DOI: 10.12677/japc.2024.133048, PDF, HTML, XML,  被引量    科研立项经费支持
作者: 郑 祺, 张腾坤, 王窦尊, 徐 航, 李嘉欣, 崔会会, 孙广平：南通大学化学化工学院，江苏 南通；王 金：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: 铜–稀土单分子磁体；结构；磁性；Cu-Ln Single Molecule Magnets； Structure； Magnetism

文章引用：郑祺, 张腾坤, 王窦尊, 徐航, 李嘉欣, 崔会会, 孙广平, 王金. 铜–稀土单分子磁体的研究进展[J]. 物理化学进展, 2024, 13(3): 427-446. https://doi.org/10.12677/japc.2024.133048

1. 引言

近年来，单分子磁体(Single-Molecule Magnets, SMMs)作为一种新兴的磁性材料，受到了广泛的关注[1]。单分子磁体是一类在低温下能够表现出磁双稳态的有机金属化合物，其独特的磁性质使其在信息存储[2]、量子计算[3]、磁制冷[4]等领域具有重要应用前景。在众多类型的单分子磁体中，过渡–稀土配合物因其独特的磁各向异性，成为研究的热点[5] [6]。

铜–稀土单分子磁体(Cu-Ln SMMs)是过渡金属–稀土配合物中的一个重要分支。铜离子Cu²⁺具有较高的电子自旋态(S = 1/2)，与稀土离子(如Dy³⁺、Tb³⁺)的强磁各向异性相结合，可以形成具有显著单分子磁性的配合物[7]。这类配合物在低温下能够表现出磁滞回线等典型的单分子磁体特性。近年来，随着合成技术和表征手段的进步，研究者们在铜–稀土单分子磁体的结构设计、磁性调控等方面取得了诸多重要进展(表1)。铜–稀土单分子磁体的结构设计是实现其优异磁性的基础，通过合理设计配体、调控金属离子间的相互作用，能够有效的提高单分子磁体的阻磁能垒[8]-[10]。例如，研究发现，使用具有强配位能力的配体可以显著增强铜离子和稀土离子之间的超交换作用，从而提升单分子磁体的磁学性能[11]。其次，磁性调控是铜–稀土单分子磁体研究中的另一重要方面。通过更换配体、外加磁场等手段，可以对单分子磁体的磁性质进行有效调控[12] [13]。近年来有研究表明，通过对配体进行官能团修饰，可以改变配合物的晶体场环境，从而调节其磁各向异性和磁弛豫行为[4] [14]-[17]。

总之，铜–稀土单分子磁体作为一种具有巨大潜力的磁性材料，近年来在结构设计、磁性调控等方面取得了显著进展[18] [19]。本文通过对近年来典型的例子进行综述，以期为3d-4f单分子磁体的发展奠定一定的基础。

2. 铜–稀土单分子磁体的研究进展

目前，已报道的铜–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，并根据其核数进行排序，以研究其结构与磁性行为之间的关系。通过对比和分析，发现配体的选择和配位方式尤为关键，通过引入不同配体可以改变配合物的构型，电荷排列方式，进一步改变配合物的弛豫路径，从而获得不同的能垒。而核数也是至关重要的，随着Cu-Ln SMMs中核数的增加，磁相互作用的复杂性也随之增加，这给预测和模拟磁行为带来了挑战。例如，随着核数的增加，使之对于结构的精确设计从而保持所需的磁特性变得越发有难度，分子内金属与金属的磁相互作用的类型增加，使磁耦合路径分析复杂化，导致对体系表现出的磁性解释更具有挑战。但同时，增加核数也可以增强总的自旋基态，增强磁各向异性，提高分子的磁性能，通常会表现出较长的弛豫时间。还有一个优点，那就是核数的增加可能会抑制量子隧穿，这也是因为多核的复杂磁相互作用增加能量势垒的原因之一。目前的研究进展就是通过不同的合成策略来调控配合物的磁性，例如，通过改变配体的种类或引入新的金属中心，优化磁各向异性和能垒大小，提高在高温区的稳定性和磁性能。

Table 1. The magnetic data of Cu-Ln SMMs

表1. 铜–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.
[TbCu(L1)(NO3)3(H2O)] (1)	1	29(2)				[20]
[TbCu(L1)(o-vanilate)(NO3)(MeOH)]·NO3 (2)	1	32.2(6)				[20]
[Cu(L2)(C3H6O)Tb(NO3)3] (3)	1	42.3(4)	7.1(9) × 10−10			[21]
[Cu(L2)(C3H6O)Dy(NO3)3] (4)	1	11.5(10)	4(2) × 10−10			[21]
[{Dy(hfac)3}2{Cu(dpk)2}] (5)	0	47(4)	1.1(5) × 10−7			[22]
[Cu2(L3)2DyCl2(H2O)]⋅Cl⋅MeCN (6)	0	39.06	1.05 × 10−5			[23]
[Cu(L4)Tb(hfac)2]2 (7)	0	21	2.7 × 10−8			[24]
[Cu2(valpn)2Tb2(N3)6]·2CH3OH (8)	0	30.1 ± 0.7	1.1 ± 0.2 × 10−6	50	2.4	[25]
[Tb2Cu3(H3L5)2(CH3COO)6]·CH3OH·2H2O (10)	0	21.4 ± 0.5	1.3 × 10−7			[26]
(NMe4)2[Tb2Cu3(H3L5)2(NO3)7(CH3OH)2]·(NO3) (11)	0	36.0 ± 0.2	1.0 × 10−7	140	1.8	[26]
(NMe4)2[Dy2Cu3(H3L5)2(NO3)7(CH3OH)2]·(NO3) (12)	0	23.9 ± 0.1	7.5 × 10−8			[26]
(NMe4)2[Ho2Cu3(H3L5)2(NO3)7(CH3OH)2](NO3) (13)	0	17.2 ± 0.2	2.3 × 10−7			[26]
(NMe4)2[Er2Cu3(H3L5)2(NO3)7(CH3OH)2](NO3) (14)	0	14.8 ± 0.1	1.2 × 10−7			[26]
[Cu4Dy2(OH)2(NO3)8{(py)2CO2}2(MeCN)4] (17)	0	20.1(2)	8.3(1) × 10−9			[27]
[EuCu5(quinha)5(sal)2(py)5]·CF3SO3·py·3H2O (18)	2	21.16	1.2(5) × 10−7			[28]
[{Cu5Tb2(L6)2(μ3-OH)4(ClO4)(NO3)3(OH2)5}(ClO4)2(H2O)4.25]∞ (21)	0	23.4	1.1 × 10−6			[29]
	1.2	27.9	6.6 × 10−7			[29]
[{Cu5Dy2(L6)2(μ3-OH)4(ClO4)(NO3)3(OH2)5}(ClO4)2(H2O)5.5]∞ (22)	0	8.3	3.1 × 10−6			[29]
[Cu4Dy4(L7)4Cl6(CH3OH)8(H2O)4]·Cl2·(CH3OH)9·(H2O)3 (24)	0	54	2.18 × 10−9			[30]
[Dy2Cu7(OH)2(L8)2(L9)2(OAc)8(NO3)2(H2O)4]·(NO3)2·8.5H2O (26)	0	18.0(3)	5.61 × 10−8			[31]
[DyCu8(OH)8(2-ma)8(Cl)2][ClO4]·xH2O (29)	0.6	27.0	4.59 ×10−8			[32]
[ErCu8(OH)8(2-ma)8(Cl)2][ClO4]·xH2O (30)	0	22.9	4.74× 10−7			[32]
	1	33.0	9.48× 10−6			[32]
[TmCu8(OH)8(2-ma)8(Cl)2][ClO4]·xH2O (31)	3	24.8	6.50× 10−6			[32]
[YbCu8(OH)8(2-ma)8(Cl)2][ClO4]·xH2O (32)	0.7	22.5	1.48× 10−8			[32]
[DyCu5(quinha)5(sal)2(py)5]·(CF3SO3 )·py·4H2O (33)	0	900(31)	2.0(10) × 10−11	20	12	[33]
[Dy2Cu10(quinha)10 (sal)2(OH)(py)9]·(CF3SO3 )3·2py·2CH3OH·2H2O (34)	0	838(53)	5(4) × 10−11	20	6	[33]
[Dy3Cu6(L10)6(μ3-OH)6(H2O)10]·Cl2·ClO4·3.5H2O	0	25	1.5 × 10−7			[34]
[L11Cu(O2COMe)Tb(thd)2]	1	13.8	3 × 10−7	70	0.7	[35]
[Cu2Tb2(L12)2(NO3)2(dae-o)2]·2(n-BuOH)	0	14.91	2.39 × 10−7			[36]
	1	23.76	7.00 × 10−8			[36]

