J. CHEW SOC. DALTON TRANS. 1984 1687 Solid State and Ethanolic Solution Behaviour of N-Tosylglycinate- Copper(ii) Complexes. Crystal and Molecular Structure t of a Strongly Cou pled Po I y rner i c N-Tosy l g I yc i na t oco p pe r (11) Corn p lex Lucian0 Antolini, Ledi Menabue, and Gian Carlo Pellacani * lstituto di Chimica Generale e Inorganica, University of Modena, Via Campi 183, 41 100 Modena, Italy Giovanna Battistuzzi Gavioli and Guilia Grandi lstituto di Chimica Fisica, University of Modena, Via Campi 183, 41 100 Modena, Italy Luigi Pietro Battaglia and Anna Bonamartini Corradi lstituto di Chimica Generale, Centro di Studio per la Strutturistica Diffrattometrica del C. N. R., University of Parma, Via D'azeglio 85, 431 00 Parma, Italy Giuseppe Marcotrigiano lstituto di Chimica, Facolti) di Medicina- Veterinaria, University of Bari, Via Gentile 182, 701 26 Bari, Italy The interaction between N-tosylglycine and the copper(i1) ion in ethanolic solution has been examined.Two compounds of formula [(C~(t~gly0)2),] (green) and Na2[Cu(tsglyNO)2] (blue) (tsglyO and tsglyNO = N-tosylglycinate monoanion and dianion, respectively) were isolated. Crystals of [(C~(tsglyO)~),,] are monoclinic, space group P2,/n, with 2 = 4 in a unit cell of dimensions a = 24.655(3), b = 7.697(2), c = 12,378(3) A, and p = 87.34(8)". Full-matrix least-squares refinement, using 1 677 independent reflections, reached R = 0.052. The structure is built up of one-dimensional polymeric chains of binuclear units, showing the copper(ii) acetate structure, linked via Cu-O(su1phonic) bonds.Its magnetic and spectroscopic properties are interpreted on the basis of the crystal structure. In particular it shows an exchange integral ( - 2 4 of 353 f 4 and a zero-field splitting, D, of 0.35 cm-'. The i.r. spectrum shows multiple sulphonamide absorption bands because only half of the SO2 groups are co-ordinated. By polarographic measurements in ethanol, the number and type of complex species, the equilibria in which they are involved, and their stability constants have been determined. For cNaOH/ccomple. ratios between 1 and 3 the species [C~(tsglyO)~] is the only one present; for ratios >4, [C~(tsglyNO)~] 2- prevails. In this paper we report an investigation of the copper(i1)- N-tosylglycinate system in ethanolic solution.The aim of this work is to determine polarographically the type, number, and stability constants of the complexes present in solution, and to characterize by means of structural, magnetic, and spectro- scopic measurements those separated in the solid state and to compare them. The results can also be compared with those found for N-tosylgtycine in aqueous solution and with those found for the other N-protected (N-acetyl or N-benzoyl) amino acids, previously investigated in the same Experimental Preparation of Polymeric N-Tosylglycinatocopper(ii), [(Cu(t~glyO)~),].-By recrystallizing at room temperature bis(N-tosylglycinato)copper(rI) tetrahydrate (prepared as reported in ref. la) from ethanol, green crystals precipitated (Found: C, 41.5; H, 3.90; N, 5.35; S, 12.3.Calc. for ClxHzo- CuNtOsSz: C, 41.55; H, 3.90; N, 5.40; S, 12.35%). Physical Measurements.