Polyhedron Vol. I I, No. I, pp. 8549, 1992 Printed in Great Britain

0277-5387/92 $5.00 + 40 0 1992 Pergamon Press plc

COMPLEXES OF COPPER AND NICKEL(II) WITH NN’-BIS-8-QUINOLYLETHYLENEDIAMINE AND AZIDO

OR CYANATO AS LIGANDS

CARMEN DIAZ and JOAN RIBAS*

Departament de Quimica Inorginica, Universitat de Barcelona, Diagonal 647, 08028-Barcelona, Spain

(Received 20 May 1991; accepted 12 August 1991)

Abstract-Four new complexes of Cu” and Ni” with the tetradentate NN’-bis-8-qui- nolylethylenediamine ligand and N3- or NCO- have been prepared and characterized. Analytical and spectroscopic data indicate that Cu” complexes are pentacoordinated, being mononuclear when the cyanato group is the fifth ligand and dinuclear with azido acting as bridging ligand. Both Ni” derivatives are dinuclear with two azido or one cyanato and one hydroxo as bridging ligands. Cu” complexes are not magnetically coupled and both Ni” are weakly antiferromagnetically coupled (from susceptibility measurements up to He liquid temperature).

The tetradentate ligand NN’-bis-8-quinolyl- ethylenediamine (hereafter abbreviated as nn’) has a great tendency to form very stable complexes with Cu”, ’ Co” ’ and Ni11.2

\-I w

We have previously reported3 the molecular struc- ture of N,N’-bis(8 - quinolylethylenediamine)mono- chlorocopper(II)perchlorate. The CuN&l chromo- phore forms an intermediate geometry between a distorted square-pyramid and a distorted tri- gonal-bipyramid. The molecular g tensor in frozen solution is most consistent with the square- pyramidal distorted geometry, in which an N atom occupies the axial position. The Ni” com- plexes with nn’ are, according to their analytical and spectroscopic data, octahedral. All of these Cu” or Ni” complexes have halide or nitrato as ligands to complete the total coor- dination. No similar complexes with azido or cyanato ligands have been reported. Taking into account the great tendency of both pseudo-halide ligands to form polynuclear complexes with inter-

* Author to whom correspondence should be addressed.

esting magnetic properties, we have carried out the synthesis and characterization of these new com- plexes in order to study : (a) the different behaviour of Cu”, which tends to form pentacoordinated com- plexes, compared to Ni” which tends to form octa- hedral complexes ; (b) the magnetic coupling of possible polynuclear complexes with pseudo-halide as bridging ligand. In the literature there are many dinuclear complexes of CU”“‘~ or Nit’ ‘h’8 with azido or cyanato as bridging ligands. The Ni” com- plexes are always octahedrally coordinated, with two pseudo-halides as bridges. The dinuclear Cu” complexes are, instead, pentacoordinated also with two pseudo-halide or one pseudo-halide and one hydroxo group as bridges. In some very particular cases, only one pseudo-halide bridge is present to form a dinuclear species. 1g-22

EXPERIMENTAL

Synthesis of the new compounds

The nn’ ligand was prepared following Jansen et a1.,23 [(nn’)CuN,Cu(nn’)](PF,), (1) and [Cu(nn’) NCO](PF,) (2), 1 g (2.23 mmol) of [Cu(nn’) (No3)21,’ was dissolved in the minimum amount of water. To this solution, another aqueous solution of 0.9 g (4.84 mmol) of KPF6 was added, precipi- tating the aquo complex [Cu(nn’)(H20)](PFb), aq.

