STRUCTURES AND PROPERTIES OF FERROMAGNETICALLY COUPLED BIS(MU-HALO)DIIRON(II) COMPLEXES

Three bis(mu-halo)diferrous complexes, [Fe-2(TLA)(2)F-2](BF4)(2) (1), [Fe-2(TMPzA)(2)Cl-2](BPh(4))(2) (2) and [Fe-2(TPA)(2)Cl-2](BPh(4))(2) (3), have been synthesized and crystallographically characterized. The crystallographic data are as follows: 1, triclinic system, space grou p P1 ($) over bar (No. 2), with cell dimensions a=8.746(7), b=11.386(4 ), c=12.018(6) Angstrom, alpha=64.44(3), beta=81.54(5), gamma=87.90(5) degrees, V=1067(2) Angstrom(3), R=0.046, R(w)=0.063; 2, triclinic syst em, space group P1 ($) over bar (No. 2), with cell dimensions a=10.440 (5), b=11.610(8), c=16.98(1) Angstrom, alpha=77.55(6), beta=79.63(5), gamma=88.90(5)degrees, V=1977(4) Angstrom(3), R=0.042, R(w)=0.050; 3, monoclinic system, space group C2/c (No. 15), with cell dimensions a=1 9.211(6), 6=15.264(9), c=24.52(2) Angstrom, beta=105.57(3)degrees, V=6 926(4) Angstrom(3), R=0.049, R(w)=0.053. All three complexes have Fe(2 )X(2) cores with Fe-Fe distances of 3.198(3) Angstrom for 1, 3.563(3) Angstrom for 2 and 3.494(3) Angstrom for 3, and Fe-X-Fe angles of 101. 72(9)degrees for 1, 91.94(6)degrees for 2 and 90.67(3)degrees for 3. M agnetization studies over the temperature range of 2 to 200 K indicate that the high spin ferrous centers are ferromagnetically coupled in a ll three complexes. The parameter sets of the best fit (H-ex=JS(1).S-2 ) are for 1:J=-1.2(2)cm(-1), \D-i\=7.2(5) cm(-1), g(i)=2.12(3); for 2: J=-2.6(2)cm(-1), \D-i\=7.2(5)cm(-1), g(i)=2.15(3); and for 3:J=-10.0(2 )cm(-1), \D-i\=13.2(5)cm(-1), g(i)= 2.15(3). The EPR signals near g=18 also indicate ferromagnetic coupling between the iron(II) centers.