Inorg. Chem. 1992, 31, 1902-1908
1902
Contribution from the Department of Chemistry, University of Florence, Via Maragliano 75/77, 50144 Florence, Italy, Department of Energetics, University of Florence, Santa Marta, Florence, Italy, Institute of Chemical Sciences, University of Urbino, Urbino, Italy, and Department of Inorganic Chemistry, University of Valencia, C/Dr. Moliner 50, 46100 Burjassot, Valencia, Spain
Thermodynamic and Structural Aspects of the Interaction between Macrocyclic Polyammonium Cations and Complexed Anions Andrea Bencini,Ia Antonio Bianchi,*,'" Paolo Dapporto,lb Enrique Garcia-Espaiia,*TlCMauro Micheloni,ld Jose Antonio Ramirez,lc Piero Paoletti,**laand Paola Paolilb Received August 6, 1991 The interaction of polyprotonated forms of [3k]aneNk (k = 7-12) macrocycles with the complexed anions Fe(CN)6&, Co(CN):-, and Pt(CN):has been studied by potentiometry in 0.15 mol dm-I NaClO, solution at 298.15 K, and the stability constants of the second-sphere complexes formed have been determined. The interaction of (Hk[3k]aneNJk+ (k = 7-1 1) cations with PtCIzNMR spectroscopy in 0.1 mol dm-' HCI solutions at 298 K. The crystal structures and Pt(CN)>- has been followed by 19sPt (1) and (H,o[30]aneNlo)(PtC~)z~~6~2Hz0 (2) solid compounds have been determined by of (Hlo[30]aneN10)[Pt(CN)4]s~2H20 X-ray analysis. In (Hlo[30]aneNlo)[Pt(CN)4]s~2H20 (space group Pi,a = 12.710 (3) A, b = 9.839 (6) A, c = 11.630 (3) A; a = 80.91 (4)O, j3 = 89.45 (2)O, y = 77.60 (6)'; V = 1402 (1) A'; 2 = 1; R = 0.032; R, = 0.028) the centrosymmetric decaprotonated macrocycle has an elliptical shape with intramolecular distances between symmetry-related nitrogens of 6.2-1 3.4 A. Two independent Pt(CN):- anions, located outside the macrocyclic cavity, form very short hydrogen bonds with the protonated (space group PI,a = 7.704 (9) A, b = 12.896 (4) A, nitrogen atoms of the ligand. Also in (Hlo[30]aneNlo)(PtC16)2Cls.2H20 c = 14.268 (10) A; a = 108.87 (3)O, j3 = 101.53 (7)O, y = 97.66 ( 5 ) O ; V = 1284 (2) A'; Z = 1; R = 0.058; R, = 0.048) the decacharged macrocyclic cation is centrosymmetric and presents an elliptical shape with intramolecular distances between symmetry-related nitrogen atoms of 9.6-1 1.4 A. In the crystal packing there exists a wide network of intermolecular contacts involving the protonated nitrogen atoms of the macrocycle, PtClz-, Cl- anions, and water molccules. Both PtCIs2- and C1- anions are located outside the macrocyclic cavity. All results have been interpreted and d i s c d in terms of electrostatic attraction and hydrogen-bond formation between the polycharged macrocyclic cations and the complexed anions, as well as in terms of the mutual conformations of both species.
