Canadian Journal of Chemistry

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1 Canadian Journal of Chemistry VOLUME 46 FEBRUARY 15, 1968 NUMBER 4 Crystal and molecular structure of the pyridine solvate of bis(8-hydroxyquinoline)silver(i) J. E. FLEMING^ AND H. LYNTON~ Departtnent of Cliemistry, Uni~~ersity of Victorin, Victorin, Rritisl~ Columbin Received June 20, 1967 Crystals of the pyridine solvate of bis(8-hydroxyquinoline)silver(i), Ag(C911fiNO)C9HfiNOH.C5H5N, are monoclinic, space group P21/n, with cell dimensions n = f 0.01 A, b = f 0.01 A, c = f 0.01 A, P = 92.6 f 0.2", Z = 4. Atomic parameters have been determined from a threedimensional analysis using 2163 independent intensities to which no absorption corrections were applied. Refinement was by observed and calculated differential syntheses using isotropic temperature factors. The final discrepancy index is R = The coordination of the silver atom is distorted tetrahedral, with bonds to the phenolic oxygen and ring nitrogen atoms of both 8-hydroxyquinoline molecules. Adjacent bis(8-hydroxyquinoline)silver molecules are linked by a hydrogen bond between two oxygen atoms. The pyridine molecules are held in the lattice by van der Waals' forces. Canadian Journal of Chemistry, 46, 471 (1968) Introduction The reaction of 8-hydroxyquinoline with silver(1) ion to give a metal chelate is well established (1,2). Both a yellow and a green form have been prepared and it has been shown that the two are identical, with the green form containing a small amount of free silver (3). The chelate has the structure Ag(C9H6NO)C9H6NOH, and is diamagnetic, as expected for a silver(1) compound (2). Therinal decomposition curves show that it is not possible to remove one of the 8- hydroxyquinoline molecules to leave the 1 :I chelate Ag(C6H9NO) (4). This indicates that both 8-hydroxyquinoline molecules are bonded directly to the central silver atom. In a recent study of the extraction into chloroform of Ag(1) ion with 8-hydroxyquinoline, measurement of stability constants led Hala (5) to conclude that the 8-hydroxyquinoline molecules act as bidentate ligands and that the structure is tetrahedral. A literature survey shows that evidence for a tetrahedral arrangement around the silver atom in Ag(1) compounds with ]Present address: Christ's Hospital, Hertford, Herts., England. 2Present address: Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick. coordination number four has been reported in several papers. Preliminary X-ray investigations of tetrakisthioacetamide-argentous chloride (6), tetrakis(monoiodotrialkylphospl~inesilver), and tetrakis(monoiodotrialkylarsinesilver) (7), and the completed structure deterininations by Brink et al. of Cs2AgC13, Cs2Ag13, Rb2Ag13, K2Ag13, (NH4)2Ag13, and CsAg213 (8-10) support this view, as do the studies of Hall, Plowman, and Preston on the infrared spectra and cond~ictivities in nitrobenzene of some complexes of Ag(1) (11). Crystallographic Data A specimen of the compound was prepared by the method of Nakatsuka (I), and recrystallized from pyridine to give thin yellow needles of the adduct Ag(C6H9NO)C6H9NOH.C,H5N. Magnetic susceptibility measurements showed the coinpound to be diamagnetic as expected. The space group was established as P21/a, and precise cell dimensions were determined using Weissenberg photographs calibrated with aluminium powder. The crystal data are given in Table I. Intensity Data The crystal chosen for intensity data collection was about 0.25 inm long and had a roughly

