (5)
Cl20.3173 (2)0.3349 (3)−0.08077 (16)0.0515 (5)
Cl30.2564 (2)0.0169 (3)0.12644 (14)0.0541 (5)
Cl40.03137 (18)0.0515 (5)−0.09460 (17)0.0714 (7)
O10.2318 (5)0.1370 (9)0.5695 (4)0.0585 (16)
O20.3732 (5)0.6144 (8)0.5857 (4)0.0541 (15)
N1A−0.039 (2)−0.010 (3)0.1458 (15)0.060 (4)0.52 (2)
H1A10.03980.01840.13450.090*0.52 (2)
H1A2−0.0863−0.00230.08890.090*0.52 (2)
H1A3−0.0418−0.12140.16930.090*0.52 (2)
C8A−0.087 (2)0.115 (3)0.2197 (13)0.051 (4)0.52 (2)
H8A1−0.17410.08890.22880.062*0.52 (2)
H8A2−0.08160.23700.19450.062*0.52 (2)
N1B−0.062 (2)0.077 (4)0.1398 (13)0.060 (4)0.48 (2)
H1B1−0.02690.18350.13030.090*0.48 (2)
H1B2−0.12270.05810.09260.090*0.48 (2)
H1B3−0.0039−0.00840.13650.090*0.48 (2)
C8B−0.1142 (17)0.073 (4)0.2386 (12)0.051 (4)0.48 (2)
H8B1−0.1541−0.04220.24830.062*0.48 (2)
H8B2−0.17750.16560.24210.062*0.48 (2)
N20.4066 (6)0.6363 (10)0.1058 (5)0.0491 (16)
H1N0.48690.61500.12360.074*
H2N0.38970.75160.11580.074*
H3N0.39160.60990.04140.074*
C10.1468 (6)0.1175 (9)0.4901 (5)0.0369 (16)
C20.1783 (7)0.2035 (10)0.4051 (5)0.0424 (18)
H20.25350.26630.40480.051*
C30.0987 (8)0.1978 (11)0.3188 (6)0.0456 (18)
H30.11990.25720.26120.055*
C4−0.0124 (7)0.1024 (10)0.3201 (5)0.0409 (18)
C5−0.0412 (7)0.0166 (11)0.4056 (6)0.049 (2)
H5−0.1157−0.04770.40610.059*
C60.0374 (7)0.0223 (10)0.4917 (6)0.047 (2)
H60.0162−0.03720.54930.057*
C70.2037 (11)0.0551 (19)0.6615 (7)0.085 (3)
H7A0.12080.08920.67810.128*
H7B0.26340.09390.71350.128*
H7C0.2078−0.07290.65490.128*
C110.3734 (7)0.5951 (10)0.4849 (5)0.0393 (16)
C120.4613 (7)0.4999 (11)0.4364 (6)0.0423 (18)
H120.52960.44870.47210.051*
C130.4466 (7)0.4808 (12)0.3325 (6)0.0450 (19)
H130.50500.41380.29970.054*
C140.3470 (6)0.5594 (13)0.2768 (5)0.0440 (16)
C150.2628 (7)0.6580 (10)0.3274 (6)0.0472 (18)
H150.19670.71400.29120.057*
C160.2727 (8)0.6769 (10)0.4303 (6)0.0468 (18)
H160.21340.74270.46290.056*
C170.4625 (10)0.5122 (14)0.6466 (6)0.070 (3)
H17A0.45410.38730.62990.105*
H17B0.44730.52920.71580.105*
H17C0.54580.55170.63460.105*
C180.3266 (7)0.5243 (12)0.1665 (6)0.054 (2)
H18A0.34370.39890.15350.065*
H18B0.23940.54700.14610.065*
U11U22U33U12U13U23
Zn10.0397 (4)0.0455 (4)0.0384 (4)−0.0002 (5)0.0005 (4)0.0012 (4)
Cl10.0524 (11)0.0456 (9)0.0416 (9)0.0014 (9)0.0070 (9)−0.0042 (9)
Cl20.0516 (11)0.0415 (10)0.0607 (11)0.0008 (10)−0.0015 (10)0.0091 (9)
Cl30.0695 (12)0.0560 (13)0.0369 (9)0.0119 (11)0.0042 (10)0.0018 (8)
Cl40.0364 (9)0.115 (2)0.0623 (12)−0.0014 (15)−0.0031 (9)−0.0049 (16)
O10.056 (3)0.076 (4)0.042 (3)0.006 (3)−0.014 (3)0.001 (3)
O20.063 (3)0.056 (4)0.044 (3)0.002 (3)0.007 (3)−0.004 (3)
N1A0.056 (7)0.077 (12)0.047 (4)−0.011 (9)−0.007 (5)−0.003 (8)
C8A0.047 (6)0.055 (7)0.052 (6)0.001 (5)−0.002 (5)0.004 (5)
N1B0.056 (7)0.077 (12)0.047 (4)−0.011 (9)−0.007 (5)−0.003 (8)
C8B0.047 (6)0.055 (7)0.052 (6)0.001 (5)−0.002 (5)0.004 (5)
N20.051 (4)0.058 (4)0.038 (3)0.006 (3)0.006 (3)0.007 (3)
C10.033 (4)0.037 (4)0.041 (4)0.003 (3)0.004 (3)−0.001 (3)
C20.037 (4)0.043 (4)0.048 (4)−0.010 (3)0.010 (3)−0.006 (3)
C30.058 (5)0.048 (4)0.031 (4)−0.005 (4)0.008 (3)−0.001 (3)
C40.041 (4)0.040 (5)0.041 (4)0.003 (3)−0.004 (3)−0.008 (3)
C50.034 (4)0.044 (5)0.069 (5)−0.010 (3)0.005 (4)−0.002 (4)
C60.052 (5)0.038 (4)0.053 (4)0.000 (4)0.014 (4)0.010 (3)
C70.105 (8)0.086 (7)0.062 (5)0.012 (9)−0.016 (6)0.013 (7)
C110.044 (4)0.034 (4)0.041 (4)−0.010 (4)0.007 (3)−0.002 (3)
C120.036 (4)0.038 (4)0.052 (5)0.002 (3)0.004 (4)0.005 (4)