85

86 C. DIAZ and J. RIBAS

0.5 g (0.72 mmol) of this aquocomplex was dis- solved in ethanol and an aqueous solution of 0.36 mmol (0.025 g) of NaN, or NaNCO were added. The corresponding complexes 1 and 2 pre- cipitated in a few minutes in a very high yield. The new complexes were filtered off, washed with ethanol and air dried. (1) Found: C, 39.3; N, 12.9; H, 3.1. Calc. for C&,H&U~F,~N,~P~: C, 38.9; N, 12.5; H, 2.9%. (2) Found: C, 44.2; N, 11.8;H,3.2.Calc.forC,,H,,CuF,N,OP:C,44.6; N, 12.4; H, 3.2%. [(nn’)Ni(N&Ni(nn’)](PF& (3) and [(nn’)Ni(OH)(NCO)Ni(nn’)](PF,), * 3Hz0 (4). One gram was (2.0 mmol) of [Ni(nn’) (NO,),]* dissolved in the minimum amount of water. The aquation process is very fast, giving a violet solution of Ir\ri(nn’)(H,O),]*+ cation. The addition of an aqueous solution of 0.8 g (4.3 mmol) of KPF, leads to the formation of a precipitate of lNi(nn’)(H20),](PF,),. To an ethanolic solution of 0.5 g (0.70 mmol) of this complex, an aqueous solu- tion containing 0.046 g (0.70 mmol) of NaN, or NaNCO was added. An immediate precipitate was formed. This precipitate, which corresponds to complexes 3 and 4, respectively, was filtered and washed with ethanol and air dried. (3) Found: C, 42.6; N, 17.5; H, 3.3. Calc. for C40H36F16Nll Ni,P,: C, 42.8; N, 17.5; H, 3.2%. (4) Found: C, 42.1 ; N, 10.9; H, 3.4. Calc. for C41H34F12N9Ni2 OsPz: C, 42.8; N, 10.9; H, 3.7%.

Techniques

IR spectra were recorded on a Perkin-Elmer 1330 spectrophotometer. Samples were prepared by using the KBr technique. Magnetic measurements were carried out with a MANICS DSM-8 mag- netometer equipped with a Helium continuous flow cryostat working in the 4-300 K range. The poly- crystalline powder samples weighed about 40 mg. For all complexes independence of the magnetic susceptibility vs the applied field was checked at room temperature. Mercury tetrakis(thiocyanato) cobaltate(I1) was used as a susceptibility stan- dard. Diamagnetic corrections were estimated from Pascal’s tables. EPR spectra were recorded at 4 K, 13 K and room temperature with a Bruker-190 spectrometer equipped with a continuous flow cryostat.

RESULTS AND DISCUSSION

IR spectra

The IR spectra for the four complexes show the typical features previously reported by us’*’ for similar complexes with nn’ tetradentate ligand. The

stretching modes of the NH group of R-NH-R’ appear in the 2800-3400 cm-’ zone. In the four complexes these bands appear at lower frequency than for the free ligand and are split into two com- ponents. This effect is convincing proof of the coor- dination of the amine groups.23-25 In the 1650-1550 cm-’ region the free ligand exhibits two resolved bands at 1600 and 1570 cm- I of relative intensity 1: 3, due to partially coupled stretching vibrations v(C=C), v(C=N) of the aromatic rings and the deformation mode of the NH group.23 Coor- dination changes the coupling of these modes. These two bands appear at higher frequencies than in the free ligand (1620 and 1585 cm- ‘) and the intensity is smaller. Finally, in the 940-970 cm-’ region there is a band corresponding to the defor- mation mode of the coordinated NH group. The behaviour of this band is analogous to that of the previously described wagging mode of the NH2 group in 8-aminoquinoline.25

The asymmetric stretching frequency of the PF,- anion is found at 840-850 cm- ‘, as a very intense band. The typical bands derived from N3- or NCO- appear in the region corresponding to the vibrations of pseudohalide ligands. The major fea- ture of this part of the spectrum is, of course, the v,,(pseudohalide) observed at 2100 cm- ‘, 2060 (sh) cm-’ for Ni-N3, at 2190 cm-‘, 2180 (sh) cm- ’ for Ni-NC0 ; 2040 cm- ’ for Cu-N, and 2200 cm- ’ for Cu-NCO. This is the usual position of bands27,28 of this type. Unfortunately, as indicated by Hendrickson et al.,*’ the position of this band cannot be used to infer the mode of pseudo-halide bridging. The other vibrational modes are expected at 1300-1400 cm- ’ (v,) and 600-700 cm- ’ (6). The bending vibration (6) is always found to be of low intensity and as such we cannot expect to locate it in a region where there are several strong counterion bands. The symmetric stretch, however, can be of varying intensity, depending upon the symmetry of the bound pseudohalide.29*30 Unfortunately, in our case, these bands appear overlapped by the strong bands of the nn’ tetradentate ligand in the same region. Finally, there is an interesting feature in the IR spectrum of the cyanato complex of Ni”: one intense band appears at 3600 cm-‘, characteristic of coordinated hydroxo group, in agreement with analytical data of this complex (see Experimental). The presence of both OH- and NCO- ’ acting as bridging ligands is frequent in dinuclear com- plexes of Cu” or Ni”.3’

