Acknowledgments
N- Based Rare Earth Complexes
4.3 Rare Earth Complexes with N-Heterocyclic Type Ligands
4.3.4 Rare Earth Complexes with Phthalocyanine Type Ligands
(a) (b) O5
O2
O4
O6
O7 O7
O6
O3 O5
O4O2
O8 Yb1
Cl1
O1O9 O12 N4N2
N3 N1 O11
O10
O1N1 O3 N2 N3
N4 Yb1
Figure 4.34 (a) Perspective view and (b) side view of compound [Yb(III)(TMPP)(H2O)3]Cl [51].
(Reproduced from W. Wonget al., “Synthesis and crystal structures of cationic lanthanide (β) mono- porphyrinate complexes,’’ Journal of the Chemical Society, Dalton Transactions, 615, 1999 (doi:
10.1039/a809696a), by permission of The Royal Society of Chemistry.)
N C
N C M(Pc')2 + M2(Pc')3
M(Pc')2 + M2(Pc')3 H2(Pc') or Li2(Pc') + M[MClx, M(OAC)3, M(acac)3]
+ M[MClx, M(OAC)3, M(acac)3] 1 Cyclic tetramerization
2 Ligands condensation R R
Figure 4.35 Schematic representation of the formation of double-decker and triple-decker phthalocyanines.
N12 N11
N6 N1 Lu
N24 OA1
OA2
OW2 OW1
N17 N23
N18
Figure 4.36 The structure of LuPc(CH3COO) [61a]. (Reprinted with permission from J. Fischer, R. Weiss,et al., “Synthesis, structure, and spectroscopic and magnetic properties of lutetium(III) phthalo- cyanine derivatives: LuPc2.CH2Cl2and [LuPc(OAc)(H2O)2].H2O.2CH3OH,’’Inorganic Chemistry,24, no. 20, 3162–3167, 1985. © 1985 American Chemical Society.)
high boiling point such as TCB (1,2,4-trichlorobenzene). It is believed that in these reactions, the protonated double-deckers M(III)H(Pc)2are the initial products, which undergo oxidation in air to give the deprotonated analogs RE(III)(Pc)2[59]. If the reaction was completed in the presence of reducing agents, the monoanionic double-deckers such as Li[RE(III)(Pc)2] (RE=La–Yb except Ce), (NBu4)[RE(III)(Pc)2] (RE=La, Ce, Pr, Nd, Sm, Gd, Ho, Lu), and (PNP)[RE(III)(Pc)2] [PNP=bis(triphenylphosphino)iminium; RE=La, Gd, Tm] can also be isolated [60].
4.3.4.1 Homoleptic Bis(phthalocyaninato) Rare Earth Double-Deckers
To date, various crystalline forms of bis(phthalocyaninato) rare earth double-decker com- plexes including neutral, protonated, and anionic species have been obtained depending on the synthesis procedure [61]. By using the cyclic tetramerization method, Weiss reported the synthesis and crystal structure of both the monomeric phthalocyaninato and bi(phthalocyaninato) lutetium complexes [61a]. Figure 4.36 shows the molecular structure of LuPc(CH3COO)(H2O)2. As can be seen, the coordination polyhedron is a slightly dis- torted square antiprism. The donor atoms consist of four phthalocyanine isoindole nitrogens, two oxygens from the acetylacetone, and two oxygens of two water molecules. The mean Lu–N, Lu–OOAc, and Lu–Owdistances are 0.2345(2), 0.2396, and 0.2331(3) nm, respectively.
The perpendicular distance between the lutetium ion and the four isoindole N4 plane of the
(a) (b) N22
N4
N27 Lu
N9 N13
N18 N33
N1 N27′
N28′
N9′ N4′
N33′
N18′
Figure 4.37 The structure of Lu(Pc)2 [61a]. (Reprinted with permission from J. Fischer, R. Weiss, et al., “Synthesis, structure, and spectroscopic and magnetic properties of lutetium(III) phthalocyanine derivatives: LuPc2.CH2Cl2and [LuPc(OAc)(H2O)2].H2O.2CH3OH,’’Inorganic Chemistry,24, no. 20, 3162–3167, 1985. © 1985 American Chemical Society.)
