Pyrophosphate complexes of copper(II)

J. inorg, nuct. Chem., 1976, Vol. 38, pp. 1371-1372, Pergamon Press. Printed in Great Britain

NOTES Pyrophosphate complexes of copper(ll) (First received 3 July 1975; in revised form 17 September 1975)

THE pyrophosphate anion is an important member of the pentavalent phosphorus compound group. Despite the number of metal complexes characterized in solution, there are only few cases where the species have been isolated[l]. We report here the preparation, characterization and solid IR spectra of a series of complexes containing both, the pyrophosphate and a nitrogen donor ligand, namely, 2,2'-bipyryl(bipy), 1,10-phenanthroline (phen), pyridine (py) and pyridine-d~ (ds-py). The complexes can be formulated as [Cu(P2OTH2)L, ] where L is any of the nitrogen donor ligand and n = 1 for bipy or phen and 2 for py or drpy.

the Instituto de Quimica and the copper and sodium analyses were by atomic absorption. Table 1 gives the analytical data for the compounds reported here. No conductivity data could be obtained as the complexes are insoluble in most of common solvents. RESULTS AND DISCUSSION The IR spectra of the compounds were recorded in the range 400(0250 cm -I. Table 2 gives the bands of the pyrophosphate ligand and their assignment. The organic ligand bands present the expected shifts upon coordination [3-5] and hence are not given in this paper. The assignment of the bands was done by comparison with the data reported for some pyrophosphate salts [6.-8] and with the aid of the deuterated pyridine complex. In most cases it was possible to identify a medium and broad band at about 2700-2600 era-' and a weak one centered at about 2100 cm ' probably due to the stretching mode of the P-OH group. According to group theoretical methods and assuming a Dsd symmetry for the pyrophosphate anion, three P-O stretching bands should appear in the IR spectrum. The appearance of a fourth stretching band at ca. 700 cm -~ which should be Raman active only and due to the symmetric P-O'-P stretching mode of A~, symmetry can be attributed to the departure of the pyrophosphate ligand from that structure. O' denotes the bridging oxygen. In fact, the X-ray structure determination[9] has shown that the P-O'-P angle in the Na4P2OT'IOH20 is ca. 134°. The

EXPERIMENTAL The compounds reported here were prepared by a general method. Copper(II) pyrophosphate was dissolved with the aid of sulfuric acid (2 M) until the pH was about 1.812]. The light blue solution so obtained was treated with a slight excess of nitrogen donor ligand dissolved in anhydrous ethanol. The precipitate was filtered off, washed with ethanol and dried in vacuum at 60°C. From the blue solution obtained by dissolving the copper(II) pyrophosphate in sulfuric acid, the compound [Cu(P2OT) (H:O)2]Na:,H20 was isolated. The rather high conductivity of this compound in water (AM2s° = 338 mhos cm 2 mol-') is probably due to a large dissociation of the complex anion in this solvent. The IR spectra were obtained in KBr and nujol mulls and recorded in Perkin Elmer 457 and 237B spectrophotometers. The analyses were obtained in the laboratory for organic analysis of

Table 1. Analytical data for the pyrophosphate complexes of copper(II)" C%

H%

N%

Cu%

Na%

[Cu(P207H2)(bipy)] 1.5H20

28.4(2B.q)

2.6(2.6)

6.3(6.9)

14.9(15.0)

--

[Cu(P2OTH2)(phen) ]

36.5(34,3)

3.0(2.8)

5.8(6,6)

15,5(15.1)

--

~u(P2Q7H2)(DV)2~

30.7(30.3)

3.1(3.0)

6.8(7.0)

15.9(16.0)

--

~u(P207H2)(ds-PV)23

29.1(29.q)

3.5(2.9)

6.2(6.9)

15.4(15.6)

--

[CU(PzOT)(H20)2] Na2.H20

.

.

.

.

.

.

18.?(18.8)

13,6(13.6)

a) Calculated velues are glwon in parentheses,

Table 2. IR bands (cm-') of the pyrophosphate ligand in complexes of the type [Cu(P207H2)L,

]"

(n

i L

O(P-O)

05

~(P-O)

011

Q(P-O') b

OCP-O')

06

~z

~(qPG)

~(OOQ)

~(OPO')--

07

~13

012

Bipy

1190m

1110s I030m

9B?ms gO6ms

?32m

n.o

556ms

510ms ~19m

Phen

1157~

1119s qO62w

999w 909vw

740m

605w

n.o

492sh ~32w

PV

1192s 1155n

ggBm 902~

7~5s

n.o

565ms

1020s

52Bs ~gBms 435ms

1100S

gs2~.a

C

568W

n.O

110Bs I058S

g91ms

760ms

605ms

55Bms

ds-Py 11558 H~O

1168@ 11&28

495rr~ ~70m q51w

Ne~P2OT,ION ~--

1162s 1112s 98Bms 935s 617w 565s 523m 1152@ 1031 908@ 576s 493m 11~@ ~ ~27e a) Assignment based on e D.~ model, 0 ,06 and ~7 ere c f svmmetrV; and ~.. ar~ of E svmm~t~V and ~ o~ A1g svmm~try. ~2u ~11'012 b) O' de~tes the b~idging oxvgen 2 c) covere~ PV a strong asborption n.o, not observeO

1371

=

1,2)

1372

Notes Table 3. IR bands (cm-~) below 500 cm-' of the complexes of the type [Cu(P2OTHz)L, ] (n = 1, 2) L:

bipy

phon

py

ds-Dy

A920

495w

H20

432e

~98s 463s A35s

~9~as 39~ 370w

398tas 372n.

