research communications
accessSynthesis and of catena-poly[[dibromidozinc(II)]-μ-2,3-dimethylpyrazine-κ2N1:N4]
aInstitut für Anorganische Chemie, Universität Kiel, Max-Eyth.-Str. 2, 24118 Kiel, Germany, and bSuman Ramesh Tulsiani Technical Campus - Faculty of Engineering, Pune, India
*Correspondence e-mail: [email protected]
The title compound, [ZnBr2(C6H8N2)2]n, was prepared by the reaction of zinc bromide with 2,3-dimethylpyrazine in acetonitrile and is isotypic to the corresponding compound with zinc chloride reported recently [Näther & Bhosekar (2025
). Acta Cryst. E4, 813–820]. The asymmetric unit consists of one zinc cation, two crystallographically independent bromide anions and one 2,3-dimethylpyrazine ligand, all of which are located in general positions. In the crystal, the Zn cations are tetrahedrally coordinated by two bromide anions and two 2,3-dimethylpyrazine ligands and are linked by bridging 2,3-dimethylpyrazine ligands into corrugated chains that proceed along the c-axis direction. Measurements using powder X-ray diffraction show that a pure crystalline phase was obtained.
CCDC reference: 2482737
1. Chemical context
We have been interested in the synthesis and structures of transition-metal halide and pseudo halide compounds with N-donor coligands for a very long time because they show a versatile coordination and structural behavior. This is especially the case for compounds based on CuI, in which the metal cations forms mono or dinuclear complexes or they are linked by the halide or pseudo halide anions into one-dimensional or two-dimensional networks (Näther et al., 2001
, 2002
; Kromp & Sheldrick, 1999
; Peng et al., 2010
; Li et al., 2005
). In most cases, for a given copper(I) halide or pseudo halide and a given coligand, compounds of different stoichiometry are observed, which include coligand-rich and coligand-deficient compounds. In this context we have found that the coligand-rich compounds can be transformed into the corresponding coligand-deficient compounds by heating (Näther & Jess, 2002
, 2004
).
In contrast to copper(I), compounds with twofold positively charged cations such as, for example, ZnII or CdII, show a limited number of MX2 networks (M = Zn, Cd). In these structures a tetrahedral and also an octahedral coordination can be observed. The former coordination dominates for ZnII, whereas the latter is frequently found for CdII (Neumann et al., 2018a
,b
). For ZnII mainly discrete complexes are observed, whereas for CdII examples are known in which the metal cations are linked into chains (Neumann et al., 2018a
,b
). The MX2 complexes or chains can additionally be connected if bridging coligands like pyrazine are used, and several such compounds are reported in the literature (Bailey & Pennington, 1997
; Pickardt & Staub, 1997
; Bhosekar et al., 2006
; Bourne et al., 2001
; Song et al., 2004
). Based on these observations, we prepared new ZnCl2 compounds with 2,3-dimethylpyrazine as ligand with the composition ZnCl2(2,3-dimethylpyrazine) and ZnCl2(2,3-dimethylpyrazine)2 (Näther & Bhosekar, 2025
). In both compounds the Zn cations are tetrahedrally coordinated, leading to the formation of discrete complexes in the 2,3-dimethylpyrazine-rich compound, whereas in the 2,3-dimethylpyrazine-deficient compounds the Zn cations are linked into chains. Very recently a corresponding compound with the composition ZnBr2(2,3-dimethylpyrazine)2 was reported that is isotypic to ZnCl2(2,3-dimethylpyrazine)2 and which was investigated for its photophysical properties (Yang et al., 2025
). Based on these results, we assumed that a further compound with ZnBr2 with the composition ZnBr2(2,3-dimethylpyrazine) could be prepared that might be isotypic to its ZnCl2 analog. Therefore, zinc bromide was reacted with equivalent amounts of 2,3-dimethylpyrazine and the crystals obtained were characterized by X-ray single crystal and powder diffraction.
