Zinc complexes of 6-methyl-2-pyridinecarboxylic acid. Crystal structure of [Zn(MeC5H3NCOO)2(H2O)] · H2O

Abstract

Reaction of Zn(AcO)2 · 2H2O with 6-methyl-2-pyridinecarboxylic acid (L) yielded a new compound [Zn(MeC5H3NCOO)2(H2O)] · H2O. This complex was characterised by elemental analyses, conductivity measurements, infrared, 1H and 13C{1H} NMR spectroscopies and single-crystal X-ray diffraction. The crystal structure consists of discrete molecules involving a pentacoordinated Zn atom with a geometry intermediate between a trigonal bipyramid and a square pyramid and with the two Npy atoms occupying the apical sites. Treatment of the complex [Zn(MeC5H3NCOO)2(H2O)] · H2O with 2,2′-bipyridine (bpy) produced [Zn(MeC5H3NCOO)2(bpy)]. The metallic atom in this complex displays a distorted octahedral geometry and is coordinated to two ligands (L) via the pyridine nitrogen and the carbonyl oxygen atoms and to one 2,2′-bypyridine (bpy).

Synthesis of complex [Zn(MeC5H3NCOO)2- (H2O)] ^. H2O

A solution of 0.16 g (0.73 mmol) Zn(AcO)2 ^. 2H2O in 10 ml of absolute ethanol was added dropwise to a solution of 0.20g (1.46 mmol) of 6-methyl-2-pyridinecarboxylic acid in 15 ml of absolute ethanol. After 15 min a white precipitate was formed. The solid was filtered off, washed with acetone, and dried in vacuum. The product was recrystallised from ethanol (yield 59%).

Anal. Calc. for C14H16N2O6Zn: C, 45.00; H, 4.29; N, 7.50. Found: C, 45.17; H, 4.32; N, 7.54%. Conductivity (Ω^{- 1} cm² mol^{- 1}, 1.2 × 10^{- 3} M in methanol): 35. IR (KBr): m(O–H) 3366; m(C–H)ar 3071; m(C–H)al 2977; m(COO)as 1639; m(C@C)as, m(C@N)as 1624, 1595; m(C@C)s, m(C@N)s 1467; d(CH3)as 1398; m(COO)s 1383; d(C–H)ip 1190, 1164, 1094; d(C–H)oop 838, 771 cm^{- 1}; IR (polyethylene): m(Zn–O) 320; m(Zn–N) 210 cm^{- 1}. 1H NMR (250 MHz, methanol-d4, ppm): d ¼ 8:06 [2H, d, J ¼ 8:1 Hz, CHar]; d ¼ 7:94 [2H, t, J ¼ 8:1 Hz, CHar]; d ¼ 7:50 [2H, d, J ¼ 8:1 Hz, CHar]; d ¼ 2:58 [6H, s, CH3]. 13C{1H} NMR (62.9 MHz, methanol-d4, ppm): ¼ 164.7 [COO]; d ¼ 153:0 [CCH3]; d ¼ 150:1 [CCOO]; d ¼ 142:7 [CHar]; d ¼ 128:2 [CHar]; d ¼ 120:1 [CHar]; d ¼ 20:3 [CH3].

Synthesis of complex [Zn(MeC5H3NCOO)2(bpy)]

A solution of 0.108 g (0.29 mmol) of [Zn(MeC5H3NCOO)2(H2O)] ^. H2O in dichloromethane (20 ml), previously refluxed for 30 min, was added to a solution of 0.141 g (0.90 mmol) of 2,20 -bipyridine in dichloromethane (10 ml). The mixture was refluxed for 4 h. From the pink solution the solvent was evaporated to dryness. The solid was washed with 5 ml of diethyl ether and dried in vacuum (yield 48%).

Anal. Calc. for C24H20N4O4Zn: C, 58.35; H, 4.09; N, 11.35. Found: C, 58.12; H, 4.32; N, 11.24%. Conductivity (Ω^{- 1}cm² mol^{- 1}, 1.3 × 10^{- 3} M in methanol): 22. IR (KBr): m(C–H)ar 3048; m(C–H)al 2985; m(COO)as 1594; m(C@C)as, m(C@N)as 1655, 1631; m(C@C)s, m(C@N)s 1452; d(CH3)as 1387; m(COO)s 1368; d(C–H)ip 1012, 908; d(C–H)oop 799, 779 cm^{- 1}; IR (polyethylene): m(Zn–O) 318; m(Zn–N) 222 cm^-1. 1H NMR (250 MHz, methanol-d4, ppm): d ¼ 8:62 (2H, m, bpy); d ¼ 8:40 (2H, m, bpy); d ¼ 8:28 (1H, m, bpy); d ¼ 8:01 [2H, d, J ¼ 7:9 Hz, CHar]; d ¼ 7:81 [2H, t, J ¼ 7:9 Hz, CHar]; d ¼ 7:44 [2H, m, bpy]; ¼ 7.31 (2H, d, J ¼ 7:9 Hz, CHar); d ¼ 2:20 [6H, s, CH3]. 13C{1H} NMR (62.9 MHz, methanol-d4, ppm): d ¼ 170:2 [COO]; d ¼ 153:4 [CCH3]; d ¼ 151:7 [bpy]; d ¼ 150:0 [CCOO]; d ¼ 143:8 [CHar]; d ¼ 140:1 [bpy]; d ¼ 130:2 [bpy]; d ¼ 128:1 [CHar]; d ¼ 123:0 [bpy]; d ¼ 121:3 [CHar]; d ¼ 22:4 [CH3]. MS (ESI): m=z (%) ¼ 494 (100) [Zn(MeC5H3NCOO)2 (bpy) + Hþ].