2 472 CANADIAN JOURNAL OF CHEMISTRY. VOL. 46, 1968 square cross section with an average thickness of 0.17 mm. The long direction corresponded to the a crystallographic axis. The calculated optimum thickness, 2/p, was 0.23 mm. No absorption corrections were applied to the data. TABLE I Crystal data for Ag(C9H6NO)CgH6NOH.CjH5N System Molecular weight Space group n 6 C P v Dm (by flotation) z Dc p, absorption coefficient for Cu Ka Systematic absences Monoclinic P21/a 10.87&0.01 A 10.65&0.01 a 16.70&0.01 A 92.6~t0.2" g cm gcm cm : 11 = 2n + 1 OkO: k = 2n + 1 Using the multiple filmpack technique, equiinclination Weissenberg photographs were taken of the hol, hko, and OkI-8kl layers. There were calculated to be 4510 permitted independent reflections within the range of the Cu Koc radiation; 3555 reflections were within the range covered by the photographs, and 2163 of these were above the minimum intensity limit for observation. The intensities of all reflections were estimated by visual comparison with a calibration strip prepared using a suitable reflection from the intensity crystal. Lorentz-polarization factors were then applied to all intensity data. Structure Analysis Patterson syntheses3 were computed for the hko, 1~01, and Okl zones and from these syntheses the positions of the silver atoms were found unambiguously. A three-dimensional Fourier synthesis was computed and from this, the coordinates of all other atoms in the structure were derived. It was noted that, whilst the electron density distribution in the region of the two 8-hydroxyquinoline rings was well shaped, the electron density distribution in the pyridine ring was somewhat irregular. 3All com~utations were carried out on an I.B.M computer using the programs of Ahmed, Gabe, Mair, and P~PPY (12). The atomic coordinates were refined by iuealls of observed and calculated differential syntheses. Initially all atoms of the same element were given the same isotropic temperature factor. Teinperature factors were then adjusted individually during the refinement. No difficulty was experienced in refiniilg the positions of the atoms in the 8-hydroxyquinoline molecules, and after several cycles had reduced the shifts to small values, the atomic arrangement in these molecules was in good agreement with that found in other metal chelates containing 8-hydroxyquinoline. In the pyridine molecule, however, the two atoms designated C(l1) and C(12) had positions which would have given interatomic distances incon~patible wit11 what is known of the geometry of the pyridine ring (13-15). The nitrogen atom could not be identified at this stage, so all pyridine atoms were given carbon scattering factors. All high intensity reflections in the range sin2 e < were examined to see if any appeared to show extinction. There were 22 reflections for which JFoI << IFcI. The IFo( values of these reflections were modified by adding either 114, 112, or 314 ~AFI depending on the magnitude of IFcl, sin2 0, and AF(/IFo( for that particular reflection. Initially, the scaling of the intensities had used only reflections common to two or more photographs. The progress of the analysis now permitted each layer of reflections to be scaled directly with the model. Refinement was continued. The 8-hydroxyquinoline molecules had large shifts indicated on the first cycle only, and their refinement appeared to be near completion. The positions of atoms C(l1) and C(12) were still improbable. The remaining four atoms refined sufficiently for tentative identification of the nitrogen atom, and the appropriate scattering curve was applied to this atom. Assuming a planar symmetric ring for the pyridine inolecule aad carbon-carbon distances of the order of 1.4 A (13-15), possible positions for C(11) and C(12) were calculated. These were found to be positions of appreciable electroll density (see Table 111). These coordillates were used in the calculation of the final set of structure factors. The temperature factors assigned to C(11) and C(12) were an average of those used for the other pyridine ring atoms. The refinement was stopped when the atomic coordinates of all the atoms undergoing refine-