2. Structural commentary
The new compound ZnBr2(2,3-dimethylpyrazine) is isotypic to the corresponding chloride compound ZnCl2(2,3-dimethylpyrazine) reported recently (Näther & Bhosekar, 2025
). The asymmetric unit of the title compound consists of one Zn cation, two crystallographically independent bromide anions and one crystallographically independent 2,3-dimethylpyrazine ligand in general positions (Fig. 1
). The Zn cations are fourfold coordinated by two N atoms of the 2,3-dimethylpyrazine coligands and two bromide anions in a distorted tetrahedral geometry. The N—Zn—Br angles deviate only slightly from the ideal tetrahedral values, whereas the Br—Zn—Br angles are larger and the N—Zn—N angles are smaller (Table 1
), presumably because of steric repulsion between the halide anions. The metal cations are linked into chains along the crystallographic c-axis direction by bridging 2,3-dimethylpyrazine ligands (Fig. 2
). These chains are corrugated because of the tetrahedral coordination (Fig. 2
).
|
| Figure 1 Crystal structure of the title compound with atom labeling and displacement ellipsoids drawn at the 50% probability level. Symmetry code for the generation of equivalent atoms: (i) −x + y + 1, −x + 1, z − |
| | Figure 2 Fragment of the extended structure of the title compound with a view of part of a chain and intrachain C⋯H—Br hydrogen bonding shown as dashed lines. |
3. Supramolecular features
In the crystal, intrachain C—H⋯Br hydrogen bonding with C—H⋯Br angles of 151 and 150° is observed (Fig. 2
and Table 2
). These chains are linked by interchain C—H⋯Br contacts that show much smaller angles and thus should represent only very weak interactions (Fig. 3
and Table 2
).
|
| Figure 3 Crystal structure of the title compound with a view along the crystallographic a-axis direction and intrachain C⋯H—Br hydrogen bonding shown as dashed lines. |
4. Database survey
As mentioned above, the title compound is isotypic to the corresponding 2,3-dimethylpyrazine compound with ZnCl2 already reported in the literature (Näther & Bhosekar, 2025
). There are two additional compounds with the composition ZnCl2(2,3-dimethylpyrazine) (Näther & Bhosekar, 2025
) and ZnBr2(2,3-dimethylpyrazine) (Yang et al., 2025
) that are isotypic and that are built up of discrete complexes with a tetrahedral Zn coordination. Further compounds with twofold positively charged transition-metal halides and 2,3-dimethylpyrazine as ligand are not reported in the CCDC database (CSD Version 5.43, January 2025; Groom et al., 2016
) using CONQUEST (Bruno et al., 2002
). However, some compounds are known with the unsubstituted ligand pyrazine. These include CdX2(pyrazine) [X = Cl, Refcode TISSUJ ( (Pickardt & Staub, 1997
)] ), X = Br, RINSIQ and RINSOW (Bailey & Pennington, 1997
); X = I, RINSIQ01 and RINSOW01 (Pickardt & Staub, 1997
)] in which the metal cations are octahedrally coordinated and are linked by pairs of halide anions into chains that are further connected into layers by the pyrazine ligands.
More compounds are reported with ZnII cations and pyrazine. In contrast to the title compound with 2,3-dimethylpyrazine as coligand, these compounds show an octahedral coordination. This is the case in, e.g., ZnCl2(pyrazine)2 (Refcode REMPAB; Bhosekar et al., 2006
) in which the Zn cations are linked into layers by the pyrazine ligands. In the pyrazine-deficient compound ZnCl2(pyrazine) (Refcode TISTAQ; Pickardt & Staub, 1997
), the Zn cations are linked into chains by pairs of bridging chloride anions that are further connected into layers by the pyrazine ligands. With ZnBr2, two compounds are known of which the pyrazine-rich compound ZnBr2(pyrazine)2 crystallizes in two modifications with layered networks of the same topology. One of them is isotypic to the corresponding chloride compound [Refcodes EBOLAI (Bourne et al., 2001
) and EBOLAI01 (Bhosekar et al., 2006
)]. They also include ZnBr2(pyrazine), which crystallizes differently from the chloride compound (Refcode EBOKUB; Bourne et al., 2001
). Finally, ZnI2(pyrazine) is reported that shows a structure similar to that of the bromide compound [Refcodes ISOPOV (Song et al., 2004
) and ISOPOV01 (Bhosekar et al., 2006
)].
