ARTICLE

DOI: 10.1002/zaac.201200139

N-Pyrazolylpropanamide – a Versatile Ligand for the Construction ofSupramolecular Hydrogen-Bonded Frameworks

Thomas Wagner,[a] Cristian G. Hrib,[a] Volker Lorenz,[a] Frank T. Edelmann,*[a]

Donna S. Amenta,[b] Christopher J. Burnside,[b] and John W. Gilje*[b]

Dedicated to Professor Rudolf Hoppe on the Occasion of His 90th Birthday

Keywords: N-Pyrazolylpropanamide; Iron; Cobalt; Nickel; Silver; Hydrogen bonds; Crystal structure

Abstract. The syntheses and single-crystal X-ray structures of severalfirst-row transition metal complexes containing the multifunctional ac-rylamide-derived ligand N-pyrazolylpropanamide (1 = L) are reported.The general synthesis involves treatment of appropriate transitionmetal salts with an excess of 1 in ethanolic solution in the presence oftriethylorthoformate as dehydrating agent. This way the perchloratesof iron(II) and cobalt(II) afforded the complexes [L2M(EtOH)2](ClO4)2

[M = Fe (2), Co (3), in good yields (82 and 85%)]. Light green

1 Introduction

Currently there is a considerable interest in the use of multi-functional ligands containing substituted pyrazole groups be-cause of their potential applications in catalysis and their abil-ity to form complexes that mimic structural and catalytic func-tions in metalloproteins.[1] As part of our continuing interestin the coordination chemistry of acrylamide[2] and acrylamide-based ligands we have earlier synthesized and characterized anacrylamide-derived pyrazole ligand, N-pyrazolylpropanamide(1 = L),[3] and its complexes L2CuCl2 and L4Co3Cl6 with cop-per(II) and cobalt(II) chlorides, respectively. Both complexescontain the ligand in a seven-membered ring chelating fashion.Especially remarkable was the unusual zwitterionic structureof the trinuclear cobalt complex, which additionally comprisesbridging N-pyrazolylpropanamide ligands.

Prior to our work[3] there has been only one earlier paper inthe literature mentioning the title compound N-pyrazolylpro-panamide, and no coordination compounds of this potentiallymultifunctional ligand had ever been prepared. More than 20years ago, de la Cruz et al. reported the syntheses and spectro-scopic properties of a series of N-azolylpropanamides includ-

* Prof. Dr. F. T. EdelmannFax: + 49-391-6712933E-Mail: frank.edelmann@ovgu.de

* Prof. Dr. J. W. GiljeE-Mail: giljejw@jmu.edu

[a] Chemisches Institut der Otto-von-Guericke-Universität Magdeburg39106 Magdeburg, Germany

[b] Department of Chemistry and BiochemistryMSC 4501, James Madison UniversityHarrisonburg, VA 22807, USA

Z. Anorg. Allg. Chem. 2012, 638, (12-13), 2129–2137 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2129

L2NiCl2 (4) was obtained analogously from NiCl2·6H2O. Hydration of4 afforded the dark green cationic nickel(II) complex [L2Ni(H2O)4]Cl2(4a). In compounds 2–4 the N-pyrazolylpropanamide acts as N,O-che-lating ligand. In contrast, monodentate nitrogen coordination via thepyrazolyl ring was found for the dicoordinate silver(I) complex[L2Ag]NO3·H2O (5). The molecular and crystal structures of 2, 3, 4a,and 5 were determined by X-ray diffraction.

ing N-pyrazolylpropanamide (82% yield) obtained from acryl-amide and the corresponding azoles using pyridine-sodiummethoxide as a basic catalyst.[4] We used instead trimethyl-benzylammonium hydroxide (Triton B, 40 % in methanol) asa basic catalyst (Scheme 1). This method provided N-pyrazo-lylpropanamide in excellent yield (94 %) and in a straightfor-ward manner.[3]

Scheme 1.

2 Results and Discussion

Until now, the coordination chemistry of 1 was limited toonly two transition metal complexes, L2CuCl2 and L4Co3Cl6(L = N-pyrazolylpropanamide).[3] Thus in the course of thepresent study we decided to investigate reactions of 1 with firstand second row transition metal salts. All reactions were car-ried out following the established procedure[3] by treatment ofthe appropriate transition metal salt with stoichiometricamounts of ligand 1 in ethanol/triethylorthoformate solutions(Scheme 1). In all cases triethylorthoformate was employed asa dehydrating agent in order to assure the formation of anhy-drous products. This way the cationic complexes [L2M(Et-OH)2](ClO4)2 [M = Fe (2), Co (3)] could be isolated in goodyields (82% and 85 %, respectively) (Scheme 2).

F. T. Edelmann, J. W. Gilje et al.ARTICLE

Scheme 2.

The iron(II) complex 2 forms light green-brown crystals,whereas the cobalt(II) derivative 3 is a pink crystalline solid.The IR spectra of 2 and 3 show strong bands, which are typicalfor the amide functionality of the N-pyrazolylpropanamide li-gand. Comparison of the IR spectra of the free ligand 1 andthe complexes 2 and 3 revealed a significant decrease to lowerwavenumbers in the CO absorptions (1690 cm–1 in 1 versus1650 cm–1 in 2 and 1656 cm–1 in 3) upon complexation. Asimilar decrease was already observed in the IR spectrum ofthe copper complex L2CuCl2 (1664 cm–1). This CO absorptionshift is consistent with a decrease in the electron density of theamide carbonyl unit resulting from coordination to the centralmetal(II) ion. Bands attributable to the N–H stretching vi-brations of the NH2 groups appear at 3356 cm–1 (2) and3361 cm–1 (3). The IR spectra of the complexes also showbands at 1597 cm–1 (2) and 1600 cm–1 (3), which may be as-signed to the ν(C=C) vibration in the pyrazolyl group of theligand upon complexation. This is consistent with the fact thatin the complexes the bond lengths within the pyrazolyl groupare elongated and less conjugated as compared to the bondlengths in the free ligand due to strong coordination of thenitrogen of the pyrazolyl group of the ligand to the centralmetal atom.