3 FLEMING AND LYNTON: CRYSTAL AND MOLECULAR STRUCTURE 473 ment began to oscillate, and when the adjustment 15 observed reflections showed relatively high of the temperature factors had given good agree- discrepancies, whilst 46 unobserved reflections ~nent between observed and calculated values of were in poor agreement. the electron densities, slopes, and curvatures. At this stage the average coordinate shift indicated TABLE 11 for the 8-ll~drox~quinoline atoms was A Fractional atomic coordinates, and e.s.d.'s (,%). All values (less than one fifth of the e.s.d.) for the atoms in have been multiplied by 104 the pyridine molecule 0.01 A. Atom x Y z "(x) "(Y) ~(z) Results Ag The final coordinates are listed in Table 11, and o(l) N(1) the electron densities, mean curvatures, and C(l) isotropic temperature parameters in Table 111. ~(2) The arrangement of the atoms in the bis(8- C(3) C(4) ~ydroxyquinoline)silver nlolecule is shown in C(5) Fig. 1. C(6) C(7) C(8) C(9) (6) O(1:) N(l ) C(1') C(2') C(3') { :; C(6) C(7') C(8:) C(9 ) N(2) C(10) C(11)" C(12)" C(13) C(14) "Denotes calculated atomic positions for which no e.s.d.'s can be quoted. The e.s.ds7s (estimated standard deviations) for the atomic parameters were calculated according to the expression of Cruickshank and Robertson (17), using the observed data only. The results are included in Table 11. No e.s.d.'s can be quoted for C(l1) and C(12) as those atoms had been FIG. 1. The arrangement of the atoms in the bis(8- placed by calculation. I~ydroxyquinoline)silver(I) molecule. Table V gives the intramolecular distances in the structure together with their e.s.d.'s which A final set of structure factors4 was computed; were estimated for atomic coordinate errors these gave a discrepancy index of R = A using the expression of Ahmed and Cruickshank detailed analysis (16) of the agreement of individ- (18). NO corrections were applied for errors in ual reflections is summarized in Table IV. 0111~ the cell dimensions. Once again, no e.s.d.'s can be quoted for bonds to the atoms C(11) and 4These data have been placed in the Depository of C(12). Table V1 gives the bond angles and their Unpublished Data. Photocopies may be obtained upon e.s.d.'s calculated according to the equation request to: Depository of Unpublished Data, National given in ref. 19. ~ ~ VII bgives l solne ~ of Science Library, National Research Council of Canada, Ottawa, Canada. intern~olecular distances shorter than 4.0 A.

4 474 CANADIAN JOURNAL OF CHEMISTRY. VOL. 46, 1968 TABLE I11 TABLE IV Electron densities (e A-31, mean curvatures (e A-51, and Agreement summary isotropic temperature parameters (A2) (overall discrepancy index R = 0.116) Atom p,,, PC PO PC" Bi0 Category Limits Number Ag observed reflections (6.5 < IF,! < 298.6) 1 I4FI < 1.OiFtt,l:', or 2031 cis? ~(6'j C(7') lafi/ifoi <2R 1.OF~I,<~AFI<~.OIF,I,~, or 117 2R< laf!/if,! <3R 3 2.0F~l,< 4Fl<3.OIFtl,), or 9 3R< IAFI/!F,I <4R 4 3.OFtl,<AFl <5.0iFtt,l, or 6 4R< 14FI/!FoI <6R 1392 unobserved reflections (F,~,,, ) 1 <1.O!Ftt,l OIFtl,l< IF, <2.0(Ftl,l OiFtl,j< <3.0iFtl,l OFtl,J<!Fc <4.OFtl,I 6 *IFtbl = threshold amplitude = 1.4 to TABLE V C(8:) Intramolecular distances with their e.s.d.'s C(9) in parentheses (A) N(2) oo C(10) Interatomic ( I I ) distance Length C(12)'$ C(13) The bis(8-hydroxyquinoline)silver molecule C(14) A* B" $:Atoms wit11 calculated atomic positions. &-Nu) (0.004) (0.004) Ag-O(l) (0.005) (0.004) Least squares planes through each of the 8-0(1)-C(8) (0.008) (0.007) l~ydroxyquinoline lnolecules were calculated :{;)I${;) (0.009) (0.010) (0.009) (0.012) (Table VIII). Distances of atoms from these ~(2)-~(3) (0.011) (0.010) planes are given in Table IX. C(3)-C(4) (0.010) (0.011) c(4)-c(5) (0.010) (0.011) C(5)-C(6) (0.010) (0.011) Discussion