Polyhedron Vol. 5. No. 12, pp. 210!-2111, 19% Printed in Great Britain.

027775387/86 53.00 + .LW 0 1986 Pergamon Journals Ltd.

COMMUNICATION

CRYSTAL STRUCTURE OF SODIUM IODIDE l (DIGLYME): AN UNPRECEDENTED BRIDGING ROLE FOR DIGLYME

ROBERT E. MULVEY*

Chemistry Department, Durham University, South Road, Durham DHl 3LE, UK.

WILLIAM CLEGG*

Department of Inorganic Chemistry, The University, Newcastle upon Tyne NE1 7RU, U.K.

and

DONALD BARR and RONALD SNAITH

Department of Pure and Applied Chemistry, Strathclyde University, 295 Cathedral St., Glasgow Gl lXL, U.K.

(Received 18 April 1986; accepted 23 June 1986)

Abstract-The diglyme adduct of sodium iodide, NaI * (CH30CH,CH&0, has been structurally characterized by X-ray diffraction. It forms infinite zig-zag chains which, unlike most complexes of the salt, retain Na-I bonds. In addition, diglyme molecules bridge pairs of Na atoms through four-co-ordinate 0 atoms, so representing a new role for this neutral oxygen donor.

Diglyme {di-(2-methoxyethyl)ther [(CHJOCH2 CH,),O]}, a high-temperature ether solvent (b.p. 162°C) which was first prepared in 1925,’ has for many years been widely employed in both organic and inorganic synthesis.2 A powerful sequestering agent, it is very effective in solvating cations of sodium salts, a property which facilitates reactions of “ionic” compounds in non-polar media. Research chemists engaged in structural studies of transition- metal species have found diglyme to be a particularly useful solvent as it frequently gives rise to stable, crystalline complexes: crystal structures of diglyme- containing Ti, Cr, Zr, MO and W systems have been reported recently in the literature.3-7

In the course of seeking a mixed-metal cluster of Li and Na we have synthesized (unintentionally) NaI * diglyme, which to the best of our knowledge has never been previously isolated. Surprisingly, no diglyme adduct of a sodium salt (or indeed of a

*Authors to whom correspondence should be addressed.

simple salt of any other alkali metal) appears to have been structurally determined by X-ray diffraction. Therefore we have carried out a structure analysis of the title compound.

EXPERIMENTAL

The method which produced NaI. diglyme was explored with a view to incorporating sodium into a lithium imide cluster, specifically the trigonal antiprismatic hexamer [LiN=C(Ph)Buq,,’ which is readily accessible from equimolar proportions of LiPh and Bu’CEN. Accordingly, LiPh (5.0 cm3 of a 2 M solution in ether-cyclohexane, 10.0 mmol) was added dropwise to a chilled mixture of NaI (OSg, 3.3 mmol) and diglyme (8.0cm3, 56.0 mmol) in a Schlenk tube under an atmosphere of dry, oxygen- freenitrogen.FollowingavigorousreactionBu’eN (1.1 cm3, 10.0 mmol) was added, generating a crimson solution. Cooling to 0°C alforded highly moisture- sensitive, colourless, needle-like crystals, identified as NaI * (CH30CH2CH&0, m.p. 78°C; cf. NaI itself,

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2110 Communication

661°C. (Found: C, 25.7; H, 5.0; Li, 0.0; I, 43.8; Na, 8.1%. C6H,,INaOJ requires: C, 25.4; H, 4.9; I, 44.7; Na, 8.1; 0, 16.9%.) A second product, an orange solid, has not yet been characterized.

A subsequent attempt to prepare the complex directly from anhydrous NaI and diglyme proved successful, although the crystals obtained were of an inferior quality. To effect complete dissolution of the salt a lo-fold excess of hot diglyme @WC) was required. The complex was rapidly precipitated, however, when the solution was agitated or cooled by a few degrees.

Crystallography

C6H,,INa0,, M = 284.1, orthorhombic, Fddd, a = 7.9147(3)& b = 23.1492(7)& c = 23.7448(8)& v = 4350.5 A3, Z = 16, D, = 1.735gcm-3, F(OO0) = 2208, p = 2.92mm- ’ for MO-Ka radiation (2 = 0.71073 A). Of 1179 reflections measured with a Siemens AED diffractometer at 293 K (28,,,= 50”), and corrected for absorption by semi-empirical methods, 966 were unique (Rin, = 0.016), and 762 with F > 4a(F) were used for structure determi- nation by Patterson and difference syntheses.’ Blocked-cascade refinement to minimize wA2 [A = IF,,1 - IFJ; w-l = a2(F)] with anisotropic ther- mal parameters for non-H atoms, constrained H atoms [C-H = 0.96& H-C-H = 109.5”, U(H) = 1.2U,,(C)] and an extinction correction Fi = F,/(l + xF:/sin 20)“4 [x = 4.0(2) x lo-‘] gave R = 0.025, R’ = (E wA~/EwF,~)“~ = 0.024, a satisfactory analysis of variance, and no significant features in a final-difference map. Tables of atomic co-ordinates and other crystallographic data have been deposited with the Editor and the Cambridge Crystallographic Data Centre.