Introduction Macrocyclic polyammonium cations have shown to be good receptors for anionic complexed species.2-8 In recent works we have found that polyammonium cations derived from polyazacycloalkanes of the series [3k]aneNk (k = 7-12) form very stable second-sphere complexes (supercomplexes) with octahedral anions such as Fe(CN)6" and CO(CN)~*!~~,~ The thermodynamic results presented revealed that the interaction between these anionic species and the macrocyclic receptors is mainly coulombic in nature. Furthermore the crystal structure of the solid compound (H8[30]aneNlo)[CO(CN)~] 2c12. 1OH20evidenced the existence of a close hydrogen-bond network between the octacharged (H8[30]aneNlo)8+and C O ( C N ) ~ ~In - .this ~ compound, the polyammonium cation, which presents an elliptical conformation, binds C O ( C N ) ~ outside ~its macrocyclic cavity. This structure suggested that the conformation of the cyclic polycharged cation could produce a geometrical discrimination in anion binding, allowing, for instance, the inclusion of planar anionic species. Indeed we demonstrated that the planar PdC142-can insert into the elongated cavity of (Hlo[30]aneNlo)10+.7However, as shown by the crystal structure of [(PdC14)(Hlo[30]aneNlo)] (PdCW2C14, (a) Department of Chemistry, University of Florence. (b) Department of Energetics, University of Florence. (c) University of Valencia. (d) University of Urbino. Peter, F.; Gross, M.; Hosseini, M. W.; Lehn, J. M.; Session, R. B. J. Chem. Soc., Chem. Commun. 1981, 1067. Dietrich, B.; Hosseini, M. W.; Lehn, J. M.; Session, R. B. J . Am. Chem. Soc. 1981, 103, 1282. Peter, F.;Gross, M.;Hosseini, M. W.;Lehn, J. M. J. Electroanal. Chem. Inierfacial Electrochem. 1983, 144, 279. Pina, F.;Moggi, L.; Manfrin, M. F.;Balzani, V.; Hosseini, M. W.; Lehn, J. M. Garz. Chim. Ital. 1989, 119, 65. Garcia-Espaiia,E.; Micheloni, M.; Paoletti, P.; Bianchi, A. Inorg. Chim. Acta 1985, 102, L9. Bianchi, A.; Garcia-Espafia,E.; Mangani, S.;Micheloni, M.; Orioli, P.; Paoletti, P. J. Chem. Soc., Chem. Commun. 1987, 729. Bencini, A,; Bianchi, A.; Garcia-Espaiia,E.; Giusti, M.; Mangani, S.;Micheloni, M.; Orioli, P.; Paoletti, P. Inorg. Chem. 1987, 26, 3902. Bianchi, A.; Micheloni, M.; Orioli, P.; Paoletti, P.; Mangani, S.Inorg. Chim. Acta 1988, 146, 153. Bencini, A.; Bianchi, A.; Dapporto, P.; Garcia-Espaiia, E.; Micheloni, M.; Paoletti, P.; Paoli, P. J . Chem. SOC.,Chem. Commun. 1990, 7 5 3 . Bencini, A.; Bianchi, A.; Micheloni, M.; Paoletti, P.; Dapporto, P.; Paoli, P.; Garcia-Espaiia, E. J. Inclusion Phenom. 1992, 12, 291. Aragb, J.; Bencini, A.; Bianchi, A.; Domenech, A,; Garcia-Espafia, E. J. Chem. Soc., Dalton Trans. 1992, 3 19.
0020-1669/92/1331-1902%03.00/0
the PdCb2-anion is placed along the minor axis of the receptor's cavity, with the chlorine atoms standing out of the macrocyclic frame, thus forming strong hydrogen bonds with the poly-
ammonium sites of the macrocycle.' Therefore it seems that both the dimensions and conformation of the macrocycle as well as the geometry of the anion and an adequate mutual disposition are required to achieve an inclusive coordination. In this paper we report further investigations on the interaction of other planar Pt(CN)42- and octahedral PtCb2complex anions with the polyammonium cations of the same series and we extend our study on the equilibria involving C O ( C N ) ~ ~ and Fe(CN)6e to all the terms of the series. Experimental Section Materials. AU potentiometric measurements were carried out in 0.15 mol dm-' NaClO, (C. Erba, ACS grade) purified accordingly to the procedure