镍–稀土单分子磁体的研究进展
Research Progress in Ni-Ln SMMs Single Molecule Magnets
DOI: 10.12677/japc.2024.133055, PDF, HTML, XML,    科研立项经费支持
作者: 李晴燕, 李 佳, 刘 雨, 胡翔宇, 崔会会, 朱金丽, 王 金：南通大学化学化工学院，江苏 南通；丁欣宇*：南通大学化学化工学院，江苏 南通；南通智能与新能源材料重点实验室，江苏 南通
关键词: 镍–稀土单分子磁体；结构；磁性；Ni-Ln Single Molecule Magnets； Structure； Magnetism
摘要: 镍(II)离子具有3d8的电子构型。在八面体场中，它们倾向于采用高自旋，表现为顺磁性，而在正方形平面场中，它们通常采用低自旋，表现为抗磁性。镍(II)可以与具有f7-f11电子构型的镧系离子进行铁磁耦合，如镝(III)。镍(II)离子内的二阶轨道角动量可以提供大量的零场分裂参数，这意味着可能存在显著的磁各向异性。因此，本文通过对近年来典型的镍–稀土单分子磁体进行综述，以期为3d-4f单分子磁体的发展奠定一定的基础。
Abstract: Nickel(II) ions possess electronic configuration of 3d8. In an octahedral field, they tend to adopt a high-spin, exhibiting paramagnetism, whereas in a square-planar field, they typically adopt a low- spin, manifesting as diamagnetism. Ni(II)can engage in ferromagnetic coupling with lanthanide ions having electronic configurations of f7-f11, such as dysprosium(III). Additionally, the second-order orbital angular momentum within Nickel(II) ions can provide substantial zero-field splitting parameters, implying the potential for significant magnetic anisotropy. Therefore, this paper reviews the typical nickel-rare earth single molecule magnets in recent years, in order to lay a certain foundation for the development of 3d-4f single molecule magnets.
文章引用：李晴燕, 李佳, 刘雨, 胡翔宇, 崔会会, 朱金丽, 王金, 丁欣宇. 镍–稀土单分子磁体的研究进展[J]. 物理化学进展, 2024, 13(3): 508-522. https://doi.org/10.12677/japc.2024.133055

1. 引言

单分子磁体(Single-Molecule Magnets, SMMs)是一类有机分子纳米磁体，晶格中分子间距远，分子间相互作用很弱，晶体的整体性质可以看做全同分子性质的叠加。它的出现使得以纳米尺度磁性配合物作为基本单元研制存储器件成为可能。SMMs在二十年来的广泛关注，主要是因为其在分子水平或纳米尺度的高密度信息存储方面的潜在应用[1]-[4]。

1993年，Sessoli R.首次报道了由12个Mn离子[Mn12O12 (OCMe)16(H2O)4] (Mn12-ac)组成的金属团簇在低温下具有类似于磁畴的单分子超顺磁性[5]，从而开启了单分子磁体的研究领域。早期阶段，研究主要围绕3d过渡金属离子展开，特别是Mn基单分子磁体，希望通过提高配合物分子内金属离子的数目以提高分子的总基态自旋值，从而增强单分子磁体的慢磁弛豫性能。单分子磁体的发展大致经历了三个阶段：nd-SMMs [10]-[12]、nd-nf-SMMs [10]-[12]和nf-SMMs [13]-[16]。

近年来，具有独特电子结构的镧系离子因其无与伦比的单离子各向异性而引起了人们的广泛关注。最显著的重镧系离子，如DyIII、TbIII、HoIII和ErIII，已被广泛用作构建SMMs的磁性中心。自第一个铁磁CuII-GdIII化合物被报道后[11]，3d-4f杂金属复合物吸引了大量的兴趣，因为他们是有效的模型化合物在理解3d和4f之间的磁交换金属离子，特别是一些3d-4f集群作为SMMs。3d和4f离子之间的强磁相互作用使其更容易显示SMM行为。三维金属离子主要包括CuII、NiII、CoII和MnIII离子，通常选择多齿状席夫碱配体来构建3d-4f异金属SMMs [17]。由镧系金属与有机配体形成的多功能配合物在许多领域表现出了其特殊的应用价值[18] [19]。首先，因为Ln (III)离子具有强大的自旋–轨道耦合和较大的磁各向异性，成为开发高性能单分子磁体(SMMs)的首选目标，这些固有的磁特性使得Ln-SMMs在高密度信息存储、量子处理、磁性制冷、自旋电子学等方面具有潜在的应用；其次，由于稀土离子本身的独特结构和性质，使其与合适的有机配体结合后，所发出的荧光兼有稀土离子发光强度高、颜色纯正和有机化合物所需激发能量低、发光效率高等优点[20] [21]。

然而，实现基于SMM的存储技术还存在两个主要问题，一个是SMMs的缓慢磁弛豫的温度，另一个是由于SMMs的单个分子，难以沉积和处理在表面[22]上，存储设备的制造遇到了很大的困难。因此，研究分子基磁体的一大挑战之一仍然是设计和合成高效的SMMs。本文按照镍–稀土单分子磁体的性质类型进行综述，总结了关于镍–稀土单分子磁体研究进展的相关报道，以期望能开发高性能的SMMs。

