J. CHEM. SOC. DALTON TRANS. 1984 2087 Crystal Structure t of Bis(2,2'-bipyridyl)monochlorocopper(11) Hexafluorophosphate Monohydrate a t 298 K and the Electron Spin Resonance Spectra of some Bis( 2,2'-bipyridyl)copper(11) Complexes to 4.2 K Suresh Tyagi and Brian Hathaway The Chemistry Department, University College, Cork, Ireland Stefan Kremer, Horst Stratemeier, and Dirk Reinen The Chemistry Department, University of Marburg, Federal Republic of Germany The crystal structure of the title compound [Cu(bipy),CI] [PF6].H20 (1 ) (bipy = 2,2'-bipyridyl) has been determined by X-ray diffraction, using diffractometer data collection. The structure was solved by the heavy-atom method and successive Fourier synthesis. Compound (1 ) crystallises in the monoclinic space group P2,/n with a = 21.403(5), b = 12.235(3), c = 8.599(2) A, p = 92.68(2)", and Z = 4.The CuN,CI chromophore involves a near-regular trigonal bipyramidal stereochemistry, but with a significant distortion of the three in-plane angles from 120" (1 15.7, 123.8, and 120.5"). The poly- crystalline and single-crystal e.s.r. spectrum of (1) and a number of other 2,2'-bipyridyl complexes with [C~(bipy)~X]"+ cations [X = CI or I, n = 1 ; X = NH3, n = 2) are reported between 300 and 4 K. The molecular g tensors are consistent with a near-regular trigonal bipyramidal or square pyramidal distorted trigonal bipyramidal stereochemistry. As the e.s.r. spectra do not change significantly with temperature a dynamic behaviour in the sense of the pseudo-rotation of the Berry-Twist mechanism is not considered to operate.There is evidence that the reported compressed trigonal bipyramidal geometry of the [CUCI~]~- anion in the compounds [M1'1(NH3)6][CuCIs] (MI1' = Cr or Co) at 298 K is the dynamic average over three elongated square pyramidal conformation^,^ which can be frozen out at low temperature. In line with this model, structural and spectro- scopic results on Cu"L5 polyhedra with L = CI or Br or a N or 0 donor are generally in accord with a square pyramidal stereochemistry which is elongated in the apical directions., A compressed trigonal bipyramid may eventually be stabilized, if geometric ligand effects (polydentate ligands) and/or pack- ing effects (bridging ligands) are pre~ent.~ In order to deter- mine whether a fluxional behaviour of the above kind also applies to the near-regular trigonal bipyramidal stereo- chemistry of the copper(1r) ion involving two bidentate 2,2'-bipyridyl (bipy) ligands and a fifth non-equivalent ligand the crystal structure of [C~(bipy)~Cl][PF,]~H~0 ( I ) has been determined.The e.s.r. spectra of this complex and of a number of comparable near-trigonal bipyramidal copper(i1) complexes have been measured to 4.2 K and are now also reported. Experimental Preparatiot~.-C~C1~~2H~O (0.737 g, 0.8 mmol) and bipy (0.25 g, 1.6 mmol) were dissolved in water-ethanol ( 1 : 1, 30 cm3), the solution was warmed, stirred, and KPF6 (0.147 g, 0.8 mmol) added. The blue solution was filtered and left to evaporate in air. After 3 - 4 d small well formed blue crystals of (1) were deposited (Found: C, 41.5; H, 3.15; CI, 6.20; Cu, 1 1.20; N, 9.70.CzoHlsC~CuF6NjOP requires c, 41.80; H, 3.15; CI, 6.70; Cu, 11.05; N, 9.75%). The complexes [ Cu (bi PY)~CI ]CI *6 HzO ( 2 ) and [ Cu( bi p ~ ) ~ ( N H3)] [ BF, ] (3) were prepared as previously Supplementary data available (No. SUP 23984,24 pp.) : all thermal parameters, H-atom co-ordinates, full bond lengths and angles, least-squares planes, non-bonded distances, structure factors. See Instructions for Authors, J. Chem. SOC., Dalton Trans., 1984, Issue 1, pp. xvii-xix. Crystar Data for [C~(bipy)~C1l[PF~]*H~0 (1).