-Physical measurements were made on the solid complexes as described in ref. la. The polaro- graphic measurements were performed with an AMEL Multipolarograph model 47 1 ; a saturated Ag/AgCl-KCl- C2H50H electrode was used as reference electrode. All half- ? Supplementary data auailable (No. SUP 23944, 19 pp.): H-atom co-ordinates, thermal parameters, bond distances and angles in the tosyl groups, least-squares planes, structure factors, electrochemical parameters. See Notices for Authors, J. Chern. SOC., Dalton Trans., 1984, Issue 1, pp. xvii-xix. Non-S.I. writs employed: G = 10-4T, = x ~ . ~ . x (106/4n). wave potentials were referred to a saturated calomel electrode (s.c.e.).All measurements were performed at constant tem- perature (25 & 0.1 "C) and drop times were 2, 3, 4, or 6 s. The solutions ([Cu"] = 1 x to 5 x loT4 mol dm-3) were prepared in anhydrous ethanol (C. Erba). NaC104, re- crystallized from this solvent, was used as base electrolyte (0.1 mol dm-3), and the ionic strength of the solution was kept constant (I = 0.1 mol dm-3). The solution of Na(tsgly0) was prepared by dissolving in anhydrous ethanol an equi- molar amount of N-tosylglycine and sodium hydroxide. The literature value of E*Cu2+lCu(Hs) = 0.12 V us. s.c.e. was used to calculate the values of the stability constants. As the polarographic reduction processes of the complexes are irreversible and diffusion controlled, their stability con- stants were determined using two different methods, which only give qualitative values.The first, (A), applied in the presence of ligand excess, uses equation (1) derived from a general expression for the current-voltage characteristic, valid for all degrees of reversibility and ligand concentrations: p = overall stability constant of the complexes (Mn+ + nL- + ML,); cL = total ligand concentration; cL(O,tl) = ligand concentration at the electrode surface and at time tl; q = the greatest number of ligand molecules; p = number of co-ordinated ligand molecules of the complex reduced at the elect rode. The second method (B) replaces the concentrations in the expression of the stability constant with the current values of the species in equilibrium in solution, since, being diffusive, the currents are proportional to their concentrations.In this method the diffusion coefficients of all the species are con- sidered equal, their activity coefficients equal to unity, and the current values are approximate to within ca. 10%.1688 J. CHEM. SOC. DALTON TRANS. 1984 The dissociation constants of N-tosylglycine were deter- mined by pH-metric titrations with a Praizious pH-Meter Knick, using an Ingold glass electrode as indicator electrode, and an aqueous s.c.e. as external reference electrode; a saturated aqueous NH4N03 solution was used as a salt bridge. The glass electrode was calibrated with two buffer ethanolic solutions, of pH 5.08 and 8.31.' E.s.r. measurements were performed on the same or more concentrated solutions than those used for the polarographic analyses ([Cu'+] G 5 x mol dm-3).X-Ray Data Collection.-Lad symmetry, systematic extinctions, compatible only with space group P21/n, and approximate lattice constants were obtained from rotation and Weissenberg photographs (Cu-K, radiation). The unit-cell dimensions were then refined by least-squares methods using 20 values of 15 high-angle reflections accurately measured on En on-line single-crystal automated Siemens AED diffracto- meter. Three-dimensional intensity data were collected at room temperature with the selected crystal mounted with the b axis along the cp axis of the diffractometer. Details specific to the X-ray data collection and processing are reported in Table 1. All data were corrected for Lorentz and polarization effects, but not for absorption in view of the small crystal size and absorption coefficient.Only the 1 677 observed reflections, placed on an (approximately) absolute scale by means of a Wilson plot, were used in the structure determination and refinement. Solution and Refinement of' the Structure.