EFFECT OF HYDROGENATION ON ELECTRONIC AND DISTANT MAGNETIC-PROPERTIESIN COPPER(II) COMPLEXES WITH DERIVATIVES OF TETRAHYDROSALEN AND SALEN- X-RAY CRYSTAL-STRUCTURE OF [CU(BU,ME(SALTMEN))] COMPLEX

The salen complex CuL and the corresponding tetrahydrosalen complex Cu [H-4]L were investigated by ESR spectroscopy and molecular orbital cal culations [H(2)L = methylsalicylidene)-2,3-diamino-2,3-dimethylbutane ; H-2[H-4]L = 2-hydroxy-3-tert-butyl-5-methylbenzyl)2,3-diamino- 2,3-d imethylbutane]. X-ray structure determination of CuL confirmed a sligh tly distorted planar geometry of the CuN2O2 coordination core. The ESR spectra of CuL at both 77 K and room temperature revealed that very w ell resolved lines cannot be attributed to the interaction with copper nuclear spin and N-14 donor nuclei alone. Computer simulation showed that in addition to copper hyperfine (g(iso) = 2.094, \A(Cu)(iso)\ = 2 70 MHz, room temperature) and nitrogen superhyperfine structure [\A(N) (iso)\ = 46 MHz] a distant interaction with two equivalent protons is also present [\A(H)(iso)\ = 23 MHz]. These protons are attached to the carbon atoms adjacent to N-14 nuclei. In contrast the number of lines in the spectrum of the hydrogenated analogue Cu[H-4]L is greatly redu ced. At room temperature only a quintet with considerable smaller nitr ogen shf constant [\A(N)(iso)\] = 25 MHz is observed. Thus, both facto rs planarity and conjugation, are essential for the observation of dis tant hydrogen shf splitting in CuL. The ESR findings are in good agree ment with calculated spin densities by QR-INDO/1 method. Copyright (C) 1996 Elsevier Science Ltd