IDdian Journal of ChemistryVol. 16A, October 1978, pp. 859·861

Studies on Nitrido Complexes of Osmium(VI) withN -Heterocyclic Bases

D. SEN & N. C. TA*Department of Chemistry, Indian Institute of Technology, Kharagpur 721302

Received 11 November 1977; revised 17 April 1978; accepted 17 May 1978

K[OsNX.(H.O)]H.O is found to react with N-heterocyctic bases (L) in HX ~iving crystallinecompounds of the type (CH) [OsNX.(H.O)]. Complexes of the type OsNXaL, OsN(QO),X andOsN(Py)Br3(H,O)(L = 2,2'·dipyridyl, 1,lO-phenanthroline; QOH = oxine, Py = pyridine; X = Cl,Br) have also been prepared. The compounds have been characterized on the basis of elementalanalyses, IR and thermal analysis data. In the IR spectra of the complexes, vOs:=N is loweredconsiderably due to the replacement of halogen by L (L = 2,2'·dipyridyl, 1,lO-phenanthroline,oxlne, pyridine) in the coordination zone. This is, most probably, due to variation of It-donorcapacity of the bases in these complexes.

BESIDES potassium nitridotetrahaloaquoosmate(VI) monohydrate, K[OsNX4(H20)]H20 (X =Cl, Br)1-3, only a [few osmium complexes of

the types R(OsNX4) (R = Ph4As, Bu4N; X = Cl,Br)'; CS2 [OSNXS]4; K[OsN(H20) (CN)J5; OsNCl3B2(B = PPh3, AsPh3, SbPh3)6 have been isolated.But for a short communication", mixed ligand nitridocomplexes of osmium(VI) with N-heterocyclic basessuch as 1,1O-phenanthroline, 2,2'-dipyridyl, oxineand pyridine have not been reported so far. Resultsof our study on formation, isolation and charac-terization of different nitrido complexes of osmium(VI) with N-heterocyclic bases are rcported in thispaper.

Materials and MethodsThe reagents used were of AR grade. Nitrogen

was estimated by Dumas sermrmcro method.Osmium was determined by spectroscopic methodas osmium-thiourea complex''. A weighed sampleof the complex was fused with sodism carbonateand sodium peroxide; halogen Was estimated assilver halide from the aqueous extract of the fusedmass. Infrared spectra were recorded in nujolmull on a Perkin-Elmer 421 infrared spectrophoto-meter.

Potassium nitridotetrahaloaquoosmate(VI) mono-hydrate, K[03NX4(H20)JH20, was prepared bydissolving potassium nitridoosmate(VIII) , KOsN03,in HX in presence of KX (X =Cl, Br)1-a.

(LH)[OsNX4(H20)] complexes - K[OsNX4(H20)].H20 (0·3 mmoles) was dissolved in concentratedHX (2 ml) and a solution of 1,10-phenanthroline or2,2'-dipyridyl (1 mmole) in 3 ml concentrated HXwas added to it with stirring. Stirring was con-tinued for 15 min. A pink crystalline compoundappeared on standing for about 30 min at room

*Present address: Chemistry Department, Jhargram RajCollege, Jhargram, Midnapur, West Bengal.

temperature. This was filtered, washed with smallquantities of concentrated HX and dried in vacuoover potassium hydroxide.

OsNBr3L complexes - K[OsNBr4 (H20)]H20 (0·33mmole) was dissolved in dried ethanol (15 ml) anda solution of the base (L) (4 mmoles) in ethanol(5 ml) was added to it. The mixture was shakenfor 30 min, filtered, washed with ethanol, aqueousmethanol, ethanol and ether. It was dried 1:n vacuo.

Chloro analogue of this compound could not beprepared by this method.

Chloro complexes, OsNC13L and their bromoanalogues were obtained by heating the complexes(LH)[OsNX4(H20)](X = Br, Cl) at 160° in solidstate for 90 min in an atmosphere of nitrogen.

OSN(QO)2X complexes - These were prepared inthe same way as the complexes OsNBr3L by theaddition. of a soluti.on of K[OsNX4(H20)]H20 (0·33mmole) m 5 ml dned ethanol to the solution ofoxine (1'5 mmoles) in 5 ml ethanol.

OsN(Py)Br3(H20) ccmple» - K[OsNBr4(H20)}H20(0·33 mmole) was dissolved in 10 ml dried ethanol.To this solution ~lried pyridine (12 mmoles) wasadded and solution shaken for 30 min. Thesolutio!! was filtered and the filtrate kept for 24hr. Diethyl ether (20 ml) was added to it andsolution was shaken again. The residue was filteredand washed with ether. The residue was againdissolved in dried ethanol and filtered. The com-pound was reprecipitated with diethyl ether fromthe filtrate.