-Neutral-atom scattering factors were used,& with anomalous dispersion corrections applied to all non-hydrogen atoms.*b Refine- ment was by full-matrix least squares with Xw(lFo/ - 1Fc1)2 Table 1. Summary of crystal data collection Diffractometer Radiation Temp. (0,l"C) Crystal system Space group QIA C I A BI" u/A3 Molecular formula M z ow &/g ~ r n - ~ D,/g ~ r n - ~ Reflections measured Scan type 8 range (") Lowest speed (" min-') Max. scan width (") Standards Collected reflections Observed reflections Crystal size (mm) Absorption coefficient (cm-') Absorption correction Siemens AED Ni-filtered Cu-IY, (A = 1.541 78 A) 20 f 2 monoclinic P21/n (Czhs, no.14) 24.655(3) 7.697(2) 12.378(3) 87.34(8) 2 346.4 CisHzoCuN~0sSz 519.85 4 1060 1.47 1.48 (by flotation in CHCIJ f h , +k, + I w-20 3-60 2.5 1.10 1 every 50 reflections (no changes) 3644 1 677 with I > 2a(Z) * -0.23 x 0.13 x 0.04 31.9 not applied * + ( I ) = (total counts) + (0.01 x intensity)2. being minimized; discrepancy indices used below are R = (EllFol -- ~ K ~ ~ ) / ~ [ ~ o ~ and R' = [WIFol - I~cl)2//CwlFo~21f, where w is the weighting factor. Major calculations were performed on a CDC Cyber 7600 computer by using the SHELX76 system of programs for Fourier and least-squares calcul- ations, and the ORTEP plotting program for drawing.1° The non-hydrogen atoms were located by Patterson and Fourier techniques, and least-squares refinement of their positional and isotropic thermal parameters led to convergence at R = 0.097 and R' = 0.125.At this stage the hydrogen atoms, treated as fixed contributors, were added to the model at locations obtained from difference maps (13 atoms), or at their calculated positions (seven atoms). Further refinement, on which the Cu, S, 0, and two C atoms were allowed to vibrate anisotropically improved the R and R' factors to 0.052 and 0.063, respectively. For the final cycle, the shifts in all the 190 varied parameters were < 0.050. A final difference density map was featureless, with no peaks higher than 0.8 e A-3, Unit weights were used at all stages; no trend of /Cw(lFol - IFc!)' us.lFoj, sine, or Miller indices was observed. During the refinement, zero weight was assigned to ten strong low- order reflections, which may be affected by secondary extinction, or, more likely, by counting errors. Final atomic co-ordinates are given in Table 2. Results and Discussion From an ethanolic solution of N-tosylglycine and copper(I1) ion two compounds, one green of formula [(Cu(t~glyO)~),] (tsglyO = N-tosylglycinate anion) and one blue of formula Na2[Cu(tsglyNO),] (tsglyNO = N-tosylglycinate dianion : also deprotonated on the NH group), were separated. The latter complex, which precipitated in the presence of sodium hydroxide, shows spectroscopic properties identical to those of the analogous blue complex K2[Cu(tsglyNO)2], isolated from aqueous solution.'" For this reason in this paper we treat only the physical properties of the solid green [(Cu(t~glyO)~},] complex.Solid State Behaviour.