C(6)--C(7) (0.010) (0.011) C(7)-C(8) 1,403 (0.009) (0.009) The silver atom is bonded to both 8-hydroxy- C(8)-C(9) (0.009) (0.008) cluinoline molecules through the phenolic oxygen C(9)-C(4) (0.009) (0.009) C(9)-N(l) (0.008) (0.008) and the ring nitrogen atoms. The arrangement about the silver atoin is distorted tetrahedfa], the The pyridine molecule angles being: O(1)-Ag-N(1) = 71.7"; O(1')- N(2)-C(10) 1.29 (0.01) Ag-N(1') = 72.0"; O(1)-Ag-N(1 ') = 113.9"; C(11 c(lo)-c(l )PC( 12) '1 1.44r O(1 ')-Ag-N(1) = 117.2". C(12)-C(13) 1.40t The Ag-0 bond lengths of and C(13)-C(14) 1.37 (0.01) Aq are significantly different (t = 8.31) according C(14).-N(2) 1.32 (0.01) to CrLlic~<sllanl<'s criterion (17). Sumlnaries of c o ~ ~ d ; ~ ~ the ~ unprimed, t O coordinates in Table 11, B to the primed Ag-0 distances in a llunlber of colnpounds are?these lengths in\zol\re atoms \\!it11 calculated atomic positions. given by Britton and Dunitz (20, 21) and Dickens (22). Consideration of these bond lengths show AgzO and Ag2Pb02; the second contains that they fall into three main groups. The lengths in the range 2.4 to 2.6 A found in comfirst contains lengths in the range 2.0 to 2.1 A pounds such as AgC103, AgCIOj, KAgC03, found in covalent silver compounds such as AgC102, AgN02, wl~icl~ are said to be partially

5 FLEMING AND LYNTON: CRYST AL AND MOLECULAR STRUCTURE TABLE VI Angles with their e.s.d.'s in parentheses (") Angle -- Measure The bis(8-hydroxyquino1ine)silver molecule A* B* The pyridine molecule '" refers to unprimed coordinates in Table 11, B to primed coordinates. TThese angles involve atoms with calculated atomic positions. ionic. Finally, a value of 2.78 A is quoted for a covalent-type bond found in silver fulminate. The lengths found in the present investigation thus lie within the range of values associated with partially ionic Ag-0 bonds. The distance between atom O(1) in one molecule and atom O(1') in an adjacent n~olecule (see Table VII) is A and is the shortest intern~olecular distance in the structure. Comparison of this bond length with those found in hydrogen-bonded cases (23) shows that it is at the low end of the range of values listed, indicating that the pllenolic hydrogen is contained between the two oxygen atoms fornling a strong hydrogen bond. There is some controversy as to whether a hydrogen bond of this length is or is not expected to have the hydrogen atom centrally located. The non-equivalence of the Ag-0 TABLE VII Some intermolecular distances -p.-.-pp x:' y 'L Distance Between two bis(8-hydroxyquino- 1ine)silver molecules o(lf)-o(l) (Dl C(8)-0(1') (D) C(8')-0(1) (D) C(7)-0(11) (Dl C(7')-0(1) (D) c(4'j-c(2/j ( ~ j s$;k;&'g) C(4 ')-C(3 ') (B) C(7)-N(1) (D) C(3')-N(1') (B) Between a bis(8-hydroxyquino- 1ine)silver molecule and a pyridine molecule C(l1)-C(3') (A) 3.48 C(12)-0(1) (B) 3.48 C(l1)-O(1') (C) 3.49 C(l0)-O(1 I) (B) 3.50 C(12)-C(3) (X) 3.53 Between two pyridine molecules C(13)-N(2) (Dl 3.79 :';Atom X is in the niolecule specified by the parameters given in Table 11 and Y is in the molecule specified by the letter in parentheses. These molecules are locatcd as follows. (A) x, y, z (adjacent cell), (B) F, j, E (same cell), (C) 1 - x, 1, + y, 7 (same cell), (D) I. + r,!, - y, z (same cell). bonds in this structure would seem to favor the idea of a nonsymmetric hydrogen bond between the oxygen atoms. The Ag-N bond distances of A and A are not significantly different. There are few precise values available for comparison, but distances of A and A have been reported for silver cyanate (20) and silver thio- cyanate (24). The bond in silver cyanate is said to be strongly covalent. The Ag-N bond lengths found in this structure would appear to be compatible with covalent bonding. It is noted that the metal-oxygen distance is about 0.3 A longer than the metal-nitrogen distance.