-C2,,HIR- CICuF,N,OP, M = 573.97, monoclinic, space group P2,/n, a = 21.403(5), b = 12.235(3), c = 8.599(2) A, j3 = 92.68(2)", U = 2 249.32 A3, D, = 1.63(2), Z = 4, D, := 1.69 g cmW3, F(OO0) = 1 156, Mo-K, radiation, h = 0.710 69 A, and ~ ( M o - K , ) = 11.75 cm-'.The unit-cell parameters were determined, the intensities collected (2 094 reflections were retained), the structure was solved by Patterson and Fourier techniques and refined by full-matrix least-squares analysis, as described previously." The refinement converged when the shift-to-error ratio of any parameter was less than 0.005, with a refined weighting scheme, w = k[o(F,,) g(F,JZ], and final values of k and g of 1.288 and 1.096 x respectively. The final R value was 0.0521 and the maximum residual electron density was 0.347 e k3. All calculations were carried out by using SHELX 76 and XANADU (C. M. Sheldrick), PLUTO (S. Motherwell), and PUBTAB (K. Henrick) systems of programs on the IBM 4341 and VAX 11/780 computers.The final atomic co-ordinates are given in Table 1, and selected bond lengths and angles in Table 2. Figure 1 illustrates the molecular structure of (l), the atom-numbering scheme used, and the crystal packing. Figure 2 illustrates the local molecular structures of complexes (l)-(5). Spectroscopic Measurements.-E.s.r. spectra were recorded on an El5 Varian spectrometer (Q- and X-band) at 298, 77, and 4.2 K, with diphenylpicrylhydrazyl (dpph) as internal standard ( g = 2.003,). The electronic reflectance spectra were recorded by a Zeiss PMQ I1 spectrophotometer (Infrasil) with a low-temperature attachment. SrzZnTeO, (4 000-1 2 000 cm-') and freshly sintered MgO (8 000-30 000 cm-') were used as standards. Results and Discussion Crystal Structure.-The crystal structure of ( I ) consists of a [C~(bipy)~CI]+ cation, a [PF,]- anion, and a molecule of non- bonded water.The structure of the cation involves a five-co- ordinate CuNrCl chromophore with an almost regular trigonal bipyramidal stereochemistry,' with no evidence for2088 J. CHEM. SOC. DALTON TRANS. 1984 Table 1. Fractional atomic co-ordinates for [C~(bipy)~Cl][PF~].H~0 (1) X - 0.029 27(4) 0.017 4(l) -0.095 5(3) - 0.137 O(4) -0.183 l(4) - 0.187 O(4) -0.144 8(4) -0.098 3(3) - 0.047 8(3) -0.039 3(4) 0.01 2 5(4) 0.052 3(4) 0.040 6(4) -0.008 O(3) 0.032 9(3) 0.094 8(3) 0.1 35 3(4) 0.1 11 9(4) 0.048 6(4) 0.010 O(3) -0.059 5(3) -0.091 5(4) - 0.155 7(4) -0.187 6(4) - 0.152 9(4) - 0.090 4(3) 0.275 4(1) 0.268 9(4) 0.292 6(3) 0.347 l(2) 0.258 5(2) 0.280 9(3) 0.202 9(2) 0.343 5(4) Y 0.747 8q8) 0.853 3(2) 0.693 8(5) 0.760 4(7) 0.720 5(7) 0.6 I0 5(8) 0.540 8(7) 0.585 8(6) 0.522 4(6) 0.410 2(6) 0.359 7(6) 0.4 I6 5(6) 0.5272(6) 0.579 8(4) 0.798 6(5) 0.781 5(6) 0.818 5(7) 0.881 7(7) 0.902 8(6) 0.857 7(5) 0.869 8(5) 0.922 5(6) 0.927 9(7) 0.878 8(7) 0.825 7(6) 0.820 3(4) -0.009 l(2) 0.093 8(5) 0.066 6(4) - 0.020 O(6) - 0.086 9(5) -0.1 I3 6(4) 0.O00 2( 5 ) 0.247 6(6) z 0.772 94( 10) 0.582 6(2) 0.621 O(7) 0.543 3(9) 0.442 6( 10) 0.419 O(9) 0.496 l(9) 0.595 3(8) 0.674 9(8) 0.647 9(9) 0.7 I7 9(9) 0.8 19 9(9) 0.844 8(8) 0.771 3(6) 0.939 l(7) 0.936 8(9) 1.056 O( 10) 1.172 6(9) 1.177 2(9) 1.056 l(8) 1.052 3(7) 1.166 4(9) 1.152 O(10) 1.026 4( 1 1) 0.917 8(9) 0.928 3(6) 0.436 9(2) 0.329 5 ( 8 ) 0.585 4(6) 0.404 5(6) 0.292 l(6) 0.547 8(7) 0.472 O(7) 0.924 5(9) Table 2.Selected bond lengths (A) and bond angles (") for [Cu- (bipy),CI] [PF61.H20 (1 ) cu-CI 2.344(2) Cu-N( 1) I .996( 6) Cu-N(2) 210x6) Cu-N(3) 2.005(6) Cu-N(4) 2.108(6) N( 1)-C( 1 ) 1.358(9) P-F(2) I .606(5) P-F( 1) I .564(6) P-F(4) 1.595(5) P-F(3) 1.578(5) P-F(6) 1.599(5) P-F(5) 1.596(6) N( I )Xu-CI 92.2(2) N(Z)-Cu-N( I ) 79.6(2) N(3)-Cu-N( I ) 175.5(2) N(4FCu-CI I20.5(2) N(4)-Cu-N(2) 123.8(2) F(2)-P-F( 1) 90.9(4) F(3)-P-F(2) 90.0(3) F(4)-P-F(2) 178.6(4) F(S)-P-F( I ) 179.0(4) F(S)-P-F(3) 89.6(4) F(6)-P-F(1) 89.7(4) F(6)-P-F(3) 179.0(4) F(6)-P-F(5) 89.4(4) N(2)-Cu-CI I 15.7(2) N(3j-Cu-Cl 92.1(2) N(3)-Cu-N(2) 99.8(2) N(4)-Cu-N( I ) 96.4(2) N(4)-Cu-N(3) 