2. 镍–稀土单分子磁体的研究进展

目前，已报道的镍–稀土单分子磁体如表1所示，本论文仅选其中一些例子进行描述，并根据其核数进行分类，以研究其结构与磁性行为之间的关系。

Table 1. The magnetic data of Ni-Ln SMMs

表1. 镍–稀土单分子磁体的磁性数据

Complexes

 Hdc/kOe

 Ueff/K

 τ0/s

 v/mT/s

 TB/K

 Ref.
[Dy2Ni2L1(bipy)2] (1)

 0

 105(1)

 1.85 × 10−11

[23]
[Dy2Ni(C7H5O2)8]∙(C7H6O2)2 (2)

 1.5

 55.19

 5.21 × 10−8

[24]
[Dy2Ni2(bipy)2(HC6H5COO)10] (3)

 0

 57.06

 1.80 × 10−8

[25]
[Dy2Ni2(bipy)2(CH3C6H4COO)10] (4)

 0

 37.04

 1.16 × 10−6

[25]
[Dy2Ni2(bipy)2(NO3C6H4COO)10] (5)

 0

 4.0

 5.47 × 10−6

[25]
[Ni2Dy2(L2)4(NO3)2(DMF)2] (6)

 0

 18.5

 5.4 × 10−7

 140

 1.1

 [26]
[Ni2Dy2(L2)4(NO3)2(MeOH)2]∙3MeOH (8)

 0

 21.3

 1.5 × 10−6

[26]
[Tb2Ni4(L3)2Cl2(OH)2(CH3O)2(CH3OH)6] (11)

 0

 30

 2.09 × 10−9

[27]
[Dy2Ni4(L3)2Cl2(OH)2(CH3O)2(CH3OH)6] (12)

 0

 32

 1.41 × 10−8

[27]
[Dy2Ni2(H2L5)2(μ3-OMe)2(CH3CN)2(NO3)4]∙4H2O (15)

 0

 48.2

 3.6 × 10−8

[28]
[Tb2Ni2(HL4)2(μ3-OMe)2(CH3CN)2(NO3)4]∙4H2O (16)

 0

 86.2

 2.3 × 10−7

[28]
[Dy2Ni2(HL4)2(μ3-OMe)2(CH3CN)2(NO3)4]∙4H2O (17)

 0

 56.6

 3.3 × 10−8

[28]
[Ni2Dy3(HL6)4]Cl (18)

 0

 U1 = 53.5

 τ1 = 2.3 × 10−8

 50

 3

 [29]
U2 = 85

 τ2 = 5.9 × 10−7
[Ni6Dy3(OH)6(HL7)6(NO3)3]∙2MeCN∙2.7Et2O∙2.4H2O (23)

 0

 23.84

 3.63 × 10−8

[30]
[HoNi5(quinha)5F2(dfpy)10] (25)

 0

 U1 = 32.7

 τ1 = 9.4(2) × 10−4

 20

 4

 [32]
U2 = 825.1

 τ2 = 3.3(5) × 10−13
[Ni4Dy2(CO3)2Cl2(L8)2(L9)2(CH3CN)2]∙4CH3CN∙2H2O (26)

 2

 43(7)

 3 × 10−12

[32]
[{Dy(hfac)3}2{Ni(bpca)2}]∙CHCl3

 1

 4.9

 1.3(0.2) × 10−6

[33]
[(L10)2Ni2Dy][ClO4]

 3.5

 10.8

 2.3 × 10−5

[34]
[{LMe2Ni(H2O)Tb(dmf)2.5(H2O)1.5}{W(CN)8}]∙H2O·0.5dmf

 0

 15.3

 4.5 × 10−7

[35]
[Ni(μ-L11)(μ-NO3)Dy(NO3)2]3∙2CH3OH

 1

 19.1

 7.2 × 10−7

[36]
[Dy2Ni2(μ3-OH)2(OH)(OAc)4(HL12)2(MeOH)3](ClO4)·3MeOH

 1.2

 7.6

 7.5 × 10−6

[37]
[Ni(μ-L11)(μ-OBz)Dy(NO3)2]∙CH3OH

 1

 9.2

 4.4 × 10−6

[38]
[Ni(μ-L11)(μ-9-An)Dy(9-An)(NO3)2]∙3CH3CN

 1

 10.1

 3.4 × 10−6

[38]
[Dy42Ni10(μ3-OH)68(CO3)12(CH3COO)30(H2O)70]∙(ClO4)24·80H2O

 0

 3.43

 1.27 × 10−6

[39]
[(μ4-CO3)2{Ni(3-MeOsaltn)(MeOH)Tb(NO3)}2]

 1

 12.2(7)

 4.6(11) × 10−7

[40]
[(μ4-CO3)2{Ni(3-MeOsaltn)(MeOH)Dy(NO3)}2]

 0

 6.6(4)

 1.6(3) × 10−6

[40]
1

 18.1(6)

 1.8(4) × 10−7

[(μ4-CO3)2{Ni(3-MeOsaltn)(H2O)Tb(NO3)}2]∙2CH3CN·2H2O

 1

 6.1(3)

 9.7(15) × 10−7

[40]
[(μ4-CO3)2{Ni(3-MeOsaltn)(H2O)Dy(NO3)}2]∙2CH3CN∙2H2O

 1

 14.5(4)

 4.2(8) × 10−8

[40]
[Ni(3-MeOsaltn)(MeOH)x(ac)Tb(hfac)2]

 1

 14.9(6)

