Structural Trends in a 3 d‐4 f System: Ln(NO₃)₃−Cu(2,2‐bipyridine)₂(NO₃)₂ (Ln=La−Nd, Sm−Yb)

Abstract

A series of thirteen complexes which may be formally considered as assembled from Cu(bpy)2(NO3)2 and Ln(NO3)3 (Ln=La−Yb excluding Pm, bpy=2,2’‐bipyridine) have been characterized. The crystals may be grouped into four classes: A, [Cu2(bpy)4(μ‐NO3)][Ln(NO3)6] (Ln=La−Nd); B, [Cu(bpy)2(NO3)]2[Ln(NO3)4(OH2)2](NO3) (Ln=Sm−Dy); C, [Cu(bpy)2(NO3)]2[Ln(NO3)5] (Ln=Ho−Tm); D, [Cu(bpy)2(NO3)]2 [Ln(NO3)3(OH2)3](NO3)2⋅2H2O (Ln=Yb). The coordination numbers of the nitrato or aquonitrato lanthanide anions range from 9 to 12. The dinuclear cation in Class A having a linear monoatomic nitrate bridge is new and is seen to produce weak antiferromagnetic coupling in these compounds. The other classes contain distortion isomers of [Cu(bpy)2NO3]+. The structural trends are analysed in terms of lanthanide contraction and non‐covalent interactions in the crystals. EPR and electronic spectral characteristics are discussed for the four classes of compounds.

Structural Trends in 3 d–4 f Systems. Part II: Ln(NO3)3‐Cu(NO3)2‐2,2‐biyridine/5,5‐dimethyl‐2,2‐bipyridine (Ln=La‐Nd, Sm‐Lu)

“…Coming to the bis‐chelate ion, [Cu(5,5‐dmbpy) 2 (NO 3 )] + , in all crystals in which these are formed (La−Tb), the anion is [ Ln (NO 3 ) 5 (OH 2 )] − . This is in contrast to bpy analogs where, across the La−Yb series three different anions, [ Ln (NO 3 ) 6 ] 3− , [ Ln (NO 3 ) 5 ] 2− , [ Ln (NO 3 ) 4 (OH 2 ) 2 ] − , and one neutral lanthanide complex [Yb(NO 3 ) 3 (OH 2 ) 3 ] are formed in the crystals [2e] . The Cu 2+ ion in [Cu(5,5‐dmbpy) 2 (NO 3 )] + cation is six‐coordinate with a [4+1+1] coordination which may be viewed as a greatly compressed tetrahedron of [Cu(5,5‐dmbpy) 2 ] 2+ coordinating to an unsymmetrically chelating nitrate ion [2e] .…”

“…This is in contrast to bpy analogs where, across the La−Yb series three different anions, [ Ln (NO 3 ) 6 ] 3− , [ Ln (NO 3 ) 5 ] 2− , [ Ln (NO 3 ) 4 (OH 2 ) 2 ] − , and one neutral lanthanide complex [Yb(NO 3 ) 3 (OH 2 ) 3 ] are formed in the crystals [2e] . The Cu 2+ ion in [Cu(5,5‐dmbpy) 2 (NO 3 )] + cation is six‐coordinate with a [4+1+1] coordination which may be viewed as a greatly compressed tetrahedron of [Cu(5,5‐dmbpy) 2 ] 2+ coordinating to an unsymmetrically chelating nitrate ion [2e] . The unsymmetry in the nitrate chelation to Cu 2+ varies from 0.05 Å to 0.14 Å for the first seven lanthanide crystals (La to Gd) while it abruptly increases to 0.61 Å in the Tb compound (Table S11).…”

“…[CuL 3 ] 2+ salts (L=bpy, 5,5‐dmbpy) of the isovalent anions [ Ln (NO 3 ) 5 (H 2 O) y ] 2− ( y =0 or 1) are obtained for the full lanthanide series for both bpy and 5,5‐dmbpy. With regard to the bis‐chelate cation [CuL 2 (NO 3 )] + , while the full series is known for bpy, [2e] 5,5‐dmbpy gives lanthanide complex salts only for eight members of the series (La–Tb, excluding Pm). Attempts to prepare analogous compounds beyond Tb always resulted in the formation of the nitrate salt [7a] of [Cu(5,5‐dmbpy) 2 (NO 3 )] + .…”

“…We have in the past explored the changes in structure and properties brought about in particular systems by varying the lanthanide ions, including as many elements as possible from La to Lu [2e,i,k] . In this paper we examine the Cu(II) tris‐ and bis‐chelates of 2,2‐bipyridine (bpy) and 5,5‐dimethyl‐2,2‐bipyridine (5,5‐dmbpy) across the series of lanthanide nitrate anions.…”

“…Only a few examples of deformation of [Cu(bpy) 3 ] 2+ crystallized with various anions such as ClO 4 − , PF 6 − , BF 4 − , BPh 4 − , SO 4 2− , CrO 4 2− , Br − , I − have been reported in the literature [6] . We had previously reported bis‐chelates with bpy for the lanthanide nitrates [2e] . For 5,5‐dmbpy, only three Cu(II) complexes [7] are known: [Cu(5,5‐dmbpy) 2 (NO 3 )](NO 3 ), [Cu(5,5‐dmbpy) 3 ](PF 6 ) 2 ⋅CH 3 CN and [Cu(5,5‐dmbpy) 3 ](BF 4 ) 2 ⋅EtOH.…”