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Journal of Crystal Growth 275 (2005) e2049–e2053

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Synthesis and crystal structure of M(hmt)2(H2O)6(NO3)2.4H2Ocomplexes, where M ¼Mn2+, Co2+

Deepak Chopraa,�, Pritesh Dagurb, A.S. Prakasha, T.N. Guru Rowa, M.S. Hegdea

aSolid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, IndiabMaterials Research Centre, Indian Institute of Science, Bangalore 560012, India

Available online 25 December 2004

Abstract

A series of M-hmt complexes, where M ¼Mn2þ; Co2+ were synthesized and studied by single crystal X-ray

diffraction. The cobalt complex crystallizes in the triclinic space group P-1 with a ¼ 9:098ð2Þ (A; b ¼ 9:390ð2Þ (A; c ¼

9:649ð2Þ (A; a ¼ 88:3ð1Þ1; b ¼ 75:6ð2Þ1; g ¼ 61:64ð3Þ1 with Z ¼ 1: The Mn complex crystallized in the monoclinic spacegroup P21/n with a ¼ 9:511ð3Þ (A; b ¼ 16:232ð4Þ (A; c ¼ 19:426ð5Þ (A; b ¼ 90:6ð4Þ1 with Z ¼ 4: The structure consists ofhexa-coordinated metal cations with water as the ligand having slightly distorted octahedral geometry. The organic

ligand, hexamethylenetetramine is not directly coordinated to the metal ion but its presence stabilizes the molecular

assembly because of the presence of a rich variety of intermolecular interactions.

r 2004 Elsevier B.V. All rights reserved.

PACS: 60

Keywords: A1. Crystal structure; A1. Single-crystal growth; A1. X-ray diffraction; B1. Inorganic compounds; B1. Metals; B1. Organic

compounds

1. Introduction

Hexamethylenetetramine (hmt), a universal andversatile ligand [1] having three fused rings in thechair conformation and four bridgehead nitrogenatoms is well known to form coordinationcompounds with metal salts [2–6]. One suchcompound with dichromate as the counter-ion

e front matter r 2004 Elsevier B.V. All rights reserve

ysgro.2004.11.195

ng author. Tel.: +9180 22932336 (ext. 23);

01310.

ss: deepak@sscu.iisc.ernet.in (D. Chopra).

has recently been reported [7]. Although apotentially tetradentate ligand [8], hmt acts as abidentate ligand [9], bridging between two metalatoms and retaining the chair conformation of theuncoordinated molecule in its structures.Binary, ternary and quaternary oxides are easily

synthesized by a novel combustion method byheating an aqueous solution of metal nitrates andan organic fuel in which the nitrate is reduced towater and nitrogen by an organic fuel. We haveshown that hmt is an excellent, cheap and easilyavailable fuel to prepare nano-oxide materials.

d.

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D. Chopra et al. / Journal of Crystal Growth 275 (2005) e2049–e2053e2050

The metal complexes with hmt are used asprecursor for the synthesis of a variety of oxides[10]. Here, we report the synthesis and structuresof these complexes of hmt with Co [11], Mndivalent transition metal ions.

2. Experimental procedure

The title compounds were prepared by mixing10ml aqueous solution of the metal nitrates(0.01M) and 10ml aqueous solution of hmt(0.02M) in a 25.0ml beaker at room temperature(293K) and allowing the solution to stand for 2weeks, whereupon crystals were obtained by aslow evaporation process at room temperature andpressure. Colourless crystals were obtained in thecase of Mn-hmt complex whereas pink-coloured

Table 1

Crystal data for the transition metal hmt complexes

Data Co-hmt(1:2)

Formula weight (gmmol�1) 639.5

Temperature/K 293(2)

Radiation MoKa

Wavelength (/A) 0.7107

Crystal system Triclinic

Space group P-1

a/A 9.098(2)

b/A 9.390(2)

c/A 9.650(2)

a/A 88.3(3)

b/A 75.6(3)

g/A 61.6(3)