Both cationic complexes were also structurally characterizedthrough single-crystal X-ray diffraction. In both cases, singlecrystals suitable for X-ray analysis were obtained by slow

Table 1. Crystallographic data for 2, 3, 4a, and 5.

2 3 4a 5

Empirical formula C16H30Cl2FeN6O12 C16H30Cl2CoN6O12 C12H26Cl2N6NiO6 C24H38Ag2N14O11

a /Å 8.2685(17) 8.0501(16) 7.8837(16) 22.8054(11)b /Å 9.869(2) 10.166(2) 7.7861(16) 7.2978(4)c /Å 15.879(3) 16.463(3) 16.735(3) 21.8302(13)α /° 90 90 90 90β /° 99.25(3) 91.43(3) 102.93(3) 107.919(4)γ /° 90 90 90 90V /Å3 1278.9(5) 1346.9(5) 1001.2(4) 3456.9(3)Z 2 2 2 4Formula weight 625.21 628.29 480.00 914.42Space group P21/c P21/c P21/c C2/cT /°C –120 –60 –140 –130λ /Å 0.71073 0.71073 0.71073 0.71073Dcalcd. /g·cm–3 1.624 1.544 1.592 1.757μ /mm–1 0.869 0.902 1.277 1.209R(Fo or Fo

2) 0.0365 0.0351 0.0375 0.0438Rw(Fo or Fo

2) 0.0926 0.0902 0.0824 0.0936

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cooling of a saturated solution in ethanol to 5 °C. Crystallo-graphic data for all compounds are summarized in Table 1.Selected bond lengths and angles are listed in Table 2, Table 3,and Table 4, and Figure 1, Figure 2, Figure 3, and Figure 4show the molecular and crystal structures of 2 and 3.

The molecular structures of 2 and 3 are virtually identical.In the [L2M(EtOH)2]2+ cations of 2 and 3, the central metalatoms are octahedrally coordinated by two neutral chelatingN-pyrazolylpropanamide ligands and two ethanol molecules.Although generally less favorable, N,O-coordination of N-pyr-azolylpropanamide results in formation of seven-memberedchelate rings. This suggests that the ligand has a potential forapplications in catalysis. The weaker coordinating donor atomin these multifunctional ligands readily dissociates from themetal during catalysis to accommodate reacting groups on themetal, but recombines with the metal when a coordinative un-saturation develops to stabilize the catalytic intermediate.[5]

Two ethanol ligands in the trans positions complete the dis-torted octahedral coordination environment around the centralmetal atom. The metal atom in both cations is located on aninversion center. The M–N(pyrazole) distances are Fe–N2.1366(15) Å in 2 and 2.1051(19) Å in 3. The latter value com-pares favorably with the Co–N distances of 2.091(3) and2.119(2) Å in the previously reported trinuclear N-pyrazolyl-propanamide complex L4Co3Cl6.[3] In the free ligand 1, theC=O and C–NH2 bond lengths of the amide group are1.2286(10) Å and 1.3281(11) Å, respectively. Upon coordina-tion to iron or cobalt, the C=O bond length becomes slightlyelongated [C–O 1.243(2) Å in 2 and 1.241(3) Å in 3], whereasthe C–N distances are virtually identical with that in the freeligand [C–N 1.321(3) Å in 2 and 1.327(4) Å in 3]. The bondlengths within the pyrazole rings are in the narrow ranges of1.333(2)–1.386(3) for 2 and 1.331(3)–1.386(4) for 3. In thefree ligand, the range of bond lengths (C–C, C–N, and N–N)in the pyrazole ring is 1.3314(13)–1.3932(13) Å.[3] The crystalstructure of 2 differs from that of the cobalt derivative 3 inthat it comprises O–H···O as well as N–H···O hydrogen bondsbetween the perchlorate anions and both the ethanol OH func-tions and the NH2 groups of the amide functionality of the N-

N-Pyrazolylpropanamide for Supramolecular Hydrogen-Bonded Frameworks

Table 2. Bond lengths /Å and angles /° for 2.