C130.038 (4)0.047 (4)0.052 (5)0.000 (4)0.016 (4)0.000 (4)
C140.043 (4)0.042 (4)0.048 (4)−0.006 (5)0.010 (3)0.007 (4)
C150.042 (4)0.043 (4)0.057 (4)0.004 (4)0.007 (4)0.010 (4)
C160.051 (4)0.039 (4)0.052 (4)0.006 (4)0.015 (4)−0.002 (3)
C170.093 (7)0.071 (7)0.045 (5)0.000 (6)−0.004 (5)0.001 (5)
C180.048 (4)0.067 (6)0.047 (4)−0.016 (4)0.002 (4)−0.006 (4)
Zn1—Cl12.249 (2)C2—C31.393 (11)
Zn1—Cl32.2595 (19)C2—H20.9300
Zn1—Cl42.275 (2)C3—C41.385 (11)
Zn1—Cl22.289 (2)C3—H30.9300
O1—C11.363 (8)C4—C51.363 (11)
O1—C71.424 (11)C5—C61.385 (11)
O2—C111.359 (9)C5—H50.9300
O2—C171.435 (11)C6—H60.9300
N1A—C8A1.473 (10)C7—H7A0.9600
N1A—H1A10.8900C7—H7B0.9600
N1A—H1A20.8900C7—H7C0.9600
N1A—H1A30.8900C11—C121.371 (11)
C8A—C41.523 (15)C11—C161.403 (11)
C8A—H8A10.9700C12—C131.398 (11)
C8A—H8A20.9700C12—H120.9300
N1B—C8B1.469 (10)C13—C141.392 (11)
N1B—H1B10.8900C13—H130.9300
N1B—H1B20.8900C14—C151.372 (11)
N1B—H1B30.8900C14—C181.504 (10)
C8B—C41.510 (15)C15—C161.384 (11)
C8B—H8B10.9700C15—H150.9300
C8B—H8B20.9700C16—H160.9300
N2—C181.474 (10)C17—H17A0.9600
N2—H1N0.8900C17—H17B0.9600
N2—H2N0.8900C17—H17C0.9600
N2—H3N0.8900C18—H18A0.9700
C1—C21.366 (10)C18—H18B0.9700
C1—C61.369 (10)
Cl1—Zn1—Cl3107.25 (8)C5—C4—C3119.2 (7)
Cl1—Zn1—Cl4112.41 (10)C5—C4—C8B110.5 (11)
Cl3—Zn1—Cl4109.72 (9)C3—C4—C8B130.3 (11)
Cl1—Zn1—Cl2108.22 (8)C5—C4—C8A129.8 (11)
Cl3—Zn1—Cl2110.50 (9)C3—C4—C8A110.9 (11)
Cl4—Zn1—Cl2108.73 (11)C4—C5—C6122.0 (7)
C1—O1—C7117.6 (7)C4—C5—H5119.0
C11—O2—C17117.9 (6)C6—C5—H5119.0
C8A—N1A—H1A1109.5C1—C6—C5118.5 (7)
C8A—N1A—H1A2109.5C1—C6—H6120.7
H1A1—N1A—H1A2109.5C5—C6—H6120.7
C8A—N1A—H1A3109.5O1—C7—H7A109.5
H1A1—N1A—H1A3109.5O1—C7—H7B109.5
H1A2—N1A—H1A3109.5H7A—C7—H7B109.5
N1A—C8A—C4111.8 (14)O1—C7—H7C109.5
N1A—C8A—H8A1109.3H7A—C7—H7C109.5
C4—C8A—H8A1109.3H7B—C7—H7C109.5
N1A—C8A—H8A2109.3O2—C11—C12124.6 (7)
C4—C8A—H8A2109.3O2—C11—C16115.1 (6)
H8A1—C8A—H8A2107.9C12—C11—C16120.3 (6)
C8B—N1B—H1B1109.5C11—C12—C13119.0 (7)
C8B—N1B—H1B2109.5C11—C12—H12120.5
H1B1—N1B—H1B2109.5C13—C12—H12120.5
C8B—N1B—H1B3109.5C14—C13—C12121.7 (7)
H1B1—N1B—H1B3109.5C14—C13—H13119.1
H1B2—N1B—H1B3109.5C12—C13—H13119.1
N1B—C8B—C4110.6 (15)C15—C14—C13117.7 (7)
N1B—C8B—H8B1109.5C15—C14—C18121.2 (7)
C4—C8B—H8B1109.5C13—C14—C18120.9 (7)
N1B—C8B—H8B2109.5C14—C15—C16122.3 (8)
C4—C8B—H8B2109.5C14—C15—H15118.9
H8B1—C8B—H8B2108.1C16—C15—H15118.9
C18—N2—H1N109.5C15—C16—C11119.0 (7)
C18—N2—H2N109.5C15—C16—H16120.5
H1N—N2—H2N109.5C11—C16—H16120.5
C18—N2—H3N109.5O2—C17—H17A109.5
H1N—N2—H3N109.5O2—C17—H17B109.5
H2N—N2—H3N109.5H17A—C17—H17B109.5
O1—C1—C2114.5 (6)O2—C17—H17C109.5
O1—C1—C6124.9 (7)H17A—C17—H17C109.5
C2—C1—C6120.6 (7)H17B—C17—H17C109.5
C1—C2—C3120.6 (7)N2—C18—C14112.9 (7)
C1—C2—H2119.7N2—C18—H18A109.0
C3—C2—H2119.7C14—C18—H18A109.0
C4—C3—C2119.1 (7)N2—C18—H18B109.0
C4—C3—H3120.5C14—C18—H18B109.0
C2—C3—H3120.5H18A—C18—H18B107.8
D—H···AD—HH···AD···AD—H···A
N1A—H1A1···Cl30.892.323.19 (2)164
N1A—H1A2···Cl2i0.892.753.26 (2)118
N1A—H1A3···Cl4i0.892.643.34 (2)137
C8A—H8A2···Cl4ii0.972.773.72 (2)168
N1B—H1B1···Cl4ii0.892.783.61 (3)154
N1B—H1B2···Cl2i0.892.663.33 (2)133
N1B—H1B3···Cl30.892.803.45 (2)131
C8B—H8B2···Cl1ii0.972.823.60 (2)138
N2—H1N···Cl1iii0.892.653.364 (7)138
N2—H1N···Cl2iii0.892.753.336 (7)125
N2—H2N···Cl3iv0.892.453.279 (8)156
N2—H3N···Cl1iv0.892.723.331 (7)127
N2—H3N···Cl20.892.713.452 (7)141
C2—H2···Cg10.932.623.432 (8)146
C6—H6···Cg2i0.932.863.579 (8)135
  6 in total