phthalocyanine ring is 0.126 nm. The dihedral angle between the mean plane of the N4 isoindole of phthalocyanine and the mean plane of the four oxygen atoms bonded to lutetium atom is 1.9◦. Similar to the monomeric phthalocyaninato lutetium counterpart, the coordination poly- hedron for the bi(phthalocyaninato) lutetium complex Lu(Pc)2 in the solvated crystal Lu(Pc)2·CH2Cl2is again a square-antiprism, with the lutetium atom occupying a central posi- tion between the two phthalocyanine rings A and B, Figure 4.37 [61a]. As a result, the lutetium ion is eight-coordinate with eight nitrogen atoms from the isoindole nitrogens of the two phthalocyanine rings. The Lu–N bond distance from ring a and b is 0.2381(5), 0.2392(7), 0.2369(5), and 0.2375(4) nm, respectively, with an average of 0.238 nm. The metal atom, the two isoindole nitrogens N1 and N13 of ring a, and the two azamethine nitrogens N22 and N34 of ring b are located in the crystallographic symmetry plane. The two phthalocyanine molecules are saucer-shaped and the skew angle of the two phthalocyanine planes is exactly 45◦. The perpendicular distances between the lutetium atom and the four isoindole N4 plane of ring a and ring b are 0.135 and 0.134 nm, respectively, longer than that in the monomeric phthalocyaninato lutetium compound, indicating the stronger repulsion interaction between the adjacent phthalocyanine rings of the double-decker. The separation between the two parallel isoindole N4 planes is 0.269 nm, shorter than the distance of 0.306 nm between the planes through the 24 atoms (C16N8) of the Pc ring framework. This makes the two phthalocyanine rings of whole complex form a biconcave lens structure with a doming degree of 0.2◦. The π–πdistance, defined between the average planes composed of the four isoindole and the four nitrogen atoms connecting them (C16N8) of the phthalocyanine ring is 0.308 nm.
Interestingly, the single crystal molecular structure for the protonated species HLu(Pc)2
was also determined by X-ray diffraction analysis [61b]. Figure 4.38 displays the geometry of HLu(Pc)2without the acidic hydrogen. The mean Lu–N length and the separation between the two parallel isoindole N4 planes are 0.2371(4) and 0.2676 nm, respectively, a little smaller than those found in its neutral analog Lu(Pc)2·CH2Cl2. It is worth noting that although the crystal structure of complex HLu(Pc)2was determined, it did not provide any information concerning the location of the unique proton.
Figure 4.38 The structure of HLu(Pc)2[61b]. (Reprinted with permission from J. Fischer, R. Weiss, et al., “Synthesis, structure and spectroscopic properties of the reduced and reduced protonated forms of lutetium diphthalocyanine,’’Inorganic Chemistry, 27, no. 7, 1287–1291, 1988. © 1988 American Chemical Society.)
On the basis of analysis of many X-ray crystallographic results for bis(phthalocyaninato) rare earth double-decker complexes, there appears to exist a linear relationship between the size of the central rare earth ion and the skew angle. The skew angle increases along with a decrease in the rare earth ion radius. For example, in the tetrabutylammonium salts of bis(phthalocyaninato) complexes with Nd, Gd, Ho, and Lu, the skew angle increases from 6, 34.4, 43.2, to 45◦along with the decrease in the rare earth ionic radius in the order of 0.1249, 0.1193, 0.1155, and 0.1117 nm [62]. Usually, the skew angle for almost all the sandwich type bis(phthalocyaninato) rare earth double-decker complexes reported thus far lies between 37 and 45◦and the distance between the two mean planes of the 24 atoms (C16N8) of the Pc ring framework (π–πinteraction distance) is in the range of 0.28–0.3 nm. With the decrease in the skew angle, theπ–πinteraction distance increases and meanwhile the deformation of the macrocyclic phthalocyanine ligands from their normal plane becomes smaller.
4.3.4.2 Monomeric Phthalocyaninato Rare Earth Complex Sm2µ2Pc(dpm)4
By reaction between Li2Pc and RE(III)(dpm)3 (dpm=2,2,6,6-tetramethylheptane-3, 5-dionato), a series of RE2µ2Pc(dpm)4(RE=Sm–Yb, and Y) have been prepared [63]. For the lutetium ion, the reaction gave only a 1 : 1 complex and for the rare earth ions whose ionic radius is larger than the neodymium ion, the compounds were too unstable to be isolated as analytically pure crystals. The crystal structure of Sm2µ2Pc(dpm)4is shown in Figure 4.39.
The crystal belongs to the triclinic crystal system andP1 space group with the cell parameters ofa=1.2941(6) (nm),b=1.4680(4) (nm),c=2.1205(4) (nm),α=88.22(2)◦,β=86.54(3)◦, γ=71.32(3)◦,V=3.8089 nm3, andZ=2. The phthalocyanine plane lies between the two samarium atoms, with four nitrogen atoms coordinating to each of the samarium ions. Fur- thermore, each samarium ion also coordinates to four oxygen atoms from two dpm molecules.