续表

{[CuTb(L12)(n-BuOH)0.5]2(dae-c)3}·5(DMF)·4(n-BuOH)·2(H2O)	0	12.13	3.03 × 10−6			[36]
	1	22.04	2.11 × 10−7			[36]
[TbCu(sal)(NO3)2(L1)(MeOH)]	1	32.9(4)	3.0(8) × 10−8			[37]
[DyCu(sal)(NO3)2(L1)(MeOH)]	1	26.0(5)	1.02(11) × 10−5			[37]
[Cu5Tb4O2(teaH)4{O2CC(CH3)3}2(NO3)4(OMe)4]·2MeOH·2Et2O	0	11.9 ± 0.8	(9 ± 6) × 10−6			[38]
[Cu5Dy4O2(teaH)4{O2CC(CH3)3}2(NO3)4(OMe)4]·2MeOH·2Et2O	0	7 ± 1	(1.3 ± 0.2) × 10−5			[38]
[Cu5Ho4O2(teaH)4{O2CC(CH3)3}2(NO3)4(OMe)4]·2MeOH·2Et2O	0	10 ± 4	(3 ± 2) × 10−6			[38]
[Cu5Dy2(L6)2(μ3-OH)4(μ-H2O)2(μ-OAc)2(OAc)2(OH2)2]·(NO3)2·(H2O)2	0	4	3 × 10−6			[39]
	0.9	6	3 × 10−6			[39]
[Cu3Tb(LBu)(NO3)2(MeOH)(H2O)](NO3)·3H2O	0	19.5(5)	3.4 × 10−7			[40]
[Dy9Cu8(NO3)2(OH)10(L13)4(OAc)18(H2O)4]	0	11.5(4)	1.86 × 10−6			[41]
[Cu3Dy2(hfac)8(OH)4(N3tempo)]	4	24	5 × 10−9			[42]
[CuDy2(hfac)8(H2O)2(N3tempo)2]	4	21	1 × 10−6			[42]
[(CuL14)2Tb(H2O)(NO3)3]·MeOH·H2O	1	20.3(7)	1.5(4) × 10−7			[43]
[{(CuL14)2Tb(H2O)(NO3)3}2bpy]·2MeOH·4H2O	1	18.0(10)	1.2(5) × 10−8			[43]
{[(CuL14)2Tb(NO3)3bpy]·MeOH·2H2O}∞	1	23.1(5)	1.9(4) × 10−9			[43]
[Cu(H2L15)(CH3OH)]2Tb(H2O)0.57(DMF)0.43Fe(CN)6·5.5H2O	2	13	10−7			[44]
[TbCu3(H2edte)3(NO3)][NO3]2·0.5MeOH	0	17.3(4)	2.2(3) × 10−7	140	1.6	[45]
	1	19.3(1)	1.4(1) × 10−7			[45]
[DyCu3(H2edte)3(NO3)][NO3]2·0.5MeOH	1.5	16.2(4)	1.8(3) × 10−7			[45]
[Cu6Dy2((L16)3-)4(NO3)3(OAc)(CH3OH)6]·NO3·OAc·3CH3OH·2H2O	0	5.2	6.5 × 10−6			[46]
[Cu6Tb2((L16)3-)4(NO3)3(OAc)2(CH3OH)5]·NO3·CH3OH·6H2O	0	15.6(1)	6.9(2) × 10−7			[46]
[Cu4Dy8(OH)6(NO3)2(O2CCH2But)16(pdm)4]	0	7.9(3)	4.9(4) × 10−7			[47]
[Dy2Cu2(hfac)10(NIT-3py)2(H2O)2]	0	12.51	8.74 × 10−7			[48]
	2	13.14	1.77 × 10−6			[48]
[Dy4Cu4(H2L17)4Cl8(H2O)4]·Cl4·28H2O	0	32.2	8.1 × 10−9			[49]
[Cu3Tb(LEt)(NO3)3(MeOH)]·MeOH	1	11.3(5)	2.1 × 10−7			[50]
[Cu(L18)(C3H6O)Dy(NO3)3]	1	11.42				[51]
[Cu(L18)(C3H6O)Tb(NO3)3]	1	42.04				[51]
[Dy6Cu6(H2L17)6Cl12(H2O)6]·5ClO4·OH·30H2O	0	19.6	1.67 × 10−7			[52]
[Dy4(H2L17)4Cu5(SCN)8]	0	11.94	1.52 × 10−6			[53]
[Cu6Dy12(OH)20(N3)6(NO3)8(dapdo)6(H2O)18](OH)2	0	17	3 × 10−11	140	1.1	[54]
[Dy3Cu2(HL19)4(MeOH)]·ClO4	0	7.7	(2.6 ± 0.1) × 10−5			[55]
[Dy2Cu4(HL19)4]·(ClO4)2	0	9.3	(2.9 ± 0.2) × 10−7			[55]
[Cu5Dy5(µ4-O)(µ3-OH)3(L20)3(HL1)4(NO3)2(MeOH)2]	0.5	8.1	9.7 × 10−7			[56]
[Cu2Dy2(µ3-OMe)2 (HL21)2(NO3)4]·2MeOH	1.5	16.5	4.5 × 10−7			[56]
{[Ho(hfac)3]2[Cu(hfac)2]3(NIT-Pyrim)2(H2O)2}	0	10.27	6.4× 10−7			[57]