C(1)–O(1) 1.243(2) O(1)–C(1)–N(3) 121.3(2)C(1)–N(3) 1.321(3) O(1)–C(1)–C(2) 122.12(17)C(1)–C(2) 1.505(3) N(3)–C(1)–C(2) 116.51(18)C(2)–C(3) 1.515(3) C(1)–C(2)–C(3) 114.53(15)C(3)–N(2) 1.459(2) N(2)–C(3)–C(2) 113.98(14)C(4)–N(2) 1.344(2) N(2)–C(4)–C(5) 107.98(18)C(4)–C(5) 1.368(3) C(4)–C(5)–C(6) 104.84(17)C(5)–C(6) 1.386(3) N(1)–C(6)–C(5) 111.32(17)C(6)–N(1) 1.333(2) O(2)–C(7)–C(8) 111.43(16)C(7)–O(2) 1.443(2) C(6)–N(1)–N(2) 105.22(15)C(7)–C(8) 1.500(3) C(6)–N(1)–Fe 125.33(12)N(1)–N(2) 1.359(2) N(2)–N(1)–Fe 129.34(11)N(1)–Fe 2.1366(15) C(4)–N(2)–N(1) 110.64(15)O(1)–Fe 2.1166(13) C(4)–N(2)–C(3) 127.69(16)O(2)–Fe 2.1365(13) N(1)–N(2)–C(3) 121.67(14)O(3)–Cl(2) 1.426(2) C(1)–O(1)–Fe 134.84(12)O(4)–Cl(2) 1.4386(15) C(7)–O(2)–Fe 127.01(11)O(5)–Cl(2) 1.398(2) O(5)–Cl(2)–O(6) 111.19(17)O(6)–Cl(2) 1.4155(18) O(5)–Cl(2)–O(3) 108.94(17)Fe–O(1)#1 2.1166(13) O(6)–Cl(2)–O(3) 109.62(17)Fe–O(2)#1 2.1365(13) O(5)–Cl(2)–O(4) 111.32(13)Fe–N(1)#1 2.1366(15) O(6)–Cl(2)–O(4) 107.93(11)

O(3)–Cl(2)–O(4) 107.76(12)O(1)#1–Fe–O(1) 180.0O(1)#1–Fe–O(2) 91.49(6)O(1)–Fe–O(2) 88.51(6)O(1)#1–Fe–O(2)#1 88.51(6)O(1)–Fe–O(2)#1 91.49(6)O(2)–Fe–O(2)#1 180.0O(1)#1–Fe–N(1) 89.65(5)O(1)–Fe–N(1) 90.35(5)O(2)–Fe–N(1) 89.89(5)O(2)#1–Fe–N(1) 90.11(5)O(1)#1–Fe–N(1)#1 90.35(5)O(1)–Fe–N(1)#1 89.65(5)O(2)–Fe–N(1)#1 90.11(5)O(2)#1–Fe–N(1)#1 89.89(5)N(1)–Fe–N(1)#1 180.000(1)

Symmetry transformations used to generate equivalent atoms: #1–x, –y+1, –z+1

Table 3. Hydrogen bonds /Å,° for 2.

D–H···A d(D–H) d(H···A) d(D···A) �(DHA)

O(2)–H(20)···O(4)#1 0.71(3) 2.09(3) 2.788(2) 166(3)N(3)–H(3NA)···O(6)#2 0.90(3) 2.20(3) 3.082(4) 168(3)N(3)–H(3NB)···O(3)#3 0.76(3) 2.33(3) 3.068(4) 165(3)

Symmetry transformations used to generate equivalent atoms: #1–x, –y+1, –z+1 #2 x, –y+1/2, z–1/2 #3 –x+1, –y+1, –z+1.

pyrazolylpropanamide ligands (Table 3). This leads to a three-dimensional hydrogen-bonded framework in the crystal struc-ture, in which a single perchlorate anion interconnects three[L2Fe(EtOH)2]2+ ions by one N–H···O and two O–H···O hydro-gen-bonding interactions. A view of the crystal packing andhydrogen-bonding framework in 2 is shown in Figure 2. In asimilar fashion, the crystal structure of 3 consists of [L2Co(Et-OH)2]2+ cations and perchlorate anions joined by hydrogen-bonding interactions between the perchlorate anions and theethanol OH functions (Figure 3 and Figure 4). In this case,however, the lower quality of the X-ray diffraction data didnot allow a detailed evaluation of the hydrogen-bonding in thesolid-state structure of 3.

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Table 4. Bond lengths /Å and angles /° for 3.

Co–O(6) 2.0859(19) O(6)–Co–O(6)#1 180.00(11)Co–O(6)#1 2.0859(19) O(6)–Co–N(1)#1 87.46(7)Co–N(1)#1 2.1051(19) O(6)#1–Co–N(1)#1 92.54(7)Co–N(1) 2.1051(19) O(6)–Co–N(1) 92.54(7)Co–O(5) 2.1472(19) O(6)#1–Co–N(1) 87.46(7)Co–O(5)#1 2.1472(19) N(1)#1–Co–N(1) 180.00(11)Cl–O(1) 1.357(7) O(6)–Co–O(5) 89.71(8)Cl–O(4) 1.371(11) O(6)#1–Co–O(5) 90.29(8)Cl–O(2) 1.381(6) N(1)#1–Co–O(5) 87.60(8)Cl–O(3) 1.387(7) N(1)–Co–O(5) 92.40(8)Cl–O(2F) 1.417(8) O(6)–Co–O(5)#1 90.29(8)Cl–O(3F) 1.424(12) O(6)#1–Co–O(5)#1 89.71(8)Cl–O(1F) 1.424(8) N(1)#1–Co–O(5)#1 92.40(8)Cl–O(4F) 1.430(14) N(1)–Co–O(5)#1 87.60(8)O(6)–C(6) 1.241(3) O(5)–Co–O(5)#1 180.00(13)N(1)–C(1) 1.331(3) O(1)–Cl–O(4) 110.5(6)N(1)–N(2) 1.358(3) O(1)–Cl–O(2) 109.8(6)N(2)–C(3) 1.345(3) O(4)–Cl–O(2) 111.5(6)N(2)–C(4) 1.457(3) O(1)–Cl–O(3) 110.4(7)N(3)–C(6) 1.327(4) O(4)–Cl–O(3) 107.8(8)C(1)–C(2) 1.386(4) O(2)–Cl–O(3) 106.7(6)C(2)–C(3) 1.355(5) O(1)–Cl–O(2F) 140.6(7)C(4)–C(5) 1.517(4) O(4)–Cl–O(2F) 84.2(7)C(5)–C(6) 1.504(4) O(2)–Cl–O(2F) 33.5(6)O(5)–C(7) 1.437(7) O(3)–Cl–O(2F) 98.4(7)O(5)–C(7F) 1.616(14) O(1)–Cl–O(3F) 89.8(9)C(7)–C(8) 1.491(11) O(4)–Cl–O(3F) 118.1(8)C(7F)–C(8F) 1.40(3) O(2)–Cl–O(3F) 115.0(6)