5. Synthesis and crystallization
Zinc bromide and 2,3-dimethylpyrazine were purchased from Sigma-Aldrich.
Synthesis
0.5 mmol (112.6 mg) of zinc bromide were reacted with 0.5 mmol (54.1 mg) of 2,3-dimethylpyrazine in 1 mL of acetonitrile. The reaction mixture was stirred for 3 d and the precipitate was filtered off and dried. Single crystals were obtained using the same ratio of reactants without stirring.
The title compound was additionally investigated by X-ray powder diffraction, which shows that a pure sample has been obtained (Fig. 4
).
| Figure 4 Experimental (top) and calculated (bottom) X-ray powder pattern of the title compound. |
Experimental details
The PXRD measurements were performed with Cu Kα1 radiation (λ = 1.540598 Å) using a Stoe Transmission Powder Diffraction System (STADI P) that is equipped with a MYTHEN 1K detector and a Johansson-type Ge(111) monochromator.
6. Refinement
Crystal data, data collection and structure details are summarized in Table 3
. Hydrogen atoms were positioned with idealized geometry (methyl H atoms allowed to rotate but not to tip) and were refined isotropically with Uiso(H) = 1.2 Ueq(C) (1.5 for methyl H atoms).
|
Supporting information
CCDC reference: 2482737
contains datablocks I, global. DOI: https://doi.org/10.1107/S2056989025007613/nx2028sup1.cif
Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989025007613/nx2028Isup2.hkl
| [ZnBr2(C6H8N2)2] | Dx = 2.277 Mg m−3 |
| Mr = 333.33 | Mo Kα radiation, λ = 0.71073 Å |
| Trigonal, P31 | Cell parameters from 7962 reflections |
| a = 7.3972 (3) Å | θ = 10.4–27.1° |
| c = 15.3874 (8) Å | µ = 10.69 mm−1 |
| V = 729.17 (7) Å3 | T = 220 K |
| Z = 3 | Block, light yellow |
| F(000) = 474 | 0.11 × 0.07 × 0.06 mm |
| Stoe IPDS-1 diffractometer | 2231 reflections with I > 2σ(I) |
| Phi scans | Rint = 0.076 |
| Absorption correction: numerical (X-Red and X-Shape; Stoe, 2008) | θmax = 28.0°, θmin = 3.2° |
| Tmin = 0.067, Tmax = 0.156 | h = −9→9 |
| 7080 measured reflections | k = −9→9 |
| 2343 independent reflections | l = −20→20 |
| Refinement on F2 | H-atom parameters constrained |
| Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0647P)2 + 0.5878P] where P = (Fo2 + 2Fc2)/3 |
| R[F2 > 2σ(F2)] = 0.040 | (Δ/σ)max < 0.001 |
| wR(F2) = 0.102 | Δρmax = 0.71 e Å−3 |
| S = 1.06 | Δρmin = −0.73 e Å−3 |
| 2343 reflections | Extinction correction: SHELXL-2016/6 (Sheldrick 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| 103 parameters | Extinction coefficient: 0.043 (4) |
