Two Concomitant Polymorphs of 1,2-Naphthoquinone-2-semicarbazone

1,2-Naphthoquinone-2-semicarbazone (i.e., naftazone) has been characterized by structural analysis (single-crystal X-ray diffraction, powder X-ray diffraction) and by thermal analysis (differential scanning calorimetry, DSC). Although this molecule has no chiral center, the two forms crystallize in chiral space groups: the stable form I (P212121, Z = 4, a = 5.1187(7) Å, b = 5.6092(7) Å, c = 34.847(5) Å; V = 1000.5(2) Å3) and the metastable form II (P21, Z = 2, a = 6.3349(1) Å, b = 3.9263(1) Å, c = 19.790(5) Å, β = 92.424(4)°; V = 491.8(2) Å3). At high concentration (c = 30 g·L−1), the pure stable form I crystallizes regardless of the antisolvent (water) addition rate. At low concentration (c = 15 g·L−1), the pure metastable form II crystallizes at low water addition rate (ψ = 100 mL·h−1); however, the structurally pure form I is also obtained with a high water addition rate (ψ = 72 × 103 mL·h−1). Concomitant polymorphs crystallize at intermediate antisolvent addition rate and concentration. Therefore in the majority of the operative conditions, these results appear to be in contradiction with Ostwald’s rule of stages.1,2-萘醌-2-缩氨基脲（1,2-Naphthoquinone-2-semicarbazone，即萘法宗（naftazone））已通过结构分析（单晶X射线衍射、粉末X射线衍射）与热分析（差示扫描量热法（differential scanning calorimetry, DSC））完成表征。尽管该分子无手性中心，但其两种晶型均在手性空间群中结晶：稳定晶型I（空间群P2₁2₁2₁，Z=4，晶胞参数a=5.1187(7) Å，b=5.6092(7) Å，c=34.847(5) Å；晶胞体积V=1000.5(2) ų）与亚稳定晶型II（空间群P2₁，Z=2，a=6.3349(1) Å，b=3.9263(1) Å，c=19.790(5) Å，β=92.424(4)°；晶胞体积V=491.8(2) ų）。当浓度较高（c=30 g·L⁻¹）时，无论抗溶剂（水）的添加速率如何，均可结晶得到纯的稳定晶型I。当浓度较低（c=15 g·L⁻¹）时，在低水添加速率（ψ=100 mL·h⁻¹）下仅得到纯的亚稳定晶型II；但当水添加速率较高（ψ=72×10³ mL·h⁻¹）时，同样可获得结构纯的晶型I。在抗溶剂添加速率与浓度处于中间区间时，会同时结晶得到两种多晶型。因此在多数操作条件下，该结果与奥斯特瓦尔德分步规则（Ostwald’s rule of stages）相悖。