Charge-transfer two-dimensional layers constructed from a 2: 1 assembly of paddlewheel diruthenium(II,II) complexes and bis[1,2,5]thiadizolotetracyanoquinodimethane: bulk magnetic behavior as a function of inter-layer interactions

Two new charge-transfer compounds, [{Ru-2(O2CPh-x-F)(4)}(2)(BTDA-TCNQ)].n(solv) (x-F-PhCO2- = x-fluorobenzoate; x = o-, 4; p-, 5; BTDA-TCNQ bis[1,2,5] thiadizolotetracyanoquinodimethane), have been prepared from reactions of paddlewheel diruthenium(II, II) complexes, [Ru-2(II,II)(O2CPh-x-F) (4)] (x = o-, p-) and BTDA-TCNQ. Compounds 4 and 5 crystallize as two- dimensional (2-D) layered structures composed of [ Ru2] units and BTDA-TCNQ in a 2 : 1 ratio. The isomer with the m-fluorobenzoate-bridged [Ru2] unit (3) exhibits a three-dimensional (3-D) structure. The oxidation states of the constituent units were evaluated from their crystal structures, and assigned to be close to the charge-polarized state represented formally as [Ru-2(5+)]-[BTDA-TCNQ(-)]-[Ru-2(4+)] including two types of [ Ru2] units that are electronically and structurally different and a one-electron-transferred BTDA-TCNQ radical anion. The data indicate that a 1-e(-) transfer from one site of [Ru-2] units to BTDA-TCNQ has likely occurred. The units are paramagnetic with heterospin states for [ Ru2 II, II] ( S 1), [Ru-2(II,III)] (S = 3/2), and BTDA-TCNQ(.-) (S = 1/2), which lead to magnetic ordering in the layer. In the case of 4, antiferromagnetic ordering occurs at T-N = 93 K due to inter-layer antiferromagnetic interactions which involve two steps, namely canting of the ordered spins at T-c1 = 87 K followed by rearrangement of the canted spin states at T-c2 = 13 K. Compound 5 exhibits 3-D ferromagnetic ordering at T-c = 83 K. Consequently, 4 and 5 behave as magnets although the origin of their spontaneous magnetization is different. The bulk magnetic properties of 4 and 5 are in contrast to what was observed in a similar layered compound [{Ru-2(O2CCF3)(4)}(2)TCNQF(4)] (2; TCNQF(4) = tetrafluoro-7,7,8,8-tetracyanoquino-dimethane). This compound is an antiferromagnet (at H = 0) with T-N = 95 K with the behavior being strongly dependent on the environment between the layers: in particular the stacking motif can either be "in-registry'' with an overlap between analogous groups ( for 2) or "out-of-registry'' which involves a misalignment of similar groups between layers ( for 4 and 5).