Bromidobis[3-(1H-pyrazol-1-yl-κN 2)propionamide-κO]copper(II) bromide methanol monosolvate

Thomas Wagner; Cristian G Hrib; Volker Lorenz; Frank T Edelmann; John W Gilje

doi:10.1107/S1600536812038111

. 2012 Sep 8;68(Pt 10):m1253–m1254. doi: 10.1107/S1600536812038111

Bromidobis[3-(1H-pyrazol-1-yl-κN ²)propionamide-κO]copper(II) bromide methanol monosolvate

Thomas Wagner ^a, Cristian G Hrib ^a, Volker Lorenz ^a, Frank T Edelmann ^a,^*, John W Gilje ^b

PMCID: PMC3470141 PMID: 23125585

Abstract

The title copper(II) N-pyrazolylpropanamide (PPA) complex, [CuBr(PPA)₂]Br, was obtained in 78% yield by treatment of CuBr₂ with an excess of the ligand in methanol. Crystallization from the mother liquid afforded the title compound, i.e. the methanol solvate [CuBr(C₆H₉N₃O)₂]Br·CH₃OH or [CuBr(PPA)₂]Br·MeOH, as bright green crystals. In the solid state, the title salt comprises isolated [CuBr(PPA)₂]⁺ cations, separated bromide ions and methanol of crystallization. In the cation, the central Cu^II ion is coordinated by two N,O-chelating PPA ligands and one Br⁻ ion. The coordination geometry around the Cu^II ion is distorted trigonal–bipyramidal with the bromide ligand and the amide O atoms occupying the equatorial positions [Cu—Br = 2.4443 (4) Å; Cu—O = 2.035 (2) and 2.179 (2) Å], while the pyrazole N atoms coordinate in the axial positions [Cu—N = 1.975 (2) and 1.976 (2) Å]. In the crystal, the three constituents are linked by N—H⋯Br, O—H⋯Br, and N—H⋯O hydrogen bonds, forming a three-dimensional network.

Related literature

For related complexes containing multifunctional ligands with substituted pyrazole groups, see: Gracia-Anton et al. (2003 ▶); Mukherjee (2000 ▶); Pal et al. (2005 ▶); Shaw et al. (2004 ▶). For acrylamide complexes, see: Girma et al. (2005a ▶,b ▶,c ▶, 2006 ▶). For related complexes containing 3-pyrazol-1-yl-propionamide, see: Girma et al. (2008 ▶); Wagner et al. (2012 ▶).

Experimental

Crystal data

[CuBr(C₆H₉N₃O)₂]Br·CH₄O
M _r = 533.73
Monoclinic,
a = 10.5075 (4) Å
b = 12.6951 (4) Å
c = 15.1551 (7) Å
β = 102.821 (3)°
V = 1971.19 (13) Å³
Z = 4
Mo Kα radiation
μ = 5.19 mm⁻¹
T = 150 K
0.40 × 0.40 × 0.30 mm

Data collection

Stoe IPDS 2T diffractometer
Absorption correction: multi-scan (Blessing, 1995 ▶) T _min = 0.046, T _max = 0.139
22729 measured reflections
5320 independent reflections
4728 reflections with I > 2σ(I)
R _int = 0.048

Refinement

R[F ² > 2σ(F ²)] = 0.041
wR(F ²) = 0.079
S = 1.21
5320 reflections
231 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.74 e Å⁻³
Δρ_min = −0.70 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2002 ▶); cell refinement: X-AREA; data reduction: X-RED (Stoe & Cie, 2002 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: XP in SHELXTL (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812038111/qk2039sup1.cif

e-68-m1253-sup1.cif^{(21.1KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812038111/qk2039Isup2.hkl

e-68-m1253-Isup2.hkl^{(260.5KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1NB⋯O3ⁱ	0.88	2.07	2.926 (3)	163
N1—H1NA⋯Br2	0.88	2.56	3.434 (3)	173
N4—H4NA⋯O3ⁱⁱ	0.88	2.09	2.956 (3)	168
O3—H1O⋯Br2	0.81 (5)	2.41 (5)	3.215 (3)	175 (5)
N4—H4NB⋯Br2ⁱⁱⁱ	0.88	2.71	3.548 (3)	160

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

supplementary crystallographic information

Comment

Currently there is a considerable interest in the use of multifunctional ligands containing substituted pyrazole groups because of their potential applications in catalysis and their ability to form complexes that mimic structural and catalytic functions in metalloproteins (Gracia-Anton et al., 2003; Mukherjee, 2000; Pal et al., 2005; Shaw et al., 2004). As part of our continuing interest in the coordination chemistry of acrylamide (Girma et al., 2005a; Girma et al., 2005b; Girma et al., 2005c; Girma et al., 2006) and acrylamide-based ligands we have earlier synthesized and characterized an acrylamide-derived pyrazole ligand, N-pyrazolylpropanamide (= PPA) (Girma et al., 2008). This ligand is readily accessible in large quantities by base-catalyzed Michael addition of pyrazole to acrylamide. The first PPA complexes to be reported were (PPA)₂CuCl₂ and (PPA)₄Co₃Cl₆ with copper(II) and cobalt(II) chlorides, respectively. Both complexes contain the ligand in a seven-membered ring N,O-chelating fashion. Especially remarkable was the unusual zwitterionic structure of the trinuclear cobalt complex, which additionally comprises bridging N-pyrazolylpropanamide ligands (Girma et al., 2008). Most recently, the syntheses and single-crystal X-ray structures of several new first-row transition metal complexes containing the multifunctional acrylamide-derived PPA have been reported. The general synthesis involved treatment of the appropriate transition metal salts with an excess of PPA in ethanolic solution in the presence of triethylorthoformate as dehydrating agent. This way the perchlorates of iron(II) and cobalt(II) afforded the complexes [(PPA)₂M(EtOH)₂](ClO₄)₂ (M = Fe, Co) in good yields (82% resp. 85%). Light green (PPA)₂NiCl₂ has been obtained analogously from NiCl₂.6H₂O. Hydration of (PPA)₂NiCl₂ afforded the dark green cationic nickel(II) complex [(PPA)₂Ni(H₂O)₄]Cl₂. In the complexes with M = Fe, Co, and Ni the N-pyrazolylpropanamide acts as N,O-chelating ligand. In contrast, monodentate N-coordination via the pyrazolyl ring was found for the dicoordinate silver(I) complex [(PPA)₂Ag]NO₃.H₂O (Wagner et al., 2012).

