hing the part&I quadrupole splitting v&es (PQS) for ~hgands such as CI-' CN-and NHj derived from Messbauer spectra of Fe(H) low spin compounds. the sign of Vzz is obtained for &qQ)Co lu'isoek&ro_nic compokds of Co(IH) low spin. The.predicted:sigus of V&, are: tmns_ [Cb(NH&CIsl+,posi~, [Co(NHs)&Il?.positive. and lCoWH&CNI ++; d&ative. A value of the 57Fequadrupole moment of 0,X * 0.03 has been determined by comparing the observed e2qQ vahmsfo; the above Co(III) compounds with these cakuhtted from PQS vshres for ^&e corresponding hypothetical Fe(H) compounds. ,.. 5gCo quadrupole coupling constants (e2@)Co have The sign and magnitude of ($e2&&+ for three recently been measured for a numbed of Co(W) com--Fe(H) compounds are given in table I [ 181 . As dis .pounds [l-6] _ However, the sign of these e2qQ values cussed previously [ 141, the QS for ttmrs-FeA2B4 cannot be obtained by nuclear quadrupole resonance. compounds is given by 41.4 j -4[e], where [A] and This drawback has made it impossible to interpret .the results completely [I]. From molecular orbital c&u-'.