We have designed and synthesised a series of organic ligands as well as used commercially available ligands (Figure 2) to make a series of polymetallic clusters/cages.
1. We for the first time have reported Mn18 wheel, complex 1, which consists of two square [MnIII6MnII2] wheels linked via two MnII ions. An interesting magnetic feature along with available empty spaces in the centre makes complex 1 a suitable guest for large host cages and a suitable host for small organic molecules (Figure 3).
2. We have reported the first example of a heterometallic [Mn2Gd] triangle, Complex 2, containing Mn in the III+ and II+ oxidation states. Susceptibility, magnetisation and detail DFT and ab initio studies highlighting the importance of MnIII/MnII-O-GdIII angle and the rigidity of the 2,2’-bis-p-tBu-calix[4]arene (L2H8) ligand in governing the sign and magnitude of the exchange interactions (Figure 4).
3. It is somewhat unusual for synthetic chemists to employ two different metal salts for the formation of homometallic cluster compounds and we were able to do so by making (complex 3 [Fe15]) cage where the high symmetry of the metallic skeleton leads to the presence of competing for antiferromagnetic exchange interactions and spin frustration. Combined experimental and computational studies reflect the presence of a large density of low-lying spin states (Figure 5).
4. We for the first time have reported complex 4, where the bpptz•- radical ligand enwraps two CoII centres within quasi-TPR geometries, which are further bridged by the tetrazine radical in trans mode. The magnetic and theoretical studies revealed that the interaction between the Co centres and the tetrazine radical is strongly antiferromagnetic with typical SMM behaviour with an attractive effective energy barrier for spin reversal, among the largest for polynuclear transition metal SMMs. Apparently, the presence of strong exchange effectively suppresses the QTM effect (Figure 6).
5. We have reported a series of novel lantern-like guest⸦[M2L44]4+ coordination cages (here, M = CuII and PdII) through simple self-assembly of four molar equivalents of the ligand molecule (L4 = 1,3-bis(3-ethynylpyridyl)benzene) with two molar equivalents of the corresponding metal salt, followed by one molar equivalent of guest, forming [CuII2L44(H2O)(OTf)3](OTf)·MeCN (complex 5), ReBr6⸦ [PdII2L44](BF4)2 (complex 6) and ReBr6⸦[CuII2L44(OTf)2] (complex 7), respectively. Complex formation was confirmed by ESI–MS and 1H NMR, both revealing solution stability. Magnetic measurements combined with theoretical calculations show that: (a) there is no magnetic interaction between the CuII ions in the “empty” [Cu2L44]4+ cage, complex 5. (b) The geometry of the encapsulated [ReBr6]2- ion remains essentially unchanged with respect to its metal salt and thus the axial zero-field splitting parameter, DRe, also remains the same. (c) The ingress of the ReBr62- ion induces a magnetic exchange interaction between the ReIV guest and the CuII host (Figure 7).
6. We have synthesised a smaller member of this molecular iron oxide family, an [Fe8] cage (complex 8· 3H2O·2MeO-Py). For complex 8, the metallic skeleton conforms to a hexagonal bipyramid with metal-oxygen core related to the mineral magnetite. Magnetic and theoretical studies reveal an S = 10 ground state (Figure 8).
7. We have synthesised a series of molecular cages, Co2L44X4 Cages (X = NCS (complex 9), F(complex 10), Cl(complex 11), Br(complex 12)). The atomic-level fine-tuning results in fascinating anisotropy parameters with the D values ranging between -80 ≤ D ≥ +100 cm-1. To the best of our knowledge, this is the first-ever report where atomic-scale fine-tuning on cages has been performed to get such a huge change in the D parameter, which is essential for many magnetic applications (Figure 9).