The analytical data of the compounds are givenin Table 1.

The thermal decompositions of the complexes,~LH)[OS~X4(H20)] have been studied up to 250<>m a mtrogen atmosphere. The decompositioncomme~ced.at 160°. The temperature of the systemwas maintained between 160° and 170° for 90 min.The ana}y~is o! the residue corresponds to OSNX3L(L =2,2 -dipyridyl, 1,lO-phenanthroline, X=Cl, Br).

85~

INDIAN J. CHEM., VOL. 16A, OCTOBER 1978

TABLE 1 - ANALYTICAL DATA AND COLOUR OF THECOMPLEXES

Compound Colour Found (Calc.), %

Os X Halogen

(PhenH) [os~·mr.(H20)J Pink 26'68 6·03 44'09(26'28) (5'81) (44'26)

(PhenH) [OsNCI.(H20)J do 34·73 7·51 26·65(34-86) (NO) (26'05)

(DipHl[OsXBr.(H2O)J do 26·81 6·32 46·21(27'18) (6'01) (45,78)

(DipH)[OsNCI.(H2O)j do 36·05 7·71 27'60(36,47) (8'07) (27-25)

C'sNBr3(Phen) Violet 30·04 6·81 38·09(30'44) (6,73) (38-46)

OsXBrs(Dip) Deep 31'12 6·71 40·32red (31,66) (7'00) (40'00)

OsXBr(QO). do 33-72 7·63 14'52(33-21) (7,34) (13'99)

GsXCI(QO)2 do 35-61 7'74 7'29(36,02) (7'96) \6'73)

OsX(Py)Br3(H2O) Red 35'52 5·41 45'02(35'10) (5'20) (44·36)

OsXCIJ(Phen) do 38·74 8·56 21·70(38'25) (8'50) (22'03)

()sXCI3(Dip) do 40·75 8·10 22'82(41'8) (8'28) (23'25)

Results and DiscussionThe anionic complexes, which are represented

as (LH)[03NX!(H20)], can be prepared by theaddition of K[OsNX.1(H20)]H20 to the bases (L)like 2,2'-dipyridyl and Ll.Oephenanthroline in con-centrated HX. These substances are insoluble innon-polar or weakly polar solvents like benzene,chloroform, carbon tetrachloride, diethvl ether,ethanol, etc., but ale readily soluble -in polarsolvents like methanol, acetone and Iormarnide.Their dilute aqueous solutions slowly decomposegiving a brown precipitate producing a weakly acidicsolution containing the corresponding halogen atom.This may be due to the following type of hydrolysis(Eg. 1).[Os NX4(H20)]- +H20-+[OsNX3(OH) (H20)J-

+H++X- ... (1)Most probably the halogen atom trans to Os = N

is replaced by the OH group. The compounds aremoderately soluble in concentrated HX givingintense red colour.

The anionic complexes (LH)[03NX4(H20)](L =2,2'-dipyridyl, 1,l0-phenanthroline) decomposerapidly in the temperature range 160-170° due tosimultaneous elimination of a molecule of waterand HX as given by Eq. (2).(LH)[OsNX4(H20)J = OSNX3L+HX+H20 ... (2)

The IR spectra (Table 2) of all the complexes (LH)[OsNX.1(H20)] show bands in the region 1100-1120crrr ' which may be due to vOs=N vibrationvs,The complexes show a strong band in the region3100-3300 cm! due to vOH. It is difficult to locatethe o(H-O-H) mode of water in the spectra of thecomplexes as both 2,2'-dipyridyl and 1,10-phenan-throline absorb in the region 1580-1650 cm! (ref. 9).A band appears around 900 crrr+ also showingcoordinated watera•lo molecule.

860

IlH) [

N

X <, 'II./" X 1/05 <,

II I HzOII

(:r)

t m ( ~)

(I). L = 2.2'-dipyridyl or 1.10-phenanthrolineX = CI or Br

(II), L = 2.2'-dipyridyl or 1.10·phenanthroline; (III). L =oxinate ion; (IV), py = pyridine

The physico-chemical properties of all these anioniccomplexes (LH)[OsNX£(H20)] indicate the octa-hedral environment of each metal ion as representedin (I).