- Description of' the structure. Tables 3 and 4 contain selected bond lengths and angles, with atoms numbered as in Figure 1. A detailed view of the copper atom environment is shown in Figure 2. The structure is composed of one-dimensional polymeric chains, extended along the b axis, of binuclear centrosym- metric Cu2(tsglyO), units. The co-ordination polyhedron shows the dimeric copper(I1) acetate s t r u ~ t u r e , ~ ~ - ~ ~ with four bidentate carboxylate groups forming syn-syn bridges between the copper atoms; the axial co-ordination site is occupied by a sulphonic 0 atom from a neighbouring tsglyO- ion, which links the dimeric units into linear chains.The same polymeric structure occurs in copper(1r) 2-acetoxyben~oate,'~ where the oxygen atoms of the acetyl residue act as terminal ligands. The structural features of the co-ordination poly- hedron compare well with those reported for many binuclear copper(i1) carboxylate complexes.'** 15--19 The Cu-O(carboxy1ic) bond distances, equal within one standard deviation, average 1.955(7) A, and the unique Cu-O(su1phonic) bond length of 2.168(7) 8, is consistent with previously reported Cu-0- (water) apical bond distances [2.161(2) 8, in [CU(O~CM~)~- (H2O)],I3 2.1 7(2) 8, in [(CU(O-B~C,H~CO~)~(H~O))~],~~ and 2.1 56(4) A in [(Cu[OzCCH2CHzNHC(0)~e]2(Hz0)~21~2H20 (green f~rm)~"].The bridge lengths (the sum of Cu-0-C-0- Cu distances) of 6.41 and 6.42 A, respectively, are withinJ. CHEM. SOC. DALTON TRANS. 1984 1689 Table 2. Atomic co-ordinates with estimated standard deviations in parentheses X - 0.037 9( 1 ) -0.014 6(3) 0.048 6(3) 0.024 l(4) 0.042 l(4) 0.051 l(3) 0,105 l(1) 0.1 15 5(3) 0.100 2(3) 0.157 7(4) 0.207 2(5) 0.251 3(5) 0.244 7(5) 0.194 5(5) 0.149 9(5) 0.292 2(6) Y 0.893 7(2) 0.740 l(9) 0.931 7(9) 0.790 4( 1 5 ) 0.668 8(14) 0.490 7( 10) 0.450 O(3) 0.581 2(10) 0.274 3(9) 0.450 4( 14) 0.516 7(15) 0.497 6( 17) 0.425 8( 17) 0.363 8(18) 0.377 7( 16) 0.404 3(21) Z 0.531 6(1) 0.412 2(6) 0.354 7(6) 0.350 8(9) 0.294 4(7) 0.358 4(2) 0.435 2(5) 0.396 4(6) 0.257 2(8) 0.284 O(9) 0.204 9(10) 0.111 7(10) 0.085 7(10) 0.159 3(10) 0.028 3(13) 0.260 q 9 ) X 0.017 7(2) 0.082 9(3) 0.065 l(4) 0.107 2(4) 0.088 2(3) 0.128 3(1) 0.104 l(3) 0.138 2(3) 0.189 8(4) 0.235 9(5) 0.283 2(5) 0.285 7(5) 0.238 7(5) 0.191 l(5) 0.336 7(6) Y 0.781 9(9) 0.972 3(9) 0.838 5(14) 0.742 4(14) 0.564 7(11) 0.448 3(4) 0.279 9(10) 0.540 9(12) 0.430 4( 15) 0.520 l(17) 0.508 6( 1 8) 0.416 9(18) 0.329 7(17) 0.335 4(15) 0.403 8(22) Z 0.614 8(6) 0.564 3(6) 0.613 6(9) 0.675 5(9) 0.701 O(7) 0.771 5(3) 0.779 2(8) 0.866 7(7) 0.695 7(9) 0.726 l(l0) 0.661 6(11) 0.567 8( 1 I ) 0.536 5( 11) 0.601 2(9) 0.495 7(15) Table 3.Selected bond distances (A) with estimated standard deviations in parentheses * C( 22)-N( 2) 1.48( 1) CU-o(l1) 1.957(7) Cu-0(21) 1.95 l(7) C( 12)-N( 1 1 1.46( 1) Cu-o( 12‘) 1.955(7) cu-O(22’) 1.958(7) N( 1 )-S( 1 ) 1.61 l(8) N(2)--S(2) 1.620(9) S(2)-O(23) 1.428(8) Cu-0( 14’’) 2,168(7) c u * .CU’ 2.577(3) S( 1)-O( 13) 1.419(7) O( 1 I)<( 1 1 ) 1.25( 1) O(2 1 )-c( 2 1 ) 1.25( I) S( 1 )-o( 14) 1.435(7) S(2)-O(24) 1.409(9) 0(12)-C(11) 1.25( 1) W2)-C(2 1) 1.26( 1) S( 1)-C( 13) 1.76(1) W-C(23) 1.75( 1) C(ll)-C(12) 1.51(1) C(2 1 )-C(22) 1.51(1) * Primed atoms: symmetry transformation - x , 2 - y, 1 - z. Doubly primed atoms: symmetry transformation - x , 1 - y , 1 - z. Table 4. Selected bond angles (”) with estimated standard deviations in parentheses * 0(1 l)-Cu-0(12’) 169.6(4) 0(21)-C~-0(14”) 91.2(3) 0(12’)-C~-O(21) 89.9(3) CU-O(12’)-C(ll’) 125.3(7) O( 1 1)-Cu-0(21) 86.W) 0(22’)-Cu-O(14’’) 98.8(4) O( 12’)-Cu-O(22’) 90.7(3) CU-O(~~)-C(~I) 121.4(7) 0(11)-Cu-0(22‘) 90.9(3) 0(14‘))-Cu * * CU‘ 173.3(2) 0(12’)-Cu-0(14”) 92.6(3) Cu-O(22‘)-C(21’) 121.9(7) 0(1 l)-C~-O(l4”) 97.3(4) Cu-O(l l)-C(11) 117.3(7) 0(21)-Cu-O(22’) 169.9(4) C~-0(14”)-S(l”) 138.1(3) the range (6.40-6.46 .