1.  Crystal engineering of NLO materials based on metal--organic coordination networks.

Authors:  Owen R Evans; Wenbin Lin
Journal:  Acc Chem Res       Date:  2002-07       Impact factor: 22.384

2.  Molecular engineering of octupolar NLO molecules and materials based on bipyridyl metal complexes.

Authors:  Olivier Maury; Hubert Le Bozec
Journal:  Acc Chem Res       Date:  2005-09       Impact factor: 22.384

3.  Hydrogen bonding and perhalometallate ions: a supramolecular synthetic strategy for new inorganic materials.

Authors:  Lee Brammer; John K Swearingen; Eric A Bruton; Paul Sherwood
Journal:  Proc Natl Acad Sci U S A       Date:  2002-04-16       Impact factor: 11.205

4.  SHELXT - integrated space-group and crystal-structure determination.

Authors:  George M Sheldrick
Journal:  Acta Crystallogr A Found Adv       Date:  2015-01-01       Impact factor: 2.290

5.  Crystal structure refinement with SHELXL.

Authors:  George M Sheldrick
Journal:  Acta Crystallogr C Struct Chem       Date:  2015-01-01       Impact factor: 1.172

6.  The Cambridge Structural Database.

Authors:  Colin R Groom; Ian J Bruno; Matthew P Lightfoot; Suzanna C Ward
Journal:  Acta Crystallogr B Struct Sci Cryst Eng Mater       Date:  2016-04-01
  6 in total

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