O(3)–Cl–O(3F) 20.6(9)O(2F)–Cl–O(3F) 116.0(9)O(1)–Cl–O(1F) 35.8(5)O(4)–Cl–O(1F) 120.0(8)O(2)–Cl–O(1F) 74.5(6)O(3)–Cl–O(1F) 128.1(7)O(2F)–Cl–O(1F) 104.9(7)O(3F)–Cl–O(1F) 110.3(8)O(1)–Cl–O(4F) 84.1(6)O(4)–Cl–O(4F) 27.6(6)O(2)–Cl–O(4F) 131.2(8)O(3)–Cl–O(4F) 111.4(8)O(2F)–Cl–O(4F) 110.2(8)O(3F)–Cl–O(4F) 111.5(9)O(1F)–Cl–O(4F) 102.9(6)C(6)–O(6)–Co 140.15(16)C(1)–N(1)–N(2) 105.9(2)C(1)–N(1)–Co 125.63(18)N(2)–N(1)–Co 128.45(15)C(3)–N(2)–N(1) 109.9(2)C(3)–N(2)–C(4) 127.3(2)N(1)–N(2)–C(4) 122.80(19)N(1)–C(1)–C(2) 110.5(3)C(3)–C(2)–C(1) 105.4(3)N(2)–C(3)–C(2) 108.3(3)N(2)–C(4)–C(5) 114.6(2)C(6)–C(5)–C(4) 115.2(2)O(6)–C(6)–N(3) 120.0(3)O(6)–C(6)–C(5) 123.0(2)N(3)–C(6)–C(5) 116.9(3)C(7)–O(5)–C(7F) 34.8(4)C(7)–O(5)–Co 134.6(3)C(7F)–O(5)–Co 113.1(5)O(5)–C(7)–C(8) 109.6(6)C(8F)–C(7F)–O(5) 106.1(17)

Symmetry transformations used to generate equivalent atoms: #1–x, –y, –z

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Figure 1. ORTEP view of 2 with thermal ellipsoids at the 50% prob-ability level.

Figure 2. Crystal packing view of 2.

Figure 3. ORTEP view of 3 with thermal ellipsoids at the 50% prob-ability level.

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Figure 4. Crystal packing view of 3.

The reaction of hydrated nickel(II) chloride and 1 wasstudied. Once again, the reaction was carried out in a 1:2 molarratio and in the presence of triethylorthoformate as dehydratingagent (Scheme 3). In contrast to the perchlorate reactionsshown in Scheme 2, the resulting nickel complex precipitateddirectly from the reaction mixture after prolonged reaction atroom temperature. Work-up afforded L2NiCl2 (4) as a lightgreen, microcrystalline solid in 79% isolated yield. An IRspectrum showed basically the same features as those of 2 and3, showing again the typical decrease to lower wavenumbersin the CO absorptions (very strong band at 1646 cm–1 in 4versus 1690 cm–1 in the free ligand 1) upon complexation. ThisCO absorption shift is consistent with a significant decrease inthe electron density of coordinated amide oxygen atoms to thecentral Ni2+ ion. The IR spectrum of the complex also showsa strong band at 1601 cm–1, which may be assigned to theν(C=C) vibration in the pyrazolyl group of the ligand uponcomplexation. This is consistent with the fact that the bondlengths in the pyrazolyl group in the complex are elongatedand less conjugated as compared to the bond lengths in thefree ligand due to coordination of the nitrogen atom of thepyrazolyl group of the ligand to the central metal atom. Theelemental analysis was in excellent agreement with the pres-ence of the neutral unsolvated bis(ligand) complex L2NiCl2 (4)in close analogy to the known copper(II) complex L2CuCl2.[3]

Scheme 3.

N-Pyrazolylpropanamide for Supramolecular Hydrogen-Bonded Frameworks

Despite many attempts we have not been able to grow sin-gle-crystals of 4, which are suitable for X-ray diffraction. Oc-casionally, however, large, dark green crystals grew during thepreparations of compound 4. Whereas numerous experimentswere performed using various mixtures of ethanol, water, andtriethylorthoformate, we were unable to develop a reproduciblesynthesis. However, X-ray quality crystals and samples forspectroscopic, elemental, and thermogravimetric analysiscould be manually removed from mixtures containing themand microcrystalline L2NiCl2. An X-ray structure and elemen-tal analysis established them as [L2Ni(H2O)4]Cl2 (4a) (cf.Scheme 3). Selected bond lengths and angles for 4a are listedin Table 5 and Table 6. Figure 5 and Figure 6 illustrate the mo-lecular structure as well as the crystal structure of 4a.

Table 5. Bond lengths /Å and angles /° for 4a.