| 1 restraint | Absolute structure: Flack x determined using 1049 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013) |
| Hydrogen site location: inferred from neighbouring sites | Absolute structure parameter: 0.01 (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. |
| x | y | z | Uiso*/Ueq | ||
| Zn1 | 1.06358 (14) | 0.65633 (14) | 0.01689 (5) | 0.0206 (3) | |
| Br1 | 1.31606 (14) | 0.58557 (16) | 0.07229 (6) | 0.0339 (3) | |
| Br2 | 1.18263 (16) | 1.01071 (14) | −0.01098 (6) | 0.0364 (3) | |
| N1 | 0.8300 (11) | 0.5540 (10) | 0.1140 (4) | 0.0214 (13) | |
| C1 | 0.7097 (13) | 0.3550 (13) | 0.1380 (5) | 0.0218 (14) | |
| C2 | 0.5591 (13) | 0.3036 (12) | 0.2051 (5) | 0.0209 (14) | |
| N2 | 0.5454 (10) | 0.4553 (11) | 0.2470 (4) | 0.0203 (12) | |
| C3 | 0.6710 (12) | 0.6539 (12) | 0.2219 (5) | 0.0217 (14) | |
| H3 | 0.662006 | 0.761430 | 0.250495 | 0.026* | |
| C4 | 0.8122 (13) | 0.7038 (12) | 0.1554 (5) | 0.0222 (15) | |
| H4 | 0.896891 | 0.844010 | 0.138842 | 0.027* | |
| C5 | 0.7352 (15) | 0.1869 (14) | 0.0961 (6) | 0.0286 (17) | |
| H5A | 0.644589 | 0.133729 | 0.045754 | 0.043* | |
| H5B | 0.698387 | 0.074531 | 0.137308 | 0.043* | |
| H5C | 0.879174 | 0.243448 | 0.078088 | 0.043* | |
| C6 | 0.4191 (16) | 0.0817 (14) | 0.2324 (7) | 0.0322 (19) | |
| H6A | 0.502059 | 0.028064 | 0.258741 | 0.048* | |
| H6B | 0.346705 | −0.002001 | 0.181996 | 0.048* | |
| H6C | 0.317974 | 0.075293 | 0.274258 | 0.048* |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Zn1 | 0.0210 (4) | 0.0201 (4) | 0.0207 (4) | 0.0102 (3) | −0.0004 (3) | −0.0012 (3) |
| Br1 | 0.0299 (4) | 0.0399 (5) | 0.0389 (5) | 0.0228 (4) | −0.0114 (4) | −0.0094 (4) |
| Br2 | 0.0393 (5) | 0.0218 (4) | 0.0445 (6) | 0.0126 (4) | 0.0007 (4) | 0.0070 (4) |
| N1 | 0.022 (3) | 0.025 (3) | 0.020 (3) | 0.014 (3) | 0.001 (2) | −0.001 (3) |
| C1 | 0.023 (4) | 0.023 (3) | 0.020 (3) | 0.012 (3) | 0.002 (3) | 0.000 (3) |
| C2 | 0.023 (3) | 0.018 (3) | 0.022 (3) | 0.010 (3) | −0.002 (3) | 0.002 (3) |
| N2 | 0.020 (3) | 0.022 (3) | 0.017 (3) | 0.009 (3) | 0.003 (2) | 0.000 (2) |
| C3 | 0.022 (3) | 0.018 (3) | 0.025 (3) | 0.010 (3) | 0.003 (3) | 0.001 (3) |
| C4 | 0.024 (3) | 0.016 (3) | 0.025 (4) | 0.008 (3) | 0.003 (3) | 0.000 (3) |
| C5 | 0.037 (4) | 0.024 (4) | 0.028 (4) | 0.018 (3) | 0.008 (4) | 0.002 (3) |
| C6 | 0.037 (5) | 0.022 (4) | 0.033 (4) | 0.011 (3) | 0.011 (4) | 0.005 (3) |
