X-ray Crystal Structures of[XF_6][Sb_2Fn](X=Cl,Br,I);~(35,37)CI,~(79,81)Br,and ~(127)I NMR Studies and Electronic Structure Calculations of the XF_6 Cations

摘要

The single-crystal X-ray structures of[XF_6][Sb_2F_(11)](X=Cl,Br,I)have been determined and represent the first detailed crystallographic study of salts containing the XF_6~+ cations.The three salts are isomorphous and crystallize in the monoclinic space group P2_1ln with Z=4:[CIF_6][Sb_2Fn],a=11.824(2)A,b=8.434(2)A,c=12.088(2)A,beta=97.783(6)deg,V=1194.3(4)A~3,R_1=0.0488 at-130 degC;[BrF_6][Sb_2F_(11)],a=.11.931(2)A,b=8.492(2)A,c=12.103(2)A,p=97.558(4)deg,1/=1215.5(4)A~3,ft,=0.0707 at-130 degC;[IF_6][Sb_2Fn],a=11.844(1)A,b=8.617(1)A,c=11.979(2)A,beta=98.915(2)deg,V=1207.8(3)A~3,R_1,=0.0219 at-173 degC.The crystal structure of[IF_6][Sb_2Fn]was also determined at-100 degC and was found to crystallize in the monoclinic space group P2_1/m with Z=4,a=11.885(1)A,b=8.626(1)A,c=12.000(1)A,beta=98.44(1),V=1216.9(2)A~3,R_1=0.0635.The XF_6~+ cations have octahedral geometries with average Cl-F,Br-F,and I-F bond lengths of 1.550(4),1.666(11)and 1.779(6)[-173 degC]/1.774(8)[-100 degC]A,respectively.The chemical shifts of the central quadrupolar nuclei,~(35,37)CI,~(79,81)Br,and ~(127)I,were determined for[CIF_6][AsF_6](814 ppm),[BrF_6][AsF_6](2080 ppm),and[IF_6][Sb_3F_(16)](3381 ppm)in anhydrous HF solution at 27 degC,and spin-inversion-recovery experiments were used to determine the T_1-relaxation times of ~(35)CI(1.32(3)s),~(37)CI(2.58(6)s),~(79)Br(24.6(4)ms),~(81)Br(35.4(5)ms),and ~(127)I(6.53(1)ms).Trends among the central halogen chemical shifts and T_1-relaxation times of XF_6~+,XO_4~-,and X~-are discussed.The isotropic ~1J-coupling constants and reduced coupling constants for the XF_6~+ cations and isoelectronic hexafluoro species of rows 3-6 are empirically assessed in terms of the relative contributions of the Fermi-contact,spin-dipolar,and spin-orbit mechanisms.Electronic structure calculations using Hartree-Fock,MP2,and local density functional methods were used to determine the energy-minimized gas-phase geometries,atomic charges,and Mayer bond orders of the XF_6~+ cations.The calculated vibrational frequencies are in accord with the previously published assignments and experimental vibrational frequencies of the XF_6~+ cations.Bonding trends within the XF_6~+ cation series have been discussed in terms of natural bond orbital(NBO)analyses,the ligand close-packed(LCP)model,and the electron localization function(ELF).