Peter Pogány, Attila Kovács, Katalin Mészáros Szécsényi and Vukadin M. Leovac

FT-IR and theoretical study of 3,5-dimethyl-1H-pyrazole-1-carboxamidine (L) and the complexes CoL2(H2O)2(NO3)2 and NiL2(H2O)2(NO3)2

Spectrochimica Acta A, 71 (2008) 1466-1473

 

 

In the paper a joint experimental and theoretical study of 3,5-dimethyl-1H-pyrazole-1-carboxamidine (L) as well as its complexes CoL2(H2O)2(NO3)2 and NiL2(H2O)2(NO3)2 is reported. On the basis of FT-IR experiments and a DFT-derived scaled quantum mechanical force field the normal coordinate analysis of L was carried out. The FT-IR spectra of the two complexes were interpreted using the present assignment of L and computed vibrational data of the complexes. The ionic and charge transfer interactions in the complexes were assessed by means of natural bond orbital (NBO) analysis.

                   L·HNO3                                         CoL2(H2O)2(NO3)2  and  NiL2(H2O)2(NO3)2

 

In the vibrational analysis we tried to model the crystal structure of the ligand:

 

The best agreement between the experimental and computed IR spectra was achieved using the following model structure:

 

And the results of the SQM analysis (the normal modes of the ligand):

Assignment of the FT-IR spectrum of solid L·HNO3 on the basis of the SQM results.a

Exp.

Computed

 

Scaled

Unscaled

TEDb

3290

s, br

3484

3628

(141)

62% νasNH2, 38% νsNH2

3112

vs,br

3065

3191

(2271)

62% νsNH2, 38% νasNH2

1693

s

1694

1736

(590)

66% νC=Nam, 17% δsciNH2

1644

m

1640

1673

(205)

76% δsciNH2, 13% βNH…O

1592

m

1579

1618

(102)

31% νC=C, 18% νCNpy, 16% δsciNH2

1563

sh

1565

1599

(22)

49% δsciNH2, 15% νC=Nam, 10% βNH…O

1546

s

1510

1547

(224)

21% νNpy-Cam, 15% νC=Nam, 15% δasCH3, 12% νCNpy

1479

sh

1479

1510

(84)

80% δasCH3

1479

sh

1476

1509

(71)

47% δasCH3, 18% νCNpy

1462

m

1457

1486

(24)

83% δasCH3

1441

sh

1442

1475

(10)

43% δasCH3, 19% νCNpy, 15% νCC

1409

w

1411

1444

(69)

27% νC=C, 23% δsCH3, 16% δasCH3

1384

s

1413

1450

(1226)

77% νasNO3, 11% δasNO3

1367

sh

1376

1404

(6)

76% δsCH3, 11% νC=C

1328

s

1318

1349

(302)

53% νCNpy, 25% βpy

1319

s

1294

1327

(475)

71% νasNO3, 15% δasNO3

1204

w

1188

1217

(16)

29% νNN, 19% βpy, 11% νC=C, 11% νNpy-Cam

1159

w

1154

1178

(5)

58% βCH, 11% νCC

1117

w

1109

1135

(16)

34% νNN, 17% νCC, 11% δrCH3

1092

w

1074

1099

(39)

50% δrNH2, 36% νC=Nam

1064

w

1053

1072

(4)

78% δrCH3, 11% δasCH3

1047

sh

1043

1062

(2)

81% δrCH3, 11% γC-CH3

1040

w

1031

1060

(48)

92% νsNO3

1030

w

1031

1052

(4)

31% δrCH3, 27% βpy, 12% νCNpy

990

w

985

1005

(26)

42% δrCH3, 25% δrNH2

971

m

964

986

(22)

33% δrCH3, 33% νC=C, 12% βpy

805

w

799

808

(28)

100% γCH

782

w

771

790

(8)

33% νCC, 14% βpy, 14% νCNpy

738

m

849

864

(54)

100% τNH

701

m, br

835

849

(185)

65% τNH, 30% γNO3

720

w

714

728

(21)

56% τCNam, 25% τNH, 14% δasNO3

686

sh

702

714

(9)

74% δasNO3, 15% νasNO3

666

w

658

670

(1)

70% τpy, 12% γC-CH3, 10% τNH

653

w

639

652

(32)

19% βNCN, 17% βpy, 14% νNpy-Cam, 10% τNH

612

w

613

625

(14)

58% τpy, 12% γC-CH3

587

w

577

590

(1)

45% νCC, 35% βpy

536

s

531

540

(16)

22% βNCN, 20% βCCN, 13% βCNN

430

s

422

429

(24)

45% βNCN, 17% νNpy-Cam, 11% βpy

399

m

393

399

(12)

46% βCCN, 24% βNCN

347

m

339

344

(12)

62% γC-CH3, 14% τpy

288

w

283

288

(10)

62% βCCN

224

m

208

212

(4)

39% βCNN, 15% βCCN, 14% τCH3

176

w

187

190

(4)

57% γC-CH3, 27% τpy

163

w

150

153

(14)

36% γNpy-Cam, 24% βH…ON, 23% τNH

138

m

132

130

(32)

60% γH…O, 16% νH…O

121

m

127

135

(16)

47% βH…ON, 18% νH…O, 13% γNpy-Cam

113

w

106

108

(1)

45% τCNam, 30% γH…O, 23% βH…ON

106

w

94

96

(2)

87% τCH3

88

w

84

87

(33)

73% νH…O

65

w

68

70

(5)

43% νH…O, 27% βH…ON, 10% τH...O

aThe wavenumbers are given in cm-1. The abbreviations vs, s, m, w, vw, sh and br mean very strong, strong, medium, weak, very weak, shoulder and broad, respectively. The unscaled calculated data (in parentheses the calculated IR intensities, km/mol) were obtained at the B3LYP//-311++G** level. For details of scaling see text.

bTED = total energy distribution [46,47]; only contributions larger then 10 % are given. The abbreviations py, s, as, n, d, b, sci, r, w, t, tw mean pyrazole ring, symmetric, asymmetric, stretch, deformation, bend, scissoring, rock, wag, torsion and twist, respectively. In ambiguous cases the C and N atoms belonging to the pyrazole or carboxamidine groups are indicated by subscripts py and am, respectively.