already described? &[Fe(CN),].3H2O (C. Erba, ACS grade) was used without further purification. K'[CO(CN)~](Aldrich, reagent grade) was recrystallized twice from an ethanol/water mixture. Samples of K2PtC16 and K2Pt(CN)4.3H20, purchased from Aldrich, having purity greater than 99% were used without further purification. The hydrochloride salts of [3k]aneNk (k = 7-12) ligands were obtained as previously reported.I0 Crystals of (Hlo[30]aneN10)[Pt(CN)4]5~2Hz0 and (Hlo[30]aneNlo)(PtC~)zC16.2H20 were obtained by slow evaporation at room temperature of 1 mol dm-' HC1 solutions (20 cm-') containing 0.1 mmol of [30]aneNloand 0.3 mmol of K2Pt(CN),.3H20 and KzPtC&,respectively. Satisfactory elemental analyses were obtained for both compounds. Emf Measurements. The potentiometric titrations were carried out, in 0.15 mol dm-' NaCIO4 solutions at 298.15 K, by using the equipment (potentiometer, cell, burette, stirrer, microcomputer, etc.) that has previously been fully described." The reference electrode was an Ag/AgCl electrode in saturated KCI solution. The glass electrode was calibrated (9) Micheloni, M.; May, P. M.; Williams, D. R. J. Inorg. Nucl. Chem. 1978.40, 1209. (10) Micheloni, M.; Paoletti, P.; Bianchi, A. Inorg. Chem. 1985, 24, 3702. Bianchi, A.; Mangani, S.;Micheloni, M.; Nanini, V.; Orioli, P.; Paoletti, P.; Seghi, B. Inorg. Chem. 1984, 23, 1182. Bencini, A,; Bianchi, A.; Garcia-EPpaiia, E.;Giusti, M.; Micheloni, M.; Paoletti, P. Inorg. Chem. 1987,26, 681. Bencini, A.; Bianchi, A.; Garcia-Espaila, E.; Giusti, M.; Mangani. S.;Micheloni, M.; Orioli, P.; Paoletti, P. Inorg. Chem. 1987, 26, 1243. Bencini, A.; Bianchi, A.; Garcia-Espaiia, E.; Micheloni, M.; Paoletti, P. Inorg. Chem. 1988. 27, 176. (1 1) Bianchi, A.; Bologni, L.; Dapporto, P.; Micheloni, M.; Paoletti, P. Inorg. Chem. 1984, 23, 1201.
0 1992 American Chemical Society
Inorganic Chemistry, Vol. 31, No. 10, 1992 1903
Macrocyclic Polyammonium Cations
Table 11. Positional Parameters (X104) with their Esds in Table I. Crystal and Refinement Data for Parentheses for (Hlo[30]aneNlo)[Pt(CN)4I5.2H20 (H [ 301aneNlo)[Pt(CN),] 5.2H20and for (H,o[3O]aneNlo)(PtCls)2C16.2H20 atom xla ylb ZJC mol formula CaHwN3002Pts C ~ O H ~ C ~ I ~ N I O O ~ P ~Ptl ~ 0 -5000 0 mol wt 1972.55 1505.11 488 (8) -2622 (10) N11 1313 (9) 0.1 X 0.2 X 0.5 0.2 X 0.5 X 0.6 cryst dimens, mm 328 (9) -3480 (12) c11 793 (10) a, A 12.710 (3) 7.704 (9) -1757 (8) 1870 (8) -4766 (10) N12 b, A 9.839 (6) 12.896 (4) -1137 (10) 1171 (9) -4824 (10) c12 c, A 11.630 (3) 14.268 (10) -2629 (1) 8331 (1) Pt2 8008 (1) a,deg 80.91 (4) 108.87 (3) -4734 (10) 6859 (8) N21 8839 (9) d, deg 89.45 (2) 101.53 (7) -3972 (12) 7381 (10) c 21 8538 (10) 7 . deg 77.60 (6) 97.66 (5) -913 (11) 7316 (8) N22 9959 (9) v,A3 1402 (1) 1284 (2) -1519 (12) 7647 (10) c22 9215 (10) Z 1 1 -4555 (10) 6223 (9) 9452 (8) N23 space group Pi Pi -3832 (14) 6872 (13) 9061 (11) C23 Dc,g 2.34 1.95 -342 (10) 9717 (8) N24 7314 (9) radiation graphite monochromated -1200 (12) 7555 (10) 9244 (10) C24 Mo-Ka (A = 0.7107 A) -1546 (1) 5724 (1) Pt3 6160 (1) temp, K 298 298 -3431 (10) N3 1 7237 (9) 4176 (9) p , cm-’ 120.1 64.8 -2768 (12) 6837 (11) 4738 (9) C31 range of transm factors 0.09-0.30 0.14-0.29 542 (12) 4627 (9) N32 7819 (10) Ip 0.032 0.058 C32 -210 (13) 7206 (11) 5062 (10) Rwb 0.028 0.048 -3799 (10) 6580 (8) N33 4543 (9) -2938 (13) 5124 (10) 6310 (11) c33 -245 (12) 5462 (10) 6675 (10) c34 494 (9) 7200 (8) N34 5086 (9) as a hydrogen concentration probe by titration of well-known amounts -1563 (7) -712 (9) N1 1928 (8) of HCl with C02-free NaOH solutions