Ni–O(2) 2.0555(17) O(2)–Ni–O(2)#1 180.00(7)Ni–O(2)#1 2.0555(17) O(2)–Ni–O(1) 92.50(7)Ni–O(1) 2.0680(15) O(2)#1–Ni–O(1) 87.50(7)Ni–O(1)#1 2.0680(15) O(2)–Ni–O(1)#1 87.50(7)Ni–N(1) 2.0697(18) O(2)#1–Ni–O(1)#1 92.50(7)Ni–N(1)#1 2.0698(18) O(1)–Ni–O(1)#1 180.00(6)O(1)–C(6) 1.240(3) O(2)–Ni–N(1) 88.25(7)N(1)–C(1) 1.332(3) O(2)#1–Ni–N(1) 91.75(7)N(1)–N(2) 1.351(2) O(1)–Ni–N(1) 93.60(7)N(2)–C(3) 1.347(3) O(1)#1–Ni–N(1) 86.40(7)N(2)–C(4) 1.457(3) O(2)–Ni–N(1)#1 91.75(7)N(3)–C(6) 1.326(3) O(2)#1–Ni–N(1)#1 88.25(7)C(1)–C(2) 1.392(3) O(1)–Ni–N(1)#1 86.40(7)C(2)–C(3) 1.372(3) O(1)#1–Ni–N(1)#1 93.60(7)C(4)–C(5) 1.519(3) N(1)–Ni–N(1)#1 180.0C(5)–C(6) 1.506(3) C(6)–O(1)–Ni 141.55(15)

C(1)–N(1)–N(2) 105.04(18)C(1)–N(1)–Ni 127.02(15)N(2)–N(1)–Ni 127.91(14)C(3)–N(2)–N(1) 111.24(18)C(3)–N(2)–C(4) 126.43(18)N(1)–N(2)–C(4) 122.29(17)N(1)–C(1)–C(2) 111.6(2)C(3)–C(2)–C(1) 104.4(2)N(2)–C(3)–C(2) 107.7(2)N(2)–C(4)–C(5) 112.90(18)C(6)–C(5)–C(4) 114.58(17)O(1)–C(6)–N(3) 120.6(2)O(1)–C(6)–C(5) 123.75(18)N(3)–C(6)–C(5) 115.69(18)

Symmetry transformations used to generate equivalent atoms: #1–x+1, –y, –z+1

Table 6. Hydrogen bonds /Å,° for 4a.

D–H···A d(D–H) d(H···A) d(D···A) �(DHA)

O(2)–H(8)···O(3) 0.83(4) 1.84(4) 2.661(3) 168(4)O(2)–H(7)···Cl#2 0.83(4) 2.34(4) 3.1442(19) 163(3)O(3)–H(9)···Cl#3 0.84(4) 2.47(4) 3.313(2) 178(3)O(3)–H(10)···Cl#1 0.79(3) 2.40(3) 3.167(2) 163(3)N(3)–H(5)···Cl#4 0.86(4) 2.45(4) 3.295(2) 168(3)

Symmetry transformations used to generate equivalent atoms:: #1–x+1, –y, –z+1 #2 x+1, –y–1/2, z+1/2 #3 x+1, –y+1/2, z +1/2, #4 –x,y–1/2, –z+1/2

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Figure 5. ORTEP view of 4a with thermal ellipsoids at the 50% prob-ability level.

Figure 6. Nickel cation chain of 4a.

The X-ray diffraction study revealed the presence of[L2Ni(H2O)2]2+ cations bridged by an unusual hydrogen-bond-ing network involving two non-coordinated water moleculesand two chloride counterions. The inner coordination arrange-ment around nickel in the cation is again octahedral as in 2and 3 with coordinated water molecules replacing the ethanolligands in the iron and cobalt derivatives (Figure 5). Bondlengths and angles within the cation are unexceptional, as arebond lengths and angles in the coordinated N-pyrazolylpropan-amide ligands. Once again, the central metal ion is located onan inversion center. With 2.0555(17) Å the Ni–N distance fitsnicely into the series Fe � Co � Ni. The most interestingstructural feature, however, involves an unusual array of threedifferent types of hydrogen bonds (O–H···O, N–H···Cl, andO–H···Cl).

The crystal structure consists of chains of [L2Ni(H2O)2]2+

cations linked by N–H···Cl and Cl···H–O hydrogen bonds (Fig-ure 6). In this arrangement a coordinated H2O in one[L2Ni(H2O)2]2+ cation joins to the amido group in the secondthrough a bridging Cl–. These chains form sheets of interdigi-tized chains through a complicated hydrogen-bonding network

F. T. Edelmann, J. W. Gilje et al.ARTICLEthat involves chlorides and the lattice waters (Figure 7). Theamide and coordinated water in an individual [L2Ni(H2O)4]2+

are joined by a N–H···Cl···H–O···H–O hydrogen bonds linkage.A second nickel is linked through the same Cl– and an uncoor-dinated H2O by Cl···H–O···H–O hydrogen bonds. The hydro-gen-bond network is not symmetrical and the pentagonal hy-drogen bonded arrays of heavy atoms that join [L2Ni(H2O)2]2+

cation chains is shown in Figure 7. Figure 8 illustrates detailsof theconnectivitybetweenindividual interchain[L2Ni(H2O)2]2+

cations.

Figure 7. Nickel cation sheet of 4a.

Figure 8. Nickel cation sheet packing of 4a.