$) reported for most dimeric copper(r1) carboxylate cornplexe~.’~*~~ A relevant feature appears to be the very short Cu Cu’ separation [2.577(3) A], only slightly longer than that (2.565 .$) in copper(I1) propi~nate,’~ as a confirmation of the shortening of the copper-copper distances in the dimeric units of polymeric structures with respect to the discrete dimers.16 The copper atom is displaced from the least-squares plane of the four oxygen atoms (deviations fO.OO1 .$ from this plane) 0.171 .$ towards the apical 0 atom, the shortest devia- tion yet discovered for a dimeric copper(r1) ~arboxylate.’~ The corresponding bond distances and bond angles within the two crystallographically independent tsglyO - ligands are not significantly different, and compare well with those observed in other tosyl or sulphonic derivatives.’**20-2s As in copper(ri) 2-a~etoxybenzoate,’~ both the ligands are co- ordinated to two metal ions in the same binuclear unit, but, in addition, one is also bonded to the copper atom from an adjacent dimeric unit.Nevertheless, their mode of bonding appears rather surprising. There are no previous examples of bond interactions between sulphonamidic 0 atoms and metal ions. In square-pyramidal [Cu(tsglyNO)(H20),] lo and in the distorted square-planar K2[Cu(tsglyNO)2] complex lo the ligand acts as bidentate toward a single metal atom through the deprotonated amide nitrogen and one carboxylate oxygen atom, with only a weak Cu O(su1phonic) axial inter- action [2.717(3) .$] in the latter compound.Furthermore, dimeric copper(r1) acetate structures of N-substituted amino acid complexes have previously been reported only for aqua bis( N-ace t ylgl yci na to)cop per( n), Zb and for [ { C u [02CCH2- CH2NHC(0)Me]2(H20))2]*2H20 (green form).2u The packing is determined by normal van der Waals distances, with only one intra-chain hydrogen-bond inter- action, N(1)-H(1) * O(21) ( - x , 1 - y , 1 -- z ) = 2.89 A (N-H 0 135”). Magnetic atid spectroscopic mensirrements. The room- temperature e.s.r. spectrum (Table 5 ) of our compound, typical of dimeric or polymeric copper(i1) carbo~ylates,~ shows a zero-field splitting D parameter of 0.35 cm-’.At 123 K the absorption of the lowest magnetic field shows the seven-line hyperfine splitting from the two equivalent copper nuclei (All = 77 x cm-I).1 690 J. CHEM. SOC. DALTON TRANS. 1984 Figure 1. ORTEP drawing of [{Cu(t~glyO)~),] showing the atom numbering and thermal ellipsoids (40%) for non-hydrogen atoms. The spheres of the hydrogen atoms are of arbitrary radius O(14') Figure 2. A portion of the linear-chain structure of [{Cu(tsgly0)2S,] with interatomic distances (A) Its magnetic susceptibility data, obtained on powdered samples over the temperature range 110-310 K, are indicative of binuclear species with strong antiferromagnetic exchange. The experimental data (Figure 3) were closely fitted by the Bleaney-Bowers equation for magnetically coupled pairs of copper(n) ions.26 This equation was used unmodified, because Table 5.Room-temperature magnetic and spectroscopic results for the solid [(Cu(tsglyO)zf,] complex a gii 2.363 0,'crn-l 0.35 81 2.083 IWl/cm-l 353 rf 4 E 2.180 A 1 I/cm-' 77 x 10-4 1.33 15 150 2& 340 3 285s, 3 210s 1 648vs 1 428vs 1 340ms, 1 325s, 1 290s br 1 170s, 1 145s * 892m b, 865m a The e.s.r. data are reported for the dimer. Band associated with the co-ordinated SO, group. very little amount of mononuclear impurities of spin S = + were present, as observed in the region around 3 000 G of the e.s.r. spectra. By using for the Land& splitting factor 2 = [(g$ 4- 2g1*)/3]* (ref. 27) the value of 2.180, determined by e.s.r., and for the Van Vleck temperature-independent constant N a = 60 x loF6 e.m.u.mol-', a 12JI value of 353 i 4 cm-' is calculated, in agreement with those found for similar dimeric copper(i1) N-protected amino acid and carb- oxylate complexe~.