 2.1(5) × 10−7

[41]
[Ni2Dy2(CH3CO2)3(HL13)4(H2O)2](NO3)3

 0

 19

 4.23 × 10−7

[42]
[Ni3Dy3(μ3-O)(μ3-OH)3(L14)3(μ-OOCCMe3)3]

 3

 10

 10−6

[43]
[Ni2Dy2(μ3-OH)2(O2CtBu)10[Et3NH]2]

 0

 20

 6.0 × 10−7

[44]
[Ni2Er2(μ3-OH)2(O2CtBu)10[Et3NH]2]

 1

 18

 3.9 × 10−6

[44]

续表

{[NH2(CH3)2]2[NiDy2(HCOO)2(abtc)2]}n

 1

 42

 4.7 × 10−6

[45]
{[Ni(Me2valpn)]2Dy(H2O)Cr(CN)6}2∙14H2O∙2DMF

 0

 38.9

 4.89×10−9

[46]
{[Ni(Me2valpn)]2Dy(H2O)Cr(CN)6}2∙24H2O∙2PPPO·2CH3CN

 0

 37.2

 6.44×10−9

[46]
{[Ni(Me2valpn)]2Dy(H2O)Co(CN)6}2∙8H2O·2DMF·6CH3CN

 0

 24.4

 4.94×10−7

[46]
{[Ni(Me2valpn)]2Tb(H2O)Cr(CN)6}2·12H2O·3DMF

 0

 21.9

 4.71×10−8

[46]
{[Ni(Me2valpn)]2Tb(H2O)Fe(CN)6}2·13.31H2O·2DMF·2.69CH3CN

 0

 29.6

 4.52×10−10

[46]
[Ni2Dy2(Hhms)2(CH3COO)6(CH3OH)2(H2O)2]·(NO3)2

 0

 16.9

 6.5 × 10−7

[47]
[Ni6Dy(L15)4(Htea)4](ClO4)2.5(NO3)0.5·5.5MeCN·H2O

 0

 10

 1.5 × 10−5

[48]
[Dy45Ni7(OH)68(CO3)12(CH3COO)26(CH3CH2COO)6(H2O)70]

 0

 3.42

 9.25 × 10−7

[49]
[Ni2Dy2(L16)4(NO3)2(H2O)2]·2H2O

 0

 35.75

 8 × 10−8

[50]
[Ni4Dy2(μ3-OH)2(L17)4(OAc)8]·H2O

 0

 11.2(2)

 8.9(6) × 10−6

[51]
[Ni4Dy2(L18)2(μ-Cl)2(μ3-OH)4(H2O)6]Cl4·2H2O

 0

 23.0

 4.52 × 10−9

[52]
[Ni4Tb2(L18)2(μ-Cl)2(μ3-OH)4(H2O)6]Cl4·2H2O

 0

 26.3

 1.07 × 10−9

[52]
[Ni4Dy2(L18)2(μ-NCS)2(μ3-OH)4(NCS)4(H2O)2]·2MeOH·4H2O

 0

 26.0

 1.56 × 10−8

[52]
[Ni4Tb2(L18)2(μ-NCS)2(μ3-OH)4(NCS)4(H2O)2]·14.1H2O

 0

 30.6

 5.03 × 10−9

[52]
[NiDy(L19)(Pc)(CH3OH)]·CH3OH

 1

 6.2

[53]
[NiCe(L20)(NO3)3]

 0.5

 8.5

 7.7 × 10−5

[54]
[NiNd(L20)(NO3)3]

 1

 9.2

 1.9 × 10−5

[54]
[NiDy(L20)(NO3)3]

 1

 9.3

 2.1 × 10−5

[54]
[NiEr(L20)(NO3)3]

 1

 18.4

 1.7 × 10−6

[54]
[NiYb(L20)(NO3)3]

 1

 18.1

 2.1 × 10−6

[54]
[Ni2Dy2(L21)2(CH3CN)3(H2O)(NO3)6]·(CH3CN)2·(H2O)

 1

 19

 1.6×10−8

[55]
[Ni2Dy2(L22)2(CH3CN)4(NO3)6]·(CH3CN)x

 1

 15.9

 2.6×10−7

[55]
[Dy2Ni2(3, 4-DCB)10(2, 2’-bpy)2]

 2

 7.0

 6.8 × 10−5

[56]
[Ni(L23)Dy(H2O)4][Co(CN)6]·3H2O

 0.8

 47.02

 6.7×10−9

[57]
[Dy2Ni4(L24)4(μ1, 3-CH3CO2)2(μ3-OH)4(MeOH)2]·4CH3OH

 0

 13.4(5)

 3.4(2) × 10−7

 60

 0.7

 [58]
[Dy2Ni2Mn2(L24)4(μ1, 3-CH3CO2)2(μ3-OH)4(MeOH)2](NO3)2·2CH3OH

 0

 13.0(5)

 2.8(5) × 10−7

[58]
[{(NiL25)2Tb}2(μ2-Cl)2Cl2(μ3-OH)4(OH2)2]Cl2·12H2O

 0

 13.3(5)

 3.8(8) × 10−9

[59]
[{(NiL25)2Dy}2(μ2-Cl)2Cl2(μ3-OH)4(OH2)2]Cl2·16H2O

 0

 U1 = 19.4(8)

 τ1 = 5(1) × 10−11

[59]
U2 = 19.8(3)

 τ2 = 9(1) × 10−10

[{(NiL25)2Ho}2(μ2-Cl)2(μ3-OH)4(OH2)4]Cl4·CH3CN·1.8H2O

 0

 U1 = 19.8(8)