and determining the equivalent -1709 (9) -1855 (12) 2865 (10) c1 point by the Gran method,I2 which gives the standard potential Eo, and -1 100 (8) -1867 (12) 3983 (10) c2 the ionic product of water. The computer program SUPERQUADI3 was -2516 (9) N2 3928 (8) 85 (7) used to calculate the equilibrium constants. The titration curves for each 697 (9) -2204 (1 1) 4923 (10) c3 system were treated either as a single set or as separated curves without c4 1625 (8) -3413 (11) 5405 (10) significant variations in the values of the equilibrium constants. Fur2684 (7) 4914 (7) -3312 (9) N3 thermore, the sets of data were merged together and treated simultane2771 (9) -3298 (12) c5 3643 (9) ously to give the final equilibrium constants. To avoid protonation of the -3256 (12) 3966 (9) 3319 (10) C6 Fe(CN)6& anion, all experiments were carried out at a pH higher than N4 4153 (7) 2094 (7) -3413 (8) 3.5. Protonation of the other anions does not take place over the pH c7 -2242 (1 1) 3578 (9) 1226 (10) range (2.5-1 1) investigated, as proved by potentiometric titration. 3895 (9) -19 (10) C8 -2397 (12) specbwrcopy. The 43.00-MHz I9’Pt NMR spectra were recorded at 3056 (7) N5 -2868 (9) -668 (8) 298 K in a Bruker AC-200 spectrometer. All samples were prepared in 2070 (10) -993 (10) c9 -1754 (12) 0.1 mol dm-j HCI. Chemical shifts are referred to solvated PtCb2- and -701 (11) 2266 (9) c10 -2012 (10) P t ( C N ) p under the same experimental conditions. Addition of an excess -3277 (9) 6133 (6) 01 1444 (8) of chloride anion does not affect the chemical shift of the free anions. Collection and Reduction of X-ray Intensity Dnta. A pale yellow Table III. Positional Parameters (X104) with their Esds in (1) and a yellow prismatic crystal of (Hlo[30]aneNlo)[Pt(CN)4]5-2H20 Parentheses for (Hio[30]aneN1o)(PtC16)2C16’2H20 (2) were epoxied prismatic crystal of (Hlo[30]aneN10)(PtCb)2C~2Hz0 to glass fibers and mounted on an Enraf-Nonius CAD4 automatic difatom xla ylb ZJC fractometer, which uses the equatorial diffraction geometry. A summary Ptl 6465 (1) 4440 (1) -2585 (1) of crystallographic data is reported in Table I. Unit cell parameters of c11 5425 (6) 2499 (3) -3284 (3) both compounds were determined by least-squares refinement of difc12 7396 (6) 6369 (3) -1918 (4) fractomcter setting angles of 25 carefully centered reflections. During C13 8481 (7) -3593 (4) 4282 (4) data collections, three reflections were monitored periodically to check C14 4255 (8) 4575 (4) -3880 (4) for the stability of the diffractometer and of the crystals: no loss of 4582 (4) c15 4435 (8) -1587 (5) intensity was noticed during data collections. Intensities were corrected 4313 (4) C16 8654 (7) -1298 (4) for Lorentz and polarization effects; an absorption correction was applied, c1 7592 (23) 3169 (13) 980 (13) once the structures were solved, by using the Walker and Stuart meN1 1933 (9) 6816 (16) 223 (9) th0d.l‘ No extinction correction was applied. 1893 (13) 5858 (20) -838 (11) c2 (Hld30~N1,)[Pt(CN)&2H20. A total of 3916 unique reflections 2258 (12) 4111 (20) c3 -781 (11) (5 5 20 S 45O, Mo K a radiation) were collected of which 3341 having -1867 (10) 1831 (10) 2969 (16) N2 I > 3u(n were used in the structure solution and refinement. The -1954 (12) 2197 (13) 1161 (20) c4 structure was solved by the heavy-atom technique, which showed the -3046 (12) 28 (20) 1790 (13) c5 platinum atoms. Subsequent Fourier maps showed all non-hydrogen N3 -3491 (9) 570 (10) -795 (16) atoms. Refinement was performed by means of the full-matrix least-3152 (12) 218 (12) -2426 (19) C6 squares method. Hydrogen