X-ray and NQR studies of bromoindate(III) complexes: [C2H5NH3]4InBr7, [C(NH2)3]3InBr6, and [H3NCH2C(CH3)2CH2NH3]InBr5

The crystal structures of [C₂H₅NH₃]₄InBr₇( 1), [C(NH₂)₃]₃InBr₆( 2), and [H₃NCH₂C(CH₃)₂CH₂NH₃]InBr₅( 3) were determined at 100(2) K: monoclinic, P2₁ /n, a=1061.94(3), b=1186.40(4), c=2007.88(7) pm, β= 104.575(1)°, Z=4 for 1; monoclinic, C2/ c, a=3128.81(12), b=878.42(3), c=2816.50(10) pm, β=92.1320(10)°, Z=16 for 2; orthorhombic, P2₁2₁2₁, a=1250.33(5), b=1391.46(6), c=2503.22(9) pm, Z=4 for 3. The structure of 1 contains an isolated octahedral [InBr₆]³⁻ ion and a Br⁻ ion. The structure of 2 contains three different isolated octahedral [InBr₆]³⁻ ions. The structure of 3 has a corner-shared double-octahedral [In₂Br₁₁]⁵⁻ ion and an isolated tetrahedral [InBr₄]⁻ ion. The ⁸¹Br nuclear quadrupole resonance (NQR) lines of the terminal Br atoms of the compounds are widely spread in frequency, and some of them show unusual positive temperature dependence. These observations manifest the N−H···Br−In hydrogen bond networks developed between the cations and anions to stabilize the crystal structures. The ⁸¹Br NQR and differential thermal analysis (DTA) measurements have revealed the occurrence of unique phase transitions in 1 and 3. When the bond angles were estimated from the electric field gradient (EFG) directions calculated by the molecular orbital (MO) methods, accurate values were obtained for [InBr₆]³⁻ of 1 and for [In₂Br₁₁]⁵⁻ and [InBr₄]⁻ of 3, except for several exceptions in those for the latter two ions. On the other hand, the calculations of ⁸¹Br NQR frequencies have produced up to 1.4 times higher values than the observed ones. [ABSTRACT FROM AUTHOR]