[Fe(bpp)₂][ClO₄]₂ (bpp = 2,6-bis{pyrazol-1-yl}pyridine; monoclinic, C2/c) is high-spin between 5–300 K, and crystallises with a highly distorted molecular geometry that lies along the octahedral–trigonal prismatic distortion pathway. In contrast, [Ni(bpp)₂][ClO₄]₂ (monoclinic, P2₁) adopts a more regular, near-octahedral coordination geometry. Gas phase DFT minimisations (ω-B97X-D/6-311G**) of [M(bpp)₂]²⁺ complexes show the energy penalty associated with that coordination geometry distortion runs as M²⁺ = Fe²⁺ (HS) ≈ Mn²⁺ (HS) < Zn²⁺ ≈ Co²⁺ (HS) ≲ Cu²⁺ ≪ Ni²⁺ ≪ Ru²⁺ (LS; HS = high-spin, LS = low-spin). Slowly crystallised solid solutions [Fe_xNi_1−x(bpp)₂][ClO₄]₂ with x = 0.53 (1a) and 0.74 (2a) adopt the P2₁ lattice, while x = 0.87 (3a) and 0.94 (4a) are mixed-phase materials with the high-spin C2/c phase as the major component. These materials exhibit thermal spin-transitions at T_½ = 250 ± 1 K which occurs gradually in 1a, and abruptly and with narrow thermal hysteresis in 2a–4a. The transition proceeds to 100% completeness in 1a and 2a; that is, the 26% Ni doping in 2a is enough to convert high-spin [Fe(bpp)₂][ClO₄]₂ into a cooperative, fully SCO-active material. These results were confirmed crystallographically for 1a and 2a, which revealed similarities and differences between these materials and the previously published [Fe_xNi_1−x(bpp)₂][BF₄]₂ series. Rapidly precipitated powders with the same compositions (1b–4b) mostly resemble 1a–4a, except that 2b is a mixed-phase material; 2b–4b also contain a fraction of amorphous solid in addition to the two crystal phases. The largest iron fraction that can be accommodated by the P2₁ phase in this system is 0.7 ± 0.1.

中文翻译：

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用惰性非同晶分子掺杂剂激活高自旋铁 (II) 配合物以实现热自旋交叉

[Fe(bpp) ₂ ][ClO ₄ ] ₂（bpp = 2,6-双{吡唑-1-基}吡啶；单斜晶系，C 2/ c）在 5–300 K 之间具有高自旋，并以沿着八面体-三棱柱扭曲路径的高度扭曲的分子几何形状。相比之下，[Ni(bpp) ₂ ][ClO ₄ ] ₂（单斜晶系，P 2 ₁）采用更规则的、接近八面体的配位几何形状。 [M(bpp) ₂ ] ²⁺配合物的气相 DFT 最小化 (ω-B97X-D/6-311G**)显示与配位几何畸变相关的能量损失，即 M ²⁺ = Fe ²⁺ (HS) ≈ Mn ²⁺ (HS) < Zn ²⁺ ≈ Co ²⁺ (HS) ≲ Cu ²⁺ ≪ Ni ²⁺ ≪ Ru ²⁺ (LS；HS = 高自旋，LS = 低自旋)。缓慢结晶的固溶体[Fe _x Ni _{1− x} (bpp) ₂ ][ClO ₄ ] ₂，其中x = 0.53 ( 1a ) 和0.74 ( 2a ) 采用P 2 ₁晶格，而x = 0.87 ( 3a ) 和0.94 (图4a )是以高自旋C 2/ c相为主要成分的混合相材料。这些材料在T _½ = 250 ± 1 K处表现出热自旋跃迁，这在1a中逐渐发生，并在2a–4a中突然发生且具有窄热滞后。1a和2a中的过渡已达到 100% 完成度；也就是说，2a中26%的Ni掺杂足以将高自旋[Fe(bpp) ₂ ][ClO ₄ ] ₂转化为协同的、完全SCO活性的材料。这些结果在1a和2a中得到了晶体学证实，揭示了这些材料与之前发表的 [Fe _x Ni _{1− x} (bpp) ₂ ][BF ₄ ] ₂系列之间的相似性和差异。具有相同成分的快速沉淀粉末（1b-4b）大多类似于1a-4a，只是2b是混合相材料；2b–4b除了两个晶相之外，还含有一小部分无定形固体。该系统中P 2 ₁相所能容纳的最大铁分数为0.7±0.1。