cyclo-Tetra-μ-fluorido-1:2κ2 F;2:3κ2 F;3:4κ2 F;1:4κ2 F-octa­nitrato-1κ8 O,O′;3κ8 O,O′-tetra­kis­(1,10-phenanthroline)-2κ4 N,N′;4κ4 N,N′-2,4-dichromium(III)-1,3-dineodymium(III) methanol tetra­solvate monohydrate

In the title compound, [Cr2Nd2F4(NO2)8(C12H8N2)4]·4CH3OH·H2O, two cis-difluoridobis(1,10-phenanthroline)chromium(III) fragments containing octa­hedrally coordinated chromium(III) bridge via fluoride ions to two tetra­nitratoneodymate(III) fragments, forming an uncharged tetra­nuclear square-like core. The fluoride bridges are fairly linear, with Cr—F—Nd angles of 168.74 (8)°. Cr—F bond lengths are 1.8815 (15) Å, slightly elongated compared to those of the parent chromium(III) complex, which has bond lengths ranging from 1.8444 (10) to 1.8621 (10) Å. The tetra­nuclear complex is centered at a fourfold rotoinversion axis, with the Cr and Nd atoms situated on two perpendicular twofold rotation axes. The uncoordinated water mol­ecule resides on a fourfold rotation axis. The four methanol solvent mol­ecules are located around this axis, forming a cyclic hydrogen-bonded arrangement. The title compound is the first structurally characterized example of unsupported fluoride bridges between lanthanide and transition metal ions

X-ray Magnetic Circular Dichroism (XMCD) Study of a Methoxide-Bridged Dy^III-Cr^III Cluster Obtained by Fluoride Abstraction from cis-[Cr^III F_2 (phen)_2]^+

An isostructural series of dinuclear chromium(III)-lanthanide(III) clusters is formed by fluoride abstraction of cis-[CrF2(phen)(2)](+) by Ln(3+) resulting in LnF(3) and methoxide-bridged Cr-Ln clusters (Ln = Nd (1), Tb (2), Dy (3)) of formula [Cr-III(phen)(2)(mu-MeO)(2)Ln-(NO3)(4)].xMeOH (x = 2-2.73). In contrast to fluoride, methoxide bridges in a nonlinear fashion, which facilitates chelation. For 3, X-ray magnetic circular dichroism (XMCD) provides element-specific magnetization curves that are compared to cluster magnetization and susceptibility data acquired by SQUID magnetometry. The combination of XMCD and SQUID is able to resolve very small magnetic coupling values and reveals a weak Cr-III-Dy-III coupling of j = -0.04(3) cm(-1). The Dy-III ion has a ground-state Kramers doublet of m(J) = +/- 13/2, and the first excited doublet is found to be m(J) = +/- 11/2 at an energy of delta = 57(21) cm(-1). The Cr-III ion exhibits a uniaxial anisotropy of D-Cr = 1.7(1.0) cm(-1). Further, we observe that a weak anisotropic coupling of dipolar origin is sufficient to model the data, suggesting that methoxide bridges do not play a significant role in the magnetic coupling for the present systems