Crystallography

Recrystallisation of [Zn(MeC5H3NCOO)2(H2O)] ^.(H2O) in ethanol gave colourless single crystals. Data were collected on an Enraf-Nonius CAD-4 diffractometer and measured at room temperature (293(2) K) using graphite-monochromatised Mo Ka radiation (λ= 0.71069 Å). The structure was solved by Patterson and successive difference Fourier syntheses, and refined by full-matrix least squares methods (SHELX-76). The H atoms were placed at their geometrically calculated positions. Weights according to x ¼ 0:4836= r2ðF Þ þ 0:0024ðF 2Þ. The final RðF Þ and RwðF Þ values as well as the number of parameters refined and other details concerning the refinement of the crystal structure are summarised in Table 1.

Results and discussion

Crystal and molecular structure of [Zn(MeC5H3- NCOO)2H2O] ^. H2O

The crystal structure consists of discrete [Zn(MeC5H3NCOO)2(H2O)] molecules and solvent molecules (H2O) (Fig. 2). The metal atom is coordinated to two 6-methyl-2-pyridinecarboxylate ligands via one pyrazole nitrogen and one oxygen acetate, and to one molecule of H2O. The 6-methyl-2-pyridinecarboxylate behaves as a bidentate ligand forming a five-membered metallocycle.

The geometry around this pentacoordinated Zn atom is intermediate between a trigonal bipyramid and a square pyramid. The trigonality index is τ=0.63 and the angle N(1)–Zn–N(2) is 167.4(1). Two N-pyridine occupy the apical sites. Three oxygens, two of the acetate groups and one of the water molecules, describe the base of the trigonal bipyramid. Selected distances and angles are given in Table 2.

The interatomic Zn–N bond distances (2.148(3) and 2.156(3) Å) are significantly longer than other Zn–N bond distances reported in the literature, in particular for complex [Zn(C5H4NCOOH)(C5H4NCOO)Cl] (2.040(8) Å) and for complexes of Zn(II) with esters 2-pyridinecarboxylic acid (2.098(2)–2.141(4) Å). The Zn–N(methylpyridine) bond distances are signifi- cantly longer, possibly due to steric-effects of methyl groups. The Zn–O and Zn–OH2 distances are consistent with those reported in the literature.

The N(2)–Zn–O(3) bite angle of 79.1(1) is signifi- cantly higher than those found in other complexes described in the literature. For complex [Zn(C5H4NCOOH)(C5H4NCOO)Cl] the bite angle is 76.6(3) and for complexes of Zn(II) with esters of 2-pyridinecarboxylic acid the values of the bite angle are between 71.47(13) and 73.9(2). Similar behaviour is found for the Co(II), [Co(MeC5H3NCOO)2(H2O2)2] (77.65(8)and 77.84(8) ) and [CoCl2(C5H4NCOOPri )2] (75.12(5) )

Sixty-three structures with [ZnN2O3] core have been described. In sixty-one cases, the most common Zn(II) coordination is a trigonal bipyramid (s ¼ 0:51–1:0). Only in two cases does the N occupy the axial position.

The probable H-bond network is formed by: (i) the water molecule O2, which is directly coordinated to the Zn atom and participates in two H-bonds: O2– (H)^... O9A'= 2.675(4) and O2–(H)... O1 ¼ 2.635(4) Å (the' denotes a symmetry-related complex). (ii) The remaining water molecule O1, which is bound to O9B and O9B0 via two additional H-bridges: O1–(H)... O9B ¼ 2.729(4) and O1–(H)... O9B0 ¼ 2.774(4).

References：

[1] JOSEFINA PONS . Zinc complexes of 6-methyl-2-pyridinecarboxylic acid. Crystal structure of [Zn(MeC5H3NCOO)2(H2O)] · H2O[J]. Inorganica Chimica Acta, 2004. DOI:10.1016/j.ica.2004.03.058.

You may like