The sheeets, which are oriented in the (101) direction, stackin a corrugated fashion and are linked through long N–H···Clhydrogen bonds between amide groups in one sheet and chlor-ides in another (Figure 8). None of the water molecules istightly held in 4a as thermogravimetric analysis shows a quan-titative loss of all at 100 °C.

Silver(I) complexes containing pyrazole ligands have beenfrequently studied due to their promising luminescent and li-quid crystalline properties.[6] A cationic silver(I) complex of1 was readily obtained from silver(I) nitrate by adopting thetriethylorthoformate-assisted route as shown in Scheme 4. The63% isolated yield of colorless crystalline [L2Ag]NO3·0.5H2O(5) was somewhat lower than the yields in the other prepara-

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tions. This can be traced to the increased solubility of 5 inethanol as compared to complexes 2–4. The IR spectrum of 5showed characteristic bands of the uncoordinated amide group,thus providing a first indication for monodentate N-pyrazolylcoordination of the ligand in the silver(I) complex. Bands at3377 cm–1 as well as 1687 cm–1 could be assigned to N–Hstretching vibration and the C=O absorption, respectively, withlatter value being almost unchanged as compared to that forthe free ligand [ν(C=O) 1690 cm–1].[3]

Scheme 4.

Colorless single-crystals of 5 suitable for X-ray diffractionwere obtained by slow cooling of a saturated solution in eth-anol to 5 °C. Figure 9 shows the molecular structure of 5, andimportant bond lengths and angles are listed in Table 7 andTable 8. The supramolecular crystal structure of 5 is shown inFigure 10. Surprisingly, despite the use of triethylorthoformateduring the preparation, the X-ray structural analysis of 5 re-vealed the presence of a monohydrate. The origin of one-halfmolecule water of crystallization in compound 5 is unclear butit could have resulted from contact with moisture during thepreparation or recrystallization process. The structure also con-firmed the presence of a cationic dicoordinate complex withmonodentate N-coordination by two N-pyrazolylpropanamideligands. With an N(4)–Ag(1)–N(1) angle of 166.22(9)° the sil-ver atom in the cation shows an approximately linear coordina-tion. This value is in good agreement with the N–Ag–N angleof 162.6(4)° in the related complex bis[5-(2-naphthyl)-1H-pyr-azole-κN2]silver(I) nitrate.[7e]

Figure 9. ORTEP view of 5 with thermal ellipsoids at the 50% prob-ability level.

As can be seen in Figure 10, the supramolecular crystalstructure of 5 is again an intricate framework of O–H···O andN–H···O hydrogen bonds. Although only one molecule waterof crystallization per two formula units of [L2Ag]NO3 is incor-porated in the solid-state structure of 5, it plays a central rolein assembling the supramolecular array. This single water mo-

N-Pyrazolylpropanamide for Supramolecular Hydrogen-Bonded Frameworks

Table 7. Bond lengths /Å and angles /° for 5.

C(1)–N(1) 1.326(4) N(1)–C(1)–C(2) 110.4(3)C(1)–C(2) 1.374(5) C(3)–C(2)–C(1) 105.5(3)C(2)–C(3) 1.358(6) N(2)–C(3)–C(2) 107.8(3)C(3)–N(2) 1.339(4) N(2)–C(4)–C(5) 111.7(2)C(4)–N(2) 1.457(4) C(6)–C(5)–C(4) 113.7(2)C(4)–C(5) 1.519(4) O(1)–C(6)–N(3) 122.3(3)C(5)–C(6) 1.509(4) O(1)–C(6)–C(5) 121.4(3)C(6)–O(1) 1.231(3) N(3)–C(6)–C(5) 116.2(2)C(6)–N(3) 1.328(4) N(4)–C(7)–C(8) 111.2(2)C(7)–N(4) 1.335(3) C(7)–C(8)–C(9) 105.3(2)C(7)–C(8) 1.374(4) N(5)–C(9)–C(8) 107.1(2)C(8)–C(9) 1.379(4) N(5)–C(10)–C(11) 111.8(2)C(9)–N(5) 1.345(3) C(12)–C(11)–C(10) 113.2(2)C(10)–N(5) 1.468(3) O(2)–C(12)–N(6) 123.5(3)C(10)–C(11) 1.520(4) O(2)–C(12)–C(11) 120.8(2)C(11)–C(12) 1.510(4) N(6)–C(12)–C(11) 115.6(3)C(12)–O(2) 1.232(3) C(1)–N(1)–N(2) 106.1(3)C(12)–N(6) 1.322(4) C(1)–N(1)–Ag(1) 129.8(2)N(1)–N(2) 1.347(3) N(2)–N(1)–Ag(1) 122.70(19)N(1)–Ag(1) 2.125(2) C(3)–N(2)–N(1) 110.1(3)N(4)–N(5) 1.350(3) C(3)–N(2)–C(4) 128.1(3)N(4)–Ag(1) 2.114(2) N(1)–N(2)–C(4) 121.6(2)N(7)–O(4) 1.234(4) C(7)–N(4)–N(5) 105.4(2)N(7)–O(3) 1.240(3) C(7)–N(4)–Ag(1) 129.70(18)N(7)–O(5) 1.252(4) N(5)–N(4)–Ag(1) 124.80(16)

C(9)–N(5)–N(4) 111.0(2)C(9)–N(5)–C(10) 127.2(2)N(4)–N(5)–C(10) 121.8(2)O(4)–N(7)–O(3) 119.1(3)O(4)–N(7)–O(5) 120.8(3)O(3)–N(7)–O(5) 120.0(3)N(4)–Ag(1)–N(1) 166.22(9)

Table 8. Hydrogen bonds /Å,° for 5.

