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Hydrogen Bonding in Crystals of an Ammonium Catecholate NH4[C„H4(0 H )2][C6H4(0 H )0 | • 0.5 h 2o

Otto Kumberger, Jürgen Riede, and Hubert Schmidbaur*Anorganisch-chem isches Institut der Technischen Universität M ünchen, Lichtenbergstraße 4, D -85747 G arching

Z. Naturforsch. 48b , 9 5 8 -9 6 0 (1993); received April 7, 1993

Crystal Structure, H ydrogen Bonding, Crystal Packing, C atechol, X -R ay

A discrete am m onium catecholate hydrate o f the com position N H 4[C6H 4( 0 H ) 2][C6H 4( 0 H ) 0 ] • 0 .5 H 20 has been isolated and characterized by a single-crystal X-ray structure analysis. The crystals are m onoclin ic, space group C 2 /c (N o . 15), Z = 8, a = 24.613(3), b = 8.706(1), c = 11.890(2) Ä , ß = 110.56(1)°. The crystal lattice features a network o f hydrogen bonds, which clearly contribute significantly to the overall stability o f the lattice. The water m olecule is engaged as a donor and an acceptor in as m any as four hydrogen bonds. Surprisingly, the crystalline com pound is air-stable, while anhydrous am m onium catecholate, as obtained by d issolving catechol in dry liquid am m onia, is quickly oxidized in air.

Introduction

Although the binary systems phenol/amine, catechol/amine and catechol/ammonium have attracted some interest in the past, only few prod­ucts have actually been isolated [1-5] and struc­turally characterized [1,3]. Compounds which can be referred to as phenol or catechol ammonium complexes (especially those with quarternary am­monium cations) have been discussed as interme­diates in a number of important reactions, such as e.g. the alkylation of phenols under phase transfer conditions [6 , 7]. Furthermore these complexes may also be significant in the biochemistry of ca­techol as a target for ammonium salts, particularly if one of the components is attached to a bio­polymer [2], As part of our studies of catechol complexes of biorelevant cations [8, 9], we now report the preparation and crystal structure of N H 4[C6H 4(0 H )2][C6H4(0 H )0 ] • 0.5 h 2o .

ExperimentalCrystals of the title compound were obtained

during an attempt to reproduce the literature prep­aration of an ammonium catecholate polyberyllate complex of the composition (NH4)4[Be3(C6H 40 2)5]-2H 20 [9, 10]. Toarefluxing mixture of 3.16 g (28.70 mmol) catechol and an ex­cess of beryllium hydroxide in 40 ml water, 1.72 ml

* Reprint requests to Prof. Dr. H. Schmidbaur.

Verlag der Zeitschrift für Naturforschung,D-72072 Tübingen0932-0776/93/0700-0958/$ 01.00/0

of an aqueous solution of ammonia (25%; 0.39 g N H 3, 23 mmol N H 3) are added. The reaction mix­ture is refluxed for 3 h under nitrogen. After filtra­tion, the volume of the resulting clear solution is reduced to one third, and 1 ml of an aqueous solu­tion of ammonia (25% N H 3) is added. After 12 h at4 °C colourless, airstable crystals can be isolated. The elemental analysis of the crystals indicates the composition NH 4[C6H4(0 H)2][C6H4(0 H)0 • 0.5 H20 :

Calcd C 58.53 H 6.55 N 5.59%,Found C 58.37 H 6.54 N 5.54%.

The crystals are suitable for X-ray structure analysis.

Crystallographic dataN H 4[C6H 4(0 H )2][C6H4(0 H )0 ] ■ 0.5 H20 ;

C 120 4H ]5N 0.5H 20 , M rel = 246.265, monoclinic, space group C2/c (Nr. 15), a = 24.613(3), b = 8.706(1), c = 11.890(2) Ä, ß = 110.56(1)°, V = 2385.52 Ä3, Z = 8, Dcalc = 1.371 gem “3, F(000) = 1048, //(M oK a) = 1.0. D ata collection: Syntex P2, diffractometer (M oK a radiation, X = 0.71069 Ä, graphite m onochromator, co-scan, T = -5 0 °C). Lp correction, 1873 independent structure factors, 1501 observed [F0 > 4cr(F0)]. R{R^) — 0.045(0.036) for 223 refined parameters, residual electron density +0.19/-0 .27 eÄ-3. Final atomic coordinates and equivalent displacement parame­ters are presented in Table I. Further details of the crystal structure determination are available on re­quest from the Fachinformationszentrum Karls­ruhe, Gesellschaft für wissenschaftlich-technische Information mbH, D-76344 Eggenstein-Leopolds- hafen, on quoting the depository number CSD 57295, the names of the authors, and the journal citation.