atoms, except those of the water molecule, -1003 (13) -3087 (21) c7 -3747 (12) were included in calculated positions with an overall temperature factor -1374 (9) -4719 (17) N4 -3429 (9) U of 0.05 A2. Anisotropic thermal parameters were used for all the -2637 (12) -5609 (17) C8 -3932 (11) non-hydrogen atoms. The final atomic coordinates for non-hydrogen -7223 (22) c9 -2926 (13) -3589 (11) atoms are listed in Table 11. -6611 (18) N5 -3033 (10) -2553 (10) (Hld30laneN~,)(PtC&)~~2H~O. A total of 4223 unique reflections -3235 (13) -8217 (23) c10 -2084 (12) (5 S 28 S 50°, Mo Ka radiation) were collected of which 3225 having -879 (3) -1084 (3) -3677 (6) C17 I > 3 4 4 were used in the structure analysis. The structure was solved -2581 (6) C18 152 (3) 4256 (3) by the heavy-atom technique, with the use of a Patterson map, which 1966 (3) 510 (3) -1388 (7) C19 showed the position of the platinum atom. Subsequent Fo and A F Fourier 01 -28 (14) 1290 (8) -151 (8) ~
~~~~
~
~
~
(12) Gran, G. Analysr (London) 1952, 77,661. Rossotti, F. J.; Rossotti, H. J . Chem. Educ. 1989, 28, 1188. (13) Gans, P.;Sabatini, A.; Vacca, A. J. Chem. Soc., Dalton Trans. 1985, 1195.
(14) Walker, N.; Stuart, D. D. Acra Crysrallogr.,Sect. A 1983, A39, 158.
syntheses showed the positions of all non-hydrogen atoms; the hydrogen atoms, except those of the water molecule, were included in calculated positions. Refinement was performed by means of the full-matrix least-squares method. Anisotropic thermal parameters were used for all the non-hydrogen atoms. The final atomic coordinates for all the non-
1904 Inorganic Chemistry, Vol. 31, No. 10, 1992
Bencini et al.
Table IV. Dihedral Angles (deg) for the Macrocyclic Ligands
(HIo[~~I~~~NIo)[P~(CN)~IS.~H~~
NlCI-C2-N2 ClC2-N2-C3 C2-NZC3C4 N2C3-C4-N3 C3-C4-N3C5 C4-N3-CS-C6 N3CS-C6-N4 C5C6-N4-C7
-78 (1) 167 (1) 144 (1) 95 (1) -61 (1) -177 (1) 173 (1) 67 (1)
C6-N4C7-C8 N4-C7-C8-N5 C7-C8-NS-C9 C8-NS-C9-C10 N5C9-ClO-Nl’ Cl-Nl-C10’-C9’ ClO’-NI-Cl-C2
174 (1) 103 (1) 73 (1) 76 (1) -150 (1) -178 (1) -81 (1)
(Hlo[30]aneNlo)(PtC16)2C16-2H20 Nl-C1ClO’-NS’ C1O’-Cl-Nl-C2 Cl-NlC2-C3 Nl-C2- = [LH7Pt(CN)4IS' 3.83 (2) 3.36 (3) 5.46 (4) LHg8' Pt(CN),Z- = [ L H B P ~ ( C N ) ~ ] ~ ' 3.71 (7) 4.17 (3) 3.44 (4) 5.83 (4) L H P + Pt(CN):- = [LH9Pt(CN).J7' 3.83 (4) 6.09 (5) Pt(CN)4'- = [LH1oPt(CN)4I8' LHlo'O' 6.67 (4)
+ +
+
" Values in parentheses are standard deviations in the last significant figure. observed from [30]aneNloto [33]aneNll(Figure 7). As previously reported,s a similar increase was observed for the analogous supercomplexes of C O ( C N ) ~and ~ - attributed to the inclusion of the anion into the receptor's cavity.s This increase is so large that Pt(CN),2- interacts with the protonated species of [33]aneN11 stronger than the more charged C O ( C N ) ~(Tables ~V and VII). As previously observed,5 for similar systems in which many species are formed whose formation constants differ very slightly, great care has to be taken in the species selection criteria. Independent techniques to determine both the stoichiometry and the stability constants of the species formed are advisable. In the case of the Fe(CN)64-complexes electrochemical measurements were carried out at different macrocyc1e:anion molar ratios and at various pH's, and the results obtained were in good agreement with those obtained from potentiometry, confirming the 1:1 monomeric nature of the supercomplexed species f ~ r m e d . ~In, ~ the case of Pt(CN)42-the variation of the 195PtNMR chemical shift with the (Hk[3k]aneNk)?anion molar ratio (R) has been followed. A t R > 