6 CANADIAN JOURNAL OF CHEMISTRY. VOL. 46, 1968 TABLE VIII Least squares planes -- Direction cosines X 104 with respect to directions Distance to. Plane a b C+ orlgln Description of plane I hydroxyquinoline molecule, atoms O(1)-C(9) I hydroxyquinoline molecule, atoms O(1 ')-C(9') The calculation of the least squares planes (see Tables VIII and IX) shows that each 8-hydroxyquinoline molecule is substantially planar. The mean distance of an atom from the best plane : i A for the molecule O(1)-C(9) and A for the nlolecule O(1 ')-C(9'). The angle between the two best planes is 89". The Ag atom is displaced by a distance of A from the first plane and A froin the second plane. Figures 2 and 3 show the structure as viewed along the c* and b axes. TABLE IX Deviations (A) from least squares planes. All values multiplied by 103 Plane Plane Atom I Atom I1 Corresponding distances in the two 8-hydroxyquinoline rings in the molecule were compared (see Table V). The average difference between corresponding distances is A, and the largest difference is A. This difference is significant (t = 3.81) according to Cruickshank's criterion (17) and there are three more differences on the border of significance. However, there are no other distinguishing features about these particular bonds, so it is not possible to conclude from this alone whether the two groups are really not chemically equivalent or whether the method of calculation of the e.s.d.'s used in the analysis has given too low a value for the coordinate errors. A literature survey shows that there are a number of recent reports of the structures of 8- hydroxyquinoline metal cllelates (25-34). Accurate values are quoted for the bis(8-hydroxyquinoline)zinc(ii) complex (33), and the a: and p forms of anhydrous bis(8-hydroxyquino1ine)- copper(i1) (32, 34). The nlolecules of the zinc and a-copper complexes are essentially planar, whilst the p-copper coinplex has a distorted planar arrangement. There is good agreement shown between equivalent bond distances in these structures, and a comparison with the bond distances found in the present structure shows no major differences. It would thus appear that FIG. 2. The structure of the pyridine adduct of bis(8-hydroxyquinoline)silver(i) viewed along the c' axis. Solid lines indicate the edges of the best planes through the 8-hydroxyquinoline molecules. The pyridine rings are shown by broken lines.

7 FLEMING AND LYNTON: CRYSTA AND MOLECULAR STRUCTURE 477 Fit. 3. The structure of the pyridine adduct of bis(8-hydroxyquinoline)silver(i) viewed along the b axis. Solid lines show the bis(8-hydroxyquino1ine)silver molecules, with broken lines indicating the hydrogen bonds. The pyridine molccules are omitted for clarity. the 8-hydroxyquinoline groups are not significantly affected by the nature of the central metal atom. It was not possible to refine two atoms in the pyridine molecule and for the four other atoms the positional accuracy is low. The identification of the nitrogen atom is not certain. Examination of the nearest intermolecular approach distances (see Table VII) shows there are no short distances between atoms in a pyridine molecule and a bis(8-1~ydroxyquinoline)silver molecule. This indicates that the pyridine molecule is held in the lattice