续表

[CuLdpen(1R2R/1S2S)Tb(NO3)2]2	0	29.4(6)	1.5(3) × 10−8			[58]
[CuLdpen(1R2R/1S2S)Dy(NO3)2]2	0	13.1(9)	1.9(7) × 10−7			[58]
[DyCu(hfac)5(NIT-Ph-p-OCH2trz)]·0.5C6H14	0	21.0	5.37 × 10−8			[59]
[DyCu(hfac)5(NIT-Ph-p-OCH2trz)]	0	29.0	6.1 × 10−10			[59]
[Cu5Tb2(O2CMe)2(NO3)4(L22)2(HL22)2]	0	9.4 ± 0.1	1.1 ± 0.2×10−7			[60]
[{Cu5Dy2(L23)2(μ3-OH)4(NO3)4(MeOH)2}(NO3)2]∞	0	12	10−6			[61]
[Cu2Dy2(H2L24)2(L25)2(OMe)(NO3)]·8MeOH	0	8.1	1.4 × 10−5			[62]
[Cu2Dy2(HL24)2(L25)2(MeOH)2]·8.5MeOH	0	2.84	1.97 × 10−5			[62]
[Cu2Tb2(H2L24)2(L25)2(H2O)(OMe)(NO3)]·0.5H2O·7MeOH	1	8.85	3.2 × 10−7			[62]
[Dy2Cu2(hfac)10(NITPhOPybis)2]	0	20.1(4)	2.0(4) × 10−5			[63]
	0.8	21.9(1)	1.6(9) × 10−5			[63]
[Cu3TbCl3(phenox)6(MeOH)3]	1	14.4	1.7 × 10−6			[64]
[Cu3DyCl3(phenox)6(MeOH)3]	1	7.7	5.1 × 10−6			[64]
[Dy4Cu4(H2L17’)4(H2L17)4Cl4(OH)4]·Cl4·24H2O	0	10.6	2.3 × 10−6			[65]
[Tb6Cu6(H2L17)6Cl12(H2O)6]·5ClO4·OH·xH2O	0	12.98	1.13×10−6			[66]
[Cu3Ho2(L26)2(teaH)2(N3)2Cl2]·3CH3CN	1	4.9	2.0 × 10−6			[67]
[Cu3Dy2(L26)2(teaH)2(N3)2Cl2]·2CH3CN	1	0.7	7.0 × 10−7			[67]
[Cu5Dy2(O2CMe)2(NO3)4(L27)2(HL27)2(Me2CO)2]	0	13(5)	1.2(5) × 10−6			[68]
[Cu5Dy2(O2CMe)2(NO3)4(L28)2(HL28)2]	0	9.9(4)	1.2 (2) × 10−6			[68]
[(CuL29)Tb(NO3)3]	2	28.5(5)	4.1(6) × 10−8			[69]
[(CuL29)Dy(NO3)3]	2	53(2)	6(5) × 10−9			[69]
[(μ4-CO3)2{(CuL30)(MeOH)Dy(NO3)}2]	1.5	6.5	4.2 × 10−7			[70]
[(μ4-CO3)2{(CuL30)(MeOH)Tb(NO3)}2]	1.5	4.5	2.2 × 10−6			[70]
[Tb2Cu3(hfac)12(4-NIT-MePyz)4]	2	13	1.84 ×10−7			[71]
[Dy(hfac)3Cu(hfac)2(bisNITPhPyrim)]	0.5	8.13	1.07 × 10−6			[72]
[Tb(H2O)3{Cu(pyzha)}5(H2O)3] (TfO)2·3(H2O)·(MeOH)	0	5.42	8.09 × 10−7			[73]
[Yb{Cu4(butyrat)4}2]·Cl3·MeOH·26H2O	1	6.84	1.04×10−5			[74]
[CuL31(μ-NO3)Tb(NO3)2(H2O)]·CH3CN	2	19.3(8)	8(2) × 10−8			[75]
[CuL31(μ-NO3)Dy(NO3)2(H2O)]·CH3CN	2	26.1(10)	1.6(5) × 10−8			[75]
[CuL32(μ-NO3)Tb(NO3)2(H2O)]·CH3CN	2	23.8(10)	9.1(39) × 10−10			[75]
[CuL32(μ-NO3)Dy(NO3)2(H2O)]·CH3CN	2	28.2(5)	7.2(9) × 10−8			[75]
[HoCu(hfac)5NIT-Ph-p-OCH2trz·0.5C6H14]n	2	4.93	1.64 × 10−6			[76]
[[CuL33]Ln(NO3)3·H2O]·CH3CN	5	15.4	2.15 × 10−6			[77]
[[CuL34]Ln(NO3)3·H2O]·CH3CN	5	17.9	1.1 × 10−6			[77]
[Dy2Cu2(hfac)10(PPNIT)2(H2O)2]·CHCl3	1.5	17.8 (6)	3.4(3) × 10−6			[78]
[Cu(Cl)(valen)Tb(NO3)(CH3OH)(H2O)(dca)]	0	21.85	7.65 × 10−4			[79]
[LnCu(hfac)5NIT-Ph-p-OCH2trz]n	0	7.3	2.93 × 10−6			[80]
[(L35)3Cu3TbCl2(NO3)2(H2O)2]	0	10.49(8)	5.02(14) × 10−8			[81]
	1	13.3(2)	3.1(2) × 10−8			[81]