In the electronic absorption spectrum, the longest absorption band at about 700 nm in the nonpolar solvent CH2Cl2was found to blue-shift to about 670 nm in the polar solvent DMF, indicating a dissociation equation of the complex owing to the solvation by a polar solvent of the rare earth atoms, Figure 4.40.
O1 O2 O4
O3A
O3A O2A
O1
N1A N2A
N2 N1
O4
Figure 4.39 The structure of Sm2µ2Pc(dpm)4[63]. (Reproduced from H. Sugimotoet al., “Preparation and X-ray crystal structure (for Ln=Sm) of (µ-phthalocyaninato)bis[di(2,2,6,6-tetramethylheptane-3,5- dionato)LnIII](Ln=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y),’’Journal of the Chemical Society, Chemical Communications, 1234, 1983, by permission of The Royal Society of Chemistry.)
[(REIII)2(Pc2–)(β-diketonato)4] [REIII(Pc2–)(β-diketonato)2]– [REIII(β-diketonato)2]+ Figure 4.40 Schematic representation of the dissociation equation.
4.3.4.3 Mixed Sandwich-Type Phthalocyaninato and Porphyrinato Rare Earth Double-Decker Complexes
The synthesis of mixed phthalocyaninato and porphyrinato rare earth double-decker complexes is a natural pursuit extending from the homoleptic/heteroleptic phthalocyaninato/porphyrinato rare earth sandwich analogs. Usually, mixed (phthalocyaninato)(porphyrinato) rare earth double-deckers are prepared by [RE(III)(Por)(acac)]-induced cyclic tetramerization of phthalonitriles or treating metal-free porphyrins with Li2Pc in the presence of rare earth salts [64]. To date, many mixed (phthalocyaninato)(porphyrinato) rare earth double-deckers includ- ing [La(III)H(Pc)(TPP)] [65a], [RE(III)H(Pc)(TPyP)] (RE=Gd, Eu, Y) [65b], Li[RE(III) (Pc)(TPyP)] (RE=Eu, Gd) [65c] have been isolated and characterized. Figure 4.41 shows the molecular structure of the neutral nonprotonated and protonated (phthalocyani- nato)(porphyrinato) rare earth double-decker complexes, [Sm(III){Pc(α-OC5H11)4}(TClPP)]
(Figure 4.41a) and [Sm(III)H{Pc(α-OC5H11)4}(TClPP)] (Figure 4.41b), given as examples to illustrate the molecular structural feature of these complexes [66]. As can be seen, in both
(a) (b)
CI(1A)
N(4) N(6A) N(3) N(2)
N(5A)
N(1) N(3A)
N(5) Sm(1)
N(1A) N(2A)
O(2A)
N(6) N(4A)
O(1) CI(2)
CI(1) O(2)
O(1A)
CI(2A)
CI(1)
CI(2)
CI(7)
CI(6) CI(5)
CI(4) CI(3)
N(8) N(1)
N(10) N(3) N(2)
O(2)
N(11) Sm(1)
N(4)
O(3) N(9)
N(7)N(12) N(5)
N(6)
O(4) O(1)
Figure 4.41 The structures of (a) [Sm(III){Pc(α-OC5H11)4}(TClPP)] and (b) [Sm(IIIH{Pc(α- OC5H11)4} (TClPP)] [66]. (Reproduced with permission from R. Wanget al., “Controlling the nature of mixed (phthalocyaninato)(porphyrinato) rare-earth(III) double-decker complexes: the effects of non- peripheral alkoxy substitution of the phthalocyanine ligand,’’Chemistry – A European Journal, 2006, 12, 1475. © Wiley-VCH Verlag GmbH & Co. KgaA.)
compounds the central samarium ion is eight-coordinate with four nitrogen atoms from tetra- α-substituted phthalocyaninato ligands and four nitrogen atoms from porphyrinato ligands.
Both coordination polyhedrons adopt a slightly distorted square-antiprismatic structure around the metal center. The average twist angel for [Sm(III){Pc(α-OC5H11)4}(TClPP)] is 43.8◦, larger than that for [Sm(III)H{Pc(α-OC5H11)4}(TClPP)], 38.3◦. The average Sm–N4[Pc(α- OC5H11)4] plane distance of 0.1557 nm for [Sm(III){Pc(α-OC5H11)4}(TClPP)] is similar to that of 0.1558 nm for [Sm(III)H{Pc(α-OC5H11)4}(TClPP)]}. However, the distance between the central samarium ion and the N4plane of TClPP is significantly different, 0.1334 nm for [Sm(III){Pc(α-OC5H11)4}(TClPP)] and 0.1363 nm for [Sm(III)H{Pc(α-OC5H11)4}(TClPP)].
This evidence, together with other crystal structural parameters for these complexes, clearly indicates the structural difference between the two series of double-deckers.