D–H···A d(D–H) d(H···A) d(D···A) �(DHA)

N(3)–H(3NA)···O(2) 0.80(4) 2.11(4) 2.901(4) 169(4)#1N(3)–H(3NB)···O(3) 0.77(4) 2.33(4) 3.069(4) 162(4)#2N(6)–H(6NA)···O(1) 0.69(4) 2.28(4) 2.971(4) 172(3)#3N(6)–H(6NB)···O(6) 0.87(4) 2.11(4) 2.984(3) 177(3)#4O(6)–H(6OA)···O(5) 0.83(4) 2.00(4) 2.815(4) 168(5)

Symmetry transformations used to generate equivalent atoms:, #1 x,y+1, z #2 –x+1/2, –y+3/2, –z+1 #3 x, y–1, z, #4 –x, –y, –z+1

lecule serves both as a donor by O–H···O hydrogen bonds withtwo nitrate ions and as an acceptor with two N–H···O hydro-gen-bonds involving NH2 functional groups of neighboringcations. In addition, adjacent amide functionalities are con-nected through N–H···O to form eight-membered rings such asthose found in carboxylic acid dimers (Figure 10). Each cationis linked to two others forming chains of of [L2Ag]+ cations.The hydrogen-bonding network involving the water and nitrateions link these chains into bilayered sheets, in which the outersides are composed of pyrazole rings and the amide functional-ities are oriented toward the center (Figure 11). The overallcrystal structure contains these sheets packing in an interdigi-tated fashion (Figure 12).

Z. Anorg. Allg. Chem. 2012, 2129–2137 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 2135

Figure 10. Crystal packing view of 5.

Figure 11. Silver cation sheets of 5.

3 Conclusions

We have established the readily accessible N-pyrazolylpro-panamide (1) as a versatile ligand for first-row transition met-als. Whereas 1 acts as an N,O-chelating ligands towards iron,cobalt, and nickel, monodentate nitrogen coordination wasfound for the silver(I) complex 5. In three cases (2, 4a, and 5)single-crystal X-ray structural analyses revealed the presenceof different hydrogen-bonded supramolecular structures in thesolid state. In any case the results reported herein can be ex-pected to stimulate further research on the coordination behav-ior of 1.

F. T. Edelmann, J. W. Gilje et al.ARTICLE

Figure 12. Silver sheet packing of 5.

4 Experimental Section

4.1 General Procedures

All transition metal salts used in this study were obtained from com-mercial suppliers and used as received. N-Pyrazolylpropanamide (1)was prepared according to the published procedure.[3] Microanalysesof the compounds were performed with a Leco CHNS 923 apparatusand by Galbraith Laboratories, Inc, Knoxville, TN, USA. CHN valuesoutside the +/– 0.4% range can be traced back to the presence ofvolatile ligands such as ethanol. Melting points were determined witha Büchi B-450 digital melting point apparatus. IR spectra were re-corded using KBr pellets with a Perkin-Elmer FT-IR spectrometer sys-tem 2000 or ThermoNicolet Avatar 370 FT-IR between 4000 cm–1 and400 cm–1. Thermogravimetric analysis was conducted with a MettlerToledo TGA/SDTA 851e thermogravimetric analyzer. The intensitydata of 2, 3, 4a, and 5 were collected with a Bruker CDD SMARTdiffractometer with Mo-Kα radiation. The data were collected with theBruker SMART[8] program using ω-scans. The space group was deter-mined with Bruker SAINT[8] program. The structure was solved bydirect methods (SHELXS-97) and refined by full-matrix least-squaresmethods on F2 using SHELXL-97.[9]

Caution! Transition metal perchlorate compounds should always behandled with caution as possible energetic materials.

4.2 Synthesis of [L2Fe(EtOH)2](ClO4)2 (2)

A solution of N-pyrazolylpropanamide (0.39 g, 2.8 mmol) in ethanol(20 mL) was added to an ethanol solution (20 mL) of iron(II) perchlo-rate hexahydrate (0.50 g, 0.5 mmol) and triethylorthoformate (4 mL)for dehydration. After stirring for 24 h, the volume of the reactionmixture was reduced in vacuo until the first small amounts of solidbecame visible (ca. 2/3 of the original volume). Crystallization at 5 °Cfor 14 d afforded [L2Fe(EtOH)2](ClO4)2 (2) (0.27 g, 82%) as lightgreen-brown crystals. Elemental C16H30Cl2FeN6O12 (625.20): calcd. C30.74; H 4.84; N 13.44 %, found: C 29.90; H 4.66; N 12.85%. IR(KBr): ν̃ = 3449 (br) s, 3356 s, 3288 m, 3155 m, 3132 m, 3005 w,2916 w, 2752 w, 2018 w, 1650 vs, 1597 m, 1522 w, 1444 m, 1409 m,1381 w, 1356 w, 1287 m, 1219 w, 1090 vs, 994 m, 967 m, 920 w, 897w, 876 w, 805 w, 777 m, 761 m, 675 w, 627 s, 536 m, 513 m cm–1.