~ The e.s.r. spectra show resolved copper hyperfine structure. Therefore, magnetic exchange between dimers through axially co-ordinated SO2 groups is weaker than the hyperfine coupling. The electronic spectrum of the compiex (Table 5 ) is also characteristic of dimeric carboxylate-bridged structures.16 Its i.r. spectrum is assigned by comparison with those of other previously examined N-tosylglycinatocopper(i1) com- plexes, in which the ligand is co-ordinated only through the carboxylate group.'a However, in agreement with the structural features of the present complex, in which 50% of the SO2 groups are bonded to a copper atom, all the bands assignable to the sulphonamide group (NH, SO2, SN) appear to split, as reported in Table 5 .J. CHEN.soc. DALTON TRANS. 1984 1691 700 v! 9, V --. 500 (D E! 300 too 200 ~ 300 T / K Figure 3. Corrected molar susceptibilities (0) and best-fit curve for the complex [{Cu(t~glyO)~)~] a I 2. .- U 0.~1 111 0.51 I I I 1 1 1 2 3 4 104[NaOH JImol dm-3 +D Figure 4. Plots of id values of waves I, 11, and I11 us. c N ~ O H ; dropping time = 2 s Ethanolic Solution Behauiour.-The behaviour of N- tosylglycine in ethanolic solution closely resembles that found in aqueous solution, presenting two dissociation PKa values, PIC,, = 7.5 (3.5 in aqueous solution) and pK2a - 12 (1 1.6 in aqueous solution lb) corresponding to the equilibria (2).1 I - 0 1 2 3 4 5 [CUL, I /[CU2+1 Figure 5. Plots of id(II) values us. the molar ratio of the complex (L = tsglyO-) to Cu2+ ion concentration at two different initial concentrations: (0) cCu2+ = mol dm-j mol dm-3; (0) ccuz+ = 2.5 x value with increasing amounts of base, while wave I decreases until it disappears. The E+ and id values of wave I1 are constant for cNaOH/ccomplex ratios between 1 and 3 (E* = 0.070 V; Figure 4); for ratios > 3, a third wave (wave 111) appears at more negative potential values, whose E+ value remains constant (E; = -0.275 V) and limiting current values increase for increasing base concentr- ation. The sum of the limiting current values of waves I and I1 and of waves I1 and 111, respectively, remains nearly constant (Figure 4).For c ~ ~ ~ ~ ratios > 4 a blue complex of formula Na2 [ Cu(t ~glyNO)~] precipitated. To determine the physicochemical characteristics of the species present in ethanolic solution, the Na(tsgly0)-Cu2 + system was investigated at varying tsglyO- concentrations. For a deficiency of ligand two waves (I and 11) appear, corresponding to the reduction of Cu2+ ion and of [Cu- (t~glyO)~] complex, respectively ; at increasing ligand con- centration only wave I1 is present. The sharp break of Figure 5 [id(II) us. ligand/metal ion molar ratios] corresponding to a molar ratio of 2, indicating the number of ligand molecules co-ordinated to the Cu2+ ion, is independent of the initial concentration of the metal ion.28 Furthermore, the E+ value of wave I1 does not vary even in the presence of a ligand excess.The reduction process then may be summarized by (2) pK2a CH3C6H4S02NHCH2COOH CH3C6H4S02NHCH2C00 - CH3C6H4SO2NCHzC00 - (tsgly) (tsgly0 - 1 (tsglyN02 -) Therefore