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

Abstract

Abstract 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.