Synthesis, Crystal Structures, and Magnetic Properties of a New Family of Heterometallic Cyanide-Bridged Fe2IIIM2II (M = Mn, Ni, and Co) Square Complexes

New heterobimetallic tetranuclear complexes of formula [Fe-III{B(pz)(4)}(CN)(2)(mu-CN)Mn-II(bpy)(2)](2)(ClO4)(2)center dot CH3CN (1), [Fe-III{HB(pz)(3)}(CN)(2)(mu-CN)Ni-II(dmphen)(2)](2) (ClO4)(2)center dot 2CH(3)OH (2a), [Fe-III{B(pz)(4)}(CN)(2)(mu-CN)NiII(dmphen)(2)](2)(ClO4)(2)center dot 2CH(3)OH (2b), [Fe-III-(HB(pz)(3)}(CN)(2)(mu-CN)Co-II(dmphen)(2)](2)(ClO4)(2)center dot 2CH(3)OH (3a), and [Fe-III{B(pz)(4)}(CN)(2)(mu-CN)Co-II (dmphen)(2)](2)(ClO4)(2)center dot 2CH(3)OH (3b), [HB(pz)(3)(-)= hydrotris(1-pyrazoly)borate, B-(Pz)(4) = tetralds(1-pyrazoly0borate, dmphen = 2,9-dimethy1-1,10-phenanthroline, bpy = 2,2'-bipyridine] have been synthesized and structurally and magnetically characterized. Complexes 1-3b have been prepared by following a rational route based on the self-assembly of the tricyanometalate precursor fac-[Fe-III(L)(CN)(3)](-) (L = tridentate anionic ligand) and cationic preformed complexes [M-II(L')(2)(H2O)(2)](2+) (L' = bidentate alpha-diirnine type ligand), this last species having four blocked coordination sites and two labile ones located in cis positions. The structures of 1-3b consist of cationic tetranudear Feni2M112 square complexes [M = Mn (1), Ni (2a and 2b), Co (3a and 313)] where corners are defined by the metal ions and the edges by the Fe CN M units. The charge is balanced by free perchlorate anions. The [Fe(L)(CN)(3)](-) complex in 1-3b acts as a ligand through two cyanide groups toward two divalent metal complexes. The magnetic properties of 1-3b have been investigated in the temiperature range 2-300 K A moderately strong antiferromagnetic interaction between the low-spin Fe-III (S = 1/2) and high-spin Mn-II (S = 5/2) ions has been found for 1 leading to an S = 4 ground state (J(1) = -6.2 and J(2) = -2.7 cm(-1)), a moderately strong ferromagnetic interaction between the low-spin Fe-III (S = 1/2) and high-spin Ni-II (S = 1) and Co-II (S = 3/2) ions has been found for complexes 2a-3b with S = 3 (2a and 2h) and S = 4 (3a and 3h) ground spin states [J(1) = +21.4 cm(-1) and J(2) = +19.4 cm(-1) (2a); J(1) = +17.O cm(-1) and J(2) = +12.5 cm(-1) (2b); J(1) = +5.4 cm(-1) and J(2) = +11.1 cm(-1) J(1)= +8.1 cm(-1) and J(2) = +11.0 cm(-1) (3b)] [the exchange Hamiltonian being of the type (H) over cap = -J((S) over cap (i).(S) over cap (j))]. Density functional theory (DFT) calculations have been used to substantiate the nature and magnitude of the exchange magnetic coupling observed in 1-313 and also to analyze the dependence of the exchange magnetic coupling on the structural parameters of the Fe-C-N-M skeleton.