续表

[(L35)3Cu3Gd(NO3)2(H2O)2(MeOH)](NO3)	2	10.8(2)	8.8(6) × 10−8			[81]
[(L35)3Cu3Dy(NO3)2(H2O)2(MeOH)](NO3)	1	7.82(4)	6.05(11) × 10−8			[81]
[Cu6Dy3(R-L36)6(OH)6(H2O)6](ClO4)(NO3)2·4.75H2O·8.5MeOH	0	19.5(0.6)	4.1(0.1) × 10−8			[82]
[Cu6Dy3(S-L36)6(OH)6(H2O)6] (ClO4)(NO3)2·5.5H2O·8MeOH	0	21.4(0.4)	2.7(0.1) × 10−8			[82]
H2L1 = 2, 2-dimethyl-N, N-bis(3-methoxysalicylal)-1, 3-propanediamine; o-vanilate = 2-hydroxy-3-(methyloxy)benzaldehyde; H2L2 = N, N’-bis(3-methoxysalicylidene)-1, 3-diamino-2, 2-dimethylpropane; H2valpn = 1, 3- propanediylbis(2-iminomethylene-6-methoxyphenol); H2L3 = N, N’-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3-diamine; H3L4 = 1-(2hydroxybenzamido)-2-(2-hydroxy-3-methoxy-benzylideneamino)ethane; Hhfac = hexafluoroacetylacetone; dpk- = di-2-pyridyl ketoximate; H6L5 = 2, 2’-(propane-1, 3-diyldiimino)bis[2-(hydroxylmethyl)propane-1; H3L6 = N, N’-bis(3-methoxysalicylidene)-1, 3-diamino-2-propanol; 2-ma = 2-methylalanine; (py)2CO = di-2-pyridyl ketone; H3L7 = 2-[2-(2-hydroxy-3-methoxybenzylidene)-hydrazineyl]-2-oxo-N-(pyridin-2-ylmethyl)acetamide; H2quinha = quinaldichydroxamic acid; Hsal = salicylaldehyde; py = pyridine; L8 = hydroxy(pyridin-2-yl)methanolate; L9 = (S)-((R)-hydroxy(pyridin-2-yl)methoxy)(pyridin-2-yl)methanolate; H2L10 = 1, 1, 1-trifluoro-7-hydroxy-4-methyl-5- azahept-3-en-2-one; (L11)2- = N, N’-2, 2-dimethylpropylenedi(3-methoxysalicylideneiminato); thd = tetramethylheptanedionato; H2L12 = 1, 3-bis((3-methoxysalicylidene)amino)propane; H2dae = 1, 2-bis(5-carboxyl-2-methyl-3-thienyl)perfluoropentene; teaH3 = triethanolamine; H6LBu = (2E, 8E, 11E, 17E, 20E, 26E)-3, 8, 12, 17, 21, 26-hexaaza-1, 10, 19(1, 4)-tribenzenacycloheptacosaphane-2, 8, 11, 17, 20, 26-hexaene-12, 13, 102, 103-tetraol; H2L13 = (Z)-1, 3-di(pyridin-2-yl)but-1-ene-1, 3-diol; N3tempo = 4-azido-2, 2, 6, 6- tetramethylpiperidine-1-oxyl radical; H2L14 = N, N’-bis(salicylidene)-1, 3-propanediamine; bpy = 4, 4’-bipyridine; H4L15 = N, N’-ethylenebis(3-hydroxysalicylidene); H4edte = 2, 2’, 2”, 2”’-(ethane-1, 2-diyldinitrilo)tetraethanol; (L16)3- = in situ prepared acylhydrazone ligand; pdmH2 = pyridine-2, 6-dimethanol; ButCH2CO2- = tert-butylacetate ion; NIT-3py = 2-(3-pyridyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide; H4L17 = tritopic hydrazone ligand; tpa = terephthalate; H6LEt = [3+3] imine macrocycle derived from 1, 4-diformyl-2, 3-dihydroxybenzene and 1, 2-diaminoethane; H2L18 = N, N’-bis (3-methoxysalicylidene)-1, 3-diamino-2, 2-dimethylpropane); dapdoH2 = 2, 6-diacetylpyridine dioxime; H4L19 = 2, 2’- {2-hydroxy-3-[(2-hydroxyphenylimino)methyl]-5-methylbenzylazanediyl}diethanol; H3L21 = (E)-2-((2-hydroxy-3-methoxybenzylidene)amino)propane-1, 3-diol; H3L22 = (E)-2-ethyl-2-((2-hydroxy-3-methoxybenzylidene)amino)propane-1,3-diol; NIT-Pyrim = 2-(5-pyrimidinyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide; H3Ldpen(1R2R) = N-((1R, 2R)-2-(((E)-3-Ethoxy-2-hydroxybenzylidene)amino)-1, 2-diphenylethyl)-2-hydroxybenzamide; NIT-Ph-p-OCH2trz = 2-[4-[(1H-1,2,4-triazol-1-yl)methoxy]phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate; H3L21 = OH-C10H7-CH=NC(C2H5)(CH2OH)2; H3L23 = N, N’-bis-(3-methoxysalicylidene)-1, 3-diamino-2-propanol; H4L24 = butanedihydrazide-bridged bis(3-ethoxysalicylaldehyde); H2L25 = 2-salicylideneaminophenol; NITPhOPybis = 5-(4-oxypyridinium-1-yl)-1, 3-bis (1’-oxyl-3’-oxido-4’, 4’, 5’, 5’-tetramethyl-4, 5-hydro-1H-imidazol-2-yl)benzene); phenoxH = hrenedione-9-oxime; H2L26 = N1, N3-bis(3-methoxysalicylidene)diethylenetriamine; H2L27 = OH-C10H6-CH=NC(CH3)(CH2OH)2; H2L28 = OH-C10H6-CH=NC(C2H5)(CH2OH)2; H2L29 = N-a-methylsalicylidene-N’-3-methoxysalicylidene-1, 3-propanediamine; H2L30 = N-3-ethoxysalicylidene-N’-3- methoxysalicylidene-1, 3-propanediamine; 4-NIT-MePyz = 2-{4-(1-methyl)-pyrazolyl]}-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide; bisNITPhPyrim = 5-(5-pyrimidyl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene; TfO = trifluomethanesulfonate; H2pyzha = pyrazinehydroxamic acid; H2butyrat = 3-aminobutyric hydroxamic acid; H2L31 = N-salicylidene-N’-3-ethoxysalicylidene-1, 3-propanediamine; H2L32 = N-salicylidene-N’-3-methoxysalicylidene-1, 3-propanediamine;; H2L34 = N-Salicylidene-N’-3-methoxysalicylidenepropane-1, 2-diamine; H2L35 = N-3-Methoxysalicylidene-N’-salicylidenepropane-1, 2-diamine; PPNIT = 2-(1-(pyrazin-2-yl)-1H-pyrazole)-4, 4, 5, 5-tetramethyl-imidazoline-1-oxyl-3-oxide; H2valen = 1, 2-ethanediylbis(2-iminomethylene-6-methoxy-phenol); dca = dicyanamide; H2L35 = diformylnaphthalene-2, 3-diol; R-H2L36 = 1-((E)-(((1R, 2R)-2-hydroxycyclohexyl)imino)methyl)naphthalen-2-ol; S-H2L36 = 1-((E)-(((1S, 2S)-2-hydroxycyclohexyl)imino)methyl)naphthalen-2-ol

2009年，Takashi Kajiwara及其同事报道了两种配合物，[TbCu(L¹)(NO₃)₃(H₂O)] (1, H₂L¹ = 2, 2-dimethyl-N,N-bis (3-methoxysalicylal)-1,3-propanediamine)和[TbCu (L¹) (o-vanilate) (NO₃) (MeOH)] NO₃ (2)。在这两种配合物中，席夫碱配体(L¹)²⁻为Cu^II和Tb^III提供近乎共面的配位原子N₂O₂和O₄，分别与两个苯氧氧原子桥接了Cu^II和Tb^III。因此，1和2中的[TbCu (L¹)]³⁺部分表现出显著的结构相似性(图1)。直流磁化率测量表明，两种配合物的铁磁相互作用较弱，同时观察到Tb^III具有显著的磁各向异性。交流磁化率测试分别在低于5 K和6 K的温度下，观察到了1和2的SMM行为。将数据拟合到阿伦尼乌斯方程中，1和2的有效能垒∆/k_B分别为29(2) K和32.2(6) K (图2)。此外，DFT计算表明，由于在与Tb (III)桥接的苯氧原子相反的位置引入了苯氧配体，导致负电荷的单轴排列，从而增强了Tb^III的轴向磁各向异性，配合物2具有更大的有效能垒[20]。