 τ1 = 1.6(5) × 10−10

[59]
U2 = 18.5(6)

 τ2 = 2.4(5) × 10−9

[Ni4Dy(L26)2(LH)2(CH3CN)3Cl]·5H2O·CH3OH

 4

 35.9

 4.36 × 10−9

[60]
[Ni4Er(L26)2(LH)2(CH3CN)3Cl]·2H2O·2CH3OH

 4

 31.6

 7.94 × 10−11

[60]
[Ni2Dy(EtOH)(L27)4(NO3)2Cl]·CH3CN

 3

 9.48

 2.25×10−6

[61]
[NiDy(L28)(dca)2(NO3)]n

 1

 26.2(5)

 2.8(4) × 10−7

[62]
[Tb(hfac)3Ni(hfac)2NIT-4py(H2O)2]

 0

 7.0

 7.8 × 10−7

[63]
[Dy2Ni4(L29)8(CH3COO)4(NO3)2]

 0

 7.43

 9.19 × 10−7

[64]
[Dy4Ni8(μ3-OH)8(L30)8(OAc)4(H2O)4]·3.5EtOH·0.5CH3CN·5H2O

 0

 7.66

 1.45 × 10−6

[65]
[Ni2(valpn)2Dy2(DMF)5(H2O)][Fe(1-CH3im)(CN)5]3·4DMF·12H2O

 0

 14.8(3)

 1.4(9) × 10−6

[66]

续表

[Dy2Ni2(2, 3-DCB)10(2, 2’-bpy)2]

 2

 4.4

 3 × 10−5

[67]
[Dy4Ni8(μ3-OH)8(L31)8(OAc)4(H2O)4]·3.25EtOH·4CH3CN

 1

 81.14(3)

 6.21(2) × 10−11

2

 [68]
[Gd2Ni3(dto)6(H2O)10]·12H2O

 2.5

 22.7

 1.54(5) × 10−6

[69]
[Gd2Ni3(dto)6(H2O)10]·2H2O

 2.5

 18.33

 3.25(5) × 10−6

[69]
[NiEr(L32)2(NO3)3]·0.5H2O

 1

 12.1(2)

 3.49(2) × 10−7

[70]
[NiDy(H2L33)(NO3)3]·(CH3OH)2

 0.6

 17.01

 4.09 × 10−8

[71]
[Ni2Dy2(L34)4(Ac)2(DMF)2]·3CH3CN

 0

 18

 6.85 × 10−6

[72]
[Ni2Dy(Hhmmp)2{(py)2CO2}(CH3COO)2]OH

 0

 6.44

 1.29 × 10−7

[73]
[Ni2Dy(TTTTMe)2(DMF)]BPh4

 0

 582

 1.4(4) ×10−11

[74]

0.3

 582

 1.3(4) ×10−11

[74]
[Dy2Ni2(2, 5-DCB)10(phen)2]