RESULTS AND DISCUSSION

The molecular structure consists of polymeric chains (viewed end-on in Fig. 1) of NaI * diglyme units. These chains are built-up in a zig-zag arrange- ment (Fig. 2). Sets of parallel two-fold axes of sym- metry pass through the I and O(1) atoms, with a second, perpendicular set passing through the Na atoms, both sets being perpendicular to the chain direction. Table 1 gives the important bond lengths and angles. The Na-I bonds are marginally shorter in length [3.164(l) A] than the closest Na-I dis- tances in the salt itself (3.231 b;),” reflecting the lower co-ordination state of the I atoms in the diglyme complex (i.e. 2 vs 6). The fact that Na-I bonds are retained at all is highly surprising. Nor- mally complexation results in “solvent-separated”

Y X

Fig. 1. Projection of NaI diglyme along the x-axis: large dots, C; small dots, H, small circles, 0; large circles, Na;

shaded circles, 1.

Table 1. Bond lengths (A) and angles (“)”

Na-I 3.164(l) Na-O(2) 2.427( 3)

O(2H2) 1.427(5)

C(lW(2) 1.481(6)

Na-I-Na(a) 86.8( 1) I-Na-O(2) 93.7( 1) I-Na-I(b) 146.8( 1) 0(2kNa-I(b) 110.7( 1) O(2)-Na-O(lb) 150.6(l)

Na--O(lW(l) looS(2)

C(lk-O(IkNa(a) 119.7(2)

Na--0(2F(2) 117.0(2)

C(2tO(2~(3) 110.8(3)

0(2tc(2tc(l) 109.7(3)

Na--O( 1)

O(lW(1) 0(2w(3)

I-Na-0( 1) 0( l)---Na-O(2) 0( lt_Na-I(b) O(l)--Na-O(lb) O(2)--Na-O(2b) Na-O(l)---Na(a) C(lWW-CUa) Na--0(2W(3) O(l)--C(lk--C(2)

2.714(2) 1.432(4) 1.423(6)

83.3( 1) 67.5( 1) 85.8( 1)

141.1( 1) 85.4(2)

106.5( 1) 110.8(4) 120.1(3) 109.8(3)

“Symmetry operators: (a) 3 - x, $ - y, z; and (b) $ - x, y, $ - z.

Communication

ion pairs, particularly with chelating ligands like diglyme but even in the case of ligands with only one co-ordinatively active atom; X-ray structure analyses of tris(acetone)- and tris(methanol)- Na+I-“,‘a exemplify this point. Our structure is more akin to that of NaI . (H,0),.13 This complex consists of sheets composed of an hexagonal array of octahedrally co-ordinated Na atoms, with each Na being linked to its three neighbouring Na atoms by a centro-symmetric pair of I atoms [at interatomic distances of 3.210(6) and 3.260(11) A] or water mol- ecules. The environment of the metal atoms in NaI . diglyme (Fig. 2) is likewise octahedral; two opposite sites are occupied by I atoms while oxygens from independent diglyme molecules participate in two terminal bonds to each Na. To complete the six-fold co-ordination ,arrangement, however, the central 0 atoms [O(l)] of the diglyme molecules bridge between pairs of Na atoms. This is the first example of pc,-bonding involving diglyme. In common with neutral oxygen donors in general, diglyme usually attaches terminally, through ~-CO- ordinate 0 atoms, to metal atoms. Examples are

(diglyme)CdCMn(CO)S1,,‘4 (~~-N~X$:rl~-Gd-b) (~-C5H5)~Ti~C(~‘:~5-C~H4)(~-C~~~)3Ti23 ‘. Ch- C,H,),(diglyme)Ti] . diglyme” and Moa(Oa- CC,H,), . 2(diglyme),16 where the ether functions as a tri-, bi- and monodentate ligand, respectively. A comparison can be made between the Na-0 bridge bonds in this system and those in “washing-soda”, which is composed of

CNM-WholZ+ and CO:- ions. In the cations, two sodium-water octahedra share an edge making eight terminal and four bridging Na-0 bonds (range of lengths: in the former, 2.39-2.51 A; in the latter, 2.31-2.49 A), l7 The interatomic distances in the diglyme complex, refined to a final R value of 0.025 (cf. 0.18 in the decahydrate), provide a more precise comparison of the different types of Na-0 bond, as those in a bridging mode are distinctly longer [2.714(2) A] than those in a terminal arrange- ment [2.427(3)A]. Finally, it should be noted that the title compound as isolated is insoluble in hydro- carbon solvents but is soluble in diglyme itself. The conclusion drawn is that excess of a strongly coordinating solvent such as diglyme cleaves the polymeric chains and presumably breaks all metal- halogen bonds, separating the metal ions to give Na(digIyme)z . . . I - solution species.

Fig. 2. Part of the zig-zag chain structure. H atoms ha ,ve

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Acknowledgements-We thank the SERC for financial support including a research grant towards crystallo- graphic apparatus, and Professor K. Wade for helpful

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discussion. 17.

been omitted for clarity.

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