Owing to a lack of structural data due to the bad quality of the microcrystals obtained, only the magnetic and EPR measurements can be used to infer the mode of coordination of the pseudo-halide ligands : monodentate or bridging mode.

Complexes of copper(I1) and nickel(I1) 81

Magnetic measurements

Both Ct.? complexes follow the Curie-law, with an XMT value constant with the temperature (ca 0.4 cm3 mall ’ K for both complexes, a typical value for one electron with a g value of ca 2.1). At very low temperatures the x~T values decrease, indi- cating crystal interactions between the molecules. According to these data we may suppose that both complexes are mononuclear ; but in the case of the azido derivative, the analytical data correspond exactly to a dinuclear complex with one azido bridge (see Experimental). Although not very frequent, there are some examples in the literature in which two Cu” ions are linked by only one azido group. In these cases, very weak antiferro- magnetic behaviour or not coupling at all is observed.2’,22

EPR spectra of both complexes can be indicative of the species present in the solid state or in solu- tion. In the solid state (room temperature and 4 K) the pattern of the azido-derivative is shown in Fig. l(a). Two bands are present : the first, very strong broad, at g = 2.20 corresponds to the AM, = ) 1 transition, and the second, weak, at g = 4.30 may correspond to the AM, = & 2 transition. This AM, = f2 transition is about 10 orders of mag- nitude less intense that the full-field (AM, = + 1) transition. The cyanato complex (Fig. lb) exhibits

1000 2000 a000 4000 (t

Fig. 1. EPR spectra of Cu” complexes in the solid state (4 K) : (a) N,- derivative; (b) CNO- derivative.

an EPR pattern quite similar to that of the azido complex: g = 2.15 and g = 4.3. The AM, = f2 transition is very weak at room temperature but very intense (about half the intensity of the full- field, AM, = f 1, transition) at 4 K. A very similar case has been reported by Hendrickson et al. ” for [Cu(tren)(NCO)](BPh,) in which tren = 2,2’,2”- triaminotriethylamine, a tetradentate ligand similar in its coordination to nn’. Hendrickson formulates this complex as dinuclear, because its X-ray molec- ular structure shows that the cyanate is N-bonded to one trigonal-bipyramidal copper cation in the axial position and hydrogen bonded through its oxygen atom with one of the nitrogen atoms of the tren ligand coordinated to the second copper atom. In Hendrickson’s complex, as in the present case, there is no exchange interaction detectable between the two Cu” ions, but AM, = +2 transitions are seen in the EPR spectra. In practice, AM, = f2 transitions are expected to be strong mainly for dimers with CuCu distances between 3 and 5 A. ’ 5-32 When the Cu-Cu distance is large and the zero-field parameter D is thus small, the in- tensity of the AM, = +2 will be low. Applying the formula reported by Bencini33 to determine weak exchange interactions from EPR spectra, the J parameter so-calculated would be of the order of - 0.10, - 0.15 cm- ’ (not detectable from suscepti- bility measurements).