for this amino acid any type of zwitterionic character may be excluded in ethanol also. The polarographic curve of the [(C~(tsglyO)~),] or [C~(tsgly0)~]*4H~O complexes in ethanol presents a well defined, quasi-reversi ble reduction wave (wave I) very similar to that found for the free copper(r1) ion reduction [E+ = +0.26 V us. s.c.e.; an = 0.89 (a = charge-transfer coefficient; n = number of electrons)], suggesting that the complexes are completely dissociated. By adding to these solutions of the complexes increasing amounts of an ethanolic NaOH solution (0.1 mol dm-3), a new wave (wave 11) appears, which has a more negative E, value and shows an increase of the limiting current equation (3).This [C~(tsglyO)~] complex corresponds to that Hg electrode [C~(tsglyO)~] + 2e- - Cu(Hg) + 2 tsglyO- (wave 11) (3) prevailing in aqueous solution in the pH range 5-7.5, for which the amino acid co-ordination through the carboxylate group has been suggested previously.'* By adding small amounts of base to the solution of the [Cu(tsglyO),] complex, the third wave (wave 111) appears, disappearing when the CNaOH/CNa(gsglyO) ratio is greater1692 J. CHEM. SOC. DALTON TRANS. 1984 than 2 for the precipitation of the NaZ[Cu(tsglyN0),] com- pound, in which the ligand co-ordinates through the amidic and carboxylate groups, the hydrogen atom of the NH group being dissociated.(This complex shows physicochemicat properties very similar to those of the blue complex KZ[Cu- (t~glyNO)~], previously examined.'"} Therefore wave I11 corresponds to the reduction process of the [C~(tsglyNO),]~- complex: equation (4). H g [Cu(t~glyNO)~]~- + 2 e- + Cu(Hg) + 2 tsglyNOZ - (4) Analysis of waves I1 and 111. The semi-logarithmic analysis of wave I1 shows that the reduction is irreversible and a diffusion-controlled process and the value of the overall stability constant (p2) of [Cu(tsglyO),] obtained is lo8 (method A) and 1.5 x lo8 (method €3). In agreement with the acceptor- donor properties of the solvent 29 the [Cu(tsglyO),] complex appears to be slightly more stable in ethanol than in water.lb The semi-logarithmic analysis of wave 111 shows that the reduction of the [Cu(t~glyNO)~]~- complex is also an irrevers- ible, two-electron diffusion-controlled process; a value for p3 of 3 x 10 l9 was calculated using method A.The chemical equilibria and the overall electrochemical reduction process, as a function of NaOH concentration, may be summarized as shown below, where pZ = KZ and p3 = K2K3. Therefore, the stability constant ( K J of the [Cu- wave I Cu2+ + 2tsglyO- ~s,- Cu(Hg) (E-1 = 0.26 V) wave 11 [Cu(tsglYO)zI -t 2 OH- ~g,- Cu(Hg) + 2 tsglyO- (E* = 0.07 V) ilK3 (t~glyNO)~]~ - complex referred to the [Cu(t~gIyO)~] complex being equal to 10'' (calculated using method B), a value of 1.5 x lo'* i s obtained for p3, in agreement with the value from method A.Acknowledgements We thank the Centro Strumenti of the University of Modena for the recording of the i.r. spectra, the Centro di Calcolo of the University of Modena for the computing facilities, and the Minister0 della Pubblica Istruzione of Italy for financial support. References 1 (a) L. Antolini, L. P. Battaglia, G. Battistuzzi Gavioli, A. Bona- martini Corradi, G. Grandi, G. Marcotrigiano, L. Menabue, and G. C. Pellacani, J. Am. Chem. SOC., 1983, 105, 4327; (b) 1983, 105, 4333. 2 (a) L. P. Battaglia, A. Bonamartini Corradi, G . Marcotrigiano, L. Menabue, and G. C . Pellacani, Znorg. 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