 2

 10

 4.0 × 10−5

[75]
HL1 = 3, 5-dichlorobenzoic acid; bipy = 2, 2’-bipyridine; C7H6O2 = salicylic aldehyde; H2L2 = (E)-2-(2-Hydroxy-3-methoxybenzylideneamino)phenol; H2L3 = N1, N3-bis(3-methoxy-salicylidene)-diethylenetriamine; H3L4 = 2-(2, 3-dihydroxpropyliminomethyl)-6-methoxyphenol; H4L5 = 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1, 3-propanedio; H4L6 = (E)-2, 2’-(2-hydroxy-3-((2-hydroxyphenylimino)methyl)-5-methylbenzylazanediyl)diethanol; H3L7 = 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol; H2quinha = quinaldichydroxamic acid, dfpy = 3, 5-difluoropyridine; H2L8 = N-salicylidene-N’-3-methoxysalicylidene-1, 3-propanediamine; H2L9 = N, N’-bis(salicylidene)-1, 3-propanediamine; hfac- =1, 1, 1, 5, 5, 5-hexafluoroacetylacetonate; bpca- =bis(2-pyridylcarbonyl)amine anion; L10 = (S)P[N(Me)N=CH-C6H3-2-O-3-OMe]3; Hdpk = di-2-pyridyl ketoxime; LMe2 = 6, 6’-((1E, 1’E)-((2, 2-dimethylpropane-1, 3-diyl)bis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol); dmf = dimethylformamide; H2L11 = N, N’, N”-trimethyl-N, N”-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine; H2L12 = 2-(benzothiazol-2-ylhydrazonomethyl)-6-methoxyphenol; OBz = benzoate; 9-An = 9-antharecenecarboxylate; 3-MeOsaltn = N, N’-bis(3-methoxy-2-oxybenzylidene)-1, 3-propanediaminato; HL13 = 2-methoxy-6-[(E)-2’-hydroxymethyl-phenyliminomethyl]-phenolate; H2L14 = 6, 6’-{(2-(dimethylamino)-ethylazanediyl)bis(methylene)}bis(2-methoxy-4-methylphenol); H4abtc = 3, 3’, 5, 5’-azobenzene-tetracarboxylic acid; H2Me2valpn = N, N’-bis(3-methoxysalicylidene)-2, 2-dimethyl-1, 3-diaminopropane); H2hms = 1-(2-hydroxy-3-methoxybenzylidene)-semicarbazide; H3tea = triethanolamine; HL15 = 11H-indeno[1, 2-b]quinoxalin-11-one ligand; H2L16 = 3-ethoxysalicylaldehyde with 2-aminophenol; HL17 = 1, 3-diamine-2-propanol; H2L18 = 2-((2-(2-(2-hydroxy-3-methoxybenzylideneamino)ethylthio)ethylimino)methyl)-6-methoxyphenol); H3L19 = 1, 1, 1- tris[(salicylideneamino)methyl]ethane; H2Pc = phthalocyanine; H2L20 = (RR)/(SS)-1, 2-diphenyl-ethylenediamine with o-vanillin; H2L21 = N, N-bis(2-hydroxy-3-methoxy-benzyliden)-1, 4- diaminobenzene; H2L22 = N, N-bis(2-hydroxy-3-methoxy-benzyliden)-1, 5-diaminonaphthalene; 3, 4-HDCB = 3, 4-dichlorobenzoic acid; H2L23 = N, N-ethylenebis(3-methoxysalicylaldiimine); H2L24 = 2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol; HL25 = 2-((3-aminopropylimino)methyl)-6-methoxyphenol; H3L26 = (E)-2-(hydroxymethyl)-6-(((2-hydroxyphenyl)imino)methyl)-4-methylphenol; HL27 = 2-methyl-8-hydroxyquinoline; H2L28 = N, N’-bis(2-hydroxy-3-methoxy-5-methylbenzyl)homopiperazine; dca = dicyanamide; hfac = hexafluoroacetylacetonate; NIT-4py = 2-(4-pyridyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide; HL29 = 8- hydroxyquinoline; H2L30 = 1-[[(2-hydroxyethyl)imino] methyl]-2-naphthalenol; H2valpn = N, N’-1, 3-propylenebis-3-methoxy-salicylideneamine; 2, 3-HDCB = 2, 3-dichlorobenzoic acid; H2L31 = 4-bromo-2-[(2-hydroxypropylimino)methyl]phenol; dto = dithiooxalate; HL32 = [2-(methylsulfanyl)phenyl]salicylaldimine; H4L33 = N, N’, N”, N”’-tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1, 4, 7, 10-tetraazacyclododecane; H2L34 = (E)-2-((2-hydroxy-3-methoxybenzylidene)amino)-4-methylphenol; H2hmmp = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol; H3TTTTMe = 2, 2’, 2”-(((nitrilotris-(ethane-2, 1-diyl))tris-(azanediyl))tris(methyl-methylene))tri-phenol; 2, 5-HDCB = 2, 5dichlorobenzoic acid; phen = 1, 10-phenanthroline

2.1. [Dy2Ni2]型单分子磁体

近年来，随着人们不断深入研究稀土金属配合物，镧系金属与有机配体形成的配合物引起了越来越多研究者的关注。2014年，郑智敏领导的研究小组用NiⅡ取代了配合物Dy2Co2(L1)10(bipy)2中的CoⅡ，得到了一个接近等结构的配合物，Dy2Ni2(L1)10(bipy)2(1) [23]。相较于其他配合物而言，所得配合物1结构简单。交流磁化率研究表明，1在零场下也表现出SMM行为，有效能势垒为105(1) K (如图1)。利用Arrhenius定律对数据进行分析表明，在1研究中至少存在两个松弛过程。高温过程可能与单个DyⅢ的自旋轨道态的弛豫有关。通过第一原理计算，发现配合物{Dy2Co2}和1中DyⅢ的第一个激发态Kramers双态分别为66和61 cm−1，与实验测量的磁反转势垒一致。低温过程可能与交换状态的逆转有关。第一原理计算表明，1中交换型的低能势垒约为8 cm−1，而在复合物27中，只有在温度低于1 K时才能观察到交换型的反转势垒。因此可以推断，配合物27和1的弛豫过程主要是由DyⅢ离子的强各向异性控制的，它们的弛豫机制的差异可能归因于过渡金属的变化。

Figure 1. lnτ versus T−1 plots for 1 under zero dc field. The red points have been obtained from the ac susceptibility measurements. The black points have been obtained from the fit of the Cole−Cole plots. The red line is obtained by a least-squares fit.

图1. 1在零直流场下的lnτ与T−1图。红点是由交流磁化率测量得到的。黑点是通过对Cole−Cole图的拟合得到的。红线是利用最小二乘拟合得到

2015年，唐金魁的课题组成功合成了另一种含有NiⅡ的三核3d-4f单分子磁体，标记为[DyⅢ2NiⅡ(C7H5O2)8]·(C7H6O2)2(2) [24]。该配合物的核心结构与配合物[Ln2CoⅡ(C7H5O2)8]·6H2O (Ln=Dy (28), Tb (29))基本相同，保持了Dy-Ni-Dy的线性排列。此外，2的离子中DyⅢ和NiⅡ离子的配位环境与配合物28-29中的配位环境相同。交流磁化率测量证实了2在1.5 kOe的外场下的SMM行为。值得注意的是，与零场条件下的情况相比，与频率相关的非相交流磁化率的峰值向较低的频率移动。在ln (τ)和T−1图中，在5 K处的明显交叉表明在2的图中存在双弛豫过程，与配合物1类似。利用Arrhenius定律拟合数据，确定低温有效势垒为12.24 K，高温有效有效势垒为55.19 K (图2)，高低温的有效势垒相差不大。这两种高、低温弛豫机制可能与DyⅢ的单离子行为和DyⅢ与NiⅡ离子之间的弱耦合相互作用有关。