| Zn1—N2i | 2.085 (6) | N2—C3 | 1.344 (10) |
| Zn1—N1 | 2.118 (7) | C3—C4 | 1.374 (11) |
| Zn1—Br1 | 2.3380 (12) | C3—H3 | 0.9400 |
| Zn1—Br2 | 2.3501 (12) | C4—H4 | 0.9400 |
| N1—C1 | 1.336 (10) | C5—H5A | 0.9700 |
| N1—C4 | 1.340 (10) | C5—H5B | 0.9700 |
| C1—C2 | 1.424 (12) | C5—H5C | 0.9700 |
| C1—C5 | 1.494 (11) | C6—H6A | 0.9700 |
| C2—N2 | 1.341 (11) | C6—H6B | 0.9700 |
| C2—C6 | 1.498 (11) | C6—H6C | 0.9700 |
| N2i—Zn1—N1 | 103.1 (3) | N2—C3—C4 | 121.6 (7) |
| N2i—Zn1—Br1 | 109.2 (2) | N2—C3—H3 | 119.2 |
| N1—Zn1—Br1 | 105.25 (19) | C4—C3—H3 | 119.2 |
| N2i—Zn1—Br2 | 115.18 (19) | N1—C4—C3 | 120.5 (7) |
| N1—Zn1—Br2 | 108.13 (19) | N1—C4—H4 | 119.8 |
| Br1—Zn1—Br2 | 114.87 (5) | C3—C4—H4 | 119.8 |
| C1—N1—C4 | 119.5 (7) | C1—C5—H5A | 109.5 |
| C1—N1—Zn1 | 124.3 (5) | C1—C5—H5B | 109.5 |
| C4—N1—Zn1 | 116.1 (5) | H5A—C5—H5B | 109.5 |
| N1—C1—C2 | 119.7 (7) | C1—C5—H5C | 109.5 |
| N1—C1—C5 | 120.4 (7) | H5A—C5—H5C | 109.5 |
| C2—C1—C5 | 119.9 (7) | H5B—C5—H5C | 109.5 |
| N2—C2—C1 | 120.1 (7) | C2—C6—H6A | 109.5 |
| N2—C2—C6 | 118.8 (7) | C2—C6—H6B | 109.5 |
| C1—C2—C6 | 121.1 (7) | H6A—C6—H6B | 109.5 |
| C2—N2—C3 | 118.5 (7) | C2—C6—H6C | 109.5 |
| C2—N2—Zn1ii | 124.8 (5) | H6A—C6—H6C | 109.5 |
| C3—N2—Zn1ii | 116.7 (5) | H6B—C6—H6C | 109.5 |
| C4—N1—C1—C2 | 2.2 (11) | C6—C2—N2—C3 | −179.8 (8) |
| Zn1—N1—C1—C2 | 179.1 (6) | C1—C2—N2—Zn1ii | −177.0 (6) |
| C4—N1—C1—C5 | −176.6 (8) | C6—C2—N2—Zn1ii | 0.8 (11) |
| Zn1—N1—C1—C5 | 0.3 (11) | C2—N2—C3—C4 | −0.5 (12) |
| N1—C1—C2—N2 | −3.3 (12) | Zn1ii—N2—C3—C4 | 179.0 (6) |
| C5—C1—C2—N2 | 175.4 (8) | C1—N1—C4—C3 | −0.2 (12) |
| N1—C1—C2—C6 | 178.9 (8) | Zn1—N1—C4—C3 | −177.4 (6) |
| C5—C1—C2—C6 | −2.3 (12) | N2—C3—C4—N1 | −0.7 (13) |
| C1—C2—N2—C3 | 2.4 (12) |
| Symmetry codes: (i) −x+y+1, −x+1, z−1/3; (ii) −y+1, x−y, z+1/3. |
| D—H···A | D—H | H···A | D···A | D—H···A |
| C3—H3···Br1ii | 0.94 | 2.95 | 3.604 (8) | 128 |
| C3—H3···Br2iii | 0.94 | 2.99 | 3.687 (8) | 132 |
| C4—H4···Br2 | 0.94 | 2.95 | 3.605 (8) | 128 |
| C5—H5C···Br1 | 0.97 | 2.95 | 3.824 (10) | 151 |
| C6—H6A···Br1iv | 0.97 | 2.99 | 3.710 (10) | 132 |
| C6—H6C···Br2ii | 0.97 | 2.95 | 3.820 (10) | 150 |
| Symmetry codes: (ii) −y+1, x−y, z+1/3; (iii) −y+2, x−y+1, z+1/3; (iv) −y+1, x−y−1, z+1/3. |
Acknowledgements
Financial support by the State of Schleswig-Holstein is gratefully acknowledged.
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