1, the interaction of Pt(CN)42- with the polyammonium (Hk[3k]aneNk)k+receptors produces a constant upfield shift of the 195PtNMR signal of about 30 ppm with respect to the free anion, which could account for the formation of stable 1:l supercomplexed species. Unfortunately a t R < 1, under the experimental conditions employed, precipitation of polyammonium salts of Pt(CN)42- occurs, preventing then the investigation of whether the formation of polynucleated species in solution takes place or not. The interaction of the octahedral anion PtCl,2- with the polyammonium cations derived for [3k]aneNk ligands ( k = 7-1 l )
can be studied only in very acidic solutions in order to prevent the formation of platinum( IV) macrocyclic complexes. Therefore the equilibria of supercomplex formation a t various pH could not be studied, and only the interaction of this anion with the fully protonated (Hk[3k]aneNJkt species has been followed by NMR spectroscopy in 0.1 mol dm-3 H C l solution. In all cases the presence of the polycharged macrocyclic receptors caused an upfield shift of the Ig5Pt NMR signal with respect to the chemical shift of the solvated PtCb2-. The upfield shift accordinglyincreases with the receptor:PtC16" molar ratio with an increasing fraction of complexed PtClb2-. As shown in Figure 8 for (Hlo[30]aneNlo)l0+the chemical shift reaches a constant value for R > 1. Apart from the main inflection observed a t R = 1, due to the formation of 1:l supercomplexed species, a less evident inflection is present a t R values of about 0.5, which can be ascribed to the interaction of two PtC16*-anions with one macrocyclic molecule. Similar plots have been obtained for all the polyammonium receptors here considered. Conclusion If the thermodynamic (Tables V-VII) and structural data up to now available for the interaction of di-, tri-, and tetracharged complex anions with the series of polyammonium receptors deriving from [3k]aneNk macrocycles are reviewed, a few features can be highlighted. (i) Coulombic Contribution. Cation-anion electrostatic attraction is the driving force in supercomplexation reactions. Coulombic interaction appears as the main contribution to the stability of these new species, regulating the stability order of
Bencini et al.
1906 Inorganic Chemistry, Vol. 31, No. 10, 1992
a
b
C
d
e
f
h
i
Figure 2. Lateral (left side) and top (right side) views of the (H8[30]aneNlo)8+cation in (H8[30]aneNlo)[Co(CN)6]2C12~10H20 (a, b) and of (Hlo[30]aneNlo)'D+ in [(PdC14)(Hlo[301aneNlo)l (PdC14)2C14 (c. d), (Hlo[301aneNIo)[Pt(CN),1~.2H20(e, f ) , and (Hlo[30]aneN,o)(PtCls)2C16.2H20 (h, i). Dotted atoms are nitrogens.
supercomplexes with di-, tri-, and tetracharged anions (Pt(CN)4z< CO(CN)~~< Fe(CN)6") as well as with differently protonated receptors. Furthermore, it seems that electrostatic forces also contribute to regulate the stoichiometry of the species formed. In fact formation of 1:2 receptoranion species have been observed for low-charged anions (PdC142-,PtCb2-), i.e., for highly charged 1:1 complexes.
The few exceptions to the above trends can be ascribed to a particular matching between the conformationa~features of both receptor and anion which optimizes electrostatic and H-bond interactions. (ii) H-BondingContribution. As previously also the crystal structures of the supercomplexed species here reported are characterized by the presence of extensive hydrogen-bond
Inorganic Chemistry, Vol. 31, No. 10, 1992 1907
Macrocyclic Polyammonium' Cations
0..
01
Figure 3.
ORTEP drawing showing the intermolecular hydrogen bonds (