Figure 2. Magnetization relaxation time, ln(τ) vs T−1 plot for 2 under 1500 Oe. The solid lines are fitted with the Arrhenius law

图2. 1500 Oe下2的磁化弛豫时间，ln(τ) vs T−1图。实线符合Arrhenius定律

2016年，赵小军、刘育[25]等人发现了三个线性{Dy2Ni2}团簇，即[Dy2Ni2(bipy)2(RC6H4COO)10)(R = H(3)、甲基(4)和二氧化氮(5))，它们表现出结构相似性。和上述的配合物相比，该类型的配合物结构组成较为复杂。以3为例，两个中央对称DyⅢ离子聚集在一起的两对羧酸同μ:η1:η1和μ:η2:η1绑定模式，导致DyⅢ协调八羧酸氧原子从七个苯甲酸阴离子，形成一个稍微扭曲的三角形十二面体。随后，{Dy2}二聚体通过三对羧酸基进一步连接到两个具有八面体配位环境的NiⅡ离子上，形成一个线性核心(如图3(a))。交流磁化率测量显示，配合物3和4在零场有明显的峰，表明存在SMM的行为。将数据拟合到一个公式中，得到3和4的有效能垒分别为57.06 K和37.04 K (如图3(b))。在4.6 kOe的外场作用下，4的有效能势垒增加到77.08 K，表明QTM被有效抑制。然而，对于配合物3，5.8 kOe的应用场几乎没有改变其有效能垒。相比之下，配合物5在零场和10 K以下的非相交流磁化率中表现出频率依赖的行为，没有可见峰。低温下失相信号的显著增加进一步证实了QTM过程在5中逐渐占主导地位。此外，配合物3-5中没有一个表现出迟滞环。理论计算表明，选择配合物3-5R组(−H，−CH3或−NO2)可以通过感应或共轭效应改变羧酸氧供体的电荷分布，从而影响基态和第一激发态DyⅢ和磁易轴的方向，进一步影响分子各向异性和偶极相互作用。因此，局部配位球内的电荷分布对影响SMMs的性能起着关键作用。

Figure 3. The molecular structure of 3 (a) and plots of ln(τ) vs T−1 for 3 (top) and 4 (bottom) under zero dc field (b). The solid lines represent fits to the Arrhenius law for 3 and 4. Color code: NiⅡ, green; Dy, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity

图3. 在零直流场(b).下，3 (上)和4 (下) (a)的分子结构和ln (τ)与T−1的图实线表示符合3和4的Arrhenius定律。颜色编码：NiⅡ、绿色；Dy、紫色；O、粉红色；N、蓝色；C、灰色。为了清晰起见，省略了H原子

2.2. 缺陷Dicubane型单分子磁体

2011年，Powell研究小组[26]报告了两对具有缺陷双元(或蝴蝶型)核心拓扑的配合物，分别为[Ni2Ln2(L58)4(NO3)2(DMF)2] (H2L58 = (E)-2-(2-Hydroxy-3-methoxybenzylideneamino)phenol, Ln = Dy (6, Tb (7))和[Ni2Ln2(L58)4(NO3)2(MeOH)2]∙3MeOH (Ln = Dy (8), Tb (9))。在结构上，配合物6-9是等结构的，唯一的区别是在配合物6和7中，与NiⅡ离子配位的DMF被MeOH分子取代。在配合物6中，两个NiⅡ离子占据了与蝴蝶身体相对应的位置，而两个DyⅢ离子则位于翅膀的位置(图4(a))。两个对称的H2L2配体采用μ3:η1:η2:η1:η2配位模式，连接外围的DyⅢ和NiⅡ离子。另外两个H2L2配体采用μ3:η0:η1:η1:η3配位模式，连接两个Ni2Dy三角形(图4(b))。此外，DMF和硝酸盐离子与NiⅡ和DyⅢ离子配位，导致NiⅡ的八面体构型略有扭曲，而DyⅢ为扭曲的四方反棱柱构型。在零直流场下对所有四种配合物进行了交流磁化率测量。配合物6和8表现出较强的频率依赖性的同相和异相信号，6和8的有效能势垒分别为18.5 K和21.3 K。通过施加4 kOe的外磁场，8有效抑制了QTM效应的存在，使有效能垒增加到28.5 K (图5)。此外，9在6 K以下表现出弱频率依赖的虚部信号，7在1.8 K以上没有表现出任何频率依赖的虚部信号。因此，综合考虑配合物6-9，LnⅢ离子的各向异性成为发展SMM性能的关键决定因素，这与我们从配合物1和27所得出的结论基本一致，可见[Dy2Ni2]型单分子磁体和缺陷Dicubane型单分子磁体在性质上有某些相同之处。此外，甲醇的能垒8高于DMF的6，表明NiⅡ上的配位取代可能显著影响LnⅢ各向异性张量的取向和大小。

Figure 4. The molecular structure of 6 (a) and the coordination modes of (L2)2− with metals in complexes 6-9 (b). Color code: NiⅡ, green; Dy, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity.

图4. 6 (a)的分子结构和配合物6-9 (b).中的((a)) 2-与金属的配位模式。颜色编码：NiⅡ，绿色；Dy，紫色；O，粉红色；N、蓝色；C、灰色。为了清晰起见，省略了H原子

Figure 5. Arrhenius semi-log plots of the relaxation time, τ vs 1/T of complexes 6 and 8 from ac susceptibility measurements both under zero and an applied dc field of 4000 Oe. The solid lines correspond to a linear fit in the thermally activated range of temperatures.

