Indian Journal of ChemistryVol. 23A, February 1984, pp. 169-171

Complexes of Some Bivalent Metals with4-Substituted Benzofuro[3,2-dJpyrimidines

A C HIREMATH*, M B HALL! & N V HUGGIDepartment of Chemistry, Gulbarga University, Gulbarga 585 106

Received 20 April 1983; revised and accepted 10 October 1983

Complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(IJ) and Hg(II) with4-hydrazinobenzofuro [3, 2-d] pyrimidine (L) and 4-aminobenzo-furo [3, 2-d] pyrimidine (L') have been isolated and characterized onthe basis of analytical, conductance, magnetic moment, electronicand infrared spectral data. The ligand field parameters such as Dq, B',p, LFSE, etc. have been evaluated for Co(II), Ni(lI) and Cu(IJ)complexes.

In continuation of our earlier work 1 on the metalcomplexes derived from 4-methoxy /ethoxybenzofuro[3, 2-d] pyrimidine, we now report here complexes ofsome bivalent metals with 4-hydrazino/aminobenzo-furo [3, 2d] pyrimidine.

All the metal chlorides used were of AR grade. Theligands, 4-hydrazinobenzofuro [3, 2-d] pyrimidine (L)and 4-aminobenzofuro [3, 2-d] pyrimidine (L') wereprepared by the reported procedure".

The complexes were prepared by treating the hotethanolic solution of the ligand L with a solution ofmetal chloride in 1: 1 (metal: ligand) molar ratio in thesame solvent. The Cu(II) and Cd(II) complexesseparated out immediately, while the rest of thecomplexes precipitated on refluxion for 2 hr andconcentration. For the complexes of ligand L', themixture of aqueous metal chloride solution and theligand in DMF (in appropriate molar ratio) was heatedwith magnetic stirring. Except for the Cu(Il) complex,the formation of complexes was facilitated by theaddition of solid sodium acetate. The reaction mixturewas concentrated when an oily mass formed; it wastreated with solvent ether to isolate the solid complex.The complexes thus separated were filtered, washedwith appropriate solvent and dried in vacuo over fusedcalcium chloride. Efforts to get Zn(II) and Hg(II)complexes of L' did not succeed.

The complexes were analysed for the metal andchloride by gravimetric methods? and the nitrogen wasanalysed by Kjeldahl's method. The measurements ofmolar conductance, magnetic susceptibility, electronicand infrared spectra were made as reported in ourearlier paper! . The electronic spectra were recorded fora few complexes in solution (DMF, _10-3 M),.in theregion 900-340 nm on an Elico model CL-24spectrophotometer.

The analytical data (Table 1) indicate 1: 1(metal: ligand) stoichiometry for all the complexes of L

and Curll) complex of L'. Rest of the complexes of L'have 1:2 stoichiometry. All the complexes are solublein DMF, DMSO and pyridine, except NiL~CI2.H20which is soluble to a limited extent in DMF. Thecomplexes are insoluble in common organic solventsexcept Co(II) and Hg(II) complexes of L, which aresoluble in acetone, nitrobenzene, acetonitrile, etc. TheCo(II), Ni(II) and Cu(II) complexes of L' are hydrated.These complexes lose water on heating in an oven at_110°, which indicates the presence of water ofcrystallization. The thermal analyses (TGA and DT A)data of the complexes show the dehydration around80-95", 80-100e and 90-110DC for the Co(II), Ni(lI) andCu(IJ) complexes respectively. According to Nikolev etai", water eliminated below l30cC can be consideredas the lattice-held water. The presence of the watermolecule is also indicated by the endothermic peaks inDTA curve.

The molar conductances in 0 MF ( - 10 - 3 M) of allthe complexes, except the Ni(JI) complexes, are in therange 1.5-23.7 ohm -1 cm 2 mol- 1 suggesting them tobe non-electrolytes. The Ni(II) complex, NiLCI2, hasan appreciable molar conductance (42.2 ohm -1 cm2

mol-I); probably it is due to solvolysis in DMF. Thevalue is, still, less than that expected for 1: 1 electrolyticnatures. However, the Ni(II) complex of L' ligand has1:1 electrolytic nature (86.15 ohm-l em" mol-I).

Table l=-Analytical and Magnetic Moment Data of theComplexes

Complex m.p. Found (Cal.), % /ld.CC) B.M.

