μ3‐ vs. μ‐Hydroxido Bridges – Peripheral Function Controls the Nuclearity of Hydroxido‐Bridged Copper(II) Complexes

The synthesis and characterization of three monohydroxido-bridged dinuclear CuII complexes, [{Cu2(L1)2(mu-OH)}(ClO4){Cu2(L1)2(mu-OH)}](ClO4)center dot 5.5H2O (1), Cu2(L2)2(OH)(ClO4)(H2O)2 (2), [{Cu2(L3)2(mu-OH)(ClO4)}2]center dot 5H2O (3) and three monohydroxido-bridged trinuclear CuII complexes, [Cu3(L4)3(mu 3-OMe)(ClO4)2] (4), [Cu3(L5)3(mu 3-OH) (ClO4)2]center dot 0.5{(CH3)2CO}center dot 0.5(H2O) (5), [Cu3(L6)3(mu 3-OH)(ClO4)2] (6), is reported (HL1HL6 = tridentate N2O ligands resulting from the Schiff base condensation of salicylaldehyde or 3-methoxysalicylaldehyde with ethylenediamine, 1,2-diaminopropane, 2-methylpropane-1,2-diamine or 1,2-diaminocyclohexane). The six new complexes are obtained through aggregation of the corresponding mononuclear precursor Cu(Li)(py)(ClO4) in the presence of HO (MeO) anions in methanol. The nuclearity of the resulting complex depends on the steric requirement of Li: in the presence of an OMe substituent a to the Ophenoxido atom (L1L3), mu-HO single-bridged dinuclear compounds are obtained (13); in the absence of an a-substituent (L4L6), the aggregation proceeds to the mu 3-OH (mu 3-OMe) bridged trinuclear compounds 46. The molecular structures of 1, 3 and 46 have been established through single-crystal X-ray studies. Antiferromagnetic interactions operate in 1 (J = 57 cm1, 2JS1S2 formalism), 2 is paramagnetic, and 3 is the first example of a ferromagnetic monohydroxido-bridged dinuclear CuII complex (J = 16 cm1). The structural and magnetic parameters for the 22 mu-HO single-bridged dinuclear CuII compounds reported to date are compared. Antiferromagnetic interactions operate in all three monohydroxido-bridged trinuclear CuII complexes 4, 5, and 6 (J = 16.9, 6.3, and 6.7 cm1, respectively). The structural and magnetic parameters for the seven mu 3-hydroxido (methoxido) bridged trinuclear CuII compounds presently known in the series based on tridentate Schiff bases that result from condensation of diamines with salicylaldehydes are compared.