图5. 在0和4000 Oe的直流场下，配合物6和8的交流磁化率测量的弛豫时间τ与1/T的Arrhenius半对数图。实线对应于热激活温度范围内的线性拟合

2014年，唐金魁领导的研究团队[27]成功合成了5个缺陷六核配合物，是目前核数最多的配合物，分别为[Ln2Ni4(L3)2Cl2(OH)2(CH3O)2(CH3OH)6] (Ln = Gd (10), Tb (11)，Dy (12))，and [Ln2Ni4(L3)2Cl2(OH)4(CH3OH)6] (Ln = Ho (13)，Y (14))。配合物10-14表现出显著的结构相似性。以配合物12为例，其核心由两个羟基和两个苯氧基氧原子组成，连接两个缺陷二元单元[Ni2DyO3Cl]。每个[Ni2DyO3Cl]单元是由连接两个NiⅡ离子和一个DyⅢ离子通过一个苯氧基，一个羟基，一个甲醇分子，一个氯离子，导致DyⅢ采用扭曲的四方反棱柱构型，而NiⅡ离子表现出扭曲的八面体构型(图6)。在零磁场下，11和12表现出较强的温度和频率相关的同相和非相交流磁化率信号，具有峰值，表明它们的SMM行为。复合物13在6 K以下仅显示出微弱的频率相关的交流信号，即使在2 kOe的外部磁场下，也没有可观测到的峰值。10和14在1.8 K以上和零外场下没有显示任何虚部磁化率信号。对11和12的磁性行为的分析表明，它们的弛豫过程可能遵循热激活机制。用Arrhenius定律拟合，得到11和12的有效能垒分别为30 K和32 K。虽然配合物6和8也表现出了较强的频率依赖性的实部和虚部信号，但有效能垒是11和12的一半。此外，11和13代表了Ni-Tb和Ni-Ho配合物的第一个实例，在零外场下观察到虚部交流磁化率信号。

Figure 6. The molecular structure of 12. Color code: NiⅡ, green; Dy, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity

图6. 12的分子结构。颜色编码：NiⅡ，绿色；Dy，紫色；O，粉红色；N、蓝色；C、灰色。为了清晰起见，省略了H原子

2015年，Fu-Pei Liang等人[28]使用两种不同的多齿席夫碱配体合成了三个蝴蝶型拓扑的SMM：[Dy2Ni2(H2L5)2(μ3-OMe)2(CH3CN)2(NO3)4]·4H2O (15, H4L5 = 2-(((2-hydroxy-3-methoxyphenyl)methylene) amino)-2-(hydroxymethyl)-1, 3-propanedio), [Ln2Ni2(HL4)2(μ3-OMe)2(CH3CN)2(NO3)4]·4H2O (Ln = Tb (16), Dy (17)) (图7(a))。磁分析显示，三种配合物在直流磁化率方面均表现出强铁磁耦合，在交流磁化率研究中表现出典型的SMM行为，各向异性势垒分别为48.2 K、86.2 K和56.6 K (图7(b))。此外，这三个复合物均表现出狭窄的滞后环。结合理论计算的结果，很明显，DyⅢ和TbⅢ离子具有更高的轴向各向异性，在这些具有蝴蝶型磁滞的配合物中，LnⅢ离子和3d金属离子之间的交换耦合可能明显弱于LnⅢ-LnⅢ的交换作用。这一结论再次验证了Powell研究小组的研究结论的正确性。

Figure 7. The molecular structure of 15 (a) and Arrhenius semi-log plots of the relaxation time vs. 1/T of complexes 15-17 (b). The solid lines correspond to a linear fit in the thermally activated range of temperatures. Color code: NiⅡ, green; Dy, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity

图7. 15 (a) 和阿伦尼乌斯与15-17 (b). 弛豫时间的半对数图实线对应于热激活温度范围内的线性拟合。颜色编码：NiⅡ、绿色、Dy、紫色、O、粉红色、N、蓝色、C、灰色。为了清晰起见，省略了H原子

2.3. 其他类型的单分子磁体

2013年，Vadapalli Chandrasekhar及其同事[29]合成了4个等结构的五核SMM，记为{Ni2Ln3} (Ln = Dy (18), Gd (19), Tb (20), Ho (21))。配合物18和19包括4个三层去质子配体(HL6)3−，其中两个位于配合物的末端，其余两个位于配合物的中心。18和19的核心由两个末端四核单元[NiDyO2]和两个四元环[Dy2O2]组成，它们是相互连接的(图8(a))。配合物20和21本质上与18和19是同结构的，唯一的区别是在配合物20和21中，中心配体上的一个苯氧原子仍然保持质子化，形成一个双脱质子配体(HL6)2−，而其余三个配体仍然保持三重脱质子(HL6)3−。在直流磁化率测量中，18表现出铁磁基态，而19-21表现出反铁磁基态。交流磁化率测量显示，18表现出具有两个热激活弛豫过程的SMM行为，与上述的11和12相似。在10~17 K的温度范围内，高温有效能垒为85 K，τ0值为5.9 × 10−7 s。当温度降至低于7 K时，低温有效势垒为53.5 K。在超过50 mT/s的扫描速率下，18的磁滞回线的开放温度高达3 K，为其单分子磁体行为提供了证据(图8(b))