In frozen ACN solution (13 K) both spectra are different. For the azido derivative two bands are present: the first, very strong and slightly aniso- tropic (Fig. 2a) with g1 = 2.10 and gll = 2.40 (as a shoulder) and the second, weak, at g = 4.30. This AM, = f 2 transition is about five orders of mag- nitude less intense than the full-field (AM, = & 1) transition and there is no possible assignment with- out the postulation of Cu-Cu pairs in ACN solu- tion. l7 This indicates that we are indeed dealing with CL? dimers. In contrast, a frozen ACN solu- tion (13 K) of cyanato derivative shows only a strong signal, slightly anisotropic with gll = 2.45 (as a weak shoulder) and g1 = 2.10 (Fig. 2b). There is no signal at g = 4 (AMs = + 2). This different behaviour for azido or cyanato complexes agrees with the analytical data : we assume that the azido complex is dinuclear, with N3- acting as bridging ligand while the cyanato complex is simply mono- nuclear with NCO- acting only as a monodentate ligand, as it is for the very similar N,N’-bis(8-qui- nolilethylenediamine)monochlorocopper(II) per- chlorate derivative, 3 previously reported by us. The EPR pattern gn > gl, even if less marked in the actual case than in the chloro derivative, 3 indicates that the coordination can best be described as a distorted tetragonal pyramid, in which the N atom

88 C. DIAZ and J. RIBAS

a

Tl . 10

,” /

b

I . 1 1 . 1 .

1000 2000 3000 4000 (1 Fig. 2. EPR spectra of Cu” complexes in ACN solution

(13 K) : (a) N,- derivative ; (b) CNO- derivative.

of the pseudo-halide occupies the axial position and the unpaired electron is in a d,z_,,z orbital.

The magnetic behaviour of both Ni” complexes is shown in Figs 3 and 4 in the form of the temperature dependence of XMT. When the bridging ligand is N3-, upon cooling down, XMT gradually decreases to zero (Fig. 3). On the other hand, there is a clear maximum of the susceptibility near 15 K. This behaviour of XM or XMT is typical of a weakly antiferromagnetic coupling. Similar results are obtained when the bridging ligand is NCO-, but in

2.375

IiT

1.9

0.475

0 0 50 100 150 200 250 T

Fig. 3. Temperature dependence of XMT for Ni-N, complex (3).

2.5

2

1.5

1

0.5

01 0 50 100 150 200 250 I 300

Fig. 4. Temperature dependence of X,T for Ni-NC0 complex (4).

this case the curve of XM vs T does not present any maximum ; upon cooling down, the curve XMT vs T is nearly constant up to 100 K and then decreases to 0 (Fig. 4). This behaviour corresponds to a very weakly antiferromagnetic coupling.

If we assume that the observed magnetic curves are intrinsic to the dinuclear entities, applying the phenomenological Hamiltonian H = - JSISz, the equation for a dinuclear Ni” complex is :

2N/12g2 XM = kT

exp (J/kT) + 5 exp (3J/kT)

x 1 + 3 exp (J/kT) + 5 exp (3 JILT) (l-6)

+ ‘W2g2 6

3kT ’

where the symbols have their usual meaning. J is the exchange coupling parameter and the molecular weight of the impurities is assumed to be equal to that of the actual complexes. J, g and 6 parameters were determined by looking for the minimum of R = &, (x“~~-x~~‘~)~/~ (xobs)2.

The values so-found were J = - 11.5 cm-‘, g = 2.14 and 6 = 0.025 for 1 and J = - 3.9 cm- ‘, g = 2.2 and 6 = 0.03 for 2. The values previously reported by Hendrickson * ‘,’ ’ for similar complexes with the tetradentate ligand 2,2’,2”-triaminotri- ethylamine (tren) are J = - 35 cm- ’ (N3- bridging ligand) and J = - 3.95 cm-’ (NCO- bridging ligand).

CONCLUSION

From analytical, spectroscopic data (EPR) and magnetic measurements we can conclude that the four complexes have different structure. We can summarize these structures as follows :

Complexes of copper(I1) and nickel(I1) 89

\\ 11.

pr\_cl/ $- 12. \

\ 1 2

13.

14.

In the case of dinuclear complexes of Ni” we must 17.

suppose that either N3- or OCN- has an end- to-end coordination, due to the antiferromagnetic 18. coupling. 6* ’ ‘* ’ 7 When both pseudo-halide ligands are bridged in end-on coordination the coupling is ferromagnetic. ‘9 ’ 4, ’ 6 19.

20. Acknowledgement-Financial assistance from the CICYT (Grant MAT88-0545) is acknowledged. 21.

22.

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