O. Kumberger et al. • Hydrogen Bonding in Crystals o f an Ammonium Catecholate 959

Table I. Fractional atom ic coord inates and thermal displacem ent param eters for N H 4[C6H 4(0 H )J [C 6H 4( 0 H ) 0 ] • 0.5 h 2o .

Table II. Bond distances [Ä] and angles N H 4[C6H 4( 0 H ) 2][C6H 4( 0 H ) 0 ] • 0.5 h 2o .

[°] in

A tom x/a y/b z/c U ec

O l 0.43865(6) 0.2074(2) 0.1393(1) 0.0290 3 0.43124(6) 0.4126(2) -0 .0 2 8 4 (1 ) 0.0320 2 0.46003(8) 0.0238(2) 0.3369(1) 0.0330 4 0.43143(7) 0.6136(2) -0 .1 9 6 2 (1 ) 0.031C l 0.40746(9) 0.0772(3) 0.1282(2) 0 .026C 2 0.41773(9) -0 .0 1 7 3 (3 ) 0.2287(2) 0 .026C3 0.3876(1) -0 .1 5 3 1 (3 ) 0.2226(2) 0.033C 4 0.3459(1) -0 .1 9 7 4 (3 ) 0.1149(3) 0.038C5 0.3348(1) -0 .1 0 6 8 (3 ) 0.0146(2) 0.038C 6 0.3652(1) 0.0298(3) 0.0207(2) 0.033C 7 0.37910(9) 0 .4756(2) -0 .0 9 6 4 (2 ) 0.025C 8 0.37882(9) 0.5800(3) -0 .1 8 5 3 (2 ) 0.026C 9 0.3274(1) 0 .6485(3) -0 .2 5 5 9 (2 ) 0 .034CIO 0.2759(1) 0.6112(3) -0 .2 3 9 3 (3 ) 0.042C l l 0.2760(1) 0.5084(3) -0 .1 5 2 0 (3 ) 0.041C 12 0.3276(1) 0.4408(3) -0 .0 7 9 7 (2 ) 0.0330 5 0.50000 0.4047(3) -0 .2 5 0 0 0 0.037N 0.0330(1) 0.2626(3) 0.4582(2) 0.034

Results

The crystal structure determination confirms the composition NH4[C6H4(0H )0][C 6H4(0H )2] 0.5H20 already suggested by the microanalysis data of the unexpected product obtained from a reaction mix­ture containing a stoichiometric am ount of beryl­lium hydroxide. In the lattice there is one catechol molecule, one catecholate monoanion, one am ­monium cation and half a water molecule. (The oxygen atom O 5 of the water molecule lies on the crystallographic two-fold axis). The crystals are monoclinic (space group C 2/c) with 8 formula units in the unit cell. The geometrical parameters of the catechol and catecholate components show no significant deviations from values determined for comparable compounds [1,3]. The carbon phenolate oxygen distance (C 1 - O 1) is significant­ly shorter than the carbon phenol oxygen distances (Table II).

0 1 - C l0 2 - C 2 C 1 - C 2 C 2 - C 3 C 4 - C 5 C 7 - C 8 C 8 - C 9 C 1 0 -C 1 1

0 1 - C 1 - C 2 C 2 - C 1 - C 60 2 - C 2 - C 3 C 2 - C 3 - C 4 C 4 - C 5 - C 60 3 - C 7 - C 8 C 8 - C 7 - C 1 20 4 - C 8 - C 9 C 8 - C 9 - C 1 0C 1 0 -C 11 - C 12

1.350(3)1.388(3)1.399(3)1.383(3)1.375(4)1.392(3)1.384(3)1.370(4)

119.0(2)117.4(2)118.9(2)119.8(2)120.3(2)117.6(2)119.4(2)122.8(2)119.9(2)120.2(3)

0 3 - C 70 4 - C 8 C 1 - C 6 C 3 - C 4 C 5 - C 6 C 7 - C 1 2 C 9 - C 1 0 C 1 1 - C 1 2

0 1 - C 1 - C 60 2 - C 2 - C 1 C 1 - C 2 - C 3 C 3 - C 4 - C 5 C 1 - C 6 - C 50 3 - C 7 - C 1 20 4 - C 8 - C 7 C 7 - C 8 - C 9 C 9 - C 1 0 - C 1 1 C 7 - C 1 2 - C 1 1