80.1(2) F(3)-P-F( I ) 9 1.4(4) F(4)-P-F( 1 ) 90.5(4) F(4)-P-F( 3) 89.9(3) F( 5)-P-F( 2) 88.8(3) F(5)-P-F(4) 89.8(3) F( 6)-P-F( 2) 89.9(3) F( 6)-P- F( 4) 90.2(3) even semi-co-ordination l2 of either the [PF,,]- anion or of the lattice water.Although the [PF6]- anion occupies a general position, it involves a near-regular octahedral s t r u c t ~ r e , ' ~ mean P-F distance, 1.59 A, and a mean F-P-F angle, 89.8", with no evidence for the disorder l4 normally associated with this anion. There are no unusual bond lengths or angles in the bipy ligands,15 the individual pyridine rings are reasonably planar (see SUP No. 23984), and within each bipy ligand the 4 cd Cl T b 0 P o 1-1171-I b C(19) Figure 1. Molecular structure of 1Cu(bipy,,Crl[PF6].H2~ (I) the atom-numbering scheme used, and the crystal packing pyridine rings are twisted with respect to each other by 9.07 and 4.1 7", respectively, within the range of 0-13" previously observed for the angle of twist of the bipy ligand.16 The mean planes of the bipy ligands make an angle of 127" to each other. Within the CuN,CI chromophore the axial Cu-N distances, mean 2.00 A, are not significantly different, and ca.0.1 A shorter than the two equatorial Cu-N distances (mean 2.1 1 A), as has been found previously for the trigonal bipyramidal stereochemistry." In the CuN4CI chromophore of (l), the out-of-plane angles are 90 & lo', and the N(l)-Cu-N(3) angle is nearly linear, at 175.5'. In the Cu,N(2),N(4),CI plane, the angles are near trigonal, but with the N(2)-Cu-N(4) (a3) angle greater than 120" (123.8') and the CI-Cu-N(2) (a,) angle less than 120" (115.7").In general, the structure of ( l ) , Figure 2(a), is comparable to that previously observed 18-21 for the [Cu(bipy),CI]+ cation in a series of five complexes; it is closest to that of complex (2) [Figure 2(6)] and signifi- cantly different from the square pyramidal distorted structure 21 of [Cu(bipy),C1][C104]. The most significant differences in complexes (1) and (2) are in the angles a l , a2, and a3, Figure 2(a), with a3 - a1 = 8", a difference that is difficult to explain if the structure of (1) lies on the structural pathway (ref. 19,J. CHEM. SOC. DALTON TRANS. 1984 2089 N ( l 1 N 11.99 N N 1 2 . 0 3 I 1-96 N 12.00 N ( d 1 N 1 2 . 0 4 N 2 06 I 2.02 NH3 Figure 4), previously suggested to correlate the structures of five cation distortion isomers 22 of the [C~(bipy)~Cl]+ cation.Thus, although the structure of (1) has been slightly more accurately determined than (2), its structure does not fit quite so neatly on the above structural pathway,19 however its structure is closer to that of (2) rather than that of [Cu- (bi py)zCI][ C104] ., Electronic Properties.-The unit cell of (1) contains CuN,CI polyhedra with two different orientations of the trigonal axes, which are misaligned 23 by 2a 2: 37” with respect to one another. The single-crystal e.s.r. spectrum (Q-band) yields two independent signals of equal intensity, indicating that no exchange-narrowing occurs, in agreement with the very long Cu-Cu distances ( > I 1 A) between the symmetry related chromophores. Hence the observed crystal g tensor equates with the local molecular g values [gz = 2.004, g, = 2.1 75.and g , = 2.1g3 (298 K, single-crystal and powder values)]. It is 1 > HIG Figure 3. E.s.r. powder spectra (Q-band frequency, 298 K) of [ C U ( ~ ~ ~ ~ ) ~ C I J C I * ~ H ~ O (2) [(a)‘and (h) different crystallisation pro- cedures] and (c) [ C U ( ~ ~ ~ ~ ) ~ ( N H , ) I [ B F , ] ~ (3) consistent with the near-regular trigonal bipyramidal structure [Figure 2(0)],,~ which implies a d,Z ground state for a regular D3h symmetry and g values 24 (second-order contributions only) according to equation (i). The g tensor does not change down to 4 K, indicating a non-fluxional geometry for the CuN4CI polyhedra.25 g, is