M N CI

CoLCI2 300 17.6S 16.37 21.44(17.85) (16.97) (21.52)

NiLCI2 300 17.89 16.69 21.32(17.80) (16.98) (21.53)

cuter, 240 18.27 16.70 21.11(18.98) (16.74) (21.22)

ZnLCI1 280 19.56 16.27 21.39(19.44) (16.65) (21.21)

CdLQl 300 29.66 14.32 18.41(29.32) (14.61) (18.52)

HgLCI1 200 42.14 11.71 IS.32(42.S3) (11.87) (1S.05)

CoL1CI1H1O 210 11.68 16.48 13.S8(11.37) (16.22) (13.71)

NiLiC12H2O 270d 11.03 IS.94 13.S7(11.34) (16.23) (13.71)

CuL'CI2HzO 280 18.96 13.2 21.41(18.81) (12.44) (21.04)

CdL1CI2 300 19.99 15.22 12.5S(20.31) (IS.18) (12.83)

4.31

3.12

1.56

4.8

3.3

1.61

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INDIAN J. CHEM., VOL 23A, FEBRUARY 1984

The observed magnetic moment (4.31 B.M.) forCoLCl2 falls in the range expected (4.3-4.6 B.M.) fortetrahedral Co(ll) complex", In the case ofCuL~CI2.H20, the ILerr value observed (4.8 B.M.) ishigher than the spin-only value, suggesting a high-spinoctahedral structure for the complex. The ILerr. values(3.12 and 3.3 B.M.) observed for the two Ni(I1)complexes are indicative of octahedral geometryaround Ni(II) ion", The Cu(II) complexes showmagnetic moments 1.56 and 1.61 B.M. which areconsistent with the presence of one unpaired electron.However, these somewhat low values may be due tospin-orbit coupling through super exchange pheno-menon 7. The CU(II) complexes may, therefore, beconsidered to have distorted octahedral symmetry.

The solid state electronic spectrum of CoLCl2 showsbands at 8333 and 15380 cm -I with a shoulder at16670 em -I attributable to characteristic tetrahedraltransitions 4A2--.4TI(F)(v2) and --.4TI(P)(V3) re-spectively. The intense band observed around 28000cm - I may be a charge-transfer band. Considering theenergy of V3transition as the average of the bands at15380 and 16670 cm-I, the various ligand fieldparameters have been evaluated" [Dq =495 em -I, B'=633 cm "", f3=0.65, f3°=34.53~~; V2/VI= 1.68 andLFSE = 16.97 kcal/mol], The light green colouredsolid CoLCl2 dissolves in DMF exhibiting anabsorption band at 15150 em-I (e=210) with ashoulder at 16670 cm -I (s = 185)which may be due toV3 transition", The V2 band could not be located(instrumental limitation). The complex on dissolutionin a strong coordinating base like pyridine shows acharacteristic band around 19300 em -I which may beprobably due to coordination of two pyridinemolecules resulting in an octahedral geometry aroundthe Co(I1) ion!". An appreciable reduction in B' (633em - I) and a spin-orbit coupling constant X (- 133)suggests a considerable covalent character of metal-ligand bond [free ion values X = - 178, and B' = 967~m-I for Co(I1) ion]",

For CoL~. H20 (light pink), the electronicabsorption bands (nujol) appear at 8333 and 19610em -1 due to 4TI9(F)--.4T29(F)(VI) and --.4TI9(P)(V3)transitions respectively in an octahedral environment.The band due to the 4TI9(F)--.4A29(F)(V2) transitioncould not be observed because of its very lowintensity I I. However, the position of V2band has beencomputed (17713 cm - I) by the equation v 2 = VI+ 10Dq. The intense band around 30000 em -I may bea charge-tranfer band. The various ligand fieldparameters calculated as Dq = 947 em -I, B' = 827cm-I, f3=0.86, PO=14.47~~, V2/VI=2.13 and LFSE= 16.22 kcal/mol, further support the aboveconclusion for an octahedral geometry.

170

Both the Ni(II) complexes show absorption bands(nujol) in the regions 8300-8400, 13700-'14100 and24400-25300 ern" I assignable to the transitions3A29(F)--.3T29(F)(vd, --.3TI9(F)(v2), and--.3TI9(P)(V3) respectively in an octahedral sym-metry+'. The Racah parameters B' (880,942 em - I) andthe spin-orbit coupling constants X ( - 213, - 275) areless than the free Ni(II) ion values (B' = 1040em -I, X =- 315)13, suggesting considerable covalent characterof the metal-ligand bonds and orbital overlap. Thevalues of ratio V2/VI(1.69 and 1.63) and LFSE (28.6kcal/mol) for the complexes clearly indicate theoctahedral configurations. The electronic absorptionspectrum of NiLCl2 in DMF solution shows V2and V3transitions at 15130 cm-1 (e=28) and 26315 cm "! (s= 220) respectively suggesting a similar geometry insolution.