Figure 8. The molecular structure (a) and magnetic hysteresis (b) of complex 18. Color code: NiⅡ, green; DyⅢ, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity

图8. 配合物18的分子结构(a)和磁滞(b)。颜色编码：NiⅡ，绿色；DyⅢ，紫色；O，粉红色；N、蓝色；C、灰色。为了清晰起见，省略了H原子

2015年，Constantinos J. Milios和同事[30]合成了三个笼状配位配合物，{Ni6Ln3} (Ln=Gd (22), Dy (23), Er (24))。配合物22和24是等结构的，而配合物23由于存在不同的共结晶溶剂分子而有所不同。以配合物24为例，它包括一个[ErⅢ3]三角形，覆盖着一个[NiⅡ6]三角棱镜。[ErⅢ3]三角形由6个μ3-OH基团锚定，每个μ3-OH部分连接两个ErⅢ离子和一个NiⅡ离子。[NiⅡ6]三角棱镜包含6个μ3-OR烷基，这6个来自6个双去质子配体(HL7)2−((H3L7 = 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol)，三角棱镜角的3对[Ni2]单元由μ:η1:η1硝酸基桥接(图9(a))。为了研究22-24团簇在零场条件下的磁性能，进行了交流磁化率测量。值得注意的是，只有23表现出SMM的特征，在3.6 K以下，虚部信号存在明显的峰(图9(b))，拟合数据得到23.84 K的有效能垒，τ0为3.63 × 10−8 s 。

Figure 9. The molecular structure of 15 (a) and plot of χM” vs T for complex 15 (b). Color code: NiⅡ, green; DyⅢ, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity

图9. 15 (a)的分子结构和配合物15 (b)的χM”与T的曲线。图颜色编码：NiⅡ，绿色；DyⅢ，紫色；O，粉红色；N、蓝色；C、灰色。为了清晰起见，省略了H原子

2021年，童明良领导的研究小组[31]采用对称组装策略和金属生长方法合成了配合物[HoⅢNiⅡ5(quinha)5F2(dfpy)10](25, H2quinha = quinaldichydroxamic acid, dfpy = 3, 5-difluoropyridine)。在配合物25中，HoⅢ位于[15-MCNi-5]环内，其中HoⅢ与赤道平面上的5个氢化氧原子和两个轴向F−配位，为D5h配位环境。5个四齿醌配体通过μ3:η2:η1:η1:η1配位模式与5个NiⅡ离子连接，形成[15-MCNi-5]环。在0~2 kOe范围内的外磁场作用下，25的交流磁化率在50 K时达到峰值。随着直流场的增加，峰值对应的频率发生变化，但变化的幅度逐渐减小。在高温区域，外磁场对有效能垒的影响可以忽略不计，Ueff为825.1 K，τ0(1)，范围为3.3 (5)~3.6 (6) × 10−13 s，是目前发现的所有单分子磁体中有效能垒最大的。这表明，在高温条件下的弛豫过程是由一个单一的HoⅢ离子主导的。此外，理论计算结果表明，HoⅢ的基态与第二激发态之间的能隙接近于825.1 K的能垒。在低温区域，能垒随外加磁场的变化而振荡，范围为26.6 (1)至32.7 (6) K，τ0 (2)范围为5.7 (1) × 10−4至9.4 (2) × 10−4 s。这些振荡可能来自于在简单单核复合体领域之外发生的超精细状态的塞曼交叉和反移动现象。这些交叉/反移动现象产生了不同的势垒，要么由超精细能级之间的非相干QTM主导，要么由涉及激发电子交换双态的类Orbach过程主导。综上所述，这一现象是由于各向异性金属离子的强超精细相互作用及其与相邻金属离子的交换耦合引起的。

3. 结论

NiⅡ在一般配位场下具有由较大的零场分裂导致的高的磁各向异性，其分子配位结构简单，这些特点引起了人们的兴趣，并提出了进一步的综合努力应该关注的方向。通过研究总结Ni-Ln单分子磁体的最新研究进展，我们发现影响SMM性能的几个重要因素，如LnⅢ离子的各向异性、Ni与Ln间耦合相互作用力、Ni离子周围配位环境及电荷分布等等，为我们后续继续研究Ni-Ln单分子磁体提供了指导方向。

但显然，我们对单分子磁体的了解还远不够，有关Ni-Ln单分子磁体的研究报告没有非常全面，并且大部分Ni-Ln配合物在奥巴赫、拉曼、量子隧穿这些弛豫过程中的参数(Ueff、τ0、QTM)普遍是利用理性数据拟合所得，并非确切真实数据，其可靠度需要评估。由于NiⅡ离子复杂而敏感的磁结构，使其磁学性质不稳定，因此目前大部分有关Ni-Ln的研究主要集中在磁体的磁学行为及性质、合成和制备技术这些方面。虽然已取得了一些重要的进展，但仍面临着磁构关系不明朗、磁性行为理解片面、合成方法不成熟，工业化生产困难、研究方向单一等问题。这些问题有不少还处于基础研究的阶段，如果可以得到解决，相信对单分子磁体的应用会有更好的指导意义

基金项目

江苏省研究生科研与实践创新计划项目(KYCX24_3546、SJCX24_1995、SJCX24_1992)资助，南通大学大型仪器开放基金资助(KFJN2471、KFJN2437)，感谢南通大学分析测试中心。

NOTES

*通讯作者Email: ding.xyu@ntu.edu.cn

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