connected with the axial Cu-N(1,3) direction, while g, has an orientation not too far from the equatorial Cu-CI direction.The electronic reflectance spectrum at 298 K shows a broad unresolved band at cu. 12 OOO cm-’ and an asymmetry around I5 OOO cm-’, which may be tentatively assigned to the A’-+E’ and E” transitions in an approximate D 3 h symmetry. With these energies and an orbital contribution, ul, of 0.03 a covalency parameter k l 2: 0.75 * can be estimated [equation (i)], in accord with comparable values for [Cu(terpy)Cl,] (terpy = 2,2’ : 6’,2”-terpyridyl) complexes.26 The e.s.r. spec- trum of (I) is very similar to that of [CU(NH~)~A~(SCN)J 27 with polyhedra of D3,, symmetry whose geometry is also non- fluxional with g values, gli = 2.00, and g l = 2.1g7, between 298 and 4.2 K. The complex [C~(bipy)~C1]C1~6H~O (2) involves CuN4CI polyhedra l8 of almost the same geometry as those of complex (1) [Figure 2(a) and (b)].Although the unit cell contains two spectroscopically different Cu2 + polyhedra,18 only one signal is observed in the single-crystal e.s.r. experiment (glex = 2.0S2, gzeX = 2.0g2, and g3cx = 2.1S7). Hence the g tensor is exchange(ex) coupled, which is expected considering the short Cu-Cu spacing of 4.3 A. The powder spectrum (298 or 100 K) is critically dependent on the velocity of crystallisation and the * k is used as an empirical parameter, which additionally confirms the assignments of the ligand-field transitions by comparison with k values for Cu-N bonds in related compounds.2090 J . CHEM. SOC. DALTON TRANS. 1984 10 15 10-3wc rn -1 20 grinding procedure used. Besides broad signals, which imply the single-crystal g values, a second g tensor with the com- ponents g, = 2.0O4, g, = 2.162, and g, = 2.2O2 is clearly visible (Figure 3).Because the additional g tensor is very similar to the one observed for (I), the e.s.r. powder spectrum of (2) appears to exhibit the molecular and co-operative g tensors side by side. Assuming axial molecular g tensors for the two CuN4CI polyhedra and misalignment angles with respect to one another of 90" ['antiferrodistortive the exchange-narrowed g tensor of equations (ii) is expected in approximate agreement with the molecular and co-operative g values of Figure 3(a) and (6). Actually the molecular g tensors are orthorhombic and the canting angles between them deviate from 90". We have calculated the orientations of the molecular g-tensor components with respect to the Cuz +- ligand directions ut ilising the general equations given by Chao,Z* which correlate the molecular with the exchange- coupled g values.We find that the smallest molecular g value (2.00,) is connected with the (pseudo) trigonal N(1)- Cu-N(3) axis within 6", while the largest g component (2.202) deviates only ca. 3" from the Cu-N(4) direction [Figure 2(6)]. The e.s.r. powder spectrum does not change down to 4.2 K. Obviously the trigonal bipyramidal geometry of the CuN4Cl chromophore in (2) is also non-fluxional. The ligand-field spectrum at 298 K is similar to the spectrum of (1). At 5 K two peaks at 10 900 and 12 800 cm-' are clearly resolved and a shoulder is indicated around 15 500 cm-' (Figure 4).With an assignment of the maxima to the split- states of the trigonal bipyramidal 'E' level and the broad shoulder to the ZE" state, the same covalency parameter, kl 21 0.75, as for compound (1) is obtained. A splitting in particular of the excited 2E' state (connected with the in- plane cr- and n-antibonding dx2-,2 and dxy orbitals) is expected, because different ligands are present in the equatorial plane of the CuN4CI chromophore (non-axial g tensor). It is finally interesting to note that the g tensor of the [C~(bipy)~CI]+ cation in dilute frozen methanol solution (gz = 2.003, g,, --= 2.16,, and g, = 2.19J is very similar to those of (1) and (2). Obviously the stable geometry of the [Cu(bipy),CI] + chromo- phore is trigonal bipyramidal.Deviations towards a square pyramid are thus presumably induced by packing effects l9 in the solid compounds. In [ C U ( ~ ~ ~ ~ ) ~ ( N H ~ ) ] [ B F ~ ~ , (3) the geometry of the CuN, chromophore [Figure 2(c)] deviates from trigonal bipyramidal towards square pyramidal 29 with one equatorial Cu-N bond length appreciably longer than the other two. This behaviour matches with the preference of Cuz+ in a ligand field of five equal unidentate ligands for an apically elongated square pyramid with respect to a compressed trigonal bipyramid.j The unit cell of (3) contains two pairs of Cuz+ polyhedra, connected by an inversion centre. The spacing between the Cu2+ ions of each pair is 8.15 8, which is still in the range where exchange interaction might occur.26 In the single-crystal e.s.r.experiment only one signal is observed with g values N LOO5, 21 2.1 35, and E 2.205. Because the crystallographic data 29 indicate that the canting angles between the molecular g tensors of the two Cu2+ sites are presumably very small, the experimental g values reflect the molecular CuN, geometry to a first approximation. The powder e.s.r. spectrum [2.01 (2.0O5), 2.137 (2.13,), 2.210(2.20,) at 298(77) K] (Figure 3) does not change significantly between 77 and 4.2 K and indicates again a non-fluxional geometry of the Cuz+ polyhedron. The ligand-field spectra are comparable to those of (2) (Figure 4). At 5 K two peaks at 11 450 and 13 200 cm-' are resolved, and a further transition appears as a distinct shoulder around 15 500 cm-'. The covalency parameter k l 2 0.74 is again consistent with those of ( 1 ) and (2).The perchlorate salt, [Cu(bipy),(NH3)][Cl0,'12, is isostructural with (3), as the A'- ray powder diagrams and e.s.r. spectra are nearly identical. The e.s.r. powder spectrum of [C~(bipy)~I]I is molecular, gl = 2.160, gli = 2.O& in close agreement with reported single-crystal data,9 and also does not change down to 4.2 K. The structural data indicate a slightly distorted trigonal bipyramid, Figure 2(d), although the standard deviations are rather large.30 The strictly axial g tensor and the significant deviation of gil from the spin-only value [equation (i)] are difficult to interpret, however. The 2% copper(i1)-doped [Zn(tren)(NH3)][C10,]z [tren = tris(2-aminoethyl)amine] system has been reported 31 to have an electronic reflectance spectrum comparable to that of the concentrated copper complex ( 5 ) , indicating that the CuNS stereochemistry, Figure 2(e), is the same in the concentrated and doped The e.s.r.spectrum of the doped complex shows 31 copper hyperfine and g values consistent with a (j;~ ground state at 298, 77, and 4.2 K at Q-band frequency, i.e. gll = 2.OOz, gl = 2.168. The spectrum also yields a weak signal at 2.08,, which may be ascribed to the gl.'" value of Cu2+-CuZf pairs [equation (ii)], and shows no variation in form down to 4 K that would be consistent with a change in stereochemistry to square pyramidal. Acknowledgements The authors acknowledge the award of a Senior Demonstrator- ship (to s. T.), and are grateful to Drs. P. G. Owston, M.McPartlin, and K. Henrick (Polytechnic of North London) for help in data collection, to Drs. G. M. Sheldrick and S. Motherwell (Cambridge University) and K. Henrick (Polytechnique of North London), for the use of their programs, the Computer Bureau, U.C.C. for computing facilities, and the Microanalysis Section, U.C.C. for micro- analysis.J. CHEM. SOC. DALTON TRANS. 1984 209 1 References 1 K. N. Raymond, D. W. Meek, and J. A. Ibers, Inorg. Chem., 2 I. Bernal, J. D. Korp, E. 0. Schlemper, and M. S. Hussain, 3 D. Reinen, Jahn-Teller Conference, Nijmegen, September I98 I ; 4 C. M. 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