For Cu(I1) complexes a single broad asymmetricband (nujol) with the maximum in the region 14300-14800em -I is observed; this band is attributable to 2 Eg--.2 T29 transition in a distorted octahedral geometry 14.An intense band around 25000 em -I may be a charge-transfer band. The absence of any band below 10000em - I or above 17000 cm - I rules out the possibility oftetrahedral I5 or square-planar 16 symmetry. Thesolution (DMF) spectra of these complexes also exhibita single asymmetric band in the region 13000-13500em - 1 due to distorted octahedral geometry.

The IR spectra of Co(II), Ni(I1) and Cu(II) complexesof L' exhibit a broad band in the region 3475-3400em -I which may be attributed to vOH mode of thelattice-held water molecule I 7. The strong to mediumintensity bands observed at 3330 and 3090 em -I in thespectrum of the ligand L are assigned to vasNH andv sNH vibrations respecti vely18ofthe secondary aminogroup. The medium to strong bands observed in theregions 3270-3200 and 3350-3170 em -I are attributedto the NH2 stretch"? of the amino group in L'and L'respectively. The bands due to v NH remain unalteredor show slight blue shifts in all the complexes of Lsuggesting no coordination through secondary aminogroup of the hydrazine residue. The NH2 stretchingfrequencies of the primary amino group in thecomplexes, however, shift to lower frequency side withloss in intensity. This is an indication of coordination ofamino group through nitrogen in the complexes ofboth the ligands. The coordination of amino group ofhydrazine residue of ligand L is further supported bythe blue shift of N-N stretch?", from 940 to 945-950em -I. Likewise, the coordination of amino group of L'is supported by positive shift ofC-N stretch+' from thefrequency range 1385-1340 em - 1 to 1390-1350 cm -I .

The strong to medium intense bands observed in theregion 1210-1140em - I in the spectra of free ligands areascribed to C-O-C stretch of the furan ring+', On

complex formation, these shift to lower frequency sidewith varying intensities suggesting the involvement offuran oxygen in coordination in all the cases. Theinvolvement offuran oxygen in coordination is furthersupported by the appearance of non-ligand bands inthe region 560-500 cm -1 in the far IR spectra of thecomplexes which are attributed to M-O stretchingmode+'. The medium to strong bands observed in theregion 416-380 cm.-I in the complexes are attributed toM-N stretching vibrations/". The M-Cl stretchingbands are attributed in the region 355-275 em -I in anthe complexes except Ni(II) and Cu(IJ) complexes of L,while in the latter complexes, both terminal andbridging M-Cl stretching vibrations." are assigned at270, 230 and 320, 260 ern - 1 respectively in view of theirhalogen bridged polymeric nature.

On the basis of analytical, solubility and spectraldata, ligand bridged polymeric octahedral structuresmay be proposed for all the complexes of L' andchloride bridged polymeric octahedral structures forNiLCI2 and CuLCI2. Both ZnLC12 and CdLCl2complexes may have ligand bridged polymerictetrahedral geometries. Further, due to the low meltingpoints and solubility in common organic solvents,CoLC12 and HgLCl2 may be assigned monomerictetrahedral configurations.

The authors are thankful to Prof. S.P. Hiremath,Head, Department of Chemistry, Gulbarga University,Gulbarga, for providing facilities and to Dr D.N.Sathyanarayana, Indian Institute of Science, Banga-lore, for fruitful discussion. One of the authors (MBH)is thankful to the CSIR, New Delhi, for a SeniorResearch Fellowship.

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NOTES

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83 (1961) 4690.10 Aggarwal R C & Narang K K, Inorg chim Acta, 7 (1973) 651.11 Lever A B P, Coord chern Rev, 3 (1968) 119.12 Lever A B P, Inorganic electronic spectroscopy (Elsevier,

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438.(b) Smith D W, Inorg.Chem, 5 (1966) 223b.

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(1977) 81.18 Giguere P A & Liu T D,} chem Phys, 20 (1952) 136.19 Rao C N R, Venkataraghavan R & Kasturi T R, Can} Chern, 82

(1964) 36.20 Sacconi L & Sabatini A,} inorg nucl Chern, 25 (1963) 1389.21 Jain S C, Gill M S & Rao G S,} inorg nucl Chem, 58 (1981) 210.22 Joseph K U & Somayajulu V V,} Indian chern Soc, 56 (1979) 465.23 (a) Sukla P R & Takru R,} Indian chern Soc, 57 (1980) 252.

(b) Savant V V, Gopalkrishnan J & Patel C C, lnorg Chern, 9(1970) 748.

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nucl Chem, 36 (1974) 73.

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