STUDIES ON H-2 NMR AND SINGLE-CRYSTAL X-RAY-DIFFRACTION OF THERMOCHROMIC BIS(N,N-DIETHYL-1,2-ETHANEDIAMINE) NICKEL(II) COMPLEXES WITH AND WITHOUT STRUCTURAL PHASE-TRANSITIONS

The thermochromic complex bis(N,N-diethyl-1,2-ethanediamine) ((C2H5)(2 )NC2H4NH2) nickel(II) perchlorate([Ni(dieten>(2)](ClO4)(2)) was studie d by single crystal X-ray diffraction and found to form a triclinic la ttice with space group P ($) over bar 1, a = 8.108(1) Angstrom, b = 8. 835(1) Angstrom, c = 9.736(1) Angstrom, alpha = 94.24(1)degrees, beta = 114.28(1)degrees, gamma = 116.49(1)degrees, and Z = 1 being isomorph ous with that of [Cu(dieten)(2)](ClO4)(2) which has been reported to h ave a thermochromic phase transition. The temperature dependences of H -2 NMR spectra in [Ni(dieten-n(2))(2)]X(2) (dieten-d(2): (C2H5)(2)NC2H 4ND(2); X: ClO4, BF4, Br, NO3, I) were observed and quadrupole couplin g constants e(2)Qq and asymmetry parameters eta were evaluated. Below room temperature, an almost rigid structure of the ND2 group was deriv ed by analyzing the spectra. For perchlorate and tetrafluoroborate wit h colour changes at respective phase transition temperatures (T-c), qu adrupole parameters were also changed discontinuously at T-c. The anal ysis of spectra observed above T-c afforded two-site jumps of the N-D bond by angles of 52-55 degrees supporting the ring-puckering model of the five-membered chelate ring. However, iodide having no phase trans ition showed continuous changes of both e(2)Qq and eta values with inc reasing temperature up to 450 K. These results which cannot be attribu ted to the puckering motion were explained by whole complex reorientat ion. These molecular motions are discussed in connection with the colo ur change observed in these complexes.