Three heterometallic oxo-bridged compounds, [Cr₂(phen)₄(μ-O)₄Nb₂(C₂O₄)₄]·2H₂O (1; phen = 1,10-phenanthroline), [Cr₂(terpy)₂(H₂O)₂(μ-O)₄Nb₂(C₂O₄)₄]·4H₂O (2; terpy = 2,2′;6′,2′′-terpyridine) and [Cr(terpy)(C₂O₄)(H₂O)][Cr₂(terpy)₂(C₂O₄)₂(μ-O)₂Nb(C₂O₄)₂]·3H₂O (3), have been synthesized using a building block approach and characterized by IR spectroscopy, single-crystal and powder X-ray diffraction, magnetization measurements, and DFT calculations. The molecular structures of 1 and 2, crystallizing in P4₂2₁2 and P2₁/n space groups, respectively, contain a square-shaped {Cr^III₂(μ-O)₄Nb^V₂} unit, while that of complex salt 3 (P space group) consists of a mononuclear cation containing Cr^III and trinuclear anions in which two Cr^III ions are bridged by a –O–Nb^V–O– fragment. Besides hydrogen-bonding patterns resulting in a 1D- or 3D-supramolecular arrangement in 1–3, an unusual intermolecular contact has been noticed between parallel oxalate moieties occurring due to the electrostatic attraction of electron-rich carbonyl oxygen and severely electron-depleted carbon atoms in the crystal packing of 2. The antiferromagnetic coupling observed in all three compounds, determined from magnetization measurements (J = −13.51(2), −8.41(1) and −7.44(4) cm⁻¹ for 1, 2 and 3, respectively) and confirmed by DFT calculations, originates from two Cr^III ions with spin 3/2 interacting through diamagnetic –O–Nb^V–O– bridge(s).

中文翻译：

---

从正方形芯到正方形开口：结构多样性和氧桥连[CR的磁特性^III的Nb ^V ]络合物†

三种杂金属氧桥化合物[Cr ₂（phen）₄（μ-O）₄ Nb ₂（C ₂ O ₄）₄ ]·2H ₂ O（1 ; phen = 1,10-菲咯啉），[Cr ₂（ terpy）₂（H ₂ O）₂（μ-O）₄ Nb ₂（C ₂ O ₄）₄ ]·4H ₂ O（2 ; terpy = 2,2'; 6'，2''-叔吡啶）和[ Cr（叔）（C ₂ O ₄）（H ₂ O）] [Cr ₂（terpy）₂（C ₂ O ₄）₂（μ-O）₂ Nb（C ₂ O ₄）₂ ]·3H ₂ O（3），已使用构造方法合成并通过IR光谱进行了表征，晶体和粉末X射线衍射，磁化强度测量和DFT计算。1和2的分子结构分别在P 4 ₂ 2 ₁ 2和P 2 ₁ / n空间基团中结晶，包含正方形{Cr ^III₂（μ-O） ₄ Nb ^V ₂ }单元，而复盐3（ P空间群）的单元由包含Cr ^III和三核阴离子的单核阳离子组成，其中两个Cr ^III离子通过–O–Nb ^V桥接–O–片段。除了氢键形成1–3或3D超分子排列之外，还发现由于富电子羰基氧和严重消耗电子的碳原子的静电吸引，在平行草酸酯部分之间出现了不寻常的分子间接触在2的水晶包装中。所有三种化合物中观察到的反铁磁性耦合，从磁化测量来确定（Ĵ = -13.51（2），-8.41（1）和-7.44（4）厘米^-1为1，2和3，分别地）和通过DFT计算确认，来自两个自旋为3/2的Cr ^III离子，它们通过反磁性–O–Nb ^V –O–桥相互作用。