Synthesis and structural studies of dimethylindium(III) complexes with polydentate nitrogen donor ligands, and of monomethylindium(III) complexes containing alkoxide-bridged binuclear cations

Abstract

Dimethylindium(III) complexes have been isolated from aqueous methanol on reaction of dimethylindium(III) nitrate with the neutral nitrogen donor ligands 1,10-phenanthroline, 2,2′-bipyridyl, and 4,4′ disubstituted 2,2′-bipyridyls, bis(pyridin-2-yl)methane [(py)₂CH₂], bis(N-methylimidazol-2-yl)methanol, 2,2′:6′,2″-terpyridyl (terpy), 4,4′,4″-triethyl-2,2′:6′,2″-terpyridyl (Et₃terpy), and N-methyl-2-(pyridin-2-yl)imidazole. X-Ray crystallographic studies at 295 K of two of the complexes reveal the formulations [InMe₂{(py)₂CH₂-N,N}(NO₃-O)(H₂O)](5) and [InMe₂(Et₃terpy-N,N′,N″)]NO₃(8), with trans methyl groups in distorted octahedral [for (5)] and five-co-ordinate geometry [for (8)]. The complexes have In–C 2.119(7)–2.131(8)Å and In–N bond distances 2.310(5)–2.439(4)Å, with In–O 2.632(4)Å(NO₃) and 2.679(5)Å(H₂O) in (5); the InMe₂ groups are bent away from the nitrogen donor ligands, forming InC₂ angles of 157.6(2)[(5)] and 132.8(3)°[(8)]. The In^IIIMe₂ complexes of terpy [(7)] and Et₃terpy [(8)] are photochromic, changing slowly from pale yellow to emerald green in bright light, and back to yellow in darkness. Reaction of [InMe₂]NO₃ with phenylbis(pyridin-2-yl)methanol [(py)₂(Ph)COH], tris(pyridin-2-yl)methanol, tris(N-methylimidazol-2-yl)methanol, bis(N-methylimidazol-2-yl)(pyridin-2-yl)methanol [(py)(mim)₂COH], and (N-methylimidazol-2-yl)bis(pyridin-2-yl)methanol, results in isolation of monomethylindium(III) complexes containing binuclear cations, with the structures of two of these established crystallographically as [I[graphic omitted],[graphic omitted]Me(NO₃)]NO₃·0.75H₂O (10) and [I[graphic omitted],[graphic omitted]Me(NO₃)]NO₃·H₂O·Me₂CO (13). Each ligand has a py group co-ordinated to one indium atom and a py [(10)] or mim [(13)] group co-ordinated to the other indium, with alkoxide bridges forming an In₂O₂ kernel with In–O distances 2.165(6)–2.266(6)Å and trans methyl groups for the ‘equatorial’ planes In₂Me₂(py)₂(µ-O)₂[(10)] and In₂Me₂(mim)₂(µ-O)₂[(13)]. Indium–carbon, 2.119(11)–2.160(13)Å, and In–N bond distances, 2.234(7)–2.409(9)Å, are similar to those for the In^IIIMe₂ complexes. Six-co-ordination for one indium is completed by a water molecule [2.304(9) in (10), 2.300(6)Å in (13)], and a nitrate group interacts unsymmetrically with the other indium [In-O 2.422(12) in (10), 2.387(7)Å in (13); In ⋯ O 2.692(15) in (10), 2.802(9)Å in (13)], with both aqua and nitrate groups trans to ‘axial’ py groups in both complexes. The geometry at the indium atoms in (10) and (13) is irregular, but, except for the orientation of the more weakly co-ordinating aqua and nitrate groups in each complex, the indium atoms have similar geometry, with analogous donor atoms of the other five groups subtending angles at indium within 6 [(10)] and 2°[(13)] of each other. The In^IIIMe₂ and In^IIIMe complexes form conducting solutions with retention of nitrogen donor co-ordination; the binuclear complexes exhibit complex variable-temperature ¹H n.m.r. spectra in CD₃OD resulting from the presence of exchange between nitrogen donor sites and also between isomers for complexes of ligands containing both py and mim donor groups. Crystals of (5), (8), and (13) are monoclinic, space group P2₁/c, and (10) is triclinic, space group P; (5) has a= 9.002(3), b= 12.538(7), c= 13.996(7)Å, β= 91.26(3)°, Z= 4; (8) has a= 8.641(3), b= 15.872(6), c= 17.242(7)Å, β= 90.78(3)°, Z= 4; (10) has a= 19.147(5), b= 11.007(4), c= 9.486(8)°, α= 76.14(6), β= 88.79(6), γ= 87.87(3)°, Z= 2; (13) has a= 14.388(6), b= 17.613(10), c= 16.403(10)Å, β= 92.18(3)°Z= 4. Residuals were 0.033, 0.047, 0.064, and 0.052 for 2 155, 4 486, and 3 676 independent reflections, respectively.