1.368(3)1.377(3)1.397(3)1.385(3)1.393(4)1.384(3)1.388(4)1.390(4)

123.6(2)119.5(2)121.7(2)119.9(2)120.9(2)122.9(2)117.1(2)120.1(2)120.2(3)120.2(2)

In the three-dimensional structure, the ammon­ium cations are linked with the catechol and ca­techolate molecules through a network o f hydro­gen bonds (Table III, Fig. 1).

The water molecule is engaged in hydrogen bonds both as a donor and as an acceptor: The hy­drogen atom H 16 and the symmetry-equivalent atom H 16' form hydrogen bonds with the phenol oxygen atoms 0 4 and 0 4 ' (Fig. 1), while the oxy­gen atom O 5 is linked to two ammonium cations via hydrogen bonds ( N - H 1 4 - 0 5 ) (Fig. 1). The catechol molecule and the catecholate anion are connected by hydrogen bonds between the pheno­late oxygen atom O 1 and the phenol oxygen atoms 0 3 ( 0 1 - H 2 - 0 3 ) and 0 4 ( 0 1 - H 3 - 0 4 ) .

The three-dimensional lattice features corrugated layers, built from catechol molecules C6H4(OH)2 and catecholate anions C6H4(0 H )0 - , which are connected by hydrogen bonds (Fig. 2). The water molecules and the ammonium cations are interca­lated between the catechol/catecholate sheets and

X - H Y X - H H - Y X - Y X - H - Y

0 3 - H 2 - • O 1(a) 0.922 1.730 2.636 166.80 4 - H 3 " O 1(b) 1.015 1.550 2.556 170.0N - H 14-'•0 5 (c ) 1.117 1.633 2.739 169.80 5 - H 16 • 0 4 ( a ) 0.957 1.750 2.707 178.7

Sym m etry positions o f atom Y: a) x, y , z; b) x , 1 —y, z -0 .5 ;c) 0 .5 - x , 0 . 5 - j , —z.

Table III. Prom inent hydrogen bonds in the struc­ture o f N H 4[C6H 4( 0 H ) 2][C6H 4( 0 H ) 0 ] • 0.5 H 20 .

960 O. Kumberger et al. • Hydrogen Bonding in Crystals o f an Ammonium Catecholate

Fig. 1. Crystal structure o fN H 4[C6H 4( 0 H ) 2][C6H 4( 0 H ) 0 ] • 0.5 H 20 with atom ic num bering (O R T E P , displacem ent parameters at the 50% probability level; H atom s with arbitrary radii.).

connect adjacent “organic layers” by hydrogen bonds (Fig. 2).

Discussion

The present investigation has established the existence of a discrete ammonium catecholate complex of the composition N H 4[C6H4(OH)2][C6H 4(OH)0] 0 .5H 20 . The crys­tal lattice features a network of hydrogen bonds, which clearly contributes significantly to the over­all stability of the lattice. The crystal water mole­cule appears to be a key-stone of the framework, which is engaged in as many as four hydrogen bonds. It is noteworthy that the crystals of the title compound are air-stable. By contrast, anhydrous ammonium catecholate, which is obtained by dis­solving catechol in liquid ammonia, followed by evaporation of the excess of ammonia, is quickly oxidized in air [11], It is tempting to attribute the greater stability of the title compound in air to the stabilizing effect o f the hydrogen bonding network in the crystal lattice. Inclusion of a water molecule and a catechol molecule leads to a balance of hy­droxyl, phenolate and ammonium functions in this system of hydrogen bonds, which make the crys­talline phase less susceptible to oxidation and hydrolysis. N ot unexpectedly therefore, aqueous solutions of ammonium catecholates are readily oxidized.

This work has been supported by Deutsche For­schungsgemeinschaft (Leibniz-Programm) and by Fonds der Chemischen Industrie (Doctorate Fel­lowship to O. K.).

Fig. 2. Crystal packing inN H 4[C6H 4(OH)2][C6H 4(O H )0 ] 0 .5 H 20 . O: heavy shad­ing; N: light shading; C: large white; H: small white. (T w o arrows mark tw o adjacent tw o-fold axes, which are perpendicular to the horizontal glide plane).

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