by van der Waals forces only. The isotropic temperature factors for the pyridine atoms are larger than for similar atoms in the 8-hydroxyquinoline rings. This, coupled with drawn out electron density of at least two pyridine atoms, suggests considerable thermal motion, as might be expected for a molecule subject only to van der Waals forces. The pyridine positions given in Table 11, at best, represent a fit of a reasonable model. This structure analysis gives definite evidence for the existence of tetrahedral bonding in a four-coordinated silver(1) complex, in agreement with the predictions of other workers. Acknowledgments We acknowledge the financial support of the National Research Council of Canada for this work, and we thank H. Lynne Dougan for estimating the intensity data used in the analysis, and Malcolm J. R. Clark for measurement of the magnetic susceptibility of the compound. 1. Y. NAKATSUKA. Bull. Chern. Soc. Japan, 11, 45 (1936). 2. B. P. BLOCK, J. C. BAILAR, JR., and D. W. PEARCE. J. Am. Chem. Soc. 73,4971 (1951). 3. W. W. WENDLANDT and J. HASCHKE. Nature, 193, 1174 (1962). 4. W. W. WENDLANDT and J. H. VAN TASSEL. Science, 127,242 (1958). 5. J. HALA. J. Inorg. Nucl. Chem. 27,2659 (1965). 6. E. G. Cox, W. WARDLAW, and K. C. WEBSTER. J. Chern. Soc. 775 (1936). 7. F. G. MANN, A. F. WELLS, and D. PURDIE. J. Chem. SOC (1937). 8. C. BRINK and C. H. MACGILLAVRY. Acta Cryst. 2, 158 (1949). 9. C. BRINK and H. A. S. KROESE. Acta Cryst. 5, 433 (1952). 10. C. BRINK, N. F. BINNENDIJK, and J. VAN DE LINDE. Acta Cryst. 7,176 (1954). 11. J. R. HALL, R. A. PLOWMAN, and H. S. PRESTON. Australian J. Chem. 18, 1345 (1965). 12. F. R. AHMED, E. J. GABE, G. A. MAIR, and M. E. PIPPY. A unified set of crystallographic programs for the I.B.M computer. Divisions of Pure Physics and Pure Chemistry, National Research Council, Ottawa, Canada. 13. K. E. MCCULLOH and G. F. POLLNOW. J. Chem. Phys. 22,681 (1954). 14. B. B. DEMORE, W. S. WILCOX, and J. H. GOLDSTEIN. J. Chem. Phvs (1954). 15. B. BAK, L. HANSEN, and J.'RASTRUP-ANDERSEN. J. Chem. Phys. 22,2013 (1954). 16. F. R. AHMED and W. H. BARNES. Acta Cryst. 16, 1249 (1963). 17. D. W. J. CRUICKSHANK and A. P. ROBERTSON. Acta Cryst. 6,698 (1953). 18. F. R. AHMED and D. W. J. CRUICKSHANK. Acta Crvst (1953). 19. ~ntkrnat'ionaf ~ablcs for X-ray Crystallography. Vol. 11. The Kynoch Press, Birmingham, England (17). 20. D. BRITTON and J. D. DUNITZ. Acta Cryst. 18, 424 (1965). 21. D. BRITTON and J. D. DUNITZ. Acta Cryst. 19, 662 (1965). 22. B. DICKENS. J. Inorg. Nucl. Chem. 28, 2793 (1966). 23. G. C. PIMENTEL and A. L. MCCLELLAN. The hydrogen bond. W. H. Freeman and Co., San Francisco p I. LINDQUIST. Acta Cryst. 10,29 (1957). 25. B. KAMENAR, C. K. PROUT, and J. D. WRIGI-IT. J. Chem. Soc (1965). 26. A. S. BAILEY and C. K. PROUT. J. Chem. Soc ( 1965). 27. C. K PROUT and H. M. POWELL. J. Chem. Soc (1965). 28. B. KAMENAR, C. K. PROUT, and J. D. WRIGHT. J. Chem. Soc. A, 661 (1966). 29. C. K. PROUT and A. G. WHEELER. J. Chem. Soc. A (1966). 30. C. K. PROUT and A. G. WHEELER. J. Chem. Soc. A, 469 (1967). 31. J. E. LYDON and M. R. TRUTER. J. Chem. Soc (1965). 32. G. J. PALENIK. Acta Cryst. 17,687 (1964). 33. G. J. PALENIK. Acta Cryst. 17,696 (1964). 34. R. C. HOY and R. H. MORRISS. Acta Cryst. 22, 476 (1967).