Figure 1. The molecular structure of 1 (a) and 2 (b). Color code: Cu^Ⅱ, green; Tb^Ⅲ, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity. Reproduced from [20]

图1. 1 (a)和2 (b)的分子结构图。颜色：Cu^Ⅱ，绿色；Tb^Ⅲ，紫色；O，粉红色；N，蓝色；C，灰色。为清楚起见，省略了H原子。转载自[20]

Figure 2. Arrhenius plots of 1 (a) and 2 (b). The solid line represents the fitting curves with the Arrhenius law. Reproduced from [20]

图2. 1(a)和2(b)的阿伦尼乌斯图。实线代表了阿伦尼乌斯定律的拟合曲线。转载自[20]

2012年，Takayuki Ishida及其同事合成了一类配合物[Cu^Ⅱ(L²)(C₃H₆O)Ln^Ⅲ(NO₃)₃] (Ln = Tb (3), Dy (4), H₂L² = N, N’-bis(3-methoxysalicylidene)-1, 3-diamino-2, 2-dimethylpropane)。在这些配合物中，Cu^Ⅱ在赤道方向上与来自席夫碱配体(L²)²⁻的两个亚胺氮原子和两个苯氧化氧原子配位，并在轴向上与一个丙酮分子配位，从而形成四方金字塔构型(图3)。Ln^Ⅲ与6个硝酸盐氧原子、2个甲醇氧原子和2个酚酸盐氧原子配位，形成具有10个配位点的配位环境。配合物3在2 K以上表现出明显的频率依赖性，当施加1 kOe的外部磁场时，QTM被有效抑制，使频率依赖性更加明显。磁化反转的能垒确定为E_a/k_B = 42.3(4) K，指前因子τ₀ = 7.1(9) × 10⁻¹⁰ s。另一方面，配合物4在1 kOe的外部磁场下也表现出频率依赖性，通过拟合阿伦尼乌斯定律，确定其磁各向异性势垒为11.5 (10) K [21]。

Figure 3. The molecular structure of 3. Color code: Cu^Ⅱ, green; Tb^Ⅲ, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity. Reproduced from [21]

图3. 配合物3的分子结构图。颜色：Cu^Ⅱ，绿色；Tb^Ⅲ，紫色；O，粉红色；N，蓝色；C，灰色。为清楚起见，省略了H原子。转载自[21]

2006年，Takayuki Ishida及其同事报道了氧化物桥接三核配合物[(Dy(hfac)₃)₂Cu(dpk)₂] (5, Hdpk = di-2-pyridyl ketoxinate)的例子。在这个配合物中，两个dpk⁻配体桥接两个Dy^Ⅲ离子和一个Cu^Ⅱ离子，导致三个金属离子的线性排列。Cu^Ⅱ采用方形平面构型，由来自两个dpk⁻基团的4个N原子进行配位。除了来自三个hfac⁻的六个氧原子外，Dy^Ⅲ还与来自dpk⁻的一个N原子和一个O原子配位，从而产生了八配位构型(图4)。在交流磁化率测量中，5的实部和虚部信号都表现出明显的频率依赖性，有效能量势垒∆/k_B = 47(4) K，指前因子τ₀ = 1.1(5) × 10⁻⁷ s。推测5的SMM行为源于Dy^Ⅲ的单离子各向异性，以及Dy^Ⅲ和Cu^Ⅱ之间的强耦合[22]。

Figure 4. The molecular structure of 5. Color code: Cu^Ⅱ, green; Tb^Ⅲ, purple; O, pink; N, blue; C, gray; F, bright green. H atoms are omitted for clarity. Reprinted with permission from Ref. [22]. Copyright 2006 American Chemical Society

图4. 配合物5的分子结构图。颜色：Cu^Ⅱ，绿色；Tb^Ⅲ，紫色；O，粉红色；N，蓝色；C，灰色；F，亮绿色。为清楚起见，省略了H原子。经参考文献[22]许可转载。版权所有2006美国化学学会

2024年，Wen-Bin Sun及其同事报道了一种配合物，[Cu₂(L³)₂DyCl₂(H₂O)]⋅Cl⋅MeCN (6), (L³ = N, N’-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3-diamine)。这种配合物具有线性Cu-Dy-Cu型配位结构，对配合物中异常离子周围局部配位环境的分析表明，它采用九配位构型(图5)。Cu (II)离子形成键的苯氧基氧原子沿着Cu-Dy-Cu轴呈现一个方向，而外部的甲氧基氧原子通常采用一个垂直于Cu-Dy-Cu的方向。每个席夫碱前驱体贡献了四个配位氧原子。直流磁化率测试表明，在300 K~50 K的温度范围内，配合物的磁化率保持相对稳定。在50 K以下，配合物快速增加趋势，在4 K时达到最大值，然后逐渐下降到2 K。交流磁化率中，配合物在零场下表现出明显的温度依赖行为，最高峰值温度为10.5 K，频率为999 Hz，表现出典型的单分子磁体行为。此外通过磁滞回线的测量，发现最大磁滞开口温度为3.5 K，这与在零直流场下交流磁化率中观察到的显著磁弛豫行为一致。通过拟合阿伦尼乌斯方程得到，配合物的有效能垒是39.06 K，τ₀ = 1.05 × 10⁻⁵ s。

Figure 5. The molecular structure of 6 Color code: Cu^Ⅱ, green; Tb^Ⅲ, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity

图5. 配合物6分子结构图。颜色：Cu^Ⅱ，绿色；Tb^Ⅲ，紫色；O，粉红色；N，蓝色；C，灰色。为清楚起见，省略了H原子

2003年，Shutaro Osa等人报道了有关3d-4f SMM的第一个实例，[Cu^Ⅱ(L⁴Tb^Ⅲ(hfac)₂]₂(7,L⁴ = 1-(2hy- droxybenzamido)-2-(2-hydroxy-3-methoxy-benzylideneamino) ethane, Hhfac = hexafluoroacetylacetone)。该配合物采用四核环状结构，Cu^Ⅱ和Tb^Ⅲ离子交替排列。Cu^Ⅱ离子表现出由H₃L⁴体提供的N₂O₂供体原子形成的方形平面配位几何形状，而Tb^Ⅲ离子实现了八面体配位，是由两个hfac⁻的四个氧原子和来自两个(L⁴⁻的四个氧原子形成的(图6)流磁化率表明Cu^Ⅱ和Tb^Ⅲ离子之间存在铁磁相互作用。交流磁化率中7的虚部信号显示出了明显的频率依赖性，证实了该配合物存在单分子磁体行为。该配合物的有效能垒∆/k_B是21 K，指前因子τ₀为2.7 × 10⁻⁸ s [24]。

Figure 6. The molecular structure of 6. Color code: Cu^Ⅱ, green; Tb^Ⅲ, purple; O, pink; N, blue; C, gray; F, bright green. H atoms are omitted for clarity. Reprinted with permission from Ref. [24]. Copyright 2003 American Chemical Society.