Volume (/A3) 699.00(16)

Z 1

Density (g/cm3) 1.50

Abs. Coeff. (mm�1) 0.699

F(000) 328.9

ymin,max 2.2,27.9

hmin,max,kmin,max,lmin,max �11,11,�12,11,�12,

Number of reflections 7712

Number of unique 3017

Number of parameters 266

Refinement method Full matrix least squ

R_all 0.032

R_obs 0.031

wR2_all 0.086

wR2_obs 0.085

Drmin,max (/eA�3) �0.334, 0.660

GooF 1.045

crystals were obtained in case of the Co-hmtcomplex. The morphology of the crystals was‘‘block’’ like. The structure was determinedunambiguously by single-crystal X-ray diffractionstudies. Hmt was taken in different ratios with themetal nitrates (1:1,2:1,3:1,4:1) but all these resultedin the formation of complexes having the samemetal ion:hmt ratio (1:2).Single-crystal X-ray diffraction data of the title

compounds was collected on a Bruker AXSSMART APEX CCD diffractometer. The X-raygenerator was operated at 50 kV and 40mA usingMoKa radiation. Data was collected with a o scanwidth of 0.31. A total of 606 frames per set werecollected in three different settings of j (01, 901and 1801) keeping the sample-to-detector distanceof 6.03 cm and the 2y value fixed at �251. The datawere reduced using SAINTPLUS [12] and an

Mn-hmt(1:2)

631.4

293(2)

MoKa

0.7107

Monoclinic

P21/n

9.511(3)

16.234(4)

19.426(5)

90.00

90.60(4)

90.00

2998.90(14)

4

1.42

0.52

1355.7

1.6,27.8

12 �11,11,�17,20,�25,25

24304

6539

528

ares on F2 Full matrix least squares on F2

0.068

0.046

0.118

0.108

�0.229, 0.37

1.059

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Table 2

Hydrogen—bonding geometry

d (D-H)/A d(H....A)/A d(DyA)/A +D-HyA(1)

Mn-hmt complex

O2 H21 N7 0.77(3) 2.05(3) 2.808(3) 168(3)

O2 H22 O7 0.83(3) 1.97(3) 2.792(3) 173(3)

O3 H31 O16 0.80(3) 1.94(3) 2.730(3) 172(3)

O4 H42 O10 0.77(3) 2.07(3) 2.818(3) 163(3)

O5 H51 N1 0.83(3) 1.99(3) 2.813(3) 169(3)

O6 H61 N2 0.76(3) 2.11(3) 2.855(3) 166(3)

O6 H62 O13 0.79(3) 1.97(3) 2.753(3) 174(3)

O13 H131 N6 0.78(4) 2.10(4) 2.868(3) 168(3)

O14 H142 O8 0.78(4) 2.22(4) 2.942(4) 155(4)

O15 H151 O12 0.84(5) 2.11(5) 2.909(4) 158(4)

O16 H161 N4 0.83(4) 2.04(4) 2.854(3) 166(4)

Co-hmt complex

O8 H8 N4 0.73(3) 2.10(3) 2.826(2) 173(4)

O1 H11 O5 0.80(3) 2.05(3) 2.835(2) 166(3)

O1 H12 N2 0.81(3) 2.02(3) 2.827(2) 172(3)

O2 H21 O6 0.77(3) 2.10(3) 2.860(3) 171(3)

O2 H22 N5 0.79(4) 2.09(4) 2.874(3) 171(2)

O3 H31 O8 0.73(3) 1.95(3) 2.665(2) 163(3)

O3 H32 N3 0.78(3) 2.01(3) 2.788(2) 172(3)

O7 H71 O4 0.80(4) 2.02(4) 2.806(3) 169(4)

O7 H72 O5 0.86(4) 2.08(4) 2.918(3) 167(4)

O8 H82 O7 0.88(4) 1.94(4) 2.808(4) 173(3)

D. Chopra et al. / Journal of Crystal Growth 275 (2005) e2049–e2053 e2051

empirical absorption correction was applied usingSADABS [12]. The crystal structure was solved bydirect methods using SIR92 [13] and refined by fullmatrix least-squares using SHELXL97 [14]. Mo-lecular and packing diagrams were generated byORTEP32 [15] and CAMERON [16] present in theWINGX (Version 1.64.03b) [17] program suite.Geometric calculations were done using PARST95[18].

