IMIDO COMPLEXES DERIVED FROM THE REACTIONS OF NIOBIUM AND TANTALUM PENTACHLORIDES WITH PRIMARY AMINES - RELEVANCE TO THE CHEMICAL-VAPOR-DEPOSITION OF METAL NITRIDE FILMS

Reactions of niobium and tantalum pentachlorides with tert-butylamine (greater than or equal to 6 equiv) in benzene afford the dimeric imido complexes [NbCl2(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) (90%) and [TaCl2(N( t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) (79%). The niobium complex exists as tw o isomers in solution, while the tantalum complex is composed of three major isomers and at least two minor isomers. Analogous treatments wi th isopropylamine (greater than or equal to 7 equiv) give the monomeri c complexes NbCl2((NPr)-Pr-i)((NHPr)-Pr-i)((NH2Pr)-Pr-i)(2) (84%) and TaCl2((NPr)-Pr-i)((NHPr)-Pr-i)((NH2Pr)-Pr-i)(2) (84%). The monomeric c omplexes are unaffected by treatment with excess isopropylamine, while the dimeric complexes are cleaved to the monomers MCl(2)(N(t)Bu)(NH(t )Bu)(NH(2)(t)Bu)(2) upon addition of excess tert-butylamine in chlorof orm solution. Treatment of niobium and tantalum pentachlorides with 2, 6-diisopropylaniline affords insoluble precipitates of 2))(2)C6H3)](2) [NbCl5(N(2,6-(CH(CH3)(2))(2)C6H3))] (100%) and ))(2)C6H3)](2)[TaCl5-(N (2,6-(CH(CH3)(2))(2)C6H3))] (100%), which react with 4-tert-butylpyrid ine to afford the soluble complexes [4-t-C4H9C5H4NH](2)[NbCl5 (N(2,6-( CH(CH3)(2))(2)C6H3))] (45%) and -C4H9C5H4NH](2)[TaCl5(N(2,6-(CH(CH3)(2 ))(2)C6H3))] (44%). Sublimation of [NbCl2(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu) ](2), MCl(2)((NPr)-Pr-i)((NHPr)-Pr-i)((NH2Pr)-Pr-i)(2), and ))(2)C6H3) ](2)[MCl(5)(N(2,6-(CH(CH3)(2))(2)C6H3))] leads to decomposition to giv e [MCl(3)(NR)(NH(2)R)](2) as sublimates (32-49%), leaving complexes of the proposed formulation MCl(NR)(2) as nonvolatile residues. By contr ast, [TaCl2(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) sublimes without chemical reaction. Analysis of the organic products obtained from thermal deco mposition of [NbCl2(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2) showed isobutylen e and tert-butylamine in a 2.2:1 ratio. Mass spectra of [NbCl2(N(t)Bu) (NH(t)Bu)(NH(2)(t)Bu)](2), [TaCl2(N(t)Bu)(NH(t)Bu)(NH(2)(t)Bu)](2), an d [NbCl3((NPr)-Pr-i)((NH2Pr)-Pr-i)](2) showed the presence of dimeric imido complexes, monomeric imido complexes, and nitrido complexes, imp lying that such species are important gas phase species in CVD process es utilizing these molecular precursors. The crystal structures of C4H 9C5H4NH](2)[NbCl5(N(2,6-(CH(CH3)(2))(2)C6H3))], [NbCl3((NPr)-Pr-i)((NH 2Pr)-Pr-i)](2), 3)(2))(2)C6H3))(NH2(2,6-(CH(CH3)(2))(2)C6H3))](2), and H3)(2))(2)C6H3))(NH2(2,6-(CH(CH3)(2))(2)C6H3))](2) were determined. - C4H9C5H4NH](2)[NbCl5(N(2,6-(CH(CH3)(2))(2)C6H3))] crystallizes in the space group P2(1)/c with a = 12.448(3) Angstrom, b = 10.363(3) Angstro m, c = 28.228(3) Angstrom, beta = 94.92(1)degrees, V = 3628(5) Angstro m(3), and Z = 4. [NbCl3((NPr)-Pr-i)((NH2Pr)-Pr-i)](2) crystallizes in the space group P2(1)/c with a 9.586(4) Angstrom, b = 12.385(4) Angstr om, c = 11.695(4) Angstrom, beta 112.89(2)degrees, V = 1279.0(6) Angst rom(3), and Z = 2. [NbCl3(N(2,6-(CH(CH3)(2))(2)C6H3))(NH2 (2,6-(CH(CH3 )(2))(2)C6H3))](2) crystallizes in the space group P2(1)/n with a = 10 .285(3) Angstrom, b = 11.208(3) Angstrom, c = 23.867(6) Angstrom, beta 97.53 degrees, V = 2727(1) Angstrom(3), and Z = 2. H3)(2))(2)C6H3))(N H2(2,6-(CH(CH3)(2))(2)C6H3))](2) crystallizes in the space group P2(1) /n with a = 10.273(1) Angstrom, b = 11.241(2) Angstrom, c = 23.929(7) Angstrom, beta = 97.69(2)degrees, V = 2695(2) Angstrom(3), and Z = 2. These findings are discussed in the context of niobium and tantalum ni tride film depositions from molecular precursors.