图6. 配合物6的分子结构图。颜色：Cu^Ⅱ，绿色； Tb^Ⅲ，紫色；O，粉红色；N，蓝色；C，灰色；F，亮绿色。为清楚起见，省略了H原子。经参考文献[24]许可转载。版权所有2003美国化学学会

2013年，由Xin-Yi Wang领导的研究小组报道了两个末端叠氮基桥接四核配合物的例子，[Cu₂(valpn)₂Tb₂(N₃)₆]·2CH₃OH(8, H₂valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxyphenol))。两个[CuTb]单元由两个末端的 ${\text{N}}_3^{-}$ 配体桥接，形成[Cu₂Tb₂]簇(图7(a))。在每个[CuTb]单元内，valpn²⁻配体给Cu^II和Tb^III离子分别提供了具有N₂O₂和O₄的配位环境。同时，其余4个 ${\text{N}}_3^{-}$ 配体也参与Tb^III和Cu^II的配位环境，导致Cu^II形成细长八面体构型，Ln^III形成八配位三角棱柱几何构型。在零外加直流场下对配合物进行交流磁化率的测量，结果表明，7表现出SMM行为，有效能量势垒为U_eff = 30.1 ± 0.7 K。此外，在扫描速率为0.05 Ts⁻¹时，8的磁滞回路的开启温度为2.4 K (图7(b)) [25]。

Figure 7. The molecular structure (a) and magnetic hysteresis (b) of 8. Color code: Cu^II, green; Dy^Ⅲ, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity. Reproduced from [25]

图7. 配合物8的分子结构图(a)和磁滞回线图(b)。颜色：Cu^II，绿色；Dy^III，紫色；O，粉红色；N，蓝色；C，灰色。为清楚起见，省略了H原子。转载自[25]

2016年，Mark Murrie等人报道了一系列的3d-4f配合物，即[Ln₂Cu₃(H₃L⁵)₂(CH₃COO)₆] (Ln = Gd (9), Tb (10) H₆L⁵ = 2, 2’-(propane-1, 3-diyldiimino) bis [2-(hydroxylmethyl) propane-1, 3-diol])和[Ln₂Cu₃(H₃L⁵)₂ (NO₃)₇(CH₃OH)₂] (Ln = Tb (11), Dy (12), Ho (13), Er (14))。化合物9-10是同构而11-14也表现出同构特征。在9-10中，两个去质子化配体(H₃L⁵)³⁻提供四个μ-O桥和两个μ₃-O桥，将两个Ln^III离子连接到线性单元[Cu₃(H₃L⁵)₂] (图8(a))。此外，这两个(H₃L⁵)³⁻配体将两个外Cu^Ⅱ离子包封在线性单元中，这就导致了外部的Cu^Ⅱ离子是扭曲方棱锥几何结构，而中心Cu^Ⅱ离子是扭曲八面体构型。Ln^Ⅲ离子的配位环境与球形帽盖正方形反棱镜非常相似(图9(a)，插图)。11-14的核心结构与9-10有相似之处，由两个Ln^Ⅲ离子和一个线性单元组成(图8(b))。区别在于存在与外部Cu^Ⅱ离子配位的单齿 ${\text{NO}}_3^{-}$ ，形成扭曲的八面体构型。此外，两个双齿和一个单齿 ${\text{NO}}_3^{-}$ 配体与MeOH一起参与了两个Ln^Ⅲ离子的配位环境。因此，两个Ln^III离子分别表现出球形带端正方形反棱镜和松饼状配位几何形状(图9(b)，插图)。通过与阿伦尼乌斯定律的拟合，确定10和11的有效能垒分别为21.4 K和36.0 K (图9)。由于配合物12-14的交流磁化率信号中没有峰值，因此使用ln(χ”/χ’) = ln(2πντ₀) + U_eff/k_BT模型，粗略估计它们的能垒分别为23.9 K、17.2 K和14.8 K。对10和11的理论计算表明，它们势垒的差异可能源于不同的Ln^III协调环境。此外，Cu^II和Tb^III之间的磁交换相互作用可以有效地抑制QTM，从而可以观察SMM在零场条件下的行为[26]。

Figure 8. The molecular structure of 10 (a) and 11 (b). Color code: Cu^Ⅱ, green; Tb^Ⅲ, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity. Reproduced from [26]

图8. 10 (a)和11 (b)的分子结构。颜色：Cu^Ⅱ，绿色；Tb^Ⅲ，紫色；O、粉红色；N、蓝色；C、灰色。为了清楚起见省略了H原子。转载自[26]

Figure 9. Magnetization relaxation time ln(τ) vs T⁻¹ plot for 10 (a) and 11 (b). The solid line is fitting curve with the Arrhenius law. Inset: The coordination environment of Ln^Ⅲ in 10 (a) and 11 (b). Reproduced from [26]

图9. 10 (a)和11 (b)的磁化弛豫时间ln(τ)与T⁻¹的关系图。实线是阿伦尼斯定律的拟合曲线。插图：Ln^Ⅲ在10 (a)和11 (b)中的配位环境。转载自[26]

2018年，Theocharis C. S.及其同事报道了一系列Cu-Ln簇，即[Cu₄Ln₂(OH)₂(NO₃)₈{(py)₂CO₂}₂(MeCN)₄] (Ln = Gd (15), Tb (16),和Dy (17))。这三种配合物表现出结构相似性，因为它们都由两个三角形[Cu₂Ln(µ₃-OH)]⁶⁺单元组成，这两个单元由两个(py)₂ ${\text{CO}}_2^{2-}$ 配体的醇盐臂桥接。在对称相关的[Cu₂Ln(µ₃-OH)]⁶⁺单元中，µ₃-OH⁻位于[Cu₂Ln]平面上方，导致四面体几何形状扭曲(图10(a)，插图)。配合物15在交流磁化率测量中仅显示出与频率相关的虚部信号的尾部，使得难以获得其各向异性值。相反，化合物16在4 K以下表现出明显的频率依赖性信号，拟合这些数据得到20.1(2) K的有效能垒(图10(a))。值得注意的是，配合物16在Cole-Cole图中显示出宽的弛豫时间分布，这可归因于QTM和热激活弛豫过程的综合效应(图10(b)) [27]。

Figure 10. The Arrhenius plot for complex 17 under zero dc field (a) and Cole-Cole plots for complex 17 (b). Inset: The molecular structure of 17. Color code: Cu^Ⅱ, green; Dy, purple; O, pink; N, blue; C, gray. The solid line corresponds to the fit of the data. H atoms are omitted for clarity. Reproduced from [27]

图10. 配合物17在零直流场下的Arrhenius图(a)，插图：17的分子结构，和配合物17的Cole-Cole图(b)。颜色：Cu^Ⅱ，绿色；Dy，紫色；O、粉红色；N、蓝色；C、灰色。实线对应于数据的拟合。为了清楚起见省略了H原子。转载自[27]