/,06~xs 36Oa~

/,06rm 37ow

---

297ms 278~rg

30~e 282s

33Os 285s

287w 265s

292s

intensity of the band at about 700cm-' in the IR spectrum suggests that the P-O'-P angle varies to accommodate the sizes of the various metal ions as well as under the presence of rigid ligands. In the sodium pyrophosphate this band appears as a strong one, whereas in the complexes reported here is of medium to weak intensity. To establish a more precise relationship it would be desirable to measure the integrated intensity of such a band and to compare with the value of some pyrophosphates of known structure. Unfortunately, the high insolubility of the pyrophosphate salts and their complexes prevent such a measurement. We tested, in a semiquantitat!ve way, the above suggestion for four pyrophosphates whose bridging angles were known[10] and find that the greater the angle the smaller is the intensity of the v2 band (see Table 2 for notation). The presence of a rigid ligand such as phenanthroline or bipyridyl exerts a stronger influence in the intensity of v2 than the size of the metal ion. Thus, in the phenanthroline and bipyridyl complexes v2 is of medium intensity, whereas in the pyridine and aquo complexes where the ligands can accommodate themselves to minimize the repulsion, such a band is of medium to strong intensity. Since the pyrophosphate is acting as a bidentate ligand the complexes seem to be four coordinated. However, we believe that copper achieves the six coordination through long contacts with oxygens of adjacent molecules on each side of the planar unit. This model would also explain the polymeric nature, although polymeric structure involving hydrogen bonding cannot completely be ruled out. The planar CuN202 group has a C2~ symmetry and hence two copper-nitrogen and two copper-oxygen stretching bands should be observed in the IR spectrum. The copper-nitrogen stretching modes were assigned to the bands observed at about 400360 cm-', whereas the copper-oxygen stretching modes occur at about 300-260cm-~[11-13]. Table 3 lists the IR bands below 500 cm -1 and their assignment. The reaction of the copper-pyrophosphate solution with ligands other than nitrogen donor are being carried out, Magnetic measurements at room temperature on the bipyridyl and phenanthroline complexes yielded values of 1.40 and 1.41 B.M.

Assig nm ~nt ligand lig~nd lig,~d lig~nd

47Oms

vibr ~tion vibration vibration vibration

~Cu-N str~tehings Cu-O strctchings

270s

respectively, whereas for the pyridine complex a value of 1.54 B.M. was found. The unexpected low values of the magnetic moment of these complexes are being reviewed and a temperature dependence study will be carried out.

Acknowledgements--This work was supported by an operating grant (No. 2.15.04) from the Scientific Research council (CIC) of the University of Concepcion. Instituto de Quimica Universidadde Concepcion Casilla 3-C, Concepcion Chile

J. G. CONTRERAS G. V. SEGUEL

REFERENCES I. C. Dragulescu and M. Valceanu, St. Cerc. Chim. Tom. 17, 357 (1%9). 2. A. Ram, S. Kumar and B. C. Sinha, Indian J. Chem. 1, 237 (1%3). 3. J. S. Strukl and J. L. Walter, Spectrochim. Acta 27A, 223 (1971). 4. R. G. Inskeep, J. lnorg. Nucl. Chem. 24, 763 (1%2) and A. A. Schilt and R. C. Taylor, Ibid. 9, 211 (1959). 5. N. S. Gill, R. H. Nuttall, D. E. Scaife and D. W. A. Sharp, J. Inorg. Nucl. Chem. 88, 79 (1961). 6. R. W. Mooney and R. U Goldsmith, J. Inorg. Nucl. Chem. 31, 933 (1%9). 7. R. Hubin and P. Tarte, Spectrochim. Acta 23A, 1815 (1967). 8. E. Steger and B. Kabher, Spectrochim. Acta 24A, 447 (1968). 9. D. M. MacArthur and C. H. Beevers, Acta Cryst. 10, 428 (1957). 10. S. D. Ross, Inorganic Infrared and Raman Spectra. McGrawHill, London (1972). I1. J. R. Ferraro, Low-Frequency Vibrations of Inorganic and Coordination Compounds. Plenum Press, New York (1971). 12. K. Nakamoto, lnfrared Spectra of Inorganic and Coordination Compounds, 2nd Edn. Wiley-Interscience, New York (1970). 13. D. M. Adams, MetaI-Ligand and Related Vibrations. St. Martin's Press, New York (1%8).

J. inorg,nucl.Chem.,1976,Vol.38, pp. 1372-1374. PergamonPress. Printedin GreatBritain

Mixed valence vanadium spinel of zinc (Received 6 February 1975) IN the course of investigation[l] of AV03 (A = divalent metal ions) oxides, compounds with large A cations were prepared by hydrogen-reduction of the corresponding vanadium(V) oxides, e.g. LaVO~ from LaVO4. Surprisingly, however, attempts to prepare AVO~ oxides with smaller A cations (r,, - 0.6 ~, e.g. Zn) by hydrogen-reduction of Zn2V207, yielded only spinel-type phases. Details of the reduction procedure and the structural and physical characterizations of this spinel phase are reported in the following sections.

EXPERIMENTAL Zn2V207 was prepared by the interaction of V205 with ZnO in an intimate 1 : 2 molar mixture at 650-7000 for 48 hrs. Reduction of Zn2V20~ was carried out by passing hydrogen slowly over it for 24 hr, at 600°C. The product was analyzed for total vanadium and that in lower oxidation states by the method described earlier [2]. The analytical results are; total V=32.12wt.%. Reducing power = 1.68 equivalents per mole. These are in agreement with the respective values required for Zn,.~Vz.~O4. As the ratio of V to