2.1. Refinement

The hydrogen atoms were located by differentialFourier technique and refined isotropically. Forthe Co-hmt complex, all the H atoms were locatedand refined isotropically. The C–H and O–H bondlengths are in the range 0.90(2)–1.00(2) A and0.73(3)–0.88(3) A, respectively. For the Mn-hmtcomplex, the C–H and O–H bond lengths are0.90(2)–1.01(2) A and 0.74(3)–0.90(6) A, respec-tively.

3. Results and discussion

Details of the crystal data and refinement aregiven in Table 1 while Table 2 contains a list ofhydrogen bonds.Fig. 1a and b shows the components of the

asymmetric unit in the title compounds. Fig. 2aand b depict the packing features of thesecomplexes, which highlight the presence of bothoctahedrally coordinated metal ions and organichmt molecules with inorganic counter-ions.The O–M–O (M ¼ Co, Mn) bond angles are not

perfect but are slightly distorted due to theinfluence of the neighbouring ligands. The organicframework consisting of hmt as the ligand is notdirectly coordinating with the transition metal ion.A set of strong O–HyO hydrogen bonds (Table2) links the solvent water molecules with thecoordinated ones. There are also O–HyO hydro-gen bonds between the nitrate ion and both thefree and coordinated water molecules. There also

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Fig. 1. (a) ORTEP diagram of Co-hmt asymmetric unit. (b)

ORTEP diagram of Mn-hmt asymmetric unit.

D. Chopra et al. / Journal of Crystal Growth 275 (2005) e2049–e2053e2052

exist O–H...N hydrogen bonds between both thecoordinated and free water molecules with the hmtunit. These strong intermolecular hydrogen bondsform a three-dimensional network.The manganese complex belongs to the mono-

clinic crystal system with four molecules in the unitcell. This complex is also stabilized by similar typeof interactions which stabilize the Co-hmt com-plexes. The hydrogen bonds are strong and highlydirectional.

Fig. 2. (a) Packing diagram of Co-hmt. (b) Packing diagram of

Mn-hmt (dotted lines represent hydrogen bonds).

4. Conclusion

Hmt has been employed as a fuel in the solutioncombustion synthesis which is a novel techniquefor the synthesis of simple and complex oxides andthese new materials are known to exhibit interest-ing magnetic, electric and catalytic properties. Thedecomposition of these metal nitrate-hmt com-plexes is highly exothermic and the in situ heat

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generated is utilized for the synthesis of complexoxides and these mostly belong to the family ofperovskites and spinels. The same combustionprocess is utilized for the preparation of high-surface area oxides such as ceria, zirconia andalumina which are used in catalysis and in all thesehmt has been used as a fuel. Because of the diverseapplication of such materials, efforts have beenmade to synthesize compounds which containboth the organic and inorganic moieties and thenheating such materials at high temperature wherethe organic moiety is eliminated in the form ofgases leading to the formation of the thermo-dynamically stable oxide.

Acknowledgement

We thank the Department of Science andTechnology, India for data collection on theCCD facility setup under the IRHPA-DST pro-gram. Deepak Chopra thanks CSIR, India forJunior Research Fellowship.

Supplementary materials

Crystallographic data (excluding structure fac-tors) for the structure of the complexes reported inthis paper have been deposited with the Cam-bridge Crystallographic Data Center as supple-mentary publication material no. CCDC 211784(Co-hmt), CCDC 211785 (Mn-hmt).

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