2019年，报道了一种杂金属冠醚化合物，表示为[EuCu₅(quinha)₅(sal)₂(py)₅]·CF₃SO₃·py·3H₂O (18, H₂quinha = quinaldichydroxamic acid, Hsal = salicylaldehyde, py = pyridine)。在该配合物中，Eu^Ⅲ离子被包裹在[15−MC_Cu(Ⅱ)−5]内，与Hsal配体衍生的两个苯氧基氧原子形成轴向配位。这种排列导致Eu^Ⅲ周围的配位几何结构非常类似于扭曲的五角双锥。[15−MC_{quinha,Cu(II)}−5]单元由五个完全去质子化的quinha²⁻配体组成，与五个Cu^Ⅱ离子配位，采用μ₃: η²: η²: η¹配位模式(图11(a))。磁化率测量显示18在零磁场条件下没有任何显示与频率相关的虚部信号。然而，在施加2 kOe的外部磁场时，它表现出缓慢的磁弛豫行为。使用τ⁻¹ = CTⁿ拟合18的弛豫时间，并确定18中的主要弛豫过程是拉曼过程，源于{Cu₅}团簇的S = 1/2基态。当用抗磁性离子Lu^Ⅲ(19)和Y^Ⅲ(20)取代Eu^Ⅲ时，两种配合物在2 kOe的外磁场下表现出相似的磁性行为(图11(b))。然而，观察到18的弛豫时间比Lu^Ⅲ和Y^Ⅲ类似物的弛豫短。这种现象可归因于Eu^Ⅲ离子基态产生的二阶效应或声子瓶颈效应的存在[28]。

Figure 11. The molecular structure for 18 (a) and the temperature-dependence of relaxation times for 18-20 under a 2 kOe DC field (b). Color code: Cu^Ⅱ, green; Eu, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity. The solid line corresponds to the fit of the data. Reproduced from [28]

图11. 18的分子结构图(a)和18-20在2 kOe 直流场下的温度依赖的弛豫时间(b)。颜色：Cu^Ⅱ，绿色；Eu，紫色；O、粉红色；N、蓝色；C、灰色。为了清楚起见省略了H原子。实线对应于数据的拟合。转载自[28]

2017年，Vadapalli-Chandrasekhar及其同事合成了一系列一维单分子磁体，表示为[{Cu₅Ln₂(L⁶)₂(μ₃-OH)₄(ClO₄)(NO₃)₃(OH₂)(ClO₄)₂(H₂O)_x]_∞(Ln = Tb (21)、Dy (22)和Ho (23)，分别为21-23的x =4.25、5.5和5，H₃L⁶= N, N’-bis(3-methoxysalicylidene)-1, 3-diamino-2-propanol)。配合物21-23表现出同构性，但具有不同数量的间隙水分子。在单元A中，外部的四个Cu^Ⅱ离子和两个Ln^Ⅲ离子通过两个(L⁶)^3-配体和两个μ: η¹: η¹- ${\text{NO}}_3^{-}$ 配体相互连接，而中心的Cu^Ⅱ离子通过四个μ₃-OH⁻和两个μ: η²- ${\text{NO}}_3^{-}$ 配体与周围的六个金属离子连接。除了上述配位基团外，水分子还参与了Ln^Ⅲ离子的配位环境。此外，μ₃: η²: η¹- ${\text{NO}}_3^{-}$ 配体桥接类似的七核单元(单元B)，从而形成整体的一维结构(图12(a))。磁化率测量证实了化合物21-23的SMM行为。化合物21表现出两种弛豫模式，这可能归因于一维结构中存在两个不同的单元。通过阿伦尼斯定律拟合，确定了3 K以上热激活弛豫过程的能垒为23.4 K。在较低的温度下，QTM主导弛豫机制，但在施加1.2 kOe的外部磁场时，有效能垒增加到27.9 K (图12(b))。对于高于3 K的热激活弛豫过程，化合物22表现出8.3 K的有效能垒，而化合物23表现出低于4 K的快速QTM，阻碍了预估的SMM能垒[29]。

Figure 12. The structure of two [Cu₅Tb₂] repeating units in the 1D coordination assembly 21 (a) and temperature dependence of the magnetization relaxation time as τ versus T⁻¹ plot for 21 in zero (red) and 1200 Oe (blue) dc field. Color code: Cu^Ⅱ, green; Tb^Ⅲ, purple; O, pink; N, blue; C, gray; Cl, bright green. H atoms are omitted for clarity. Reprinted with permission from Ref. [29]. Copyright 2013 American Chemical Society

图12. 一维的配位组件21(a)中两个[Cu₅Tb₂]重复单元的结构以及21在零(红色)和1200 Oe (蓝色)直流场中磁化弛豫时间的温度依赖性τ与T⁻¹的关系图。颜色：Cu^Ⅱ，绿色；Tb^Ⅲ，紫色；O、粉红色；N、蓝色；C、灰色；Cl，亮绿色。为了清楚起见省略了H原子。经参考文献[29]转载。版权所有2013美国化学学会

2019年，刘伟胜领导的课题组合成了两种八核配合物，[Cu₄Dy₄(L⁷)₄Cl₆(CH₃OH)₈(H₂O)₄] ∙Cl₂∙(CH₃OH)₉∙(H₂O)₃ (24, H₃L⁷ = 2-[2-(2-hydroxy-3-methoxybenzylidene)-hydrazineyl]-2-oxo-N- (pyridin-2-ylmethyl) acetamide)和[Cu₄Tb₄(L⁷)₄Cl₆(CH₃OH)₂(H₂O)₁₀]∙Cl₂∙(H₂O)_x (25)。这两个配合体表现出同构性。在化合物24中，四个Dy^Ⅲ离子几乎线性排列，四个Cu^Ⅱ离子分散在线性[Dy₄]单元的两侧。最小不对称单元可被视为由蝶形[Cu₂Dy₂]]单元组成，其中两个Cu^Ⅱ离子形成“蝴蝶”的翅膀，两个Dy^Ⅲ离子构成“蝴蝶”体，这两个Dy^Ⅲ离子由两个(L⁷)³⁻配体提供的两个μ₂-O原子桥接(图13)。24和25的直流磁化率测量表明，Cu^Ⅱ和Ln^Ⅲ离子之间存在铁磁相互作用，Ln^Ⅲ具有强磁各向异性。此外，由于Ln-Ln距离相对较短，Ln^Ⅲ离子之间的磁交换相互作用不容忽视。同时，交流磁化率测量揭示了两种配合物在零场条件下的缓慢磁弛豫行为。具体而言，24表现出54 K的有效能垒，指前因子τ₀为2.18 × 10⁻⁹ s。在配合物24中，Dy^Ⅲ离子表现为Kramers离子，3d金属与Dy^Ⅲ之间的磁耦合有效抑制了QTM。此外，Dy^Ⅲ基配合物在低对称配位环境中也表现出SMM行为。相反，在化合物25中，Tb^Ⅲ是非Kramers离子，存在于低对称配位环境中，从而阻碍了慢磁弛豫行为的观察[30]。