4.3 Synthesis of [L2Co(EtOH)2](ClO4)2 (3)

A solution of N-pyrazolylpropanamide (0.43 g, 3.1 mmol) in ethanol(20 mL) was added to an ethanol solution (20 mL) of cobalt(II) per-

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chlorate hexahydrate (0.57 g, 0.6 mmol) and triethylorthoformate(4 mL) for dehydration. After stirring for 24 h, the volume of the reac-tion mixture was reduced in vacuo until the first small amounts ofsolid became visible (ca. 2/3 of the original volume). Crystallizationat 5 °C for 14 d afforded [L2Co(EtOH)2](ClO4)2 (3) (0.32 g, 85%) inthe form of pink crystals. Elemental C16H30Cl2CoN6O12 (628.29):calcd. C 30.59; H 4.81; N 13.38%; found: C, 30.40; H, 4.61; N,12.28%. IR (KBr): ν̃ = 3464 s, 3361 s, 3220 m, 3158 m, 3140 m,3005 w, 2971 w, 2934 w, 2768 w, 2025 w, 1656 vs, 1600 m, 1518 w,1447 m, 1415 m, 1379 w, 1355 w, 1305 m, 1289 m, 1241 m, 1219 w,1110 vs, 1092 vs, 1068 s, 993 m, 938 m, 920 w, 897 w, 877 w, 806w, 788 m, 760 m, 676 w, 627 s, 575 m, 543 m cm–1.

4.4 Synthesis of L2NiCl2 (4)

A solution of N-pyrazolylpropanamide (0.28 g, 2.0 mmol) in ethanol(10 mL) was added to an ethanol solution (10 ml) of nickel(II) chloridehexahydrate (0.24 g, 1.0 mmol) and triethylorthoformate (4 mL) fordehydration. Over 8 days a light green precipitate formed, which wasisolated by filtration, washed with ethanol (10 mL) and water(2�10 mL). After drying at room temperature L2NiCl2 (0.32 g, 79%)was obtained as a light green powder. Elemental C12H18Cl2N6NiO2

(407.91): calcd. C 35.33; H 4.45; N 20.61%; found: C 35.29; H 4.20;N 20.11%. IR (KBr): ν̃ = 3427 vs, 3245 s, 3140 vs, 2992 s, 1646 vvs,1588 vs, 1428 m, 1411 s, 1404 s, 1382 m, 1304 m, 1284 m 1176 m,1098 mw, 1079 mw, 1071 mw, 932 s, 975 mw, 790 m, 787 s, 630 s,578 s, 532 mw, 502 mw cm–1.

4.5 Isolation of L2Ni(H2O)4Cl2 (4a)

Occasionally, large, dark green crystals grew during the preparationsof compound 4. An X-ray structure and elemental analysis establishedthem as L2Ni(H2O)4Cl2. Elemental C12H26Cl2N6NiO6 (479.97): calcd.C 30.04; H 5.46; N 17.51%; found: C 29.76; H 5.40; N 17.22%. IR(KBr): ν̃ = 3481 sh, 3391 vs. br, 3346 sh, 3264 sh, 3203 sh, 3171 sbr, 1645 vvs, 1594 s 1521 mw, 1442 s, 1420 s, 1406 s, 1386 m, 1307m, 1292 s, 1220 m, 1176 m, 1102 m, 1070 ms, 1062 ms, 939 m 759s, 551 m br cm–1.

Thermogravimetric analysis of L2Ni(H2O)4Cl2 shows a sharp massloss of 14.6% at 100 °C. This compares to 15.0 % expected for theloss of four H2O from L2Ni(H2O)4Cl2. With exception of this step,the L2Ni(H2O)4Cl2 and L2NiCl2 thermograms are indistinguishable,showing gradual mass loss above 100 °C, but without well-definedsteps.

4.6 Synthesis of [L2Ag](NO3)·0.5H2O (5)

A solution of N-pyrazolylpropanamide (1.64 g, 11.8 mmol) in ethanol(50 mL) was added to an ethanol solution (50 mL) of silver nitrate(0.50 g, 2.9 mmol) and triethylorthoformate (10 mL). After stirring for24 h and crystallization at 5 °C for 5 d the product [L2Ag](NO3)·0.5H2O (5) (0.85 g, 63%) was obtained as colorless crystals. Elemen-tal C12H29AgN7O5.5 (466.20): calcd. C 31.53; H 4.19; N 21.45%;found: C 30.09; H 4.09; N 20.63%. IR (KBr): ν̃ = 3377 s, 3197 m,3113 m, 3005 w, 2956 w, 2932 w, 2789 w, 2396 w, 1763 w, 1687 vs,1631 s, 1516 w, 1465 m, 1424 s, 1380 s, 1286 m, 1232 m, 1169 w,1127 w, 1091 m, 1070 w, 1042 m, 967 m, 944 w, 920 w, 885 w, 825w, 807 w, 755 m, 682 w, 654 w, 616 m, 544 w, 495 w cm–1.

Crystallographic data (excluding structure factors) for the structures inthis paper have been deposited with the Cambridge Crystallographic

N-Pyrazolylpropanamide for Supramolecular Hydrogen-Bonded Frameworks

Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copiesof the data can be obtained free of charge on quoting the depositorynumbers CCDC-865245 (2), -865246 (3), -865247 (4a), and -865248(5) (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk,http://www.ccdc.cam.ac.uk).

Acknowledgement

This work was financially supported by the Otto-von-Guericke-Uni-versität, Magdeburg. The support of the U.S. National Science Founda-tion (REU Grant CHE-0754521) and the Research Corporation Depart-mental Science Development Grant 550239 is gratefully acknowl-edged. We thank Dr. Barbara Reisner for helpful discussions ofthe crystal structures and for assistance with the thermal gravimetricanalysis.

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Received: March 27, 2012Published Online: June 6, 2012