The complexes OsNBr3L and OsN(Py)Br3(HzO)are diamagnetic in solid state and behave as non-electrolytes in nitrobenzene. These are insolublein water but are readily soluble in acetone and ben-zene. The compounds OSN(QO)2X (X = C1. Br)though stable in nonaqueous solvents, undergohydrolysis in aqueous medium with the formationof corresponding hydroxy compound, OSN(QO)20H,due to strong trans effect of Os=N bond.

The complexes OSNX3L and OSN(QO)2X(X = C1.Br, L = 2,2'-dipyridyl, Ll G-phenanthroline, QOH= oxine) exhibit strong bands in the region lO80-1090 crrr ' characteristic of vOs_N. Some otherIR bands present in the region 1500-1800 cm-l maybe due to v(C =C) or v(C =N) and ring vibrationsof the bases=!", In these complexes, "Os=N vibra-tion is found to be decreased considerably dueto replacement of halogen by L(L = 2,2'-dipyridyl.l,10-phenanthroline, oxine) in the coordinationzone. The delocalized -e-electron system of theligand, above and below the coordination plane,overlaps with the vacant metal d7t-orbitals. Thedrift of electron density from filled ligand 7t-orbitalsto the vacant d7t-orbitals of the highly oxidisedosmium atom will decrease the tendency of themetal atom to attract the nitrogen rr-electrons (inOs=)J") through -e-bonding. This will result inthe decrease of ,,03=N in these complexes.

A comparison of the spectra of OsN(Py)Bra(H20)with that of pyridine indicates the coordinationof the latterlz-l4. The strong absorption band at1110 crn' which corresponds to vOs=N in the caseof K[OsNBr4(H20)]H20 shifts to 1088 crrr ' in OsN(Py)Br3(H20). It has also been observed that theligands, Py, Br in OsN(Py)Br3(HzO) cannot behydrolysed in aqueous solution indicating strongerbond formation in the position trans to nitrido ligand.All these facts can be explained by consideringpyridine to be present in trans position to nitridoligand. The overlap of osmium d-orbital with thepyridine ring 7t-orbitals through nitrogen pz orbitalwill strengthen the pyridine-osmium bond and

SEN & TA: NITRIDO COMPLEXES OF Os (VI)

Compounds

TABLE 2 - INFRARED DATA (NUJOL MULL)

Absorption maxima (em-I)

.K[OsNBr,(H20)]H.O

-K[OsNCl.(H.O)JH20

(PhenH) [OsNBr. (H20)]

OsNBr3(Phen)

OsNC1a(Dip)

05NBr(QO).

3470 (m), 3370 (m), 1590 (m), 1110 (s)917 (w, br)3450 (rn, br), 3100 (m), 1600 (s),1100 (m), 915 (m)3350 (w, br), 3200 (m), 1620 (m),1615 (5),1580 (m), 1525 (w), 1410 (s),1370 (m), 1315 (m), 1222 (m), 1110(s),1065 (w), 915 (w, br), 845 (m), 770 (m)3330 (m), 3190 (m), 1623 (w), 1618 (5),1570 (m), 1520 (m), 1415 (m), 1365(w), 1210 (w), 1102 (5), 1000 (5),920 (m), 770 (m)1615 (5), 1585 (m), 1515 (m), 1430(w), 1350 (sh), 1220 (w), 1150 (m),1080 (5), 870 (WI, 850 (8), 745 (8),720 (sh)3200 (m, br), 3190 (m), 3080 (w),1630 (5), 1612 (m), 1575 (m), 1554 (5),1450 (w), 1330 (m), 1280 (w), 1170(m), 1105 (s), 1030 (m), 1020 (m),928 (s, br], 764 (s)1604 (m), 1582 (5), 1570 (w), 1475 (5),1450 (m), 1320 (5), 1250 (m) , 1170 (m)1135 (w), 1128 (m), 1083 (5),1030 (m)855 (m), 820 (5), 762 (m)3210 (5), 3120 (m, br), 1625 (5),1600 (w), 1522 (m), 1088 (5), 1031 (m),870 (w), 710 (m)1598 (m), 1570 (5), 1500 (s), 1495 (w),1320 (m) , 1272 (rn), 1220 (m), 1170(w), 1090 (5), 1075 (m), 920 (w),815 (s), 800 (w), 740 (w)

w = weak, m = medium, S = strong, br = broad.

consequently decrease the Os_N bond strengthresulting in the decrease of vOs=N.

The physicochemical properties of all the presentcomplexes indicate an octahedral environment forthe metal ion as represented in structures (II-IV).

Acknowled~emellt

The authors express their heartiest thanks toDr P. Pramanik, Dr C. R. Saha and ShriB. Guhaneogi for many helpful discussions.

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