Figure 13. The molecular structure of 23. Color code: Cu^Ⅱ, green; Dy, purple; O, pink; N, blue; C, gray; Cl, bright green. H atoms are omitted for clarity. Reproduced from [30]

图13. 配合物23的分子结构图。颜色：Cu^Ⅱ，绿色；Dy，紫色；O、粉红色；N、蓝色；C、灰色；Cl，亮绿色。为了清楚起见省略了H原子。经参考文献[30]转载

2013年，童明良研究组利用两步原位反应合成了一个单分子磁体Dy^Ⅲ₂Cu^Ⅱ₇(OH)₂(L⁸)₂(L⁹)₂ (OAc)₈(NO₃)₂(H₂O)₄](NO₃)₂∙8.5H₂O (26) (图14(a))。在该配合物中，两个三角形[DyCu₂]单元共享一个Dy^III离子，并由配体L⁸和L⁹桥接，形成蝴蝶形[DyCu₄]单元。随后，八个OAc⁻基团采用两种不同的配位模式，将两个[DyCu₄]单元连接起来，形成配合物26 (图14(b))。直流磁化率测量表明，在低温下，配合物26表现出主要的铁磁相互作用和显著的磁各向异性。在零外部磁场中，在26的虚部交流磁化率中观察到明显的频率依赖性行为，表明存在具有有效能量势垒U_eff = 18.0 (3) K的SMM行为[31]。

Figure 14. A two-step in situ reaction (a) and the molecular structure of 26 (b)

图14. 两步原位反应(a)和26的分子结构(b)

2017年，严振政领导的课题组合成了一系列空竹类非核团簇，表示为[LnCu₈(OH)₈(2-ma)₈(Cl)₂] [ClO₄]·xH₂O (Ln = Tb (27), Ho (28), Dy (29), Er (30), Tm (31), Yb (32), 2-ma = 2-methylalanine)。所有七个化合物都表现出同构性。在它们的金属核内，Ln^Ⅲ离子被夹在两个Cu₄(OH)₄ (8-MC-4)单元之间。每个8-MC-4单元由一个八元交替的Cu-O环组成。此外，Cu^Ⅱ离子与2-ma配体的羧酸盐氧和氨基氮配位，而氯离子位于由四个2-ma配体和Cu^Ⅱ离子形成的“碗”中(图15(a))。在零外加直流场下的交流磁化率测试中，只有配合物30表现出缓慢的磁弛豫行为。随后，在施加小的直流场时，观察到29、31和32也显示出与频率相关的行为。值得注意的是，30中虚部信号的频率依赖性更加明显。零直流场下的配合物30和直流场下配合物31在较低温度下都表现出量子磁化隧穿(QTM)。因此，通过与各种弛豫过程拟合，确定配合物29-32的能垒位于23 K至33 K的范围内(图15(b))。理论计算表明，配合物29-32的能垒差异可以忽略不计，基本上与参数|J_Cu-Cu| = 20 K一致。尽管两个{Cu₄}单元都是单线态基态，但可以推断这些化合物的慢磁弛豫行为受到Cu₄-Ln^Ⅲ-Cu₄相互作用的影响[32]。

Figure 15. The molecular structure of 30 (a) and Arrhenius plot for complex 29-32 under corresponding dc field (b). Color code: Cu^Ⅱ, green; Er, purple; O, pink; N, blue; C, gray; Cl, bright green. H atoms are omitted for clarity. The solid line corresponds to the fit of the data. Reproduced from [32]

图15. 30的分子结构图(a)和配合物29-32在相应直流场下的Arrhenius图(b)。颜色：Cu^Ⅱ，绿色；Er，紫色；O、粉红色；N、蓝色；C、灰色；Cl，亮绿色。为了清楚起见省略了H原子。实线对应于数据的拟合。转载自[32]

2021年，童明良研究团队在单层金属宏晶Dy[15−MC_Cu(Ⅱ)−5] (33)的基础上，合成了一种具有独特双层三明治结构的配合物，记为{Dy [15-MC_Cu-5]}₂(34)。值得注意的是，化合物33与化合物18具有同构性，而化合物34包含两个由OH⁻桥接的Dy [15-MC_Cu(Ⅱ)-5]单元，其中两个去质子化的水杨醛配体占据Dy [15-MC_Cu(Ⅱ)-5]单元内的轴向位置。化合物34代表了仅由OH⁻桥接的双层金属丙烯的第一个例子(图16)。磁性分析表明，33和34在Cu^Ⅱ-Cu^Ⅱ之间都表现出反铁磁相互作用，而Dy^Ⅲ-Cu^Ⅱ和/或Dy^Ⅲ-Dy^Ⅲ之间可能存在铁磁交换相互作用。33和34都表现出缓慢的磁弛豫行为，最高有效能垒分别达到900(31) K和838(53) K，显示出优异的SMM特性。此外，33呈现蝶形磁滞回线。在沿轴向引入铁磁耦合后，在较低温度下，34的磁弛豫时间明显慢于33，磁滞回线的开启温度提高到6 K。理论计算证实，当Dy^Ⅲ离子的局部磁各向异性轴几乎共线时，Dy^Ⅲ-Dy^Ⅲ的轴向铁磁耦合抑制了QTM [33]。

Figure 16. The molecular structure for 34. Color code: Cu^Ⅱ, green; Dy, purple; O, pink; N, blue; C, gray. H atoms are omitted for clarity. Reproduced from [33]

图16. 34的分子结构图。颜色：Cu^Ⅱ，绿色；Dy，紫色；O、粉红色；N、蓝色；C、灰色。为了清楚起见省略了H原子。转载自[33]

3. 结论

综合以上研究进展，本文综述了不同结构类型，包括从二核到多核的且磁学性能优异的Cu-Ln单分子磁体。二核结构表现出显著的磁性各向异性，其结构简单易于合成，是一个铜离子与一个稀土离子通过桥联配体连接而成的；多核更为复杂，选择不同配体和不同数量金属离子会形成不同的几何形态，如线性，环状，四边形等等。稀土离子的选择也是极为重要的，Dy和Tb离子具有强烈的自旋–轨道耦合和高的磁各向异性，是制备高性能SMM的理想候选，相比较而言Gd离子缺乏耦合，其磁各向异性较弱，因此磁学性能也较差，因此本综述都是铜离子与镝或铽跟不同多齿配体的结合。

尽管在过去的几年里取得了显著的进展，但仍有许多挑战需要克服，例如致力于如何提高工作温度，使其能在更宽的温度范围内表现出优异的磁性；进一步设计合成新型配体，来优化Cu-Ln单分子磁体的结构，增强其稳定性和磁学性能；同时开发多功能材料，同时具备光电磁多重响应特性的复合材料也是在传感器和信息处理领域的新方向。

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)，南通大学大型仪器开放基金资助(KFJN2471、KFJN2437)。

NOTES

^*通讯作者Email: wangjin110@ntu.edu.cn

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