In the course of these investigations we now studied the reaction of copper(II) dibromide with PPA. A reaction carried out in methanol solution using an excess over 2 equivalents of PPA afforded a green, microcrystalline solid which was shown by elemental analysis and its IR spectrum to be the bromide analogue of the previously reported (PPA)₂CuCl₂ (Girma et al., 2008), i.e. (PPA)₂CuBr₂. Comparison of the IR spectra of the free ligand PPA and (PPA)₂CuBr₂ revealed a significant decrease to lower wavenumbers in the CO absorptions (1690 cm^-1 in PPA vs. 1661 cm^-1 in (PPA)₂CuBr₂ and 1664 cm^-1 in (PPA)₂CuCl₂). This CO absorption shift is consistent with a decrease in the electron density of the amide carbonyl moiety resulting from coordination to the cationic copper(II) center. Crystallization of (PPA)₂CuBr₂ directly from the mother liquid afforded the title compound, i.e. the methanol-solvate, as bright green, X-ray quality single crystals. Surprisingly, the X-ray crystal structure determination revealed the presence of the ionic product [CuBr(PPA)₂]Br.MeOH with 5-coordinate copper. In the solid state, [CuBr(PPA)₂]Br.MeOH comprises isolated [CuBr(PPA)₂]⁺ cations, separated bromide ions and methanol of crystallization (Fig. 1). In the cation, the central Cu²⁺ ion is coordinated by two N,O-chelating PPA ligands and one Br^- ion. The coordination geometry around copper can be best described as distorted trigonal-bipyramidal with the bromo ligand and the amide O atoms occupying the equatorial positions (Cu—Br 2.4443 (4) Å; Cu—O 2.035 (2) and 2.179 (2) Å), while the pyrazolyl N-atoms coordinate in the axial positions (Cu—N 1.975 (2) and 1.976 (2) Å). This is in contrast to the neutral hexacoordinate chloro-analogue (PPA)₂CuCl₂ in which the coordination geometry around the central Cu²⁺ ion is octahedral (Girma et al., 2008). The angles at Cu in the equatorial plane of the [CuBr(PPA)₂]⁺ cation are 109.30 (8)° (O1—Cu—O2), 116.80 (6)° (O2—Cu—Br1), and 133.76 (6)° (O1—Cu—Br1), respectively. The axial angle at Cu (N3—Cu—N6) is 174.53 (9)°. The planes of the opposing pyrazole rings are inclined to each other by ~71°.

Like all previously reported transition metal PPA complexes (Wagner et al., 2012), the title compound also forms a hydrogen-bonded network in the solid state (Fig. 2). The crystal structure consists of chains of [CuBr(PPA)₂]⁺ cations linked by N—H···Br, O—H···Br, and N—H···O hydrogen bonds. The uncoordinated bromide ions are connected via O—H···Br hydrogen bonds to the methanol of crystallization and via two N—H···Br interactions with the amide NH₂ groups of different cations. N—H···O hydrogen bonds between amide NH₂ groups and the methanol of crystallization interconnect the chains.

Experimental

A solution of CuBr₂ (0.6 g, 1.69 mmol) in methanol (50 ml) was combined with a solution of N-pyrazolylpropanamide (= PPA, 0.8 g, 5.5 mmol) in methanol (30 ml). After stirring for 24 h at room temperature, the reaction mixture was concentrated in vacuo to a total volume of ca 50 ml, whereupon a large quantity of the title compound precipitated in its unsolvated form [CuBr(PPA)₂]Br in the form of a green, microcrystalline solid in 78% yield (1.05 g). Bright green, X-ray quality crystals of the title compound [CuBr(PPA)₂]Br.MeOH were obtained upon standing of the mother liquid at room temperature for 14 d.

Anal. Calcd. for unsolvated C₁₂H₁₈Br₂CuN₆O₂ (M_r = 501.66): C 28.73%; H 3.62%; N 16.75%; Br 31.86%. Found: C 28.35%; H 3.46%; N 17.03%; Br 31.47%. IR (KBr): 3436m ν(N—H), 3336m ν(N—H), 3298m, 3188m, 3020w, 2964m, 2847w, 1661s ν(C=O), 1594m; ν(C=C), 1494w, 1450m, 1429m, 1418m, 1375w, 1325m, 1285m, 1262s, 1230m, 1175m, 1098vs, 1022vs, 957m